Tesis: "Magnetic materials with perpendicular magnetic anisotropy"

1

Rasin, Boris. "Perpendicular magnetic anisotropy in ion beam sputtered Co/Ni multilayers". Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/58071.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 34-35).
Co/Ni multilayers display perpendicular magnetic anisotropy and have applications in magnetic devices that could lead to a large increase in the density of magnetic storage. Co/Ni 10-(2 Å Co/ 8Å Ni) and 10-(2 Å Co/ 4 Å Ni) multilayers were deposited with ion beam sputtering on either ion beam sputtered copper or direct current magnetron sputtered gold buffer layers of various thicknesses. The effect of the the roughness and the degree of (1 1 1) texture of the buffer layers and the multilayers on the perpendicular magnetic anisotropy of the deposited multilayers was examined. In addition the effect of the deposition method used to fabricate the samples, ion beam sputtering, was analyzed. The magnetic behavior of the multilayers was examined with alternating gradient magnetometry and vibrating sample magnetometery, the structure of the buffer layers and the multilayers was characterized with X-ray diffraction, and the roughness of the surface of the multilayers was characterized with atomic force microscopy. None of the deposited films showed perpendicular magnetic anisotropy and instead showed parallel magnetic anisotropy which was found to have occurred for every sample due to either a low degree of (1 1 1) texture in the buffer layer and the Co/Ni multilayer, a too high degree of roughness in the buffer layer and the Co/Ni multilayer or a combination of these two factors. In addition it was hypothesized that as the samples were deposited with sputtering, diffusion and alloying at the multilayer interfaces may have contributed to the multilayers having parallel magnetic anisotropy instead of perpendicular magnetic anisotropy.
by Boris Rasin.
S.B.

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2

Niesen, Alessia [Verfasser]. "Heusler materials with perpendicular magnetic anisotropy. Thin films for spintronics / Alessia Niesen". Bielefeld : Universitätsbibliothek Bielefeld, 2019. http://d-nb.info/1183256590/34.

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3

Gottwald, Matthias. "Nouveaux systèmes modèles à aimantation perpendiculaire pour l'étude des effets de transfert de spin". Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10053/document.

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Les effets de transfert de spin sont devenus un sujet de recherche majeur ces quinze dernières années. Cependant, un manque de vérifications expérimentales pour beaucoup de modèles décrivant les effets de transfert de spin peut être constaté. Ceci est surtout lié à un manque de systèmes magnétiques modèles permettant un contrôle précis des paramètres pertinents utilisés dans les modèles théoriques. Dans ce travail deux systèmes magnétiques à aimantation perpendiculaire ont été analysés : les alliages amorphes de Co1-xTbx élaborés par pulvérisation cathodique et les super-réseaux [Co/Ni](111) élaborés par épitaxie par jets moléculaires. L'anisotropie et l'aimantation, qui sont des paramètres pertinents dans beaucoup de modèles sur le transfert de spin, sont variables dans une large gamme. L'origine de cette anisotropie est discutée. La structure des domaines magnétiques est analysée et les résultats des mesures de transport sont interprétés. Pour les super-réseaux [Co/Ni](111) une forte polarisation en spin au niveau de Fermi est démontrée grâce à des expériences de photo émission résolue en spin et un coefficient d'amortissement intrinsèque [alpha] très faible est trouvé. Il est conclu que les alliages amorphes de Co1-xTbx et les super-réseaux [Co/Ni](111) sont des systèmes modèles pour le transfert de spin
Spin transfer torque effects have become a research subject of high interest during the last 15 years. However, in order to probe the fundamental physics of spin transfer torque model systems are needed. For a model system it must be as simple as possible to tune the significant parameters (magnetic and structural). In this work we analyze the suitability of two materials for this need. The studied materials are amorphous Co1-xTbx alloys elaborated by sputtering and MBE grown [Co/Ni](111) superlattices. Both systems show perpendicular magnetic anisotropy (PMA), which provides a uniaxial anisotropy to the system. This anisotropy and the magnetization, which are significant parameters for many models on spin transfer torque, can be tuned in a large range of values. The origin of this PMA is discussed. The domain structure is analyzed and transport measurements are interpreted. In addition we show a strong spin polarization of the electrons close to the Fermi level by doing photoemission experiments. A small intrinsic Gilbert damping parameter [alpha] is found by FMR spectroscopy. We conclude that both materials are good candidates to be used as model systems for spin transfer torque

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4

Kane, Margaret Marie. "Fabrication and characterization of perpendicular magnetic anisotropy thin-film CoCrPt grown on a Ti underlayer". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98555.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 57-58).
CoCrPt has potential applications as a memory storage technology because of its perpendicular magnetic anisotropy (PMA) characteristics. An underlayer can be used to ensure the out-of-plane magnetization required for PMA functionalities. Ti, with a lattice constant of a = 2.95 Å can be used to encourage uniaxial c-axis growth in CoCrPt (lattice constant a ~/= 2.55 Å, dependent on exact composition). In this report, varying thicknesses of Ti (t = 0, 20, 40, 60, 70, 80, 90, 100nm) and CoCrPt (t = 50, 75, 90, 100, 125, 150nm) were sputtered onto naturally oxidized silicon substrates. Using various characterization methods, these films were investigated in order to better understand the system. The exact composition of the CoCrPt films was found to be approximately Co₆₀.₂Cr₁₆.₄Pt₂₃.₄, with a Curie temperature of about 600 °C. The addition of a Ti underlayer resulted in an increase in coercivity to approximately 1250 Oe for t > 60nm. However, switching field distribution and saturation magnetization appear to be independent of underlayer thickness. All samples show evidence of out-of-plane growth and the roughness of the films increases until it also plateaus at about t = 60nm. When CoCrPt thickness is varied on a constant Ti underlayer, the PMA properties of the materials decrease with increasing thickness due to increased disorder and potential relaxation of the lattice in thicker films. The switching field distribution shows a significant increase, implying that a thicker film has a more homogenous distribution of grain sizes. XRD peaks confirm out-of-plane growth and suggest a trend of increasing c lattice constant as the thickness of the film increases.
by Margaret Marie Kane.
S.B.

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5

Zhang, Jinshuo Ph D. Massachusetts Institute of Technology. "Geometrical control of domain walls and the study of domain wall properties of materials with perpendicular magnetic anisotropy". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108968.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 155-168).
Magnetic based devices such as hard disk drives (HDDs) are widely used in the computer industry because of their high memory capacity, non-volatility and low cost compared to semiconductor-based solid state disk drives (SSDs). However, they also suffer from low energy efficiency and low speed, due to the requirement for mechanical motion in order to access the data. In my thesis, I will first give a brief introduction to the motivation and background in the study of magnetic domain walls (DWs), which have attracted great attention due to their ability to be moved by field and/or current and corresponding potential applications in high speed memory or logic devices. I will then discuss how to geometrically control the behaviors of DWs in a ferromagnetic nanowire. I will first discuss how natural geometry distortions such as edge tapering from sputtering on an undercut resist profile and wire width variation from the patterning process would affect DW behavior, including static configurations, stability and dynamics under current pulsing. I will then discuss how similar geometrical effects will affect the properties of materials with perpendicular magnetic anisotropy (PMA). The same geometry modulation will have different effects depending on the origin of the PMA. Such results are confirmed by observing the magnetic reversal process. Besides the study on 180DWs, we will then discuss the field and current effects on 360 degree DWs (360DWs), which have many unique properties compared to 180DWs and are an alternative candidate for DW based devices. I will then discuss control of 360DW behavior by designing a geometrical heterostructure. We have found that by utilizing the asymmetric Oersted field originated from the heterostructure, we are able to control the 360DWs depending on their chirality. The structure can function as a 360DW chirality filter, which provides extra freedom in DW-based applications. These studies were conducted by a combination of micromagnetic simulations and experimental implementations. Techniques being used including OOMMF micromagnetic simulations, Comsolfinite element simulations, electrical measurements, magnetic force microscopy and other characterization techniques.
by Jinshuo Zhang.
Ph. D.

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6

Wismayer, Matthew P. "Small angle neutron scattering studies of magnetic recording media". Thesis, St Andrews, 2008. http://hdl.handle.net/10023/471.

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7

Nguyen, Ngoc-Minh. "Propagation de parois magnétiques dans des films et des pistes à anisotropie magnétique perpendiculaire". Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112356.

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Cette thèse est consacrée à l’étude des mécanismes de propagation de parois magnétiques dans des films et des pistes magnétiques basés sur des matériaux à anisotropie magnétique perpendiculaire qui sont très prometteurs pour les mémoires magnétiques non volatiles d’ultra haute densité. Je me suis principalement intéressé à l’influence des défauts structuraux sur les mécanismes de dépiegeage de parois en utilisant la technique de microscopie Kerr ainsi que des mesures de transport. Trois résultats importants ont été mis en évidence : (1) Dans des vannes de spin de type CoNi/Cu/CoNi, il existe une forte influence du champ dipolaire généré par la couche dure qui peut influencer la nucléation parasite de paroi magnétique dans la couche libre et créer une propagation asymétrique sous l’effet d’un courant polarisé. J’ai aussi montré que dans des pistes sub-50nm, le renversement de l’aimantation s’effectue par des événements multiples de nucléation à cause de la présence de centres de piégeage fort qui bloquent la propagation ; (2) En visualisant la géométrie des domaines magnétiques et en étudiant les lois de reptation, j’ai montré la présence d’une faible densité de défauts structuraux et de faibles champs de propagation dans les multicouches texturés/amorphe de CoNi-CoFeB et cristallisés de Ta-CoFeB-MgO ; (3) J’ai finalement mis en évidence un effet du transfert de spin à de faibles densités de courant (≈5x1011 A/cm2) dans les pistes de CoNi-CoFeB. J’ai aussi montré une forte influence du champ d’Oesterd sur la propagation de parois liée à la présence de faibles champs de propagation. Finalement, dans le cas des pistes basées sur des films cristallisés de Ta-CoFeB-MgO, j’ai pu mesurer la vitesse sur 10 ordres de grandeur et montrer que les parois se propagent à des champs de propagation ultra faibles (0,1mT)
This work is focused on the study of magnetic domain wall propagation mechanisms in the thin films and wires based on materials with perpendicular magnetic anisotropy which are promissing for the non-volatile magnetic memory of ultra high density. I’m interested in the influence of structural defects on the mechanisms of domain wall propagation by using the Kerr microscopy technique and the transport measurements. Three important results were obtained: (1) In the spin valve structure of CoNi/Cu/CoNi, a strong influence of the dipolar magnetic field induced by the hard layer can generate a parasitic nucleation in the soft layer and create an asymmetric domain wall propagation driven by a spin polarized current. I also demonstrated that in sub-50nm wires, the nature of magnetization reversal process is the multiple nucleation events because of strong pinning centers that hinder the domain wall motion; (2) By observing the magnetic domain geometry et studying the creep law, I have pointed out that in the CoNi-CoFeB multilayers and the crystallized Ta-CoFeB-MgO multilayers, the structural defect density is low and the propagation fields can be reduced; (3) I found a spin-transfer effect with low current density (≈5x1011 A/cm2) in CoNi-CoFeB wires. I also demonstrated that the Oersted field can strongly influence the domain wall motion, especially in the material with low propagation field. Finally, in the Ta-CoFeB-MgO wires, I could measure a wide range of domain wall velocity and I show that the domain wall can move at a very low propagation field (0.1mT)

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8

Marcon, Paul. "Calcul ab-initio des propriétés physiques d'hétérostructures associant des matériaux ferromagnétiques à anisotropie magnétique perpendiculaire et des dichalcogénures de métaux de transition". Electronic Thesis or Diss., Toulouse 3, 2023. http://www.theses.fr/2023TOU30273.

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La possibilité de synthétiser des hétérostructures formées de matériaux 2D offre des perspectives majeures pour l'amélioration des composants spintroniques actuels ou la réalisation de nouveaux dispositifs. Le contrôle et la bonne compréhension des propriétés physiques de ces systèmes constituent de fait un enjeu technologique majeur. Au cours de cette thèse, nous avons étudié, à l'aide de calculs ab initio basés sur la théorie de la fonctionnelle de la densité (DFT), des hétérostructures formées de monocouches de dichalcogénures de métaux de transition (TMDCs) et de cristaux ferromagnétiques présentant une anisotropie magnétique perpendiculaire. Trois objectifs principaux ont été définis : (i) comprendre comment utiliser la proximité magnétique pour lever la dégénérescence des vallées et quantifier l'effet Zeeman des vallées ; (ii) évaluer la possibilité d'injecter un gaz d'électrons polarisé en spin dans des vallées spécifiques du feuillet de TMDC ; (iii) examiner l'impact de la proximité sur le couplage spin-orbite dans le feuillet de TMDC et sur les phénomènes Rashba et Dresselhaus dans ces systèmes. Nous avons d'abord étudié des multicouches possédant une électrode constituée d'un métal et d'une barrière isolante non 2D. Dans le système Fe/MgO/MoS2, nous avons calculé qu'un transfert d'électrons spontané s'opère de la couche de Fe vers le monofeuillet de MoS2, donnant lieu à la formation d'un gaz d'électrons non polarisé en spin. Nous avons établi un modèle expliquant la compétition entre les effets spin-orbite de type Rashba et Dresselhaus et les effets de proximité magnétique sur les bandes de valence de MoS2 : Ce modèle nous a permis de montrer que les effets de proximité sont prédominants pour une faible épaisseur de MgO (<0.42 nm), et tendent à disparaître au profit des effets spin-orbite pour à plus forte épaisseur (> 1.06 nm). Nous avons prédit qu'il est possible d'obtenir des effets spin-orbites plus forts en remplaçant l'électrode de Fe par une électrode non-magnétique de V. Afin d'augmenter les effets de proximité magnétique, nous avons finalement décider d'étudier des hétérostructures [Co1Ni2]n/h-BN/WSe2, dans lesquelles [Co1Ni2]n est un super réseau à anisotropie magnétique perpendiculaire et h-BN un isolant bidimensionnel. Pour ce système, nous prédisons qu'il serait possible d'avoir une polarisation en spin des vallées aux points K et K'. Finalement, nous avons étudié les propriétés particulières de l'hétérostructure de van der Waals Graphène/CrI3/WSe2,dans laquelle l'électrode magnétique est également remplacée par des matériaux 2D
The ability to synthesize heterostructures made up of 2D materials provides significant opportunities for improving current spintronic components or developing new devices. Thus, the control and deep understanding of the physical properties of these systems become a critical technological challenge. During this thesis, we examined heterostructures composed of transition metal dichalcogenide (TMDC) monolayers and ferromagnetic crystals exhibiting perpendicular magnetic anisotropy, using ab initio calculations based on density functional theory (DFT). We focus on three main goals: (i) understanding how to use magnetic proximity to lift valley degeneracy and quantify the valley Zeeman effect; (ii) assessing the possibility of injecting spin-polarized electron gas into specific valleys of the TMDC sheet; (iii) investigating the impact of proximity on spin-orbit coupling in the TMDC sheet and on the Rashba and Dresselhaus phenomena in these systems. We first studied multilayers with an electrode made up of a metal and a non-2D insulating barrier. In the Fe/MgO/MoS2 system, we computed that a spontaneous electron transfer occurs from the Fe layer to the MoS2 monolayer, leading to the formation of a non-spin-polarized electron gas. We established a model explaining the competition between Rashba and Dresselhaus-type spin-orbit effects and magnetic proximity effect on the MoS2 valence bands: This model allowed us to show that proximity effect predominate for thin MgO (<0.42 nm) and tend to disappear in favor of spin-orbit effects for thicker layers (> 1.06 nm). We predicted that stronger spin-orbit effects can be achieved by replacing the Fe electrode with a non-magnetic V electrode. To boost the magnetic proximity effects, we finally decided to study [Co1Ni2]n/h-BN/WSe2 heterostructures, in which [Co1Ni2]n is a superlattice with perpendicular magnetic anisotropy, and h-BN is a two-dimensional insulator. For this system, we predict that it could be possible to have a spin polarization of the valleys at the K and K' points. Ultimately, we explored the unique properties of the van der Waals heterostructure Graphene/CrI3/WSe2, where the magnetic electrode is also replaced by 2D materials

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9

Kugler, Zoe [Verfasser]. "Perpendicular anisotropy in magnetic tunnel junctions / Zoe Kugler". Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2012. http://d-nb.info/1023862891/34.

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10

Moutafis, Christoforos. "Magnetic elements with perpendicular anisotropy : statics and dynamics of magnetic bubbles and vortices". Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611377.

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11

Gopman, Daniel Bernard. "Switching distributions in Co-Ni nanopillars with perpendicular magnetic anisotropy". Thesis, New York University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3614870.

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This thesis reports on measurements of the switching distributions in Co-Ni nanopillars with perpendicular magnetic anisotropy. The Co-Ni nanopillars are incorporated into a spin-valve device - a two terminal device consisting of two ultrathin (1-3 nm) Co-Ni ferromagnets separated by a thin (4 nm) Cu spacer patterned into ellipses and circles with lateral sizes ranging from 40-300 nm. Magnetic fields applied along the uniaxial anisotropy axis can switch the alignment of the constituent ferromagnetic layers between anti-parallel and parallel. Electric currents flowing can also switch the nanopillar through the spin-transfer torque effect - an electric current transfers spin-angular momentum from conduction electrons to the background magnetization of a ferromagnet, ultimately manifesting as a torque on the magnetization.

Lateral geometry effects were studied on nanopillars with notches along the perimeter. Switching field measurements revealed an asymmetry between the anti-parallel (AP) to parallel (P) and P to AP switching field distributions. A phenomenological model that considers the spatially inhomogeneous dipole field from the polarizing layer explains this asymmetry.

In nanopillars with an 80 nm circular diameter, switching field measurements taken in a cryostat reveal non-uniform magnetization configurations during reversal. At the lowest temperatures (12 K), the transition between uniform states (P to AP) shows three consecutive hysteretic jumps. The thermal stability of the transition states was investigated for temperatures between 12 K and room temperature.

The thermally activated magnetization reversal model by Néel and Brown was tested on 75 nm diameter spin-valves between 20 and 400 K. The temperature dependence of the statistics of switching reflects enhanced thermal fluctuations and cannot be modeled by the Néel expression for the energy barrier. Taking into account the implicit temperature dependence of the energy barrier from the saturation magnetization and perpendicular anisotropy energy explains this discrepancy.

The effective barrier model for spin-torque thermally-activated switching of Co-Ni nanopillars was investigated. We extracted an effective energy barrier height for switching field distributions under several dc currents. The results mostly agree with the prediction that the current modifies the barrier height. However, rare switching events at the tails of the distributions reveal qualitative deviations from this model.

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12

Almasi, H., C. L. Sun, X. Li, T. Newhouse-Illige, C. Bi, K. C. Price, S. Nahar et al. "Perpendicular magnetic tunnel junction with W seed and capping layers". AMER INST PHYSICS, 2017. http://hdl.handle.net/10150/624048.

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We present a study on perpendicular magnetic tunnel junctions with W as buffer and capping layers. A tunneling magnetoresistance of 138% and an interfacial magnetic anisotropy of 1.67 erg/cm(2) were obtained in optimally annealed samples. However, after extended annealing at 420 degrees C, junctions with W layers showed extremely small resistance due to interdiffusion of W into the MgO barrier. In contrast, in Ta-based junctions, the MgO barrier remained structurally stable despite disappearance of magnetoresistance after extended annealing due to loss of perpendicular magnetic anisotropy. Compared with conventional tunnel junctions with in-plane magnetic anisotropy, the evolution of tunneling conductance suggests that the relatively low magnetoresistance in perpendicular tunnel junctions is related to the lack of highly polarized Delta(1) conducting channel developed in the initial stage of annealing. Published by AIP Publishing.

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13

Zhang, Yue. "Modélisation compacte et conception de circuit hybride pour les dispositifs spintroniques basés sur la commutation induite par le courant". Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01058504.

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La miniaturisation du nœud technologique de CMOS en dessous de 90 nm conduit à une forte consommation statique pour les mémoires et les circuits logiques, due aux courants de fuite de plus en plus importants. La spintronique, une technologie émergente, est d'un grand intérêt pour remédier à ce problème grâce à sa non-volatilité, sa grande vitesse d'accès et son intégration facile avec les procédés CMOS. Comparé à la commutation induite par le champ magnétique, le transfert de spin (STT), une approche de commutation induite par le courant, non seulement simplifie le processus de commutation mais aussi permet un fonctionnement sans précédent en termes de consommation et de vitesse. Cette thèse est consacrée à la modélisation compacte et la conception de circuit hybride pour les dispositifs spintroniques basés sur la commutation induite par le courant. La jonction tunnel magnétique (JTM), élément fondamental de la mémoire magnétique (MRAM), et la mémoire racetrack, nouveau concept fondé sur la propagation des parois de domaine induites par le courant, sont particulièrement étudiés. Ces dispositifs et circuits spintroniques sont basés sur les matériaux à anisotropie magnétique perpendiculaire (AMP) qui ouvrent la perspective d'une miniaturisation submicronique tout en conservant une grande stabilité thermique. De nombreux modèles physiques et paramètres réalistes sont intégrés dans la modélisation compacte pour obtenir une bonne cohérence avec les mesures expérimentales. En utilisant ces modèles compacts précis, certaines applications pour la logique et les mémoires magnétiques, tels que l'additionneur complet magnétique (ACM) et la mémoire adressable par contenu (CAM), sont conçues et simulées. Nous analysons et évaluons leur potentiel de performance en termes de surface, vitesse et consommation d'énergie par rapport aux circuits classiques. Enfin, afin de lutter contre la limitation de capacité entravant la large application, nous proposons deux optimisations de conception : la mémoire multivaluée (MLC) pour la STT-MRAM et l'assistance par champ magnétique pour la mémoire racetrack. Ce concept de MLC utilise le comportement stochastique des STT pour atteindre une haute vitesse tout en augmentant la densité de STT-MRAM. La mémoire racetrack assistée par champ magnétique est fondée sur l'observation d'une propagation des parois de domaine en dessous du courant critique, propagation est attribué à l'effet " Walker breakdown ". Ceci ouvre une nouvelle voie pour réduire le courant de propagation et augmenter la capacité des mémoires racetrack au-delà des améliorations des circuits périphériques et des matériaux.

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14

Almasi, Hamid y Hamid Almasi. "Perpendicular Magnetic Tunnel Junctions with MgO Tunnel Barrier". Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626332.

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Spintronics discusses about fundamental physics and material science in mostly nanometer size structures. Spintronics also delivers many promising technologies for now and the future. One of the interesting spintronic structures is called “Magnetic Tunnel junction” (MTJ). A typical MTJ consists of a thin (1-3nm) insulator layer sandwiched between two ferromagnetic layers. In this work, I present MTJ with perpendicular magnetic anisotropy (PMA) using an MgO tunnel barrier. The effect of different heavy metals (HMs) adjacent to the ferromagnets (FMs) on tunneling magnetoresistance (TMR) and PMA of the junctions are discussed. Namely, Ta, Mo, Ta/Mo, W, Ir, and Hf have been utilized in HM/FM/MgO structures, and magneto-transport properties are explored. It is shown that when Ta/Mo is employed, TMR values as high as 208%, and highly thermally stable PMA can be obtained. Some physical explanation based on electronic band structure and thermochemical effects are discussed. In the last part of this work, the newly discovered tunneling anisotropic magnetoresistance (TAMR) effect in antiferromagnets is studied, and clear TAMR is demonstrated for NiFe/IrMn/MgO/Ta structures.

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15

Mohseni, Armaki Seyed Majid. "Spin valves and spin-torque oscillators with perpendicualr magnetic anisotropy". Doctoral thesis, KTH, Materialfysik, MF, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105223.

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Researches in spintronics, especially those remarkably classified in the current induced spin-transfer torque (STT) framework, circumvent challenges with different materials and geometries. Perpendicular magnetic anisotropy (PMA) materials are showing capability of holding promise to be employed in STT based spintronics elements, e.g. spin-torque oscillators (STOs), STT-magnetoresistive random access memories (STT-MRAMs) and current induced domain wall motion elements. This dissertation presents experimental investigations into developing sputter deposited Co/Ni multilayers (MLs) with PMA and employs these materials in nano-contact STOs (NC-STOs) based on giant magnetoresistance (GMR) effect and in pseudo-spin-valve (PSV) structures. The magnetostatic stray field coupling plays an important role in perpendicular PSVs. The temperature dependent coupling mechanism recommends that this coupling can be tailored, by i) the saturation magnetization and coercivity of the individual layers, ii) the coercivity difference in layers, and iii) the GMR spacer thickness, to get a well decoupled and distinguishable switching response. Moreover, this thesis focused on the implementation and detailed characterization of NC-STOs with strong PMA Co/Ni ML free layers and in-plane Co reference layers as orthogonal (Ortho) magnetic geometry in so-called Ortho-NC-STOs. The primary target of reaching record high STO frequencies, 12 GHz, at close to zero field, 0.02 Tesla, was achieved. However, in large external fields, >0.4 Tesla, an entirely new magnetodynamic object, a “magnetic droplet”, theoretically predicted in 1977, was discovered experimentally. Detailed experiments, combined with micromagnetic simulations, demonstrate the formation of a magnetic droplet with a partially reversed magnetization direction underneath the NC, and a zone of large amplitude precession in a region bounding the reversed magnetization. The magnetic droplet exhibits a very rich dynamics, including i) auto-modulation as a combine of droplet frequency with a slow time evolution (few GHz) of un-centering the droplet mode under the NC, ii) droplet breathing as reversible deformation of droplet mode with ½ droplet frequency. All observation of droplet opens a new mechanism of excitation for future fundamental studies as well as experiments especially for domain wall electronics and nano-scopic magnetism.

QC 20121119

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16

Vopsaroiu, Marian. "Anisotropy and texture studies in magnetic media". Thesis, University of Central Lancashire, 2002. http://clok.uclan.ac.uk/20302/.

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The rapid development of magnetic materials for recording media applications increased the demands for new and more precise experimental investigation techniques. In respect with these demands, this project is focused on experimental analyses of advanced particulate media and magnetic thin film samples. A new extended rotational remanence technique for anisotropy field measurements was developed. The technique is suitable for samples that contain aligned or partially aligned particles and provides both: in-plane anisotropy field distributions and the in-plane anisotropy field. This technique was also extended to out-of-plane anisotropy field measurements. Rotational hysteresis was introduced as an alternative method for anisotropy field measurements. This applies well in the case of samples without texture or samples having very small magnetic moment (i.e. thin films). The two techniques for anisotropy field measurement compare well and the experimental results were interpreted in terms of inter-particles interactions. Two measurement methods for determination of the demagnetizing field acting perpendicular to a sample plane were also developed. The first method is based on the in-plane and out-of-plane anisotropy field determination using an extended rotational remanence technique. The second method can provide the demagnetizing field starting from in-plane and out-of-plane transverse hysteresis loops. Comparison between the results from the two methods showed good agreement. Furthermore, the demagnetizing field values were used to calculate the magnetic coating thickness, so the two methods provide a non-destructive method for magnetic thickness measurements in film samples. The in-plane easy axis distribution (EAD) was experimentally determined using vector VSM techniques. Correlations between in-plane tape texture and magnetic thickness were obtained for a series of advanced MP tapes. A theoretical approach was used in order to relate the orientation ratio to EAD. The out-of-plane EAD was derived from numerical calculations. The out-of-plane distribution also showed a variation with the magnetic thickness. In addition, the microstructure and particle morphology of the advanced MP tapes, as well as the out-of-plane component of magnetization, have been investigated using Mossbauer Spectroscopy. Finally, 3D - EAD maps were produced. All VSM experiments were fully computer controlled and the routines were designed in the LabView environment as part of this project.

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17

Jaiswal, Samridh [Verfasser]. "Investigation of the Dzyaloshinskii-Moriya interaction and perpendicular magnetic anisotropy in magnetic thin films and nanowires / Samridh Jaiswal". Mainz : Universitätsbibliothek Mainz, 2018. http://d-nb.info/116285913X/34.

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18

Huang, Efrem Yuan-Fu. "L10-Ordered Thin Films with High Perpendicular Magnetic Anisotropy for STT-MRAM Applications". Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/880.

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The objective of the research conducted herein was to develop L10-ordered materials and thin film stack structures with high perpendicular magnetic anisotropy (PMA) for spin-transfertorque magnetoresistive random access memory (STT-MRAM) applications. A systematic approach was taken in this dissertation, culminating in exchange coupled L10-FePt and L10- MnAl heterogeneous structures showing great promise for developing perpendicular magnetic tunnel junctions (pMTJs) with both high thermal stability and low critical switching current. First, using MgO underlayers on Si substrates, sputtered MnAl films were systematically optimized, ultimately producing a Si substrate/MgO (20 nm)/MnAl (30)/Ta (5) film stack with a high degree of ordering and large PMA. Next, noting the incompatibility of insulating MgO underlayers with industrial-scale CMOS processes, attention was turned to using conductive underlayers. TiN was found to excel at promoting growth of L10-MnAl, with optimized films showing improved magnetic properties over those fabricated on MgO underlayers. Although the MnAl films grown on TiN underlayers on Si substrates demonstrated good magnetic properties, it was found that the high deposition and ordering temperatures contributed to high film roughness. In an effort to reduce ordering temperature and surface roughness of L10- MnAl films, adding other materials (Ni, C, and SiOx) to the MnAl film in conjunction with various underlayers was studied. MnAl:Ni films with a fixed 3 volume% Ni content deposited on TiN underlayers revealed that PMA was reduced compared to MnAl films, and surface roughness increased dramatically below the ordering temperature. MnAl:C films with 1volume% C showed an increase in PMA, while C in excess of the solubility limit (1.7 atomic %) diffused to the grain edges, degrading PMA. MnAl:SiOx films demonstrated poor PMA. The use of different post-annealing processes was then studied as an alternative to in situ annealing. Rapid thermal annealing (RTA) was found to produce PMA in films at lower annealing temperatures than tube furnace annealing, but tube furnace annealing produced films with higher maximum PMA than RTA. While annealed samples had lower surface roughness than those ordered by high in situ deposition temperatures, relying solely on annealing to achieve L10-ordering resulted drastically reduced PMA. Since the material additions, underlayer systems, and annealing techniques studied either did not reduce film roughness or resulted in reduced PMA of thin films, attention was turned to MTJ stack structures employing heterogeneous material systems for top and bottom electrodes, which might produce film stacks with both high PMA and low surface roughness. As a way to potentially mitigate roughness issues with using MnAl-based thin films as both free and reference layers in an MTJ, exchange coupled heterogeneous structures were studied. Given the high PMA of L10-FePt and low damping of L10-MnAl, L10-FePt/MnAl heterogeneous structures were studied as a way to take advantage of STT potentially being a surface process. Unfortunately, depositing the MnAl at elevated temperatures resulted in interdiffusion between FePt and MnAl, and caused a degradation in PMA. High- and low-anisotropy thin films separated by a thin barrier were then examined in the form of in-plane hard-FePt/barrier layer/inplane soft-FePt film stacks. It was found that significant exchange coupling energy was still observed at barrier thicknesses of around 1 nm. Since scaled MTJs have tunnel barriers below 1 nm, interlayer exchange coupling between the electrodes might thus be used for partially pinning the free layer, thereby increasing effective PMA. It is suggested that pinning a low-damping free layer by a high-PMA reference layer may therefore result in an MTJ with both high effective PMA and low effective damping. Finally, heterogeneous L10-ordered FePt/MgO/MnAl film stacks were explored for pMTJs. Film stacks with MgO barrier layers thinner than 2 nm showed significant interdiffusion between the FePt and MnAl, while film stacks with thicker MgO barrier layers exhibited good ordering and high PMA in both the FePt and MnAl films. It is believed that this limitation is caused by the roughness of the underlying FePt, which was thicker than 2 nm. Unfortunately, MgO barrier layers thinner than 2 nm are needed to make good MTJs. With further study, thin, continuous barriers may be achievable for high-PMA, L10- ordered materials with more materials exploration, deposition optimization, and more advanced thin film processing techniques and fabrication equipment. Use of appropriate underlayers, capping layers, dopant elements, and improved fabrication techniques may help reduce surface roughness while preserving PMA. If smooth electrodes can be developed, the heterogeneous structures discussed have great potential in taking advantage of exchange coupling for developing pMTJs with both high thermal stability and low critical switching current.

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19

Fard, Samad Moemen Bellah. "Modelling anisotropy in electrotechnical steels". Thesis, Cardiff University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263551.

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20

Kuhrau, Susanne [Verfasser] y Hans Peter [Akademischer Betreuer] Oepen. "Surface-sensitive magnetic imaging of polycrystalline and epitaxial ultrathin cobalt films with a perpendicular magnetic anisotropy / Susanne Kuhrau ; Betreuer: Hans Peter Oepen". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1197801227/34.

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21

Jönsson, Petra. "Anisotropy, disorder and frustration in magnetic nanoparticle systems and spin glasses". Doctoral thesis, Uppsala University, Department of Materials Science, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2038.

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Magnetic properties of nanoparticle systems and spin glasses have been investigated theoretically, and experimentally by squid magnetometry.

Two model three-dimensional spin glasses have been studied: a long-range Ag(11 at% Mn) Heisenberg spin glass and a short-range Fe_0.5Mn_0.5TiO₃ Ising spin glass. Experimental protocols revealing ageing, memory and rejuvenation phenomena are used. Quantitative analyses of the glassy dynamics within the droplet model give evidences of significantly different exponents describing the nonequilibrium dynamics of the two samples. In particular, non-accumulative ageing related to temperature-chaos is much stronger in Ag(11 at% Mn) than in Fe_0.5Mn_0.5TiO₃.

The physical properties of magnetic nanoparticles have been investigated with focus on the influence of dipolar interparticle interaction. For weakly coupled nanoparticles, thermodynamic perturbation theory is employed to derive analytical expressions for the linear equilibrium susceptibility, the zero-field specific heat and averages of the local dipolar fields. By introducing the averages of the dipolar fields in an expression for the relaxation rate of a single particle, a non trivial dependence of the superparamagnetic blocking on the damping coefficient is evidenced. This damping dependence is interpreted in terms of the nonaxially symmetric potential created by the transverse component of the dipolar field.

Strongly interacting nanoparticle systems are investigated experimentally in terms of spin-glass behaviour. Disorder and frustration arise in samples consisting of frozen ferrofluids from the randomness in particle position and anisotropy axes orientation. A strongly interacting system is shown to exhibit critical dynamics characteristic of a spin-glass phase transition. Ageing, memory and rejuvenation phenomena similar to those of conventional spin glasses are observed, albeit with weak temperature-chaos effects.

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22

Ferrante, Yari [Verfasser]. "Development of tetragonal Heusler compounds with perpendicular anisotropy for Magnetic Random Access Memory applications / Yari Ferrante". Halle, 2017. http://d-nb.info/114842511X/34.

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23

Venkataramana, Vikash. "Neutrons to probe nanoscale magnetism in perpendicular magnetic recording media". Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3187.

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Magnetic recording media refers to the disc shaped thin film magnetic medium present inside the hard disk drive of a computer. Magnetic recording is an important function of the hard disk drive by which information such as text, pictures, audio and videos are stored. Information is broken down to a simple binary format and is stored as magnetised bits along the tracks of the disk forming the hard drive. Over the years advancements in research on the type of magnetic materials used has allowed increased data storage capacities by reducing magnetic bit sizes. It is with this advancement in magnetic data storage, that we have today's hard disk drive technology, which uses a perpendicular magnetic medium to store data. A perpendicular magnetic medium is a multi-layered magnetic thin film structure with the topmost layer comprising nanoscale magnetic grains of high perpendicular anisotropy. The topmost recording layer (RL) is mapped into individual bits of 80-100 nm² area that consist of 5-10 nm diameter CoCrPt grains, embedded in an oxide matrix. A bit area is defined to ensure a significant number of stable grains allowing data to be stored in each bit as a ‘0' or a ‘1' depending on its switched magnetic state. The magnetic grains if sputtered below a threshold grain size tend to suffer from thermal fluctuation and instability due to super-paramagnetic effects, hence bringing limitations to grain size. As a result of this, research in recent years has been directed at introducing a softer magnetic exchange coupled composite (ECC) layer above the recording layer. This layer facilitates the delicate balance of switching smaller grains with strong magneto-crystalline anisotropy at lower magnetic fields, by exchange coupling with the CoCrPt grains in the recording layer. However this technique of increasing the efficiency in the perpendicular magnetic medium by introducing ‘facilitating' layers is an area that is still being widely researched and understood. Although numerous surface and bulk analysis techniques exist to study magnetic and surface properties of these materials, there is limited information on the structural and magnetic properties of these materials at the nanoscale level. The reported work investigates the structural and magnetic properties of the magnetic grains and multi-layers in the perpendicular magnetic medium using polarised neutron scattering and reflectivity techniques. The work investigates the structural and magnetic properties of the CoCrPt grains, apart from understanding the CoCrPt magnetic grain switching. The work also investigates the magnetisation in the layers of the thin film perpendicular media structure using polarised neutron reflectivity (PNR). Using polarised small angle neutron scattering (PolSANS), it has been shown that ferromagnetic ordered core region of the CoCrPt grain in the recording layer is smaller than the physical CoCrPt granular structure. The magnetic switching behaviour of the CoCrPt grain at different magnetic fields is also analysed and the experimental PolSANS data is fitted with non-interacting size-dependent analytical grain switching models. This result provides significant evidence that the magnetic anisotropy increases with grain size, with larger magnetic grains having larger magnetic anisotropy. Polarised neutron scattering experiments are carried out with the magnetically softer exchange coupled composite (ECC) layer included in the thin film magnetic structure. The first experiments investigate if the ECC layer contributes to the nuclear and magnetic interference scattering term in the experimenting scattering data. The experiments clearly show that there is no contribution from the ECC layer in the nuclear and magnetic scattering interference term. The role of the ECC layer in the magnetic switching process is then investigated at different magnetic fields. The ECC layer was found to influence the size-dependent magnetic grain switching of the CoCrPt grains in the recording layer and a detailed investigation is presented in the reported work. Polarised neutron reflectivity (PNR) experiments have also been carried out with the ECC layer on the perpendicular magnetic media samples. These experiments investigate the composition and thickness of the thin film structure, while also providing information on the magnetic state of the thin films under the influence of an in-plane magnetic field. The in-plane magnetisation in the recording and ECC layer is determined at different in-plane magnetic fields. The magnetisation values determined for the ECC layer and the recording layer (RL) at different in-plane magnetic fields help better understand the differences in their magnetic properties.

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24

Costa, Marcio. "First-principles Studies of Local Structure Effects in Magnetic Materials". Doctoral thesis, Uppsala universitet, Materialteori, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-179223.

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This thesis focus on the magnetic behavior, from single atoms to bulk materials. The materials considered in this thesis have been studied by computational methods based on ab initio theory, density functional theory (DFT), including treatment of the spin-orbit coupling, non-collinear magnetism, and methods capable of treating discorded systems. Furthermore strongly correlated materials have been investigated using the dynamical mean field theory (DMFT). The uniaxial magnetic anisotropy energy (MAE) of the Fe2P was investigated using the full-potential linear muffin tin orbital (FP-LMTO) method. Based on a band structure analysis, the microscopical origin of the large magnetic anisotropy found for this system is explained. It is also shown that by straining the crystal structure, the MAE can be enhanced further. This opens up for the possibility of obtaining a room temperature permanent magnet based on the Fe2P. The spectral properties of Fe impurities in a Cs host have been investigated, for both surface and bulk systems, by means of combination of density-functional theory in the local density approximation and the dynamical mean-field theory (LDA+DMFT), using two different impurity solvers, the Hubbard I approximation (HIA) and the Exact Diagonalization (ED) method were used. It is shown that noticeable differences can be seen in the unoccupied part of the spectrum for different positions of Fe atoms inside the host. The calculations show good agreement with the experimental photoemission spectra. The stability of the 12-fold metal-phosphorous coordination, existing in the meteorite mineral melliniite has been investigated trough total energy calculations using the coherent potential approximation (CPA) combined with an analysis of the chemical bonds, performed by balanced crystal overlap population (BCOOP). It was shown that its uniquely high metal–phosphorous coordination is due to a balance between covalent Fe–P binding, configurational entropy and a weaker nickel–phosphorus binding. Supported clusters have drawn a lot of attention as possible building blocks for future data storage applications. This topic was investigated using a real space noncollinear formalism where the exchange interactions between Co atoms were shown to be tuned by varying the substrate surface composition. Furthermore the spin dynamics of small Co clusters an a Cu(111) surface have been investigated and a new kind of dynamics, where magnetization switching can be accelerated by decreasing the switching field, has been found. A method for calculating the electronic structure for both ordered and disordered alloys, the augmented space recursion (ASR) method, have been extended to treat non-collinear magnetic order. The method has been used to investigate the energy stability of non-collinear arrangements of MnPt and Mn3Rh alloys.

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25

Burkert, Till. "Materials for Magnetic Recording Applications". Doctoral thesis, Uppsala University, Department of Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5800.

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In the first part of this work, the influence of hydrogen on the structural and magnetic properties of Fe/V(001) superlattices was studied. The local structure of the vanadium-hydride layers was determined by extended x-ray absorption fine structure (EXAFS) measurements. The magnetic ordering in a weakly coupled Fe/V(001) superlattice was investigated using the magneto-optical Kerr effect (MOKE). The interlayer exchange coupling is weakened upon alloying with hydrogen and a phase with short-range magnetic order was observed.

The second part is concerned with first-principles calculations of magnetic materials, with a focus on magnetic recording applications. The uniaxial magnetic anisotropy energy (MAE) of Fe, Co, and Ni was calculated for tetragonal and trigonal structures. Based on an analysis of the electronic states of tetragonal Fe and Co at the center of the Brillouin zone, tetragonal Fe-Co alloys were proposed as a material that combines a large uniaxial MAE with a large saturation magnetization. This was confirmed by experimental studies on (Fe,Co)/Pt superlattices. The large uniaxial MAE of L1₀ FePt is caused by the large spin-orbit interaction on the Pt sites in connection with a strong hybridization between Fe and Pt. Furthermore, it was shown that the uniaxial MAE can be increased by alloying the Fe sublattice with Mn. The combination of the high-moment rare-earth (RE) metals with the high-T_C 3d transition metals in RE/Cr/Fe multilayers (RE = Gd, Tb, Dy) gives rise to a strong ferromagnetic effective exchange interaction between the Fe layers and the RE layer. The MAE of hcp Gd was found to have two principal contributions, namely the dipole interaction of the large localized 4f spins and the band electron magnetic anisotropy due to the spin-orbit interaction. The peculiar temperature dependence of the easy axis of magnetization was reproduced on a qualitative level.

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26

Wikberg, Magnus. "Fundamental Properties of Functional Magnetic Materials". Doctoral thesis, Uppsala universitet, Teknisk-naturvetenskapliga fakulteten, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-133257.

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Magnetic properties of powders, thin films and single crystals have been investigated using magnetometry methods. This thesis provides analysis and conclusions that are supported by the results obtained from spectroscopic and diffraction measurements as well as from theoretical calculations. First, the magnetic behavior of transition metal (TM) doped ZnO with respect to doping, growth conditions and post annealing has been studied. Our findings indicate that the magnetic behavior stems from small clusters or precipitates of the dopant, with ferromagnetic or antiferromagnetic interactions. At the lowest dopant concentrations, the estimated cluster sizes are too small for high resolution imaging. Still, the clusters may be sufficiently large to generate a finite spontaneous magnetization even at room temperature and could easily be misinterpreted as an intrinsic ferromagnetic state of the TM:ZnO compound. Second, influence of lattice strain on both magnetic moment and anisotropy has been investigated for epitaxial MnAs thin films grown on GaAs substrates. The obtained magnetic moments and anisotropy values are higher than for bulk MnAs. The enhanced values are caused by highly strained local areas that have a stronger dependence on the in-plane axis strain than out-of plane axis strain. Finally, spin glass behavior in Li-layered oxides, used for battery applications, and a double perovskite material has been investigated. For both Li(NiCoMn)O2 and (Sr,La)MnWO6, a mixed-valence of one of the transition metal ions creates competing ferromagnetic and antiferromagnetic interactions resulting in a low temperature three-dimensional (3D) spin glass state. Additionally, Li(NiCoMn)O2 with large cationic mixing exhibits a percolating ferrimagnetic spin order in the high temperature region and coexists with a two-dimensional (2D) frustrated spin state in the mid temperature region. This is one of the rare observations where a dimensional crossover from 2D to 3D spin frustration appears in a reentrant material.
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 720

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27

Ball, David Klaus. "From 2D CoCrPt:SiO2 films with perpendicular magnetic anisotropy to 3D nanocones — A step towards bit patterned media —". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-113029.

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Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities or magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest. The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation. In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements. Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics. Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetisation with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains. From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetisation aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derived
Aufgrund des weltweiten, immer weiter steigenden Bedarfs an Speicherplatz von digitalen Information, sind neue Technologien für größere und schnellere Speichermedien im Fokus von Forschung und Entwicklung. Ein Schritt hin zu einer höheren Speicherdichte in der magnetischen Datenspeicherung ist dabei das sogenannte Konzept der ”Bit patterned media”, das definierte Informationseinheiten auf regelmäßig angeordneten Nanostrukturen beschreibt. Dieser Ansatz ist einer der derzeit vielversprechendsten Optionen die Speicherdichte zu erhöhen. Dabei ist die Herstellung der benötigten Nanostrukturen und deren Skalierung hin zu makroskopischen Dimensionen eines der Probleme an deren Lösung die Wissenschaft und Industrie derzeit arbeitet. Desweiteren ist die Antwort auf die noch offene Frage nach der Beeinflussung der nanoskaligen Strukturen auf die magnetischen Eigenschaften von großem Interesse. Das Hauptziel in dieser Arbeit ist es, einen Beitrag zur Beantwortung der Frage, welche magnetischen Eigenschaften sich durch eine Veränderung der Oberflächenstruktur im Nanometerbereich beeinflussen lassen, zu leisten. Hierzu wurden die folgenden Eigenschaften, wie zum Beispiel die Anisotropie, Remanenz,Koerzitivität, Schaltfeldverteilung, Sättigungsmagnetisierung, Gilbertdämpfung und inhomogene Linienverbreiterung von planaren zweidimensionalen dünnen ferromagnetische Schichten mit denen von dreidimensionalen magnetischen Strukturen verglichen. Zusätzlich wurde der Einfluss der angegpassten Morphologie auf die intergranularen- beziehungsweise auf die zwischen den Strukturen wirkende (interdot) Austauschkopplung untersucht. Der Hauptaugenmerk bei den ferromagnetisch dünnen Schichten lag dabei auf den granularen CoCrPt:SiO2 und [Co/Pd] Filmen, die heutzutage ein Standardmaterial für die magnetischen Speichermedien darstellen. Diese Materialien zeichnen sich durch eine hohe Koerzivität und senkrechte Anisotropie, mit geringer räumlicher Verteilung der Vorzugsrichtung der Magnetisierung, aus. Die hier vorgestellten vorstrukturierten GaSb(001) Substrate mit selbstordnenden periodischen Nanokegeln auf der Oberfläche, sind mittels Ionenstrahlerosion einfach, schnell und sehr gut reproduzierbar herzustellen. Deshalb ist diese Methode besonders für die Grundlagenforschung von Vorteil. Um einen Vergleich zwischen 2D Filmen und 3D Strukturen ziehen zu können, wurden neben den vorstrukturierten Substraten auch planare Proben beschichtet. Eine erste Versuchsreihe wurde mit einem dünnen Py Film präpariert. Da dessen magnetische Eigenschaften wohlbekannt sind, konnten neben den Untersuchungen mit VNA-FMR und MOKE auch einige OOMF Simulationen erstellt werden. Danach wurden zwei Proben mit planarem CoCrPt beziehungsweise CoCrPt:SiO2 untersucht. Bei den planaren CoCrPt:SiO2 Proben wurden außerdem noch Co+ Ionen implantiert, um deren Auswirkungen auf die intergranulare Austauschkopplung, Schaltfeldverteilung und besonders auf die Spindynamik zu bestimmen. Bei beiden Probensystemen konnte zusätzlich die Spindynamik mittels zeitaufgelöstem MOKE gemessen werden. Im Anschluss wurden die beiden senkrechten Speichermedien CoCrPt:SiO2 and [Co/Pd] auf Substraten mit Nanokegeln vorstrukturierten GaSb(001) Oberflächen abgeschieden. Diese Proben wurden mit MFM, MOKE, SQUID und Vektor-VSM vermessen. Aus den Messungen konnnten dann die Einflüsse auf die intergranulare- beziehungsweise interdot Austauschkopplung in Abhängigkeit von der Periodizität und Höhe der Nanokegel bestimmt werden, sowie die Umorientierung der Magnetisierung bezüglich der Substratkrümmung und den Morphologie induzierten Einfluss auf die magnetischen Domänen. Anhand der Vergleiche zwischen den Messungen der planaren und den vorstrukturierten Proben konnte eine Verringerung der Austauschkopplung zwischen den Strukturen gezeigt werden, die mit der Nanokegelstrukturperiodizität skaliert. Außerdem wurde in allen dünnen magnetischen Filmen auf Nanokegeln gezeigt, dass die Magnetisierung sich in Abhängigkeit der darunterliegenden Struktur ausrichtet. Bei den Py auf Nanokegeln, den planaren CoCrPt und dem planaren CoCrPt:SiO2 Proben konnten außerdem mit VNA-FMR und TRMOKE Informationen bezüglich der Spindynamik gemessen werden. Die erzielten Ergebnisse, der beiden planaren Proben, sind vergleichbar mit denen, aus der Literatur bekannten Werten, für die Gilbertdämpfung. Darüber hinaus wurde durch die Messungen an den Py Proben gezeigt, dass die Theorie, des bisher genutzten 2D Modells, nicht mehr gültig ist, da sich die Magnetisierung entlang der Substratstruktur ausrichtet, und deshalb ein neues Model aufgestellt werden muss

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28

Kimling, Judith [Verfasser] y Guido [Akademischer Betreuer] Meier. "Magnetization Reversal in Cylindrical Nanowires and in Nanowires with Perpendicular Magnetic Anisotropy / Judith Kimling. Betreuer: Guido Meier". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2013. http://d-nb.info/104275392X/34.

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29

Almasi, H., M. Xu, Y. Xu, T. Newhouse-Illige y W. G. Wang. "Effect of Mo insertion layers on the magnetoresistance and perpendicular magnetic anisotropy in Ta/CoFeB/MgO junctions". AMER INST PHYSICS, 2016. http://hdl.handle.net/10150/621317.

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The effect of a thin Mo dusting layer inserted at the interface of Ta/CoFeB of perpendicular magnetic tunneling junction with MgO barriers was investigated. Unlike thick Mo layers that exhibited a strong (110) crystalline texture, the inserted Mo layer between Ta/CoFeB had little negative influence on the crystallization of CoFe (001), therefore combining the advantages of Mo as a good thermal barrier and Ta as a good boron sink. For optimized Mo dusting thickness, a large tunneling magnetoresistance of 208% was achieved in perpendicular magnetic tunneling junctions with superior thermal stability at 500 degrees C. Published by AIP Publishing.

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30

Ball, David Klaus. "From 2D CoCrPt:SiO2 films with perpendicular magnetic anisotropy to 3D nanocones — A step towards bit patterned media —". Doctoral thesis, Helmholtz-Zentrum Dresden-Rossendorf, 2012. https://tud.qucosa.de/id/qucosa%3A26882.

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Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities or magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest. The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation. In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements. Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics. Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetisation with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains. From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetisation aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derived.
Aufgrund des weltweiten, immer weiter steigenden Bedarfs an Speicherplatz von digitalen Information, sind neue Technologien für größere und schnellere Speichermedien im Fokus von Forschung und Entwicklung. Ein Schritt hin zu einer höheren Speicherdichte in der magnetischen Datenspeicherung ist dabei das sogenannte Konzept der ”Bit patterned media”, das definierte Informationseinheiten auf regelmäßig angeordneten Nanostrukturen beschreibt. Dieser Ansatz ist einer der derzeit vielversprechendsten Optionen die Speicherdichte zu erhöhen. Dabei ist die Herstellung der benötigten Nanostrukturen und deren Skalierung hin zu makroskopischen Dimensionen eines der Probleme an deren Lösung die Wissenschaft und Industrie derzeit arbeitet. Desweiteren ist die Antwort auf die noch offene Frage nach der Beeinflussung der nanoskaligen Strukturen auf die magnetischen Eigenschaften von großem Interesse. Das Hauptziel in dieser Arbeit ist es, einen Beitrag zur Beantwortung der Frage, welche magnetischen Eigenschaften sich durch eine Veränderung der Oberflächenstruktur im Nanometerbereich beeinflussen lassen, zu leisten. Hierzu wurden die folgenden Eigenschaften, wie zum Beispiel die Anisotropie, Remanenz,Koerzitivität, Schaltfeldverteilung, Sättigungsmagnetisierung, Gilbertdämpfung und inhomogene Linienverbreiterung von planaren zweidimensionalen dünnen ferromagnetische Schichten mit denen von dreidimensionalen magnetischen Strukturen verglichen. Zusätzlich wurde der Einfluss der angegpassten Morphologie auf die intergranularen- beziehungsweise auf die zwischen den Strukturen wirkende (interdot) Austauschkopplung untersucht. Der Hauptaugenmerk bei den ferromagnetisch dünnen Schichten lag dabei auf den granularen CoCrPt:SiO2 und [Co/Pd] Filmen, die heutzutage ein Standardmaterial für die magnetischen Speichermedien darstellen. Diese Materialien zeichnen sich durch eine hohe Koerzivität und senkrechte Anisotropie, mit geringer räumlicher Verteilung der Vorzugsrichtung der Magnetisierung, aus. Die hier vorgestellten vorstrukturierten GaSb(001) Substrate mit selbstordnenden periodischen Nanokegeln auf der Oberfläche, sind mittels Ionenstrahlerosion einfach, schnell und sehr gut reproduzierbar herzustellen. Deshalb ist diese Methode besonders für die Grundlagenforschung von Vorteil. Um einen Vergleich zwischen 2D Filmen und 3D Strukturen ziehen zu können, wurden neben den vorstrukturierten Substraten auch planare Proben beschichtet. Eine erste Versuchsreihe wurde mit einem dünnen Py Film präpariert. Da dessen magnetische Eigenschaften wohlbekannt sind, konnten neben den Untersuchungen mit VNA-FMR und MOKE auch einige OOMF Simulationen erstellt werden. Danach wurden zwei Proben mit planarem CoCrPt beziehungsweise CoCrPt:SiO2 untersucht. Bei den planaren CoCrPt:SiO2 Proben wurden außerdem noch Co+ Ionen implantiert, um deren Auswirkungen auf die intergranulare Austauschkopplung, Schaltfeldverteilung und besonders auf die Spindynamik zu bestimmen. Bei beiden Probensystemen konnte zusätzlich die Spindynamik mittels zeitaufgelöstem MOKE gemessen werden. Im Anschluss wurden die beiden senkrechten Speichermedien CoCrPt:SiO2 and [Co/Pd] auf Substraten mit Nanokegeln vorstrukturierten GaSb(001) Oberflächen abgeschieden. Diese Proben wurden mit MFM, MOKE, SQUID und Vektor-VSM vermessen. Aus den Messungen konnnten dann die Einflüsse auf die intergranulare- beziehungsweise interdot Austauschkopplung in Abhängigkeit von der Periodizität und Höhe der Nanokegel bestimmt werden, sowie die Umorientierung der Magnetisierung bezüglich der Substratkrümmung und den Morphologie induzierten Einfluss auf die magnetischen Domänen. Anhand der Vergleiche zwischen den Messungen der planaren und den vorstrukturierten Proben konnte eine Verringerung der Austauschkopplung zwischen den Strukturen gezeigt werden, die mit der Nanokegelstrukturperiodizität skaliert. Außerdem wurde in allen dünnen magnetischen Filmen auf Nanokegeln gezeigt, dass die Magnetisierung sich in Abhängigkeit der darunterliegenden Struktur ausrichtet. Bei den Py auf Nanokegeln, den planaren CoCrPt und dem planaren CoCrPt:SiO2 Proben konnten außerdem mit VNA-FMR und TRMOKE Informationen bezüglich der Spindynamik gemessen werden. Die erzielten Ergebnisse, der beiden planaren Proben, sind vergleichbar mit denen, aus der Literatur bekannten Werten, für die Gilbertdämpfung. Darüber hinaus wurde durch die Messungen an den Py Proben gezeigt, dass die Theorie, des bisher genutzten 2D Modells, nicht mehr gültig ist, da sich die Magnetisierung entlang der Substratstruktur ausrichtet, und deshalb ein neues Model aufgestellt werden muss.

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31

Steinbach, Gabi, Michael Schreiber, Dennis Nissen, Manfred Albrecht, Ekaterina Novak, Pedro A. Sánchez, Sofia S. Kantorovich, Sibylle Gemming y Artur Erbe. "Field-responsive colloidal assemblies defined by magnetic anisotropy". American Physical Society, 2019. https://monarch.qucosa.de/id/qucosa%3A70641.

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Particle dispersions provide a promising tool for the engineering of functional materials that exploit self-assembly of complex structures. Dispersion made from magnetic colloidal particles is a great choice; they are biocompatible and remotely controllable among many other advantages. However, their dominating dipolar interaction typically limits structural complexity to linear arrangements. This paper shows how a magnetostatic equilibrium state with noncollinear arrangement of the magnetic moments, as reported for ferromagnetic Janus particles, enables the controlled self-organization of diverse structures in two dimensions via constant and low-frequency external magnetic fields. Branched clusters of staggered chains, compact clusters, linear chains, and dispersed single particles can be formed and interconverted reversibly in a controlled way. The structural diversity is a consequence of both the inhomogeneity and the spatial extension of the magnetization distribution inside the particles. We draw this conclusion from calculations based on a model of spheres with multiple shifted dipoles. The results demonstrate that fundamentally new possibilities for responsive magnetic materials can arise from interactions between particles with a spatially extended, anisotropic magnetization distribution.

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32

Inglefield, Heather Elizabeth. "Misfit accomodation in thin films of Ni/Cu as measured by magnetic anisotropy". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32659.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995.
Includes bibliographical references (leaves 134-137).
by Heather Elizabeth Inglefield.
Ph.D.

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33

Vo, Van Chi. "Epitaxial graphene on metal for new magnetic manometric systems". Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00829379.

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Graphene is a candidate for next generation spintronics devices exploiting its long spin transport length and high carrier mobility. Besides, when put in interaction with a ferromagnet, it may become an active building block, as suggested by recent surface science studies revealing few tenth of a Bohr magneton magnetic moments held by carbon atoms in graphene on iron, and a Rashba spin-orbit splitting reaching about 10 meV in graphene on a high atomic number element such as gold. The extent to which graphene may influence the properties, e.g. magnetic ones, of the materials contacted to it was barely addressed thus far. High quality hybrid systems composed of graphene in contact with magnetic thin layers or nanoclusters are playgrounds for exploring both aspects, the manipulation of the properties of graphene by interaction with other species, and vice versa. In graphene contacted to ultra-thin ferromagnetic layers for instance, strong graphene/ferromagnet interface effects could be employed in the view of manipulating the magnetization in the ferromagnet. The recently discovered close-to-perfect self-organization of nanoclusters on graphene, provides a way to probe magnetic interaction between clusters, possibly mediated by graphene. Three high quality hybrid systems relying on graphene prepared by chemical vapor deposition on the (111) surface of iridium have been developed under ultra-high vacuum (UHV): cobalt ultra-thin and flat films deposited on top of graphene, and intercalated at moderate temperature between graphene and its substrate, and self-organized cobalt- and iron-rich nanoclusters on the 2.5 nm-periodicity moiré between graphene and Ir(111). Prior to these systems, 10 nm-thick Ir(111) single-crystal thin films on sapphire were developed: they were latter employed as a substrate replacing bulk Ir(111) single-crystals usually employed. This new substrate opens the route to multi-technique characterizations, especially ex situ ones which were little employed thus far for studying graphene/metal systems prepared under UHV. Using a combination of in situ surface science techniques (scanning tunneling microscopy, x-ray magnetic circular dichroism, spin-polarized low-energy electron microscopy, auger electron spectroscopy, reflection high-energy electron diffraction) and ex situ probes (x-ray diffraction, transmission electron microscopy, Raman spectroscopy, MOKE magnetometry) the structural, vibrational, electronic, and magnetic properties of the three new graphene hybrid systems were characterized and confronted to first-principle calculations. Several striking features were unveiled. The interface between graphene and cobalt involves strong C-Co interactions which are responsible for a large interface magnetic anisotropy, capable of driving the magnetization out-of-the plane of the surface of an ultra-thin film in spite of the strong shape anisotropy in such films. The effect is maximized in the system obtained by intercalation between graphene and iridium, which comes naturally air-protected. Nanoclusters, on the contrary, seem to weakly interact with graphene. Small ones, comprising ca. 30 atoms each, remain super paramagnetic at 10 K, have no magnetic anisotropy, and it turns out difficult, even with 5 T fields to saturate their magnetization. Besides, the magnetic domains size seem to exceed the size of a single cluster, possibly pointing to magnetic interactions between clusters.

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34

McClure, Adam Marc. "Epitaxial thin film deposition of magnetostrictive materials and its effect on magnetic anisotropy". Diss., Montana State University, 2012. http://etd.lib.montana.edu/etd/2012/mcclure/McClureA0512.pdf.

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Magnetostriction means that the dimensions of a material depend on its magnetization. The primary goal of this dissertation was to understand the effect of magnetostriction on the magnetic anisotropy of single crystal magnetostrictive thin films, where the epitaxial pinning of the material to a substrate could inhibit its conversion to new dimensions. In order to address this goal, several Fe-based binary alloys were deposited onto various substrates by molecular beam epitaxy. The samples were characterized by an array of techniques including electron diffraction, Rutherford backscattering, vibrating sample magnetometry, ferromagnetic resonance, and x-ray absorption spectroscopies. The attempted growths of crystalline magnetostrictive thin films resulted in successful depositions of Fe 1-xGa x and Fe 1-xZn x. Depositions onto MgO(001) substrates result in an in-plane cubic magnetic anisotropy, as expected from the cubic symmetry of the Fe-based thin films, and a strong out-of-plane uniaxial anisotropy that forces the magnetization to lie in the plane of the films. Depositions onto ZnSe/GaAs(001) substrates feature an additional in-plane uniaxial anisotropy. The magnitudes and signs of the in-plane anisotropies depend on the Ga content. Furthermore, the cubic anisotropy constant of Fe 1-xGa x samples deposited onto MgO substrates switches sign at a lower Ga concentration than is seen in bulk Fe 1-xGa x. The effect on the magnetic anisotropy of depositing a magnetostrictive material as an epitaxial thin film is influenced by the material's magnetostrictive properties and the substrate upon which it is deposited. In particular, pinning a magnetoelastic material to a substrate will modify its cubic anisotropy, and depositions on substrates compliant to an anisotropic strain relaxation may result in a strong in-plane uniaxial anisotropy. 'Co authored by Steven Albert, Tino Jaeger, Hongyan Li, Paul Rugheimer, Juergen A. Schaefer, Yves U. Idzerda, Elke Arenholz, Hongyan Li, Gerrit van der Laan, Damon A. Resnick, Christopher M. Kuster.'

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35

Richomme, Fabienne. "Etude expérimentale des propriétés structurales et magnétiques de multicouches fer/terbium : modulation de composition, anisotropie magnétique, effet d'irradiation aux ions". Rouen, 1996. http://www.theses.fr/1996ROUES008.

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Les multicouches Fe/Tb peuvent présenter une forte anisotropie magnétique perpendiculaire nécessaire à la réalisation d'un milieu d'enregistrement magnétique haute densité. Les multicouches étudiées ont été élaborées, soit par pulvérisation cathodique RF, soit par évaporation sous ultra-vide, puis caractérisées par spectrométrie Mössbauer par électrons de conversion, par diffraction de rayons X aux petits angles et grands angles et par mesures d'aimantation. Le grand nombre d'échantillons pulvérisés étudies a permis d'établir un diagramme précis des caractéristiques structurales et magnétiques des couches de fer dans un large domaine d'épaisseurs de fer et de terbium (eFe compris entre 0,22 et 3,35 nm, eTb entre 0,20 et 2,40 nm), à partir de valeurs très faibles, correspondant à des multicouches amorphes, jusqu'à présent peu explorées par spectrométrie Mössbauer. Les couches de fer cristallisent pour eFe égale à 2,3 nm. Les couches amorphes, d'abord modulées en composition, présentent aussi, à partir de 1,2 nm de fer nominal, une zone de fer amorphe pur au centre des couches de fer, qui modifie fortement les propriétés magnétiques des multicouches. Ces résultats ont été confirmés par la déposition sélective de fer 57, qui permet une analyse à l'échelle de la monocouche. L'observation séparée des deux interfaces Fe/Tb et Tb/Fe a montré qu'elles sont identiques dans les couches amorphes, mais très différentes dans les couches cristallisées. Les propriétés magnétiques, en particulier la direction d'anisotropie, ont été interprétées de manière cohérente à partir des différentes zones magnétiques observées. Le domaine d'anisotropie magnétique perpendiculaire est obtenu pour de faibles épaisseurs de fer. L'irradiation aux ions effectuée au GANIL a mis en évidence une étape inédite de démixion du fer et du terbium. L'étape usuelle de mélange n'est observée qu'au-dessus d'un pouvoir d'arrêt électronique seuil voisin de 22 keV/nm.

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36

Chapman, John Richard. "Ultrasonic wave interactions with magnetic colloids". Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366409.

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37

Le, Quang Tuan. "Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies". Doctoral thesis, KTH, Materialfysik, MF, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-191176.

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Spin-torque transfer (STT) effects have brought spintronics ever closer to practical electronic applications, such as MRAM and active broadband microwave spin-torque oscillator (STO), and have emerged as an increasingly attractive field of research in spin dynamics. Utilizing materials with perpendicular magnetic anisotropy (PMA) in such applications offers several great advantages such as low-current, low-field operation combined with high thermal stability. The exchange coupling that a PMA thin film exerts on an adjacent in-plane magnetic anisotropy (IMA) layer can tilt the IMA magnetization direction out of plane, thus creating a stack with an effective tilted magnetic anisotropy. The tilt angle can be engineered via both intrinsic material parameters, such as the PMA and the saturation magnetization, and extrinsic parameters, such as the layer thicknesses. STOs can be fabricated in one of a number of forms—as a nanocontact opening on a mesa from a deposited pseudospin-valve (PSV) structure, or as a nanopillar etching from magnetic tunneling junction (MTJ)—composed of highly reproducible PMA or predetermined tilted magnetic anisotropy layers. All-perpendicular CoFeB MTJ STOs showed high-frequency microwave generation with extremely high current tunability, all achieved at low applied biases. Spin-torque ferromagnetic resonance (ST-FMR) measurements and analysis revealed the bias dependence of spin-torque components, thus promise great potential for direct gate-voltage controlled STOs. In all-perpendicular PSV STOs, magnetic droplets were observed underneath the nanocontact area at a low drive current and low applied field. Furthermore, preliminary results for microwave auto-oscillation and droplet solitons were obtained from tilted-polarizer PSV STOs. These are promising and would be worth investigating in further studies of STT driven spin dynamics.
Effekter av spinnvridmoment (STT) har fört spinntroniken allt närmare praktiska elektroniska tillämpningar, såsom MRAM och den spinntroniska mikrovågsoscillatorn (STO), och har blivit ett allt mer attraktivt forskningsområde inom spinndynamik. Användning av material med vinkelrät magnetisk anisotropi (PMA) i sådana tillämpningar erbjuder flera stora fördelar, såsom låg strömförbrukning och funktion vid låga fält i kombination med hög termisk stabilitet. Den utbyteskoppling (”exchange bias”) en PMA-tunnfilm utövar på ett intilliggande skikt med magnetisk anisotropi i planet (IMA) kan få IMA-magnetiseringsriktningen att vridas ut ur planet, vilket ger en materialstack med en effektivt sett lutande magnetisk anisotropi. Lutningsvinkeln kan manipuleras med både inre materialparametrar, såsom PMA och mättningsmagnetisering, och yttre parametrar, såsom skikttjocklekarna. STO:er kan tillverkas som flera olika typer - som en nanokontaktsöppning på en s.k. mesa av en deponerad pseudospinnventilstruktur (PSV) eller som en nanotråd etsad ur en magnetisk tunnlingsövergång (MTJ) –och bestå av mycket reproducerbar PMA eller av skikt med på förhand bestämt lutning av dess magnetiska anisotropi. MTJ-STO:er av CoFeB med helt vinkelrät anisotropi visar högfrekvent mikrovågsgenerering med extremt stort frekvensomfång hos strömstyrningen, detta vid låg biasering. Mätning och analys av spinnvridmoments-ferromagnetisk resonans (ST-FMR) avslöjade ett biasberoende hos spinnvridmomentskomponenter, vilket indikerar en stor potential för direkt gate-spänningsstyrda STO:er. I helt vinkelräta PSV-STO:er observerades magnetiska droppar under nanokontaktområdet vid låg drivström och lågt pålagt fält. Dessutom erhölls preliminära resultat av mikrovågssjälvsvängning och av s.k. ”droplet solitons” hos PSV-STO:er med lutande polarisator. Dessa är lovande och skulle vara värda att undersökas i ytterligare studier av STT-driven spinndynamik.

QC 20160829

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38

Eggers, Tatiana M. "Surface and Interface Effects of Magnetoimpedance Materials at High Frequency". Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7282.

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Amorphous and nanocrystalline transition metal magnetic alloys (TMMAs) have been the subjects of fundamental and applied study due to their unique structure. The lack of long-range order in these materials sets the stage for their soft magnetic properties to be tuned for a variety of technological applications, such as sensitive magnetic field sensors, high frequency transformers, and stress sensors. Fundamental investigation of the magnetic and structural properties of these materials is also motivated by their unique amorphous or nanocrystalline-embedded amorphous matrix morphology, which has consequences on both the magnetism seen from both the atomic and macro-scale. The surfaces of these materials become important to their high frequency applications, where the skin depth of the excitation field is distributed near the surface. In conjunction with high frequency magnetoimpedance measurements, surface sensitive probes of magnetism and structure must be employed to provide a complete picture of the relationship between the surface and dynamic magnetism. This dissertation focuses on the surface impact of chemical composition, annealing conditions, and coatings on TMMAs on their magnetoimpedance response through multiple surface sensitive techniques such as atomic/magnetic force microscopy, magneto-optical Kerr effect, and scanning/transmission electron microscopy. These tools provide a view into the relationship between the nanostructure, microstructure and soft magnetic properties that make these materials highly desired for fundamental study and technological application.

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39

Lichter, Jenny 1982. "Iron-gallium alloys : temperature and field effects on [lambda]100 and magnetic anisotropy measurements". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32728.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, June 2004.
"May 2004."
Includes bibliographical references (leaves 18-19).
Magnetostriction measurements were taken on samples of Fe-Ga alloys (Galfenol) containing between 18% and 35% Ga in fields of 5 kOe to 24 kOe from room temperature to liquid nitrogen temperature. In addition, room temperature magnetic anisotropy measurements were conducted on samples between 8% Ga and 25% Ga. No major hysteresis was found in any of the samples and the field dependence was found to be modest (-2%). Anomalous temperature dependence was found in 22-24% Galfenol, where magnetostriction decreased with decreasing temperature, and 35% Galfenol, where magnetostriction increased dramatically (over 50% to values up to about 250 parts per million) with decreasing temperature. Quenching to retain [alpha]-iron and B2 (CsCl) phases was found to increase magnetostriction, with the B2 structure creating the largest magnetostriction. The reasons for the atypical temperature dependence and the B2 structure enhancing magnetostriction are still unexplained. K anisotropy constants were found to decrease with increasing Ga concentration, but more samples need to be measured to validate this trend.
by Jenny Lichter.
S.B.

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40

Skuza, Jonathan Ronald. "Thin Film and Chemical Ordering Effects on the Magnetic Anisotropy in Binary Alloys". W&M ScholarWorks, 2011. https://scholarworks.wm.edu/etd/1539623583.

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This dissertation presents various investigations into the structure-property correlations in highly anisotropic FePt and FePd thin films and nanostructures. These binary alloy thin films may exhibit long-range chemical ordering (e.g. L10), which induces a strong uniaxial magnetic anisotropy whose orientation is dependent on the ordering direction in the thin film. The chemical ordering, and hence the magnetic anisotropy, in these thin films can be controlled and tailored through sputter deposition and ion implantation conditions followed by subsequent processing. Two novel fabrication methods, x-ray rapid thermal annealing (XRTA) and heavy ion implantation, successfully demonstrate the ability to obtain highly anisotropic nanometer-sized L10 ordered regions in thin films. XRTA has the advantage of using high brilliance x-ray undulator radiation to simultaneously induce and probe microstructural changes in real time and is shown to favorably modify the chemical order in partially-ordered FePt thin films without affecting the average ordered grain size. Heavy ion implantation has the advantage of fabricating nonequilibrium nanocomposite thin films, which in the case of Fe+ implanted Pt thin films requires lower activation energies to nucleate and grow the L10 phase thus implying lower processing temperatures. The magnetic anisotropy in these binary alloy thin films is not only tailored through the chemical ordering, but can be further influenced by an adequate choice of the capping layer. Magnetically polarizable capping layers (e.g. Pd) decrease the perpendicular magnetic anisotropy (PMA) of FePd thin films, while non-polarizable capping layers (e.g. MgO) have no effect on the PMA. Different magnetization profiles of the films obtained from x-ray resonant magnetic scattering measurements explain this change observed in the magnetic anisotropy. The magnetic domain structure in these highly anisotropic thin films is also important and influenced by the magnetic anisotropy. An analytical model shows good quantitative agreement with experiment for FePd thin films above a critical thickness, thus showing the direct correlations between chemical order, magnetic anisotropy, and magnetic domain structure in these films.

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41

Steinke, Nina-Juliane. "Structure and magnetic properties of anisotropic ferromagnetic thin-film heterostructures". Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609919.

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42

Bochi, Gabriel 1969. "Magnetic anisotropy in epitaxial Ni/Cu (001) thin films and Cu/Ni/Cu (001) sandwiches". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11514.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995.
Vita.
Includes bibliographical references (leaves 156-161).
by Gabriel Bochi.
Ph.D.

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43

Lee, Aidan Jarreau. "Engineering Magnetism in Rare Earth Garnet and Metallic Thin Film Heterostructures". The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1589886138733333.

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44

Broddefalk, Arvid. "Magnetic properties of transition metal compounds and superlattices". Doctoral thesis, Uppsala University, Department of Materials Science, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-535.

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Magnetic properties of selected compounds and superlattices have been experimentally studied using SQUID (superconducting quantum interference device) and VSM (vibrating sample magnetometer) magnetometry, neutron diffraction and Mössbauer spectroscopy measurements combined with theoretical ab initio calculations.

The magnetic compounds (Fe_1-xM_x)₃P, M=Co or Mn have been studied extensively. It was found that Co can substitute Fe up to x=0.37. Increasing the Co content leads to a reduction of the Curie temperature and the magnetic moment per metal atom. Mn can substitute Fe up to x=0.25 while Fe can be substituted into Mn₃P to 1-x=0.33. On the iron rich side, the drop in Curie temperature and magnetic moment when increasing the Mn content is more rapid than for Co substitution. On the manganese rich side an antiferromagnetic arrangement with small magnetic moments was found.

The interlayer exchange coupling and the magnetocrystalline anisotropy energy of Fe/V superlattices were studied. The coupling strength was found to vary with the thickness of the iron layers. To describe the in-plane four-fold anisotropy, the inclusion of surface terms proved necessary.

The in-plane four fold anisotropy was also studied in a series of Fe/Co superlattices, where the thickness of the Co layers was kept thin so that the bcc structure could be stabilized. Only for samples with a large amount of iron, the easy axis was found to be [100]. The easy axis of bulk bcc Co was therefor suggested to be [111].

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45

Akcaoglu, Fehmi Umit. "Investigating The Effect Of Deformation And Annealing Texture On Magnetic Anisotropy In Low-c Steel Sheets By Magnetic Barkhausen Noise Method". Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615569/index.pdf.

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Deformation and annealing texture in the cold rolled low carbon steels is important for sheet metal forming operations and service performance. The aim of this study is to non-destructively investigate the effect of texture on magnetic anisotropy. Various samples having different textures and residual stress states, due to different % reduction in thickness, annealing and stress relieving treatment, were prepared. Texture maps were obtained by Magnetic Barkhausen noise measurements performed with 100 steps between the ranges of 00-3600 on the surface. Microstructure investigation by optical &
scanning electron microscopy
hardness and tension tests were performed
and texture was determined by X-Ray diffraction method. The results were compared, evaluated and discussed to establish relationship between texture and magnetic Barkhausen Noise emission.

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46

Yi, Jae-Young. "Microstructure and magnetic properties of Co-(CoO, CoNiO2̳, NiO) and Cox̳Ni1̳-̳x̳-CoO nanocomposite thin films /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p3000403.

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47

Apaydin, Nil. "Novel Implementations of Coupled Microstrip Lines on Magnetic Substrates". The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373897365.

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48

Kyselov, Mykola. "Phenomenological theories of magnetic multilayers and related systems". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-63594.

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In this thesis multidomain states in magnetically ordered systems with competing long-range and short range interactions are under consideration. In particular, in antiferromagnetically coupled multilayers with perpendicular anisotropy unusual multidomain textures can be stabilized due to a close competition between long-range demagnetization fields and short-range interlayer exchange coupling. These spatially inhomogeneous magnetic textures of regular multidomain configurations and irregular networks of topological defects as well as complex magnetization reversal processes are described in the frame of the phenomenological theory of magnetic domains. Using a modified model of stripe domains it is theoretically shown that the competition between dipolar coupling and antiferromagnetic interlayer exchange coupling causes an instability of ferromagnetically ordered multidomain states and results in three possible ground states: ferromagnetic multidomain state, antiferromagnetic homogeneous and antiferromagnetic multidomain states. The presented theory allows qualitatively to define the area of existence for each of these states depending on geometrical and material parameters of multilayers. In antiferromagnetically coupled superlattices with perpendicular anisotropy an applied magnetic bias field stabilizes specific multidomain states, so-called metamagnetic domains. A phenomenological theory developed in this thesis allows to derive the equilibrium sizes of metamagnetic stripe and bubble domains as functions of the antiferromagnetic exchange, the magnetic bias field, and the geometrical parameters of the multilayer. The magnetic phase diagram includes three different types of metamagnetic domain states, namely multidomains in the surface layer and in internal layers, and also mixed multidomain states may arise. Qualitative and quantitative analysis of step-like magnetization reversal shows a good agreement between the theory and experiment. Analytical equations have been derived for the stray field components of these multidomain states in perpendicular multilayer systems. In particular, closed expressions for stray fields in the case of ferromagnetic and antiferromagnetic stripes are presented. The theoretical approach provides a basis for the analysis of magnetic force microscopy (MFM) images from this class of nanomagnetic systems. Peculiarities of the MFM contrast have been calculated for realistic tip models. These characteristic features in the MFM signals can be employed for the investigations of the different multidomain modes. The methods developed for stripe-like magnetic domains are employed to calculate magnetization processes in twinned microstructures of ferromagnetic shape-memory materials. The remarkable phenomenon of giant magnetic field induced strain transformations in such ferromagnetic shape memory alloys as Ni-Mn-Ga, Ni-Mn-Al, or Fe-Pd arises as an interplay of two physical effects: (i) A martensitic transition creating competing phases, i.e. crystallographic domains or variants, which are crystallographically equivalent but have different orientation. (ii) High uniaxial magnetocrystalline anisotropy that pins the magnetization vectors along certain directions of these martensite variants. Then, an applied magnetic field can drive a microstructural transformation by which the martensitic twins, i.e. the different crystallographic domains, are redistributed in the martensitic state. Within the phenomenological (micromagnetic) theory the equilibrium parameters of multivariant stripe patterns have been derived as functions of the applied field for an extended single-crystalline plate. The calculated magnetic phase diagram allows to give a detailed description of the magnetic field-driven martensitic twin rearrangement in single crystals of magnetic shape-memory alloys. The analysis reveals the crucial role of preformed twins and of the dipolar stray-field energy for the magnetic-field driven transformation process in magnetic shape-memory materials. This work has been done in close collaboration with a group of experimentalists from Institute of Metallic Materials of IFW Dresden, Germany and San Jose Research Center of Hitachi Global Storage Technologies, United States. Comparisons between theoretical and experimental data from this cooperation are presented throughout this thesis as vital part of my work on these different subjects.

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49

Ferraro, Filippo Jacopo. "Magnetic anisotropies and exchange bias in ultrathin cobalt layers for the tunnel anisotropic magnetoresistance". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY086/document.

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Dans le cadre de l’étude des phénomènes magnétiques et de la spintronique qui sont présents aux échelles nanoscopiques nous avons étudié différents aspects des structures asymétriques de Pt/Co/AlOx. L’un des objectifs de cette thèse est le contrôle de l’oxydation et des propriétés magnétiques de ces multicouches. Nous avons combiné les mesures de structures (réflexion de Rayon-X), transports (Effet Hall anormal), et magnétiques (VSM-SQUID) afin de déterminer les rôles des effets magnétiques et d’interfaces. Un objectif était d’analyser le rôle de quelques monocouches (MCs) de CoO (qui peut se former lors de la sur oxydation de l’Al) sur les propriétés de la multicouche. Nous avons utilisé une technique de déposition avec un gradient d’épaisseur pour contrôler l’oxydation à l’échelle nanométrique. Nous avons établis que quelques monocouches (MCs) de CoO a un impact sur l’anisotropie de a multicouche. Pour approfondir l’effet de la couche de CoO, nous avons construit des bicouches ultrafines de Co(0.6nm)/CoO(0.6nm). Nous avons effectué des mesures refroidi sur champ sur ce système et trouvé un fort effet de couplage d'échange. Ces résultats indiquent que la couche CoO garde une forte anisotropie même en dans la limite des monocouches et permet de réfuter certains modèles sur l’effet d’échange bias et indique que les couches, couramment négligé, de CoO doivent être prises en considération dans le bilan énergétiques du système. Nous avons construits un appareil de mesure perpendiculaire de la magnétorésistance tunnel anisotrope (TAMR) à partir de la structure Pt/Co/AlOx. La TAMR est un effet de spintronique relativement récent dans lequel la rotation d’aimantation dans une électrode magnétique (combiné avec un couplage spin-orbite) peut entrainer un changement de la probabilité de l’effet tunnel, ce qui se manifeste comme un effet de magnétorésistance. Nous avons démontré qu’un contrôle précis de l’état d’oxydation est essentiel pour l’effet TAMR. La forte anisotropie magnétique induite nous permet d’atteindre des valeurs de TAMR plus grande comparée à celle des structures Pt/Co/AlOx
In the context of studying magnetic and spintronics phenomena occurring at the nanoscale, we investigated several aspects of Pt/Co/AlOx asymmetric structures. One of the objectives of this thesis was the control of the oxidation and the tailoring of the magnetic properties of these multilayers. We combined structural (X-Ray Reflectivity), transport (Anomalous Hall Effect) and magnetic measurements (VSM-SQUID), to study the interplay of magnetic and interfacial effects. One objective was to analyze the role that few monolayers (MLs) of CoO (which can form when overoxidizing the Al layer), could have on the properties of the stack. We used a wedge deposition techniques to control the oxidation on a subnanometer scale. We established that few MLs of CoO largely affect the total anisotropy of the stack. To further investigate the impact of the CoO, we engineered ultrathin Co(0.6nm)/CoO(0.6nm) bilayers. We performed field cooled measurements on this system and we found a large exchange bias anisotropy. These results indicate that the CoO keeps a large anisotropy even in the ML regime, help to rule out some of the models proposed to explain the exchange bias effect and imply that the usually neglected CoO presence must be considered in the energy balance of the system. We build perpendicular Tunneling Anisotropic MagnetoResistance (TAMR) devices based on the Pt/Co/AlOx structure. The TAMR is a relatively new spintronics effect in which the rotation of the magnetization in a single magnetic electrode (combined with the Spin-Orbit Coupling) can cause a change of the tunnel probability, which manifests as a magnetoresistance effect. We demonstrated that a careful control of the interface oxidation is crucial for the TAMR effect. The large induced magnetic anisotropy allowed us to achieve enhanced TAMR values compared to similar Pt/Co/AlOx structures

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50

Tang, Minao. "SYNTHESES, STRUCTURES AND MAGNETIC CHARACTERIZATION OF DI- AND TRIVALENT HYDRIDOTRIS(3,5-DIMETHYLPYRAZOL-1-YL)BORATE CYANOMANGANATES". UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_theses/546.

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The syntheses, structures, and magnetic properties of a series of di/trivalent hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) cyanomanganates were investigated. Treatment of manganese(III)acetylacetonate with KTp* followed by tetra(ethyl)- ammonium cyanide affords [NEt4][(Tp*)MnII(acac)(CN)] (1). Attempts to oxidize 1 with iodine affords {(Tp*)MnII(κ2O-acac-CN)}n (7); a minor complex {[NEt4][(Tp*)MnII(κ2O-acac-3-CN)]2(µ-CN) (8) was also isolated. The manganese(II) complex [NEt4][(Tp*)MnII(κ2O-acac-3-CN)(κ1N -3-NC-acac)] (2) was obtained via treatment of Mn(3-acacCN)3 with KTp* and [NEt4]CN. [NEt4]2[MnII(CN)4] (3) was prepared via treatment of Mn(OTf)2 with excess [NEt4]CN. [NEt4][(Tp*)MnIII(CN)3] (4), is prepared via treatment of 4 with Mn(3-acacCN)3, KTp* and excess [NEt4]CN. [PPN][(Tp*)MnIII(CN)3] (5) is obtained via treatment of [PPN]3[MnII(CN)6] with (Tp*)SnBu2Cl. Combination of 4 with [MnII(bipy)2(OH2)2][OTf]2 afforded a tetranuclear rectangular cluster {MnIII 2MnII 2} (9). At low temperature, {MnIII2NiII2} (10) was prepared via treatment of 4 and [Ni(II)(bipy)2(H2O)2][OTf]2. Treatment of 4 with [CoII(bipy)2(OH2)2][OTf]2 at low temperature failed to give the desired {MnIII2CoII2} complex. Magnetic measurements indicate that 1, 2, and 7 contain high-spin isotropic MnII with no long-range magnetic order observed for 7 (T > 2 K); 4 contains low-spin MnIII that likely adopt an isotropic 3A2 spin ground state. Surprisingly 9 and 10 do not exhibit slow relaxation of the magnetization (for T > 1.8 K) despite the presence of significant molecular anisotropy.

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Tesis sobre el tema "Magnetic materials with perpendicular magnetic anisotropy"

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