Dissertations / Theses: 'Magnetic properties in spintronics'

1

Owen, Man Hon Samuel. "Electrical gating effects on the magnetic properties of (Ga,Mn)As diluted magnetic semiconductors." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/228705.

Full text

Abstract:

The aim of the research project presented in this thesis is to investigate the effects of electrostatic gating on the magnetic properties of carrier-mediated ferromagnetic Ga1-xMnxAs diluted magnetic semiconductors. (Ga,Mn)As can be regarded as a prototype material because of its strong spin-orbit coupling and its crystalline properties which can be described within a simple band structure model. Compressively strained (Ga,Mn)As epilayer with more complex in-plane competing cubic and uniaxial magnetic anisotropies is of particular interest since a small variation of these competing anisotropy fields provide a means for the manipulation of its magnetization via external electric field. An all-semiconductor epitaxial p-n junction field-effect transistor (FET) based on low-doped Ga0.975Mn0.025As was fabricated. It has an in-built n-GaAs back-gate, which, in addition to being a normal gate, enhances the gating effects, especially in the depletion of the epilayer, by decreasing the effective channel thickness by means of a depletion region. A shift in the Curie temperature of ~2 K and enhanced anisotropic magnetoresistance (AMR) (which at saturation reaches ~30%) is achieved with a depletion of a few volts. Persistent magnetization switchings with short electric field pulses are also observed. The magnitude of the switching field is found to decrease with increasing depletion of the (Ga,Mn)As layer. By employing the k . p semiconductor theory approach (performed by our collaborators in Institute of Physics, ASCR, Prague), including strong spin-orbit coupling effects in the host semiconductor valence band, a change in sign of Kc at hole density of approximately 1.5x1020 cm-3 is observed. Below this density, the [110]/[1⁻10] magnetization directions are favoured, consistent with experimental data. A double-gated FET, with an ionic-gel top-gate coupled with a p-n junction back-gate based on the same material, was also employed in an attempt to achieve larger effects through gating. It reaffirms the results obtained and demonstrates enhanced gating effects on the magnetic properties of (Ga,Mn)As.

APA, Harvard, Vancouver, ISO, and other styles

2

Gustavsson, Fredrik. "Properties of Fe/ZnSe Heterostructures : A Step Towards Semiconductor Spintronics." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2002. http://publications.uu.se/theses/91-554-5314-7/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Lu, Yongxiong. "Synthesis and magnetic properties of Feâ‚ƒOâ‚„/GaAs(100) structures for spintronics." Thesis, University of York, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424536.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Rovinelli, Giovanni. "Magnetic, morphological and structural properties of polycrystalline ultrathin cobalt films for organic spintronics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.

Find full text

Abstract:

The opportunity of using the organic molecules in spintronic devices appeared challenging since these materials, having nominally high spin relaxation times, are suitable for coherent spin manipulation. The spin behaviour in these molecular spintronic devices has been demonstrated to strongly depend on the nature of the chemical bonds between the organic molecules and the magnetic electrodes affecting also the magnetic response of both molecular and metallic sides. In particular, the adsorption of an organic molecule on a ferromagnetic layer has been proved to change the local magnetism of a magnetic substrate. In spite of their technological interest, the investigation of such effect in the case of the polycrystalline magnetic thin film is still lacking. My work contributes to filling this gap by studying the structural, morphological and magnetic properties of ultrathin polycrystalline cobalt films covered by the well-known buckminsterfullerene organic molecule (C60). The combined investigation by AFM, TEM, SQUID magnetometry and anisotropic magnetoresistance allowed to correlate the sample microstructure with the magnetic response and to identify the main mechanism responsible for spin transport in these FM layers. Analysed films are composed of polycrystalline cobalt grains decoupled by non-crystalline amorphous regions. The volume ratio between crystalline grains and amorphous regions increases by increasing the film thickness. As expected, the values of saturation magnetisation decrease as the crystallinity decreases and a typical blocking behaviour is present. The cobalt layers are also subjected to oxidation at the interface with the single crystal oxide substrate. The presence of amorphous phase in polycrystalline cobalt ultrathin film impacts the analysis of transport properties: the anisotropic magnetoresistance slightly depends on the crystalline phase while it is mainly inherent to the amorphous component.

APA, Harvard, Vancouver, ISO, and other styles

5

Vahaplar, Kadir Tarı Süleyman. "Structural And Magnetic Properties os Si(100)/Ta/Co Multilayers For Spintronics Applications." [s.l.]: [s.n.], 2007. http://library.iyte.edu.tr/tezler/master/fizik/T000662.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Newhouse-Illige, T., Yaohua Liu, M. Xu, Hickey D. Reifsnyder, A. Kundu, H. Almasi, Chong Bi, et al. "Voltage-controlled interlayer coupling in perpendicularly magnetized magnetic tunnel junctions." NATURE PUBLISHING GROUP, 2017. http://hdl.handle.net/10150/624333.

Full text

Abstract:

Magnetic interlayer coupling is one of the central phenomena in spintronics. It has been predicted that the sign of interlayer coupling can be manipulated by electric fields, instead of electric currents, thereby offering a promising low energy magnetization switching mechanism. Here we present the experimental demonstration of voltage-controlled interlayer coupling in a new perpendicular magnetic tunnel junction system with a GdOx tunnel barrier, where a large perpendicular magnetic anisotropy and a sizable tunnelling magnetoresistance have been achieved at room temperature. Owing to the interfacial nature of the magnetism, the ability to move oxygen vacancies within the barrier, and a large proximity-induced magnetization of GdOx, both the magnitude and the sign of the interlayer coupling in these junctions can be directly controlled by voltage. These results pave a new path towards achieving energy-efficient magnetization switching by controlling interlayer coupling.

APA, Harvard, Vancouver, ISO, and other styles

7

Tsai, I.-Ling. "Magnetic properties of two-dimensional materials : graphene, its derivatives and molybdenum disulfide." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/magnetic-properties-of-twodimensional-materials-graphene-its-derivatives-and-molybdenum-disulfide(59dcba1b-332e-4a58-86f6-80ed56c7fdd1).html.

Full text

Abstract:

Graphene, an atomically thin material consisting of a hexagonal, highly packed carbon lattice, is of great interests in its magnetic properties. These interests can be categorized in several fields: graphene-based magnetic materials and their applications, large diamagnetism of graphene, and the heterostructures of graphene and other two dimensional materials. In the first aspect, magnetic moments can be in theory introduced to graphene by minimizing its size or introducing structural defects, leading to a very light magnetic material. Furthermore, weak spin-orbital interaction, and long spin relaxation length make graphene promising for spintronics. The first part of this thesis addressed our experimental investigation in defect-induced magnetism of graphene. Non-interacted spins of graphene have been observed by intentionally introducing vacancies and adatoms through ion-irradiation and fluorination, respectively. The defect concentration or the magnetic moments introduced in this thesis cannot provide enough interaction for magnetic coupling. Furthermore, the spins induced by vacancies and adatoms can be controlled through shifting the Fermi energy of graphene using molecular doping, where the adatoms were alternatively introduced by annealing in the inert environment. The paramagnetic responses in graphene induced by vacancy-type defects can only be diverted to half of its maximum, while those induced by sp3 defects can be almost completely suppressed. This difference is supposed that vacancy-type defects induced two localized states (pie and sigma). Only the latter states, which is also the only states induced by sp3 defects, involves in the suppression of magnetic moments at the maximum doping achieved in this thesis. The observation through high resolution transmission electron microscope (HR-TEM) provides more information to the hypothesis of the previous magnetic findings. Reconstructed single vacancy is the majority of defects discovered in proton-irradiated graphene. This result verifies the defect-induced magnetic findings in our results, as well as the electronic properties of defected graphene in the literatures. On the other hand, the diamagnetic susceptibility of neutral graphene is suggested to be larger than that of graphite, and vanish rapidly as a delta-like function when graphene is doped. In our result, surprisingly, the diamagnetic susceptibility varies little when the Fermi level is less than 0.3 eV, in contrast with the theory. When the Fermi energy is higher than 0.3 eV, susceptibility then reduces significantly as the trend of graphite. The little variation in susceptibility near the Dirac point is probably attributed to the spatial confinement of graphene nanoflakes, which are the composition of graphene laminates. In the end of this thesis, we discuss the magnetic properties in one of the other two dimensional materials, molybdenum disulfide (MoS2). It is a potential material for graphene-based heterostructure applications. The magnetic moments in MoS2 are shown to be induced by either edges or vacancies, which are introduced by sonication or proton-irradiation, respectively, similar to the suggestions by theories. However, no significant ferromagnetic finding has been found in all of our cases.

APA, Harvard, Vancouver, ISO, and other styles

8

Lampert, Lester Florian. "High-Quality Chemical Vapor Deposition Graphene-Based Spin Transport Channels." PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3327.

Full text

Abstract:

Spintronics reaches beyond typical charge-based information storage technologies by utilizing an addressable degree of freedom for electron manipulation, the electron spin polarization. With mounting experimental data and improved theoretical understanding of spin manipulation, spintronics has become a potential alternative to charge-based technologies. However, for a long time, spintronics was not thought to be feasible without the ability to electrostatically control spin conductance at room temperature. Only recently, graphene, a 2D honeycomb crystalline allotrope of carbon only one atom thick, was identified because of its predicted, long spin coherence length and experimentally realized electrostatic gate tunability. However, there exist several challenges with graphene spintronics implementation including weak spin-orbit coupling that provides excellent spin transfer yet prevents charge to spin current conversion, and a conductivity mismatch due to the large difference in carrier density between graphene and a ferromagnet (FM) that must be mitigated by use of a tunnel barrier contact. Additionally, the usage of graphene produced via CVD methods amenable to semiconductor industry in conjunction with graphene spin valve fabrication must be explored in order to promote implementation of graphene-based spintronics. Despite advances in the area of graphene-based spintronics, there is a lack of understanding regarding the coupling of industry-amenable techniques for both graphene synthesis and lateral spin valve fabrication. In order to make any impact on the application of graphene spintronics in industry, it is critical to demonstrate wafer-scale graphene spin devices enabled by wafer-scale graphene synthesis, which utilizes thin film, wafer-supported CVD growth methods. In this work, high-quality graphene was synthesized using a vertical cold-wall furnace and catalyst confinement on both SiO2/Si and C-plane sapphire wafers and the implementation of the as-grown graphene for fabrication of graphene-based non-local spin valves was examined. Optimized CVD graphene was demonstrated to have ID/G ≈ 0.04 and I2D/G ≈ 2.3 across a 2" diameter graphene film with excellent continuity and uniformity. Since high-quality, large-area, and continuous CVD graphene was grown, it enabled the fabrication of large device arrays with 40 individually addressable non-local spin valves exhibiting 83% yield. Using these arrays, the effects of channel width and length, ferromagnetic-tunnel barrier width, tunnel barrier thickness, and level of oxidation for Ti-based tunnel barrier contacts were elucidated. Non-local, in-plane magnetic sweeps resulted in high signal-to-noise ratios with measured ΔRNL across the as-fabricated arrays as high as 12 Ω with channel lengths up to 2 µm. In addition to in-plane magnetic field spin signal values, vertical magnetic field precession Hanle effect measurements were conducted. From this, spin transport properties were extracted including: spin polarization efficiency, coherence lifetime, and coherence distance. The evaluation of industry-amenable production methods of both high-quality graphene and lateral graphene non-local spin valves are the first steps toward promoting the feasibility of graphene as a lateral spin transport interconnect material in future spintronics applications. By addressing issues using a holistic approach, from graphene synthesis to spin transport implementation, it is possible to begin assessment of the challenges involved for graphene spintronics.

APA, Harvard, Vancouver, ISO, and other styles

9

Staneva, Maya. "Theoretical study of dilute magnetic semiconductors : Properties of (Ga,Mn)As." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-126096.

Full text

Abstract:

The dilute magnetic semiconductor (Ga,Mn)As , which is the most interesting and promising material for spintronics applications, has been theoretically studied by using Density Functional Theory. First of all, calculations on GaAs were done and it was found that GaAs is a semiconductor with a direct band gap. The calculated value of the band gap is ~ 0.5eV. Secondly, the material iron was considered and it was confirmed that iron is a ferromagnetic metal with 2.2µB net magnetic moment. Then a magnetic impurity of manganese, Mn was introduced in the nonmagnetic GaAs and it became ferromagnetic with a net magnetic moment of 4µB. The origin of the ferromagnetic behaviour is discussed and also the Curie temperature TC of the material. It appeared that (Ga,Mn)As is a suitable material for DMS but TC has to be increased before (Ga,Mn)As could be used for spintronics applications and on that account some methods of increasing TC are considered at the end.
Den magnetiska halvledaren (Ga,Mn)As som är det mest intressanta och lovande materialet för spinelektroniska tillämpningar har teoretiskt undersökts med hjälp av Täthetsfunktionalteorin. Först gjordes beräkningar på GaAs och det visade sig att GaAs är en halvledare med direkt bandgap. Det beräknade värdet på bandgapet är ca 0.5eV. Sedan var det järn som undersöktes och det blev bekräftat att järn är en ferromagnetisk metall med netto magnetisk moment lika med 2.2μB. Då magnetiska störningar i form av mangan atomer, Mn, infördes i det omagnetiska GaAs blev halvledaren ferromagnetisk med netto magnetisk moment lika med 4μB. Orsakerna till den ferromagnetiska ordningen diskuteras och även Curie temperaturen TC för materialet. Det visade sig att (Ga,Mn)As är ett lämpligt material för tillverkning av magnetiska halvledare men TC måste ökas innan (Ga,Mn)As skulle kunna användas i spinntroniska tillämpningar och av det skälet anges i slutet vissa metoder för att öka TC.

APA, Harvard, Vancouver, ISO, and other styles

10

Gupta, Shalini. "Growth of novel wide bandgap room temperature ferromagnetic semiconductor for spintronic applications." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33809.

Full text

Abstract:

This work presents the development of a GaN-based dilute magnetic semiconductor (DMS) by metal organic chemical vapor deposition (MOCVD) that is ferromagnetic at room temperature (RT), electrically conductive, and possesses magnetic properties that can be tuned by n- and p-doping. The transition metal series (TM: Cr, Mn, and Fe) along with the rare earth (RE) element, Gd, was investigated in this work as the magnetic ion source for the DMS. Single- phase and strain-free GaTMN films were obtained. Optical measurements revealed that Mn is a deep acceptor in GaN, while Hall measurements showed that these GaTMN films were semi-insulating, making carrier mediated exchange unlikely. Hysteresis curves were obtained for all the GaTMN films, and by analyzing the effect of n- and p-dopants on the magnetic properties of these films it was determined that the magnetization is due to magnetic clusters. These findings are supported by the investigation of the effect of TM dopants in GaN nanostructures which reveal that TMs enhance nucleation resulting in superparamagnetic nanostructures. Additionally, this work presents the first report on the development of GaGdN by MOCVD providing an alternate route to developing a RT DMS. Room temperature magnetization results revealed that the magnetization strength increases with Gd concentration and can be enhanced by n- and p-doping, with holes being more efficient at stabilizing the ferromagnetic signal. The GaGdN films obtained in this work are single-phase, unstrained, and conductive making them suitable for the development of multifunctional devices that integrate electrical, optical, and magnetic properties.

APA, Harvard, Vancouver, ISO, and other styles

11

Kaster, Brian C. "Magnetic Properties of Co_1-xFe_xS₂." Miami University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=miami1311874514.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Sankar, Sandrawattie. "Correlation of microstructural, magnetic, and transport properties of composite metal-insulator films /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9963657.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Шабельник, І. М. "Магнітні властивості спінових вентилів з термокерованим обміном." Thesis, Сумський державний університет, 2013. http://essuir.sumdu.edu.ua/handle/123456789/44106.

Full text

Abstract:

Однією із головних проблем прикладної спінтроніки з моменту відкриття гігантського магнітоопору, залишається проблема безпосереднього маніпулювання магнітними моментами нанорозмірних феромагнетиків. Керування обмінною взаємодією між двома нанорозмірними шарами сильних феромагнетиків (F) можливе за допомогою температури, коли змінюється відносна орієнтація їх магнітних моментів, через прошарок слабкого феромагнетика (f).

APA, Harvard, Vancouver, ISO, and other styles

14

Pu, Yong. "Spin-dependent transport properties of Ga₁₋[subscript]xMn[subscript]xAs ferromagnetic semiconductors." Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=142&did=1874094571&SrchMode=1&sid=1&Fmt=7&retrieveGroup=0&VType=PQD&VInst=PROD&RQT=309&VName=PQD&TS=1270493990&clientId=48051.

Full text

Abstract:

Thesis (Ph. D.)--University of California, Riverside, 2009.
Includes abstract. Includes bibliographical references (leaves 122-126). Issued in print and online. Available via ProQuest Digital Dissertations.

APA, Harvard, Vancouver, ISO, and other styles

15

Tang, Cheng. "Computational exploration of two-dimensional materials with novel electronic, optical and magnetic properties." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/212532/1/Cheng_Tang_Thesis.pdf.

Full text

Abstract:

This project was a step forward in discovering new two-dimensional (2D) structures for electronic and spintronic applications. This work comprehensively investigates seven intriguing 2D structures with novel electronic, optical and magnetic properties on the basis of the global structural search and first-principles calculations. These findings not only highlight the promising materials platforms for advanced nanodevices but also provide the theoretical guides for designing multifunctional 2D materials.

APA, Harvard, Vancouver, ISO, and other styles

16

Jeong, Byoung-Seong. "Growth and ferromagnetic semiconducting properties of titanium dioxide thin films an oxide-diluted magnetic semiconductor (o-dms) for spintronics /." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0004240.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Anaya, Armando Alonso. "Spin Valve Effect in Ferromagnet-Superconductor-Ferromagnet Single Electron Transistor." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6864.

Full text

Abstract:

This thesis describes a research of suppression of superconducting gap in a superconducting island of a Ferromagnetic-Superconducting-Ferromagnetic Single-Electron-Transistor due to the fringing magnetic fields produced by the ferromagnetic leads. The devices are working below the critical temperature of the superconducting gap. A model is proposed to explain how the fringing magnetic field produced by the leads is strong enough to suppress the superconducting gap. The peak of the fringing magnetic field produced by one lead reaches 5000 oe. It is observed an inverse tunneling magneto resistance during the suppression of the superconducting gap, obtaining a maximum absolute value 500 times greater than the TMR in the normal state where the efficiency of the spin injection is low. It is concluded that the suppression of the superconducting gap is due to fringing magnetic field and not to the spin accumulation because the low efficiency of the spin injection. It is suggested a new geometry to reduce the effect of the fringing magnetic field so it can be obtained a suppression of the superconductivity due to the spin accumulation. It is described the qualitatively behavior of the IV characteristic when the suppression of the superconductivity is due to spin accumulation.

APA, Harvard, Vancouver, ISO, and other styles

18

Matthes, Patrick. "Magnetic and Magneto-Transport Properties of Hard Magnetic Thin Film Systems." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-192683.

Full text

Abstract:

The present thesis is about the investigation of ferromagnetic thin film systems with respect to exchange coupling, magnetization reversal behavior and effects appearing in magnetic heterostructures, namely the exchange bias and the giant magnetoresistance effect. For this purpose, DC magnetron sputtered thin films and multilayers with perpendicular magnetic anisotropy were prepared on single crystalline and rigid as well as flexible amorphous substrates. The first part concentrates on magnetic data storage applications based on the combination of the concept of bit patterned media and three dimensional magnetic memory, consisting of at least two exchange decoupled ferromagnetic storage layers. Here, [Co/Pt] multilayers, revealing different magnetic anisotropies, have been applied as storage layers and as spacer material Pt and Ru was employed. By the characterization of the magnetization reversal behavior the exchange coupling in dependence of the spacer layer thickness was studied. Furthermore, with regard to the concept of bit patterned media, the layers were also grown on self-assembled silica particles, leading to an exchange decoupled single-domain magnetic dot array, which was studied by magnetic force microscope imaging and angular dependent magneto-optic Kerr effect magnetometry to evaluate the reversal mechanism and its dependence on the array dimensions, mainly the diameter of the silica particles and layer thicknesses. To complete the study, micromagnetic simulations were performed to access smaller dimensions and to investigate the dependence of intralayer as well as interlayer coupling on the magnetization reversal of the dot array with multiple storage layers. The second part focuses on the investigation of the giant magnetoresistance effect in systems with perpendicular magnetic anisotropy, where L10 -chemically ordered FePt alloys and [Co/Pt] as well as [Co/Pd] multilayers were utilized. In case of FePt, where high temperatures during the deposition are necessary to induce the chemical ordering, diffusion and alloying of the spacer material often prevent a sufficient exchange decoupling of the ferromagnetic layers. However, with Ru as spacer material a giant magnetoresistance effect could be achieved. Large improvements of the magnetoresistive behavior of such trilayer structures are presented for [Co/Pt] and [Co/Pd] multilayers, which can be deposited at room temperature not limiting the choice of spacer as well as substrate material. Furthermore, in systems consisting of one ferromagnet with perpendicular magnetic anisotropy and one ferromagnet with in-plane magnetic easy axis, a linear and almost hysteresis-free field dependence of the electrical resistance was observed and the behavior for various thickness series has been intensively studied. Finally, the corrosion resistance in dependence of the capping layer material as well as the magnetoresistance of a strained flexible pseudo-spin-valve structure is presented. In addition, in chapter 2.5.2 an experimental study of an improved crystal growth of FePt at comparable low temperatures by molecular beam epitaxy and further promoted by a surfactant mediated growth using Sb is shown. Auger electron spectroscopy as well as Rutherford backscattering spectrometry were carried out to confirm the surface segregation of Sb and magnetic characterization revealed an increase of magnetic anisotropy in comparison to reference layers without Sb
Die vorliegende Dissertation beschäftigt sich mit der Untersuchung ferromagnetischer Dünnschichtsysteme im Hinblick auf die Austauchkopplung, das Ummagnetisierungsverhalten und Effekte wie z.B. den Exchange Bias Effekt oder den Riesenmagnetwiderstandseffekt (GMR), welche in derartigen Heterostrukturen auftreten können. Die Probenpräparation erfolgte mittels DC Magnetronsputtern, wobei auf einkristallinen aber auch flexiblen sowie starren amorphen Substraten abgeschieden wurde. Im ersten Teil der Arbeit werden Untersuchungen mit dem Hintergrund einer Anwendung als magnetischer Datenträger vorgestellt. Konkret werden hier die Konzepte Bit Patterned Media (BPM) und 3D Speicher miteinander kombiniert. Letzteres Konzept basiert auf der Verwendung wenigstens zweier austauschentkoppelter ferromagnetischer Schichten, für welche [Co/Pt] Multilagen mit unterschiedlicher magnetischer Anisotropie verwendet wurden. Als Zwischenschichtmaterial diente Pt und Ru. Durch die Charakterisierung des Ummagnetisierungsverhaltens wurde die Austauschkopplung in Abhängigkeit der Zwischenschichtdicke untersucht. Darüber hinaus wurden jene Schichtstapel zur Realisierung des BPM-Konzeptes auf selbstangeordnete SiO2 Partikel mit unterschiedlichen Durchmessern aufgebracht, durch welche sich lateral austauschentkoppelte, eindomänige magnetische Nanostrukturen erzeugen lassen. Zur Untersuchung des Ummagnetisierungsverhaltens und der jeweiligen Größenabhängigkeiten (maßgeblich Durchmesser und Schichtdicke) wurden diese mittels Magnetkraftmikroskopie sowie winkelabhängiger magnetooptischer Kerr Effekt Magnetometrie untersucht. Zur weiteren Vertiefung des Verständnisses noch kleinerer Strukturgrößen erfolgten mikromagnetische Simulationen, bei denen die magnetischen Wechselwirkungen lateral (benachbarte 3D Elemente) als auch vertikal (Wechselwirkungen ferromagnetischer Schichten innerhalb eines 3D Elementes) im Interesse standen, sowie deren Auswirkungen auf das Ummagnetisierungsverhalten des gesamten Feldes. Der Fokus des zweiten Teils liegt auf der Untersuchung des Riesenmagnetwiderstandseffektes in Systemen mit senkrechter Sensitivität. Dafür sind ferromagnetische Schichten mit senkrechter magnetischer Anisotropie nötig, wobei hier die chemisch geordnete L10-Phase der FePt Legierung und [Co/Pt] sowie [Co/Pd] Multilagen Anwendung fanden. Für eine chemische Ordnung der FePt Legierung sind hohe Temperaturen während der Schichtabscheidung notwendig, welche eine hinreichende Austauschentkopplung beider ferromagnetischer Schichten meist nicht gewährleisten. Grund dafür sind einsetzende Diffusionsprozesse als auch Legierungsbildungen mit dem Zwischenschichtmaterial. In der vorliegenden Arbeit konnte der GMR Effekt daher ausschließlich mit einer Ru Zwischenschicht in FePt basierten Trilagensystemen nachgewiesen und charakterisiert werden. Enorme Verbesserungen der magnetoresistiven Eigenschaften werden im Anschluss für [Co/Pt] und vor allem [Co/Pd] Multilagen vorgestellt. Diese Schichtsysteme mit senkrechter magnetischer Anisotropie können bei Raumtemperatur präpariert werden und stellen daher keine weiteren Anforderungen an das Zwischenschichtmaterial sowie die verwendeten Substrate. Hier wurden neben Systemen mit ausschließlich senkrechter magnetischer Anisotropie auch Systeme mit gekreuzten magnetischen Anisotropien intensiv untersucht, da diese durch einen linearen und weitgehend hysteresefreien R(H) Verlauf imHinblick auf Sensoranwendungen enorme Vorteile bieten. Letztendlich wurde die Korrosionsbeständigkeit in Abhängigkeit des Deckschichtmaterials als auch die mechanische Belastbarkeit von auf flexiblen Substraten abgeschiedenen GMR-Schichtstapeln untersucht. Zusätzlich wird in Kapitel 2.5.2 eine experimentelle Studie zum Surfactant-gesteuerten Wachstum der FePt Legierung mittels Molekularstrahlepitaxie vorgestellt. Als Surfactant dient Sb, wodurch die Kristallinität bei geringer Depositionstemperatur deutlich verbessert werden konnte. Die Oberflächensegregation von Sb wurde mittels Auger Elektronenspektroskopie und Rutherford Rückstreuspektrometrie verifiziert und die Charakterisierung magnetischer Eigenschaften belegt einen Anstieg der magnetischen Anisotropieenergie im Vergleich zu Referenzproben ohne Sb

APA, Harvard, Vancouver, ISO, and other styles

19

Panighel, Mirco. "Adsorption, metalation and magnetic properties of tetra phenyl porphyrins on metal surfaces." Doctoral thesis, Università degli studi di Trieste, 2015. http://hdl.handle.net/10077/10898.

Full text

Abstract:

2013/2014
Traditional semiconductor technology will reach a size limit within the next few years. A possible solution could be the use of organic molecules in technological applications as single functional units in metal-organic based devices; the success of this approach strongly depends on the understanding of the behaviour of these molecules on metallic surfaces. The interaction with metallic substrates and the interaction between the molecules themselves determine the electronic and magnetic properties of the system, and it is thus of fundamental interest to study these metal-organic interfaces both in the case of single molecules and layer structures. In this thesis, an extensive study of the electronic and magnetic properties of tetra-phenyl-porphyrin (2H-TPP) molecules adsorbed on metal surfaces is reported. By means of scanning tunnelling microscopy (STM) we studied the adsorption geometry of these molecules on the Au(111), Ag(111) and Cu(100) surfaces. By using X-ray photoemission spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, a temperature-induced conformational adaptation reaction of the 2H-TPP molecules adsorbed on the Au(111) and Ag(111) surfaces, upon annealing at 550 K, is described. A possible dehydrogenation reaction, with the formation of new C-C bonds, could explain the rotation of the molecule phenyl rings parallel to the surface plane and the associated increasing in the molecule-substrate interaction. In-situ metalation of porphyrins in ultra-high vacuum is obtained by two methods: in the first one, the metalation of 2H-TPP on Ag(111) is achieved by direct metal evaporation (Mn, Rh and Fe) on the molecular layer; in the second case we report the self-metalation of 2H-TPP through the coordination with a metal atom from the Fe(110) and Al(111) substrates. In addition, we investigated the effects of metalation and temperature-induced conformational adaptation on the molecule-substrate interaction, by means of XPS and NEXAFS, in the case of CoTPP on Ag(111). The magnetic properties resulting from the metal coordination are studied by X-ray magnetic circular dichroism (XMCD). Here, a description of the magnetic coupling of a MnTPPCl single layer with a Fe(110) ferromagnetic substrate is disclosed. Moreover, we focused on the study of the magnetic properties and exchange coupling of two layer of molecule and a ferromagnetic thin film. In the case of a MnTPP layer on FeTPP/Fe(110) the magnetic coupling extends to the second layer of molecules, for which the magnetization is opposite with respect to the substrate.
Le tradizionali tecnologie utilizzate nell’industria dei semiconduttori raggiungeranno, entro breve tempo, il limite nella miniaturizzazione dei loro componenti. Una possibile alternativa potrebbe venire dall’utilizzo di molecole organiche come singole unità funzionali in dispositivi metallo-organici; d’altra parte il successo di questo approccio dipende in maniera sostanziale dalla comprensione del comportamento di queste molecole sulle superfici dei metalli. L’interazione con il substrato metallico e la stessa interazione tra le molecole determinano le proprietà elettroniche e magnetiche di questi sistemi, ed è dunque di fondamentale interesse lo studio di queste interfacce metallo-organiche sia nel caso di singole molecole che di strutture più complesse. In questa tesi è riportato uno studio dettagliato delle proprietà elettroniche e magnetiche di tetra-fenil-porfirine (2H-TPP) adsorbite su superfici metalliche. Attraverso la microscopia a scansione a effetto tunnel (STM) è stata studiata la geometria di adsorbimento di queste molecole sulle superfici Au(111), Ag(111) e Cu(100). Utilizzando le spettroscopie XPS (X-ray photoemission spectroscopy) e NEXAFS (near-edge X-ray absorption fine structure) è descritta la reazione di adattamento conformazionale delle 2H-TPP adsorbite sulle superfici Au(111) e Ag(111) a seguito del processo di annealing a 550 K. Una possibile reazione di de-idrogenazione, con la formazione di nuovi legami C-C, può spiegare la rotazione dei gruppi fenili della molecola verso la superficie e l’aumento dell’interazione molecola-substrato ad esso associato. La metallazione in-situ delle porfirine in ultra-alto vuoto è ottenuta in due modi: nel primo, la metallazione delle 2H-TPP su Ag(111) è raggiunta con la diretta evaporazione del metallo (Mn, Rh e Fe) sullo strato di molecole; nel secondo caso, sulle superfici Fe(110) e Al(111) la metallazione avviene automaticamente tramite la coordinazione della 2H-TPP con un atomo della superficie. Inoltre, gli effetti della metallazione e dell’adattamento conformazionale sull’interazione molecola-substrato sono stati studiati, tramite XPS e NEXAFS, nel caso di CoTPP su Ag(111). Le proprietà magnetiche risultanti dalla coordinazione della molecola con un atomo metallico sono state studiate per mezzo della tecnica XMCD (X-ray magnetic circular dichroism). In particolare, viene descritto l’accoppiamento magnetico di un singolo strato di MnTPPCl con un substrato ferromagnetico Fe(110). Inoltre, ci si è focalizzati sullo studio delle proprietà magnetiche tra due strati di molecole e un film sottile ferromagnetico. Nel caso specifico di MnTPP su FeTPP/Fe(110) l’accoppiamento magnetico si estende al secondo strato di molecole, per il quale la magnetizzazione è opposta rispetto al substrato.
XXVII Ciclo
1986

APA, Harvard, Vancouver, ISO, and other styles

20

Matthes, Patrick. "Magnetic and Magneto-Transport Properties of Hard Magnetic Thin Film Systems." Doctoral thesis, Universitätsverlag der Technischen Universität Chemnitz, 2015. https://monarch.qucosa.de/id/qucosa%3A20376.

Full text

Abstract:

The present thesis is about the investigation of ferromagnetic thin film systems with respect to exchange coupling, magnetization reversal behavior and effects appearing in magnetic heterostructures, namely the exchange bias and the giant magnetoresistance effect. For this purpose, DC magnetron sputtered thin films and multilayers with perpendicular magnetic anisotropy were prepared on single crystalline and rigid as well as flexible amorphous substrates. The first part concentrates on magnetic data storage applications based on the combination of the concept of bit patterned media and three dimensional magnetic memory, consisting of at least two exchange decoupled ferromagnetic storage layers. Here, [Co/Pt] multilayers, revealing different magnetic anisotropies, have been applied as storage layers and as spacer material Pt and Ru was employed. By the characterization of the magnetization reversal behavior the exchange coupling in dependence of the spacer layer thickness was studied. Furthermore, with regard to the concept of bit patterned media, the layers were also grown on self-assembled silica particles, leading to an exchange decoupled single-domain magnetic dot array, which was studied by magnetic force microscope imaging and angular dependent magneto-optic Kerr effect magnetometry to evaluate the reversal mechanism and its dependence on the array dimensions, mainly the diameter of the silica particles and layer thicknesses. To complete the study, micromagnetic simulations were performed to access smaller dimensions and to investigate the dependence of intralayer as well as interlayer coupling on the magnetization reversal of the dot array with multiple storage layers. The second part focuses on the investigation of the giant magnetoresistance effect in systems with perpendicular magnetic anisotropy, where L10 -chemically ordered FePt alloys and [Co/Pt] as well as [Co/Pd] multilayers were utilized. In case of FePt, where high temperatures during the deposition are necessary to induce the chemical ordering, diffusion and alloying of the spacer material often prevent a sufficient exchange decoupling of the ferromagnetic layers. However, with Ru as spacer material a giant magnetoresistance effect could be achieved. Large improvements of the magnetoresistive behavior of such trilayer structures are presented for [Co/Pt] and [Co/Pd] multilayers, which can be deposited at room temperature not limiting the choice of spacer as well as substrate material. Furthermore, in systems consisting of one ferromagnet with perpendicular magnetic anisotropy and one ferromagnet with in-plane magnetic easy axis, a linear and almost hysteresis-free field dependence of the electrical resistance was observed and the behavior for various thickness series has been intensively studied. Finally, the corrosion resistance in dependence of the capping layer material as well as the magnetoresistance of a strained flexible pseudo-spin-valve structure is presented. In addition, in chapter 2.5.2 an experimental study of an improved crystal growth of FePt at comparable low temperatures by molecular beam epitaxy and further promoted by a surfactant mediated growth using Sb is shown. Auger electron spectroscopy as well as Rutherford backscattering spectrometry were carried out to confirm the surface segregation of Sb and magnetic characterization revealed an increase of magnetic anisotropy in comparison to reference layers without Sb.
Die vorliegende Dissertation beschäftigt sich mit der Untersuchung ferromagnetischer Dünnschichtsysteme im Hinblick auf die Austauchkopplung, das Ummagnetisierungsverhalten und Effekte wie z.B. den Exchange Bias Effekt oder den Riesenmagnetwiderstandseffekt (GMR), welche in derartigen Heterostrukturen auftreten können. Die Probenpräparation erfolgte mittels DC Magnetronsputtern, wobei auf einkristallinen aber auch flexiblen sowie starren amorphen Substraten abgeschieden wurde. Im ersten Teil der Arbeit werden Untersuchungen mit dem Hintergrund einer Anwendung als magnetischer Datenträger vorgestellt. Konkret werden hier die Konzepte Bit Patterned Media (BPM) und 3D Speicher miteinander kombiniert. Letzteres Konzept basiert auf der Verwendung wenigstens zweier austauschentkoppelter ferromagnetischer Schichten, für welche [Co/Pt] Multilagen mit unterschiedlicher magnetischer Anisotropie verwendet wurden. Als Zwischenschichtmaterial diente Pt und Ru. Durch die Charakterisierung des Ummagnetisierungsverhaltens wurde die Austauschkopplung in Abhängigkeit der Zwischenschichtdicke untersucht. Darüber hinaus wurden jene Schichtstapel zur Realisierung des BPM-Konzeptes auf selbstangeordnete SiO2 Partikel mit unterschiedlichen Durchmessern aufgebracht, durch welche sich lateral austauschentkoppelte, eindomänige magnetische Nanostrukturen erzeugen lassen. Zur Untersuchung des Ummagnetisierungsverhaltens und der jeweiligen Größenabhängigkeiten (maßgeblich Durchmesser und Schichtdicke) wurden diese mittels Magnetkraftmikroskopie sowie winkelabhängiger magnetooptischer Kerr Effekt Magnetometrie untersucht. Zur weiteren Vertiefung des Verständnisses noch kleinerer Strukturgrößen erfolgten mikromagnetische Simulationen, bei denen die magnetischen Wechselwirkungen lateral (benachbarte 3D Elemente) als auch vertikal (Wechselwirkungen ferromagnetischer Schichten innerhalb eines 3D Elementes) im Interesse standen, sowie deren Auswirkungen auf das Ummagnetisierungsverhalten des gesamten Feldes. Der Fokus des zweiten Teils liegt auf der Untersuchung des Riesenmagnetwiderstandseffektes in Systemen mit senkrechter Sensitivität. Dafür sind ferromagnetische Schichten mit senkrechter magnetischer Anisotropie nötig, wobei hier die chemisch geordnete L10-Phase der FePt Legierung und [Co/Pt] sowie [Co/Pd] Multilagen Anwendung fanden. Für eine chemische Ordnung der FePt Legierung sind hohe Temperaturen während der Schichtabscheidung notwendig, welche eine hinreichende Austauschentkopplung beider ferromagnetischer Schichten meist nicht gewährleisten. Grund dafür sind einsetzende Diffusionsprozesse als auch Legierungsbildungen mit dem Zwischenschichtmaterial. In der vorliegenden Arbeit konnte der GMR Effekt daher ausschließlich mit einer Ru Zwischenschicht in FePt basierten Trilagensystemen nachgewiesen und charakterisiert werden. Enorme Verbesserungen der magnetoresistiven Eigenschaften werden im Anschluss für [Co/Pt] und vor allem [Co/Pd] Multilagen vorgestellt. Diese Schichtsysteme mit senkrechter magnetischer Anisotropie können bei Raumtemperatur präpariert werden und stellen daher keine weiteren Anforderungen an das Zwischenschichtmaterial sowie die verwendeten Substrate. Hier wurden neben Systemen mit ausschließlich senkrechter magnetischer Anisotropie auch Systeme mit gekreuzten magnetischen Anisotropien intensiv untersucht, da diese durch einen linearen und weitgehend hysteresefreien R(H) Verlauf imHinblick auf Sensoranwendungen enorme Vorteile bieten. Letztendlich wurde die Korrosionsbeständigkeit in Abhängigkeit des Deckschichtmaterials als auch die mechanische Belastbarkeit von auf flexiblen Substraten abgeschiedenen GMR-Schichtstapeln untersucht. Zusätzlich wird in Kapitel 2.5.2 eine experimentelle Studie zum Surfactant-gesteuerten Wachstum der FePt Legierung mittels Molekularstrahlepitaxie vorgestellt. Als Surfactant dient Sb, wodurch die Kristallinität bei geringer Depositionstemperatur deutlich verbessert werden konnte. Die Oberflächensegregation von Sb wurde mittels Auger Elektronenspektroskopie und Rutherford Rückstreuspektrometrie verifiziert und die Charakterisierung magnetischer Eigenschaften belegt einen Anstieg der magnetischen Anisotropieenergie im Vergleich zu Referenzproben ohne Sb.

APA, Harvard, Vancouver, ISO, and other styles

21

Friedrich, Rico [Verfasser], Stefan [Akademischer Betreuer] Blügel, and Jens [Akademischer Betreuer] Kortus. "Ab initio investigation of hybrid molecular-metallic interfaces as a tool to design surface magnetic properties for molecular spintronics / Rico Friedrich ; Stefan Blügel, Jens Kortus." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1130327183/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Friedrich, Rico [Verfasser], Stefan Akademischer Betreuer] Blügel, and Jens [Akademischer Betreuer] [Kortus. "Ab initio investigation of hybrid molecular-metallic interfaces as a tool to design surface magnetic properties for molecular spintronics / Rico Friedrich ; Stefan Blügel, Jens Kortus." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://nbn-resolving.de/urn:nbn:de:hbz:82-rwth-2016-107505.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Lucy, Jeremy M. "Exploration and Engineering of Physical Properties in High-Quality Sr₂CrReO₆ Epitaxial Films." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1436888316.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Li, Hua. "Transport phenomena in correlated quantum liquids: Ultracold Fermi gases and F/N junctions." Thesis, Boston College, 2016. http://hdl.handle.net/2345/bc-ir:105054.

Full text

Abstract:

Thesis advisor: Kevin S. Bedell
Landau Fermi-liquid theory was first introduced by L. D. Landau in the effort of understanding the normal state of Fermi systems, where the application of the concept of elementary excitations to the Fermi systems has proved very fruitful in clarifying the physics of strongly correlated quantum systems at low temperatures. In this thesis, I use Landau Fermi-liquid theory to study the transport phenomena of two different correlated quantum liquids: the strongly interacting ultracold Fermi gases and the ferromagnet/normal metal (F/N) junctions. The detailed work is presented in chapter II and chapter III of this thesis, respectively. Chapter I holds the introductory part and the background knowledge of this thesis. In chapter II, I study the transport properties of a Fermi gas with strong attractive interactions close to the unitary limit. In particular, I compute the transport lifetimes of the Fermi gas due to superfluid fluctuations above the BCS transition temperature Tc. To calculate the transport lifetimes I need the scattering amplitudes. The scattering amplitudes are dominated by the superfluid fluctuations at temperatures just above Tc. The normal scattering amplitudes are calculated from the Landau parameters. These Landau parameters are obtained from the local version of the induced interaction model for computing Landau parameters. I also calculate the leading order finite temperature corrections to the various transport lifetimes. A calculation of the spin diffusion coefficient is presented in comparison to the experimental findings. Upon choosing a proper value of F0a, I am able to present a good match between the theoretical result and the experimental measurement, which indicates the presence of the superfluid fluctuations near Tc. Calculations of the viscosity, the viscosity/entropy ratio and the thermal conductivity are also shown in support of the appearance of the superfluid fluctuations. In chapter III, I study the spin transport in the low temperature regime (often referred to as the precession-dominated regime) between a ferromagnetic Fermi liquid (FFL) and a normal metal metallic Fermi liquid (NFL), also known as the (F/N) junction, which is considered as one of the most basic spintronic devices. In particular, I explore the propagation of spin waves and transport of magnetization through the interface of the F/N junction where nonequilibrium spin polarization is created on the normal metal side of the junction by electrical spin injection. I calculate the probable spin wave modes in the precession-dominated regime on both sides of the junction especially on the NFL side where the system is out of equilibrium. Proper boundary conditions at the interface are introduced to establish the transport of the spin properties through the F/N junction. A possible transmission conduction electron spin resonance (CESR) experiment is suggested on the F/N junction to see if the predicted spin wave modes could indeed propagate through the junction. Potential applications based on this novel spin transport feature of the F/N junction are proposed in the end
Thesis (PhD) — Boston College, 2016
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics

APA, Harvard, Vancouver, ISO, and other styles

25

Mehdi, Aghaei Sadegh. "Electronic and Magnetic Properties of Two-dimensional Nanomaterials beyond Graphene and Their Gas Sensing Applications: Silicene, Germanene, and Boron Carbide." FIU Digital Commons, 2017. http://digitalcommons.fiu.edu/etd/3389.

Full text

Abstract:

The popularity of graphene owing to its unique properties has triggered huge interest in other two-dimensional (2D) nanomaterials. Among them, silicene shows considerable promise for electronic devices due to the expected compatibility with silicon electronics. However, the high-end potential application of silicene in electronic devices is limited owing to the lack of an energy band gap. Hence, the principal objective of this research is to tune the electronic and magnetic properties of silicene related nanomaterials through first-principles models. I first explored the impact of edge functionalization and doping on the stabilities, electronic, and magnetic properties of silicene nanoribbons (SiNRs) and revealed that the modified structures indicate remarkable spin gapless semiconductor and half-metal behaviors. In order to open and tune a band gap in silicene, SiNRs were perforated with periodic nanoholes. It was found that the band gap varies based on the nanoribbon’s width, nanohole’s repeat periodicity, and nanohole’s position due to the quantum confinement effect. To continue to take advantage of quantum confinement, I also studied the electronic and magnetic properties of hydrogenated silicene nanoflakes (SiNFs). It was discovered that half-hydrogenated SiNFs produce a large spin moment that is directly proportional to the square of the flake’s size. Next, I studied the adsorption behavior of various gas molecules on SiNRs. Based on my results, the SiNR could serve as a highly sensitive gas sensor for CO and NH3 detection and a disposable gas sensor for NO, NO2, and SO2. I also considered adsorption behavior of toxic gas molecules on boron carbide (BC3) and found that unlike graphene, BC3 has good sensitivity to the gas molecules due to the presence of active B atoms. My findings divulged the promising potential of BC3 as a highly sensitive molecular sensor for NO and NH3 detection and a catalyst for NO2 dissociation. Finally, I scrutinized the interactions of CO2 with lithium-functionalized germanene. It was discovered that although a single CO2 molecule was weakly physisorbed on pristine germanene, a significant improvement on its adsorption energy was found by utilizing Li-functionalized germanene as the adsorbent. My results suggest that Li-functionalized germanene shows promise for CO2 capture.

APA, Harvard, Vancouver, ISO, and other styles

26

Peters, Brian. "Tuning the structural, magnetic and transport properties of full Heusler Co₂FeAl_xSi_1-x compounds." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1408984221.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Васюхно, М. В. "Магнітні напівпровідники як функціональні матеріали спінтроніки." Thesis, Сумський державний університет, 2015. http://essuir.sumdu.edu.ua/handle/123456789/44036.

Full text

Abstract:

Магнітні напівпровідники – це широкий клас твердих тіл, що поєднують в собі властивості напівпровідників та магнітних матеріалів. Найбільш відомі так звані розбавлені магнітні або напівмагнітні напівпровідники, які отримуються шляхом легування напівпровідникової матриці (наприклад CdTe, ZnSe CdSe, CdS) атомами перехідних металів (наприклад Mn , Fe, Co або рідкоземельними металами).

APA, Harvard, Vancouver, ISO, and other styles

28

Ramzan, Muhammad. "Structural, Electronic and Mechanical Properties of Advanced Functional Materials." Doctoral thesis, Uppsala universitet, Materialteori, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-205243.

Full text

Abstract:

The search for alternate and renewable energy resources as well as the efficient use of energy and development of such systems that can help to save the energy consumption is needed because of exponential growth in world population, limited conventional fossil fuel resources, and to meet the increasing demand of clean and environment friendly substitutes. Hydrogen being the simplest, most abundant and clean energy carrier has the potential to fulfill some of these requirements provided the development of efficient, safe and durable systems for its production, storage and usage. Chemical hydrides, complex hydrides and nanomaterials, where the hydrogen is either chemically bonded to the metal ions or physiosorbed, are the possible means to overcome the difficulties associated with the storage and usage of hydrogen at favorable conditions. We have studied the structural and electronic properties of some of the chemical hydrides, complex hydrides and functionalized nanostructures to understand the kinetics and thermodynamics of these materials. Another active field relating to energy storage is rechargeable batteries. We have studied the detailed crystal and electronic structures of Li and Mg based cathode materials and calculated the average intercalation voltage of the corresponding batteries. We found that transition metal doped MgH2 nanocluster is a material to use efficiently not only in batteries but also in fuel-cell technologies. MAX phases can be used to develop the systems to save the energy consumption. We have chosen one compound from each of all known types of MAX phases and analyzed the structural, electronic, and mechanical properties using the hybrid functional. We suggest that the proper treatment of correlation effects is important for the correct description of Cr2AlC and Cr2GeC by the good choice of Hubbard 'U' in DFT+U method. Hydrogen is fascinating to physicists due to predicted possibility of metallization and high temperature superconductivity. On the basis of our ab initio molecular dynamics studies, we propose that the recent claim of conductive hydrogen by experiments might be explained by the diffusion of hydrogen at relevant pressure and temperature. In this thesis we also present the studies of phase change memory materials, oxides and amorphization of oxide materials, spintronics and sulfide materials.

APA, Harvard, Vancouver, ISO, and other styles

29

Bersweiler, Mathias. "From Sm1-xGdxAl2 electronic properties to magnetic tunnel junctions based on Sm1-xGdxAl2 and/or [Co/Pt] electrodes : Towards the integration of Zero Magnetization ferromagnets in spintronic devices." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0146/document.

Full text

Abstract:

Le contexte général de ce travail est le développement et l'intégration de nouveaux matériaux magnétiques ayant des propriétés originales et d'intérêt potentiel pour la spintronique. En tant que matériau ferromagnétique d’aimantation nulle, le composé Sm1-xGdxAl2 (SGA) suscite un intérêt particulier, puisqu’il est capable, dans son état magnétique compensé, de polariser en spin un courant d’électrons. Dans un premier temps, des expériences de photoémission résolues en angle et en spin sur synchrotron ont permis d’effectuer une analyse précise de la structure électronique selon diverses directions de la zone de Brillouin et d’estimer de manière directe la polarisation de spin au niveau de Fermi du composé SGA. Dans un second temps, une attention particulière a été portée aux multicouches [Co/Pt] et aux JTMs à base de [Co/Pt]. Les multicouches [Co/Pt] constituent la seconde électrode des JTMs à base de SGA. Leurs propriétés magnétiques (en particulier l'anisotropie perpendiculaire et l'aimantation à saturation) ont été soigneusement étudiées en fonction de l'épaisseur de Pt et de la nature de la couche tampon (Pt, MgO ou Al2O3), et en liaison avec leurs caractéristiques structurales. Leur intégration dans des JTMs à base de [Co/Pt] a permis ensuite de remonter d’une part à la polarisation tunnel effective des multicouches [Co/Pt] et d’autre part aux configurations magnétiques des différentes électrodes, configurations parfaitement expliquées et reproduites par des simulations micro-magnétiques. Dans un troisième temps, les résultats de magnéto-transport au sein des JTMs SGA/MgO/[Co/Pt] sont présentés et discutés
The general context of this work is the development and integration of new magnetic materials with original properties of potential interest for spintronic applications. In this field, the Sm1-xGdxAl2 (SGA) compound drives a particular attention, as a zero-magnetization ferromagnet that can exhibit a spin polarization in its magnetic compensated state. In a first step, synchrotron-based angle and spin resolved photoemission spectroscopy experiments have permitted to perform an accurate analysis of the electronic structure along various directions of the Brillouin Zone and to get a direct estimation of the spin polarization at the Fermi level. In a second step, a special attention has been the paid to [Co/Pt] multilayers and to [Co/Pt]-based MTJs. The [Co/Pt] multilayers would constitute the second electrode in SGA-based MTJs. Their magnetic properties (especially the perpendicular anisotropy and the saturation magnetization) have been carefully investigated as a function of Pt thickness and nature of the buffer layer (Pt, MgO or Al2O3), and in close connection with structural characteristics. Their integration in [Co/Pt]-based MTJs has permitted to determine the [Co/Pt] effective tunnel polarization and to unravel the magnetic configurations of both electrodes which are perfectly explained and reproduced by micromagnetic simulations. In a third step, the results concerning the magneto-transport experiments in SGA/MgO/[Co/Pt] MTJs are presented and discussed

APA, Harvard, Vancouver, ISO, and other styles

30

Gruber, Manuel. "Electronic and magnetic properties of hybrid interfaces : from single molecules to ultra-thin molecular films on metallic substrates." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE035/document.

Full text

Abstract:

Comprendre les propriétés des interfaces molécules/métaux est d’une importance capitale pour la spintronique organique. La première partie porte sur l’étude des propriétés magnétiques de molécules de phtalocyanine de manganèse. Nous avons montré que les premières couches moléculaires forment des colonnes avec un arrangement antiferromagnétique sur la surface de Co(100). Ces dernières mènent à de l’anisotropie d’échange. La seconde partie porte sur l’étude d’une molécule à transition de spin, la Fe(phen)2(NCS)2, sublimée sur différentes surfaces. Nous avons identifié les états de spin d’une molécule unique sur du Cu(100). De plus, nous avons commuté l’état de spin d’une molécule unique pourvu qu’elle soit suffisamment découplée du substrat
Understanding the properties of molecules at the interface with metals is a fundamental issue for organic spintronics. The first part is devoted to the study of magnetic properties of planar manganese-phthalocyanine molecules and Co films. We evidenced that the first molecular layers form vertical columns with antiferromagnetic ordering on the Co(100) surface. In turn, these molecular columns lead to exchange bias. The second part is focused on the study of a spin-crossover complex, Fe(phen)2(NCS)2 sublimed on different metallic surfaces. We identified the two spin states of a single molecules on Cu(100). By applying voltages pulses, we switched the spin state of a single molecule provided that it is sufficiently decoupled from the substrate

APA, Harvard, Vancouver, ISO, and other styles

31

Meyer, Tricia Lynn. "Structure, magnetism and transport properties of Ca_xSr_1-xMn_0.5Ru_0.5O₃ bulk and thin film materials." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1386001173.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Moriyama, Takahiro. "Nonlocal and local magnetization dynamics excited by an RF magnetic field in magnetic multilayers." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 152 p, 2009. http://proquest.umi.com/pqdweb?did=1650511361&sid=4&Fmt=2&clientId=8331&RQT=309&VName=PQD.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Verduci, Tindara. "Optimizing OFETs properties for spintronics applications." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE025/document.

Full text

Abstract:

Cette thèse a pour but d’étudier le transport de porteur de charge au sein de polymères conjugués, avec comme finalité d’identifier les propriétés des appareils d’électronique organique appropriées pour des applications dans la spintronique organique. Nous avons analysé des échantillons planaires, de géométries latérales, qui offrent la possibilité d’étudier les propriétés de transport sous l’application de différents stimulus et la détection le transport de longue distance du moment angulaire (spin), au sein de semi-conducteurs organiques (OSC). Dans cette configuration, des critères bien établis doivent être satisfait pour réaliser le transport diffusif d’un courant de spin polarisé au travers d’un matériel organique. Nous avons analysé ces diffèrent critères et trouvé des matériaux dont les propriétés physiques fournissent une solution satisfaisante. Le résultat de ce travail fut la création de transistors à effet de champ organiques dont les propriétés répondent au besoin des applications de spintronique
In this thesis, charge carrier transport in conjugated polymers is studied with the aim to identify organic electronics devices properties suitable for applications in organic spintronics. We investigate planar samples, in a lateral geometry, which offer the possibility to study transport properties under the application of different stimuli and to detect long-range spin transport in OSCs. In this configuration, well-established criteria must be satisfied to realize diffusive-like transport of a spin-polarized current through an organic material. We analyse these criteria and find possible materials properties solutions. The outcome is the realization of organic field-effect transistors with properties ad hoc for spintronics applications

APA, Harvard, Vancouver, ISO, and other styles

34

Huang, Lunmei. "Computational Material Design : Diluted Magnetic Semiconductors for Spintronics." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7800.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Gangmei, Prim. "Magnetisation dynamics of nanoscale magnetic materials and spintronics." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3502.

Full text

Abstract:

The magnetisation dynamics of a single square nanomagnet, the interaction between a pair of nanodiscs, a partially built writer structure and a range of magnetic tunnel junction sensor heads were studied using Time Resolved Scanning Kerr Microscopy (TRSKM) and four probe contact DC electrical transport measurements. Large amplitude magnetisation dynamics of a single square nanomagnet have been studied by TRSKM. Experimental spectra revealed that only a single mode was excited for all bias field values. Micromagnetic simulations demonstrate that at larger pulsed field amplitudes the center mode dominates the dynamic response while the edge mode is almost completely suppressed. The magnetisation dynamics occurring in a system comprised of two laterally separated magnetic nano-discs were also investigated. The polar Magneto-Optical Kerr Effect was used to measure the dynamic response of each disc independently so as to demonstrate that dynamic dipolar interactions between non-uniform spin wave modes in the different discs may be identified from the difference in their phase of oscillation. Results show a stronger dynamic dipolar interaction than expected from micromagnetic simulations highlighting both the need for characterisation and control of magnetic properties at the deep nanoscale and the potential use of dynamic interactions for the realization of useful magnetic nanotechnologies. TRSKM measurements were made simultaneously of the three Cartesian components of the magnetisation vector, by means of a quadrant photodiode polarisation bridge detector, on partially built hard disk writer structures. The rise time, relaxation time, and amplitude of each component has been related to the magnetic ground state, the initial torque, and flux propagation through the yoke and pole piece. Dynamic images reveal “flux-beaming” in which the magnetisation component parallel to the symmetry axis of the yoke is largest along that axis. A comparison of the magnetisation dynamics excited with different pulsed excitation amplitudes was also made. The results shows that more effective flux beaming is observed for higher pulse amplitudes. Lastly the microwave emission of Tunnel Magnetoresistance (TMR) nanopillars has been measured using a four probe contact DC electrical transport measurement technique as a magnetic field is applied in the plane of the film at different angles (ϕ_H ) with respect to the easy axis. Experimental spectra revealed that a more complicated spectrum containing several modes is observed as ϕ_H is increased. The modes were identified as edge and higher order modes from the statistical distribution of modes from different devices and micromagnetic simulations. The in-plane and out-of-plane components of the Spin Transfer Torque (STT) were estimated by analytical fitting of experimental data for the lowest frequency edge mode for the value of ϕ_H where the amplitude of the said mode was a maximum and its frequency a minimum. The estimated values are larger than expected perhaps due to the macrospin approximation made in deriving the analytical model. The results presented in this thesis can contribute to the understanding of magnetisation dynamics in industrially relevant data storage devices as well as the realization of a dipolar field coupling mechanism for arrays of nanooscillators.

APA, Harvard, Vancouver, ISO, and other styles

36

Diallo, Mamadou Lamine. "Apport de la sonde atomique tomographique dans l'étude structurale et magnétique du semi-conducteur magnétique 6H-SiC implanté avec du fer : vers un semi-conducteur magnétique à température ambiante." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMR051/document.

Full text

Abstract:

Dans la réalisation de nouveaux composants innovants de la spintronique, de grands espoirs sont placés sur les semi-conducteurs magnétiques dilués (DMS). L’enjeu technologique est de développer des matériaux ayant à la fois des propriétés semi-conductrices et ferromagnétiques. Le but de ce travail est de réaliser une étude nanostructurale et magnétique détaillée du système Fe :SiC candidat prometteur pour devenir un semi-conducteur magnétique dilué à température ambiante. Cependant les propriétés magnétiques du matériau (6H-SiC) implanté avec des métaux de transitions (MT) dépendent fortement de sa microstructure (concentration et nature du dopant, précipitation du dopant…). Afin d’appréhender l’ensemble des propriétés nanostructurales et magnétiques, nous avons étudié le système Fe :SiC à l’échelle de l’atome en utilisant la sonde atomique tomographique (SAT) couplée à la spectrométrie Mössbauer 57Fe. Des monocristaux 6H-SiC (0001) de type p et n (~10+18/cm3) ont été multi-implantés en 56Fe et 57Fe à différentes énergies et différentes fluences conduisant à une concentration atomique de (6% et 4%) de 20 à 120 nm de la surface. Dans le cadre de ce travail, nous avons pu suivre l’effet de la nanostructure du système Fe :SiC en fonction de la concentration de fer et des températures d’implantation et de recuit. Nous avons établi de nouveaux résultats : nature et dimension des nanoparticules, évaluation précise du nombre d’atomes de fer dilué dans la matrice SiC. Les différentes contributions ferromagnétiques et paramagnétiques sont identifiées et clairement expliquées grâce au couplage de techniques expérimentales comme la SAT, la spectrométrie Mössbauer, la magnétométrie SQUID (Superconducting Quantum Interference Device). Nous avons réussi à déterminer des conditions optimales pour l’obtention d’un DMS à température ambiante. En effet dans les échantillons implantés 4% Fe à 380°C, plus de 90% des atomes de Fe sont dilués. Ces atomes de Fe dilués contribuent majoritairement aux propriétés ferromagnétiques mesurées par SQUID et par spectrométrie Mössbauer à 300 K. Ces différents résultats expérimentaux mettent en lumière la possibilité de réalisation d’un nouveau (DMS) à température ambiante
Great hopes are placed on diluted magnetic semiconductors (DMS) for new components of spintronics. The challenge is to develop materials with both semiconducting and ferromagnetic properties. The aim of this work is to carry out a detailed nanostructural and magnetic study of the Fe: SiC candidate promising system to become a magnetic semiconductor diluted at room temperature. However, the magnetic properties observed in (6H-SiC) implanted with transition metals (TM) depend strongly on the material microstructure (content and nature of the dopant, precipitation of the dopant, etc.). In order to understand all the nanostructural and magnetic mechanisms, we studied the Fe: SiC system at the atomic scale using atom probe tomography (APT) and Mössbauer spectrometry. p and n single crystalline 6H-SiC near (0001)-oriented samples were submitted to multi-step implantations with 56Fe and 57Fe ions at different energies and fluences leading to an iron concentration (Cat =6 and 4%) at a depth between 20 nm and 120 nm from the sample surface. In this work, we were able to follow the effect of the nanostructure of the Fe: SiC system as a function of the iron concentration and the temperatures of implantations and annealing. We have established new results: nature and size of the nanoparticles, precise evaluation of the number of iron atoms diluted in the SiC matrix. The ferromagnetic and paramagnetic contributions are identified and clearly explained by the coupling of experimental techniques such as APT, Mössbauer spectrometry, SQUID (Superconducting Quantum Interference Device) magnetometry. We were able to put the material in optimal conditions for obtaining a DMS at room temperature. Indeed, the implanted samples (4% Fe) at 380°C more than 90% Fe atoms were distributed homogeneously. These Fe atoms are the main source of the ferromagnetic properties measured by SQUID and Mössbauer spectrometry at 300 K. These experimental results highlight the possibility of obtaining a new (DMS) at room temperature

APA, Harvard, Vancouver, ISO, and other styles

37

SOARES, GABRIEL. "Magnetization dynamics and spintronics of soft magnetic thin films." Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2841180.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Wang, Weigang. "Spin-dependent transport in magnetic tunnel junctions and diluted magnetic semiconductors." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 184 p, 2009. http://proquest.umi.com/pqdweb?did=1654494821&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Xiao, Jiang. "Spin-transfer Torque in Magnetic Nanostructures." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11513.

Full text

Abstract:

This thesis consists of three distinct components: (1) a test of Slocnzewski's theory of spin-transfer torque using the Boltzmann equation, (2) a comparison of macrospin models of spin-transfer dynamics in spin valves with experimental data, and (3) a study of spin-transfer torque in continuously variable magnetization. Slonczewski developed a simple circuit theory for spin-transfer torque in spin valves with thin spacer layer. We developed a numerical method to calculate the spin-transfer torque in a spin valve using Boltzmann equation. In almost all realistic cases, the circuit theory predictions agree well with the Boltzmann equation results. To gain a better understanding of experimental results for spin valve systems, current-induced magnetization dynamics for a spin valve are studied using a single-domain approximation and a generalized Landau-Lifshitz-Gilbert equation. Many features of the experiment were reproduced by the simulations. However, there are two significant discrepancies: the current dependence of the magnetization precession frequency, and the presence and/or absence of a microwave quiet magnetic phase with a distinct magnetoresistance signature. Spin-transfer effects in systems with continuously varying magnetization also have attracted much attention. One key question is under what condition is the spin current adiabatic, i.e., aligned to the local magnetization. Both quantum and semi-classical calculations of the spin current and spin-transfer torque are done in a free-electron Stoner model. The calculation shows that, in the adiabatic limit, the spin current aligns to the local magnetization while the spin density does not. The reason is found in an effective field produced by the gradient of the magnetization in the wall. Non-adiabatic effects arise for short domain walls, but their magnitude decreases exponentially as the wall width increases.

APA, Harvard, Vancouver, ISO, and other styles

40

Kao, Chi-Yueh. "Thin films of organic-based magnetic semiconductors for organic spintronics." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343748166.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Iusan, Diana Mihaela. "Density Functional Theory Applied to Materials for Spintronics." Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-119887.

Full text

Abstract:

The properties of dilute magnetic semiconductors have been studied by combined ab initio, Monte Carlo, and experimental techniques. This class of materials could be very important for future spintronic devices, that offer enriched functionality by making use of both the spin and the charge of the electrons. The main part of the thesis concerns the transition metal doped ZnO. The role of defects on the magnetic interactions in Mn-doped ZnO was investigated. In the presence of acceptor defects such as zinc vacancies and oxygen substitution by nitrogen, the magnetic interactions are ferromagnetic. For dilute concentrations of Mn (~ 5%) the ordering temperature of the system is low, due to the short ranged character of the exchange interactions and disorder effects. The clustering tendency of the Co atoms in a ZnO matrix was also studied. The electronic structure, and in turn the magnetic interactions among the Co atoms, is strongly dependent on the exchange-correlation functional used. It is found that Co impurities tend to form nanoclusters and that the interactions among these atoms are antiferromagnetic within the local spin density approximation + Hubbard U approach. The electronic structure, as well as the chemical and magnetic interactions in Co and (Co,Al)-doped ZnO, was investigated by joined experimental and theoretical techniques. For a good agreement between the two, approximations beyond the local density approximation must be used. It is found that the Co atoms prefer to cluster within the semiconducting matrix, a tendency which is increased with Al co-doping. We envision that it is best to describe the system as superparamagnetic due to the formation of Co nanoclusters within which the interactions are antiferromagnetic. The magnetic anisotropy and evolution of magnetic domains in Fe81Ni19/Co(001) superlattices were investigated both experimentally, as well as using model spin dynamics. A magnetic reorientation transition was found.

APA, Harvard, Vancouver, ISO, and other styles

42

Chen, Kai, and Kai Chen. "Spin Transport in Magnetic Nano-Structures." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626524.

Full text

Abstract:

Since the discovery of giant magnetoresistance in 1980s, Spintronics became an exciting field which studies numerous phenomena including the spin transport in magnetic heterostructures, magnetization dynamics and the interplay between them. I have investigated different topics during my graduate research. In this dissertation, I summarize all my projects including spin pumping, spin convertance and spin injection into ballistic medium. First, we develop a linear response formalism for spin pumping effect. Spin pumping refers that a precessing emits a spin current into its adjacent nonmagnetic surroundings, which was originally proposed using scattering theory. The newly developed formalism is demonstrated to be identical the early theory in limiting case. While our formalism is convenient to include the effects of disorders and spin-orbit coupling which can resolve the quantitative controversies between early theory and experiments. Second, the spin pumping experiments indicates a much smaller spin Hall angle compared with the results obtained via the spin transfer torque measurements. We found that such issues can be resolved when taking into consideration the effects of non-local conductivity. And we conclude neither of the two methods measures the real spin Hall angle while the spin pumping methods provides much accurate estimations. Third, we developed the spin transport equations in weak scattering medium in the presence of spin-orbit coupling. Before this, all spin dependent electron transport has been modeled by the conventional spin diffusion equation. While recent spin injection experiments have seen the failure of spin diffusion equation. As the experimental fitting using spin diffusion models led to unrealistic conclusions. At last, we study the spin convertance in anti-ferromagnetic multilayers, where the spin information can be mutually transferred between ferromagnetic/anti-ferromagnetic and conduction electrons. Our theory successfully explained the experiment results that the insertion of thin NiO film between YIG/Pt largely enhances the spin Seebeck currents.

APA, Harvard, Vancouver, ISO, and other styles

43

Oyarzún, Medina Simón. "Spintronics in cluster-assembled nanostructures." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10166/document.

Full text

Abstract:

Dans les dernières années, la miniaturisation progressive des dispositifs de stockage magnétique a rendu nécessaire de comprendre comment les propriétés physiques sont modifiées par rapport à l'état massif lorsque les dimensions sont réduites à l'échelle nanométrique. Pour cette raison, une méthode précise de préparation et caractérisation de nanostructures est extrêmement importante. Ce travail se concentre sur les propriétés magnétiques et de transport de nanoparticules de cobalt incorporées dans des matrices de cuivre. Notre dispositif expérimental nous permet de contrôler indépendamment la taille moyenne des agrégats, la concentration et la composition chimique. La production des agrégats de cobalt est basée sur la pulvérisation cathodique et l'agrégation dans la phase gazeuse. Cette source permet de produire des agrégats dans une large gamme de taille, de un à plusieurs milliers d'atomes. Dans un premier temps, nous avons étudié le rôle des interactions entre particules dans les propriétés de transport et magnétiques, en augmentant la concentration des nanoparticules de cobalt (à partir de 0.5 % à 2.5 % et 5 %). Nos résultats démontrent les précautions nécessaires et constituent une base solide pour de futures études sur les propriétés spintroniques des systèmes granulaires. Dans le but de décrire les propriétés magnétiques intrinsèques d'agrégats, nous avons préparé des échantillons fortement dilués (_0.5%) pour différents diamètres d'agrégats de 1.9 nm à 5.5 nm. Nous avons constaté que les propriétés magnétiques sont dépendantes de la taille. L'utilisation d'une caractérisation magnétique complète, sensible à la variation de l'anisotropie magnétique efficace, nous montre que l'anisotropie magnétique est dominée par les contributions de la surface ou de la forme des nanoparticules
In the last years, the progressive miniaturization of magnetic storage devices has imposed the necessity to understand how the physical properties are modified with respect to the bulk when the dimensions are reduced at the nanometric scale. For this reason an accurate method of preparation and characterization of nanostructures is extremely important. This work focuses on the magnetic and transport properties of cluster-assembled nanostructures, namely cobalt nanoparticles embedded in copper matrices. Our setup allows us to independently control the mean cluster size, the concentration and the chemical composition. The cobalt cluster production is based on magnetron sputtering and gas phase aggregation. The performance of the source permits a wide range of cluster masses, from one to several thousand atoms. As a first step we studied the role of inter-particle interactions in the transport and magnetic properties, increasing the cobalt nanoparticle concentration (from 0.5% to 2.5% and 5%). Our results demonstrate the necessary precautions and constitute a solid basis for further studies of the spintronic properties of granular systems. Finally, in order to describe the intrinsic magnetic properties of cluster-assembled nanostructures, we prepared strongly diluted samples (_0.5%) for different cluster sizes from 1.9 nm to 5.5 nm. We found that the magnetic properties are size-dependent. Using a complete magnetic characterization, sensitive to the change in the effective magnetic anisotropy, we show that the magnetic anisotropy is dominated by the contributions of the surface or of the shape of the nanoparticles

APA, Harvard, Vancouver, ISO, and other styles

44

Kane, Matthew Hartmann. "Investigaton of the Suitability of Wide Bandgap Dilute Magnetic Semiconductors for Spintronics." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16166.

Full text

Abstract:

New semiconductor materials may enable next-generation â spintronicâ devices which exploit both the spin and charge of an electron for data processing, storage, and transfer. The realization of such devices would benefit greatly from room temperature ferromagnetic dilute magnetic semiconductors. Theoretical predictions have suggested that room temperature ferromagnetism may be possible in the wide bandgap semiconductors GaMnN and ZnMnO, though the existing models require input from the growth of high-quality materials. This work focuses on an experimental effort to develop high-quality materials in both of these wide bandgap materials systems. ZnMnO and ZnCoO single crystals have been grown by a modified melt growth technique. X-ray diffraction was used to examine the structural quality and demonstrate the single crystal character of these devices. Substitutional transition metal incorporation has been verified by optical transmission and electron paramagnetic resonance measurements. No indications of ferromagnetic hysteresis are observed from the bulk single crystal samples, and temperature dependent magnetization studies demonstrate a dominant antiferromagnetic exchange interaction. Efforts to introduce ferromagnetic ordering were only successful through processing techniques which significantly degraded the material quality. GaMnN thin films were grown by metalorganic chemical vapor deposition. Good crystalline quality and a consistent growth mode with Mn incorporation were verified by several independent characterization techniques. Substitutional incorporation of Mn on the Ga lattice site was confirmed by electron paramagnetic resonance. Mn acted as a deep acceptor in GaN. Nevertheless, ferromagnetic hysteresis was observed in the GaMnN films. The apparent strength of the magnetization correlated with the relative ratio of trivalent to divalent Mn. Valence state control through codoping with additional donors such as silicon was observed. Additional studies on GaFeN also showed a magnetic hysteresis. A comparison with implanted samples showed that the common origin to the apparent strong ferromagnetic hysteresis related to contribution from Mn substitutional ions. The observed magnetic hysteresis is due to the formation of Mn-rich regions during the growth process. This work demonstrated that the original intrinsic models for room temperature ferromagnetism in the wide bandgap semiconductors do not hold and the room temperature ferromagnetism in these materials results from extrinsic contributions.

APA, Harvard, Vancouver, ISO, and other styles

45

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.

Full text

APA, Harvard, Vancouver, ISO, and other styles

46

Murase, Hideaki. "Development of Magnetic Semiconductor Based on Spinel-type Oxide for Spintronics Application." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120877.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Benini, Mattia. "Investigations of ferromagnet-organic bilayers for application in spintronics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15788/.

Full text

Abstract:

La spintronica è una branca dell’elettronica che sfrutta oltre alla carica, lo spin dell’elettrone per il trasporto dell'informazione. Il dispositivo spintronico modello, chiamato spin valve, è costituito da strati ferromagnetici disaccoppiati tra loro attraverso un materiale non magnetico di diversa natura. Più recentemente il campo della spintronica si è orientato verso l’uso di semiconduttori organici come materiali non magnetici dando origine alla cosiddetta “organic spintronics”. Dopo i primi successi di integrazione di materiali organici in dispositivi spintronici, sono emerse alcune peculiarità dei comportamenti magnetoresistivi che indicano come le molecole giochino un ruolo maggiore rispetto al mero trasporto di correnti spin-polarizzate. A questo concetto è stato associato al termine spinterface. Questo nuovo tipo di interfacce è di notevole interesse in molteplici campi oltre la spintronica, come l’optoelettronica o le memorie magnetiche. In questo lavoro di tesi si sono studiate proprietà magnetiche di bistrati cobalto/fullerene e cobalto/gallio-quinolina, con l’obiettivo di verificare il ruolo del materiale organico nella definizione delle proprietà magnetiche dello strato di cobalto, con l’obiettivo di verificare la presenza di effetti di “spinterface”.

APA, Harvard, Vancouver, ISO, and other styles

48

Brangham, Jack T. "Spin Transport and Dynamics in Magnetic Heterostructures." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1511351075684389.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Amthong, Attapon. "Electronic states in externally modulated dilute magnetic semiconductor/superconductor hybrids." Thesis, University of Bath, 2012. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.563997.

Full text

Abstract:

Dilute magnetic semiconductors (DMSs) are attractive. They are candidate materials for applications in novel spintronic devices. Because of the giant Zeemaneect in the paramagnetic state, a magnetic eld can be used to manipulate the spin and charge of carriers in DMSs. One possibility is to exploit the nonhomogeneous magnetic elds due to superconductors. In this thesis, the heterostructures of the planar DMS and superconductors in dierent geometries and superconducting states are investigated to understand the electronic structure of electrons in the DMS. The combination of a superconducting disk in the Meissner state and the planar DMS is studied using both simple and realistic models of the magnetic eld associated with the disk. The giant Zeeman interaction is found to substantially inuence the energies of magnetically conned states in the adjacent DMS. In the simple model eld, the giant Zeeman energy acts as an extra conning potential and results in spin dependent electron states exhibiting dierent spatial distributions, while the more realistic model eld results in conned states exhibiting a variety of mixed spin characters. The hybrid of a superconducting lm in a superconducting vortex state and the DMS is then explored. The concentrated magnetic eld due to an isolated vortex is shown to trap strongly spin polarised electron states. In the case of an Abrikosov lattice of vortices, interactions between vortex-bound states result in a band structure which can be controlled by the magnitude of an external uniform magnetic eld. It is found that the numerical band structures obtained using a basis of Landau states dier from those previously reported, leading to the development of a tight-binding theory to conrm their corrections. Another hybrid investigated is a square superconductor above the DMS. In this case, the arrangement of vortices is distorted by the boundary of the sample, leading to the possibility of multivortex state and/or giant vortex states. It is discovered that the magnetic eld due to the former state induces \molecular" electron states in the DMS, while that due to the latter state induces electron states with increased spatial distribution. Tight-binding theory is again used to describe the observed energy levels and the interactions between electron states induced by the magnetic elds due to separated vortices in the multivortex state.

APA, Harvard, Vancouver, ISO, and other styles

50

Diaz, BegonÌƒa Ruiz. "Magnetic properties of granular magnetic materials." Thesis, University of York, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428429.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Magnetic properties in spintronics'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles