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Dissertations / Theses on the topic 'Stochastic Magnetic Tunnel Junctions'

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Published: 10 December 2022
Last updated: 28 January 2023

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1

Wong, Pak Kin. "Magnetic tunnel junctions." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624388.

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2

Almasi, Hamid, and 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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3

Kaiser, Christian. "Novel materials for magnetic tunnel junctions." kostenfrei, 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97561388X.

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4

Eames, Matthew E. "The theory of magnetic tunnel junctions." Thesis, University of Exeter, 2007. http://hdl.handle.net/10036/38673.

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Within this work an investigation into the tunnelling magnetoresistance (TMR) will be presented. A base numerical model is developed to describe the tunnelling through a magnetic tunnel junction (MTJ) so that a simple analytic model can be compared. These models have been extended to the crystalline barrier MTJs. This numerical model was based upon an enhanced Wentzel-Kramers-Brillouin (EWKB) method to describe the tunnelling current density. By correctly considering realistic MTJ parameters, the key result was found to be the correct handling of the effective masses in of the three MTJ layers. The extracted barrier-heights of 3.5-4eV is much higher than found previously and closer to the half band-gap result expected. It is then clear that the correct treatment of the parameters produces a far more realistic result. The key parameter which can be extracted from the I-V characteristics is the product b m*d V , where m* is the effective mass of the barrier, d is the effective barrier thickness and Vb is the effective barrier height. The analytic solution is a transparent model in which the key material parameters are visible and simple enough to be applied by experimental researchers to MTJs. The accurate modelling of both the prefactor and exponent are crucial to estimating the TMR. A simplified analytic result was produced that is in good agreement with numerical and experimental results. The numerical and analytic model are then extended to describe the TMR through a crystalline Fe(001)/MgO(001)/Fe(001) trilayer system. The calculation is based on the free-electron-like numerical solution providing a functional dependence of the TMR. The results were found to be in excellent agreement with the ab initio models and experiment. Furthermore a simplified analytic expression shows the TMR is dependent on the band-widths of the tunnelling electron states, the coupling and the thickness of the barrier. These models will be of great benefit to both experimental and theoretical researchers.
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5

Yu, Chak Chung Andrew. "Electron microscopy studies of magnetic tunnel junctions." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302402.

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6

Suszka, Anna Kinga. "Resonant spin transfer in magnetic tunnel junctions." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493600.

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Despite an extensive study and deep analysis of the tunnelling assisted transport the detailed processes that occur inside dielectrics are still unknown. The knowledge of these processes is crucial for the design and studies on future spintronic nanostructures. We propose a system of dusted MgO-based magnetic tunnel junctions to probe the processes inside the insulating barrier in order to gain more information about the physics of electron tunnelling.
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7

Kirk, Daniel James. "A TEM Study of Magnetic Tunnel Junctions and Magnetic Materials." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491270.

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Since 1995, magnetic tunnel junction structures have been of great commercial interest because of their use in magnetic recording and data storage applications. In addition, the complex way in which the properties of the junction are influenced by the microstructure makes these structures of great scientific interest. The development of the capabilities of devices based on these structures has also lead to new applications for various materials. In particular, amorphous ferromagnets have become popular choices for use as ferromagnetic layers in these structures. Since the properties of magnetic tunnel junctions are determined by structural features less than 1 nm in size, a technique capable of studying these junctions with very high resolution is needed. In this thesis tunnel junction structures with two different types of barrier material are studied using a variety of transmission electron microscopy techniques. The effects of processing conditions were investigated for both structures. Electron microscopy was also used to investigate the origins ofuniaxial magnetic anisotropy in an important amorphous ferromagnet. The TiOx barrier of IrMnlCoFeffiOx/CoFe tunnel junctions formed by radical oxidation was found to be amorphous and its thickness highly dependent on oxidation time. Increased oxidation times led to the formation of oxides of Co and Fe from the lower ferromagnetic layer. Annealing was shown to have little effect on barrier thickness but does lead to diffusion of Mn to the barrier. Mn was observed to reduce oxides of Co and Fe and form MnOx in the barrier. In a study of PtMnlCoFe/AIOxfNiFe junctions, in which the barrier was formed by natural oxidation, the amorphous AIOx barrier width was found to be independent of oxidation time. The increase in the magnetoresistance of the higher oxidation time junctions was attributed to an increase in the barrier height of the oxide. In addition, evidence of oxidation of the ferromagnetic layers was found in a sample which had not been annealed. Magnetic anisotropy, induced by in-field annealing, was measured in amorphous CoFeB thin films and these films were then studied by electron diffraction to examine the short range order in this material. G(r) was obtained for directions parallel and perpendicular to the easy axis of magnetisation. No bond-length anisotropy was observed and an upper limit for the magnitude of the pair-ordering effect on the coordination of the transition metal and metalloid atoms was established.
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8

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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9

Anderson, Graham Ian Robert. "The effects of annealling on magnetic tunnel junctions." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485761.

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Magnetic tunnel junctions (MTJs) have come to the technological fore in recent times due to their high applicability to recording media, and the wealth of information that can be obtained in understanding spin-polarised tunnelling phenomena. In 1997 it was first reported that performing a high-vacuum annealling step on MTJs significantly increased tunnelling magnetoresistance (TMR), the figure-of-merit in these devices. Since then research has continued apace into both understanding this increase and determining how to maximise TlvlR via annealling. Recently the annealling step has taken an even larger role in MgO based MTJs, as it is integral in creating the interfaces needed to obtain giant TMR. This thesis contains work based on annealling MTJs using two techniques that have previously not been used to study annealling, despite being highly applicable. The first technique is in situ transport measurements during annealling, which can be used to determine the barrier profile throughout the anneal process. The second technique is soft X-ray resonant magnetic scattering (SXRMS) which has two advantages; firstly, using the incoming X-rays tuned to an absorption edge, buried .interfaces can be probed and, secondly, by switching the photon helicity, magnetic properties of these interfaces can be monitored. The first study comprises the development of MgO plasma oxidised MTJs and uses in situ transport measurements to show that during annealling the Mn moves to the barrier interfaces, which affects the sample performance. The second and third studies use in situ transport in conjunction with SXRMS. One study investIgates the barrier evolution and interface sharpness during the anneal using AIO based MTJs. This shows that the improvement of the barrier quality appears to playa larger role than improving the magnetic interfaces. Lastly; CoFeBjMgOjCoFeB MTJs are measured by both techniques as they are annealed at various temperatures around the CoFeB crystallisation temperature. Upon annealling at 200°C the barrier quality is improved and TMR increases. Annealling at temperatures above this does not im;prove the barrier but causes part-crystallisation of the CoFeB causing a large increase in TMR. SXRMS results showed conflicting results depending upon the cumulative anneal process. These results were modelled qualitatively to understand the crystallisation/ diffusion behaviour seen in the MTJ.
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10

Romero, Dominguez Saul. "Noise and electrical characterization in magnetic tunnel junctions." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611223.

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11

Bonholzer, Michael. "Magnetic Tunnel Junctions based on spinel ZnxFe3-xO4." Doctoral thesis, Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-212756.

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Die vorliegende Arbeit befasst sich mit magnetischen Tunnelkontakten (magnetic tunnel junctions, MTJs) auf Basis des Oxids Zinkferrit (ZnxFe3-xO4). Dabei soll das Potential dieses Materials durch die Demonstration des Tunnelmagnetowiderstandes (tunnel magnetoresistance, TMR) in zinkferritbasierten Tunnelkontakten gezeigt werden. Dazu wurde ein Probendesign für MTJs auf Basis der „pseudo spin valve“-Geometrie entwickelt. Die Basis für dieseStrukturen ist ein Dünnfilmstapel aus MgO (Substrat) / TiN / ZnxFe3-xO4 / MgO / Co. Dieser ist mittels gepulster Laserabscheidung (pulsed laser deposition, PLD) hergestellt. Im Rahmen dieser Arbeit wurden die strukturellen, elektrischen und magnetischen Eigenschaften der Dünnfilme untersucht. Des weiteren wurden die fertig prozessierten MTJ-Bauelemente an einem im Rahmen dieser Arbeit entwickeltem und aufgebautem TMR-Messplatz vermessen. Dabei ist es gelungen einen TMR-Effekt von 0.5% in ZnxFe3-xO4-basierten MTJs nachzuweisen. Das erste Kapitel der Arbeit gibt eine Einführung in die spintronischen Effekte Riesenmagnetowiderstand (giant magnetoresistance, GMR) und Tunnelmagnetowiderstand (TMR). Deren technologische Anwendungen sowie die grundlegenden physikalischen Effekte und Modelle werden diskutiert. Das zweite Kapitel gibt eine Übersicht über die Materialklasse der spinellartigen Ferrite. Der Fokus liegt auf den Materialien Magnetit (Fe3O4) sowie Zinkferrit (ZnxFe3-xO4). Die physikalischen Modelle zur Beschreibung der strukturellen, magnetischen und elektrischen Eigenschaften dieser Materialien werden dargelegt sowie ein Literaturüberblick über experimentelle und theoretische Arbeiten gegeben. Im dritten Kapitel werden die im Rahmen dieser Arbeit verwendeten Probenpräparations- und Charakterisierungsmethoden vorgestellt und technische Details sowie physikalische Grundlagen erläutert. Die Entwicklung eines neuen Probendesigns zum Nachweis des TMR-Effekts in ZnxFe3-xO4-basierten MTJs ist Gegenstand des vierten Kapitels. Die Entwicklung des Probenaufbaus sowie die daraus resultierende Probenprozessierung werden beschrieben. Die beiden letzten Kapitel befassen sich mit der strukturellen, elektrischen und magnetischen Charakterisierung der mittels PLD abgeschiedenen Dünnfilme sowie der Tunnelkontaktstrukturen.
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12

Price, Edward P. "Characterization of transport processes in magnetic tunnel junctions /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3022231.

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13

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.

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14

Bernert, Kerstin. "Spin-transfer torques in MgO-based magnetic tunnel junctions." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-135339.

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This thesis discusses spin-transfer torques in MgO-based magnetic tunnel junctions. The voltage-field switching phase diagrams have been experimentally determined for in-plane CoFeB/MgO/CoFeB magnetic tunnel junctions. In order to limit the effect of thermal activation, experiments have been carried out using nanosecond voltage pulses, as well as at low-temperature (4.2 K). The bias-dependence of the two spin-torque terms (Slonczewski-like and field-like) has been determined from thermally-excited ferromagnetic resonance measurements, yielding values which are in good agreement with previous reports. Additionally, material parameters such as the effective magnetisation and the damping factor have also been extracted. Using these values as input, the switching voltages as function of the applied magnetic field have been calculated numerically and analytically by solving the modified Landau-Lifshitz-Gilbert equation. Unlike previous studies, the field-like spin-torque has also been included. Moreover, different configurations have been considered for the magnetic anisotropy directions of the reference and free layer, respectively
Diese Arbeit befasst sich mit Spin-Transfer-Torque-Effekten in MgO-basierten magnetischen Tunnelstrukturen. Die Phasendiagramme als Funktion von Spannung und Magnetfeld von CoFeB/MgO/CoFeB-Tunnelstrukturen mit Magnetisierung in der Ebene wurden experimentell bestimmt. Um thermische Anregungseffekte zu limitieren, wurden die Experimente einerseits mit nanosekundenlangen Spannungspulsen und andererseits bei niedrigen Temperaturen (4.2 K) durchgeführt. Die Spannungsabhängigkeit der beiden Spin-Torque-Parameter (in-plane und senkrechter Spin-Transfer-Torque) wurde aus Messungen der thermisch angeregten ferromagnetischen Resonanz bestimmt, wobei sich Werte ergaben, die gut mit vorangegangenen Untersuchungen übereinstimmen. Zusätzlich wurden Werte für Materialparameter wie die effektive Magnetisierung und den Dämpfungsparameter gewonnen. Unter Verwendung der erhaltenen Werte wurden die Schaltspannungen als Funktion des angelegten Magnetfeldes analytisch und numerisch berechnet, indem die erweiterte Landau-Lifshitz-Gilbert-Gleichung gelöst wurde. Im Gegensatz zu vorangegangenen Untersuchungen wurde der senkrechte Spin-Transfer-Torque dabei mit einbezogen. Darüber hinaus wurden verschiedene Konfigurationen für die Richtung der magnetischen Anisotropie der freien und fixierten Schicht berücksichtigt
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15

Platt, Christopher L. "Magnetic and transport properties of spin-dependent tunnel junctions /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952654.

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16

Elwell, Clifford Alastair. "The development of magnetic tunnel junction fabrication techniques." Thesis, University of Cambridge, 2002. https://www.repository.cam.ac.uk/handle/1810/34611.

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The discovery of large, room temperature magnetoresistance (MR) in magnetic tunnel junctions in 1995 sparked great interest in these devices. Their potential applications include hard disk read head sensors and magnetic random access memory (MRAM). However, the fabrication of repeatable, high quality magnetic tunnel junctions is still problematic. This thesis investigates methods to improve and quantify the quality of tunnel junction fabrication. Superconductor-insulator-superconductor (SIS) and superconductor-insulator ferromagnet(SIF) tunnel junctions were used to develop the fabrication route, due to the ease of identifying their faults. The effect on SIF device quality of interchanging the top and bottom electrodes was monitored. The relationship between the superconducting and normal state characteristics of SIS junctions was investigated. Criteria were formulated to identify devices in which tunneling is not the principal conduction mechanism innormal metal-insulator-normal metal junctions. Magnetic tunnel junctions (MTJs) were produced on the basis of the fabrication route developed with SIS and SIF devices. MTJs in which tunneling is the principal conduction mechanism do not necessarily demonstrate high MR, due to effects such as magnetic coupling between the electrodes and spin scattering. Transmission electron microscope images were used to study magnetic tunnel junction structure, revealing an amorphous barrier and crystalline electrodes. The decoration of pinholes and weak-links by copper electrodeposition was investigated. A new technique is presented to identify the number of copper deposits present in a thin insulating film. The effect of roughness, aluminium thickness and voltage on the number of pinholes and weak-links per unit area was studied. High frequency testing of read heads at wafer level was performed with a network analyser. Design implications for read head geometry were investigated, independent of magnetic performance. This technique has great potential to aid the rapid development of read and write heads whilst improving understanding of the system.
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17

Temple, Rowan Caradoc. "Spin accumulation and transport studied in double magnetic tunnel junctions." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/8259/.

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Magnetic CoFe nanoparticles have been produced by gas-aggregation and incorporated into sputtered MgO tunnel junction structures. Scanning tunnelling microscopy (STM) has been developed as a technique for examining spin accumulation and transport in these nanoscale junctions. The particles were initially characterised for their magnetic properties; x-ray magnetic circular dichroism on 11-14~nm diameter clusters was performed. The orbital-to-spin moment ratio was found to be enhanced over the bulk value and to decrease with increasing average diameter, which complements previous studies on smaller particles. The size dependence of the combined data is found not to follow predicted trends based on reduced orbital moment quenching in the outer shell. In particular for these large particles, the quenching is far more rapid than expected. Magnetometry studies on random arrays of nanoparticles at percolation show interesting effects attributed to complex magnetic dipolar interactions. This includes very broad range anisotropy and large blocking temperatures. For transport measurements, cryogenic STM is used to address individual islands and forms the top electrode of a double magnetic tunnel junction. Single electron charging effects are observed in these confined structures and the charging energy correlates to the size of the particle. New theory was developed to simulate these structures, giving an analytical solution to the current numerical orthodox theory. These solutions showed that TMR measurements, a current major barrier to studying nanospintronics using STM, were unnecessary. We are able characterise the tunnel junction parameters, including spin polarisation and accumulation, in a single I-V sweep of high information density. The spin polarisations of the opposing electrodes are found to be aligned anti-parallel despite a parallel magnetisation axis. Finally the spin lifetime on the island was calculated and found to exceed 1 us, longer than measured in previous studies.
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18

Yang, Hangfu [Verfasser]. "Thermal and magnetoelastic effects in magnetic tunnel junctions / Hangfu Yang." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2018. http://d-nb.info/1172414521/34.

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19

Zhang, Zhaohui. "Spin-dependent electrical and thermal transport in magnetic tunnel junctions." APS, 2012. http://hdl.handle.net/1993/31947.

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Thermoelectricity can directly convert a temperature difference into a voltage or charge current. Recently, the development of spin caloritronics has introduced spin as another degree of freedom in traditional thermoelectrics. This discovery bodes a new generation of magnetic random access memories (MRAMs), where thermal spin-transfer torque (TSTT) rather than voltage driven spin-transfer torque (STT) is used to switch the magnetization in magnetic tunnel junctions (MTJs). To advance the rising trend of spin caloritronics, the coupling of charge, spin, and heat flow during electron transport in MTJs was systematically studied in this thesis. To begin with, the static transport properties of MTJs were studied by observing current dependent tunnel magnetic resistance (TMR). The observed decrease of TMR with a biased current is attributed to the change in spin polarization of the free ferromagnetic layer. A phenomenological model has been built based on the current dependent polarization, which agrees with our experimental results. Next, the Seebeck rectification effect in MTJs was studied. By applying microwave currents to MTJs, an intrinsic thermoelectric coupling effect in the linear response regime of MTJs was discovered. This intrinsic thermoelectric coupling contributes a nonlinear correction to Ohm's law. In addition, this effect can be controlled magnetically since the Seebeck coefficient is related to magnetization configuration. Finally, TSTT in MTJs was systematically studied. A laser heating technique was employed to apply a temperature difference across the tunnel barrier and ferromagnetic resonance (FMR) spectra were measured electrically through spin rectification. By analyzing the FMR spectra, TSTT in MTJs was observed and the angular dependence of TSTT was found to be different from dc-biased STT. By solving the Landau-Lifshitz-Gilbert equation including STT, the experimental observations were well explained. The discovery of Seebeck rectification refines the previous understanding of magneto-transport and microwave rectification in MTJs and provides a new possibility for utilizing spin caloritronics in high-frequency applications. The study of TSTT in MTJs shows clear experimental evidence of TSTT in MTJs. Further optimization of the design of MTJs may succeed in decreasing the necessary switching fields strength or even achieve a switching by only TSTT in MTJs.
February 2017
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20

Lytvynenko, Ia M. "Magnetic tunnel junctions as a storage element for memory device." Thesis, Сумський державний університет, 2014. http://essuir.sumdu.edu.ua/handle/123456789/35037.

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Spin-dependent tunneling in magnetic tunnel junctions (MTJs) has recently aroused great research interest and has developed into a separate branch of materials science. The large tunneling magnetoresistance (TMR) observed in MTJs got much attention due to possible applications in non-volatile random access memories and next generation sensors of magnetic field. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35037
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21

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.

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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.
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22

Gokce, Aisha. "Low frequency current and resistance fluctuations in magnetic tunnel junctions." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 203 p, 2009. http://proquest.umi.com/pqdweb?did=1896928791&sid=9&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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23

Kurij, Georg. "Magnetic tunnel junctions for ultrasensitive all-oxide hybrid sensors for medical applications." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS051/document.

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La détection des très faibles valeurs de champ magnétique est un enjeu important pour l’émergence à plus grande échelle de techniques pour le domaine du médical telles que la magnéto cardiographie, ou la magnétoencéphalographie. Les solutions existantes industrialisées reposent sur l’utilisation de jonctions tunnels supraconductrices qui permettent de fabriques des SQUIDS (Superconducting Quantum Intereference Device) qui sont les briques de base des magnétomètres avec des sensibilités de l’ordre de la dizaine de femtotesla. Cependant cette approche impose de travailler à des températures très basses qui ne sont accessibles qu’avec de l’hélium liquide. Un approche récente, développée par le Spec-CEA permet de travailler à l’azote liquide (77K) ce qui lève un certain nombre de contraintes. Le dispositif est un capteur mixte composé d’une boucle supraconductrice de grande taille qui contient une constriction de taille micrométrique sur laquelle est rapportée une magnétorésistance tunnel qui sert de sonde locale du champ magnétique. L’objectif du travail dans ce travail de thèse est de poursuivre le développement de ce type de capteur en utilisant visant des structures tout oxyde. En effet l’intégration complète de ce type de capteur permettrait de gagner encore en termes de performances et d’atteindre une résolution de l’ordre du femtotesla. Pour ce faire le travail vise à intégrer une jonction tunnel tout oxyde directement par épitaxie sur la constriction. La jonction tunnel sera réalisée à partie d’oxydes magnétiques tels que les composés LaSrMnO3 ou SrRuO3 qui sont deux matériaux ferromagnétiques à la température de l’azote liquide
Sensing of extremely weak magnetic signals, such as produced by electrical activity of the human heart and brain, still remains a challenge. A very promising alternative to established field-sensing techniques is a novel, spin electronic based, ultrasensitive device called an all-oxide mixed sensor. It is formed by a superconducting loop, acting as a flux-to-field transformer and field amplifier, combined with a magnetic tunnel junction sensing the field.Our research activities have the goal to improve the performance of the mixed sensor, focusing on its core component – the magnetic tunnel junction (MTJ). The capability of an MTJ is predominantly determined by the quality of the tunnel barrier and by the stability of magnetization states. In this context, oxide materials, known for their remarkable physical properties, have already shown their advantages. Thus, studies on La0.7Sr0.3MnO3/SrTi0.8Nb0.2O3 functional oxide interfaces, exploration of SrRuO3/ La0.7Sr0.3MnO3 exchange bias system, and the final integration of these two components into a magnetic tunnel junction form the main part of our work.In the presented thesis, oxide thin films and heterostructures used for studies were grown by pulsed laser deposition (PLD). We fabricated electronic devices for investigations using clean room microfabrication techniques , e.g. optical lithography, chemically assisted ion beam etching (CAIBE) and sputtering. Temperature dependent magnetic and (magneto-) transport measurements were performed.Metal-semiconductor interfaces formed by the half-metallic ferromagnet La0.7Sr0.3MnO3 (LSMO) and heavily doped semiconductor SrTi0.8Nb0.2O3 (Nb:STO) were studied. Antiferromagnetic coupling at the interface of the LaSrMnO3 and itinerant ferromagnet SrRuO3 was explored. Magnetic tunnel junctions with Schottky barrier were investigated (MTJs with Nb:STO and LSMRO)
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24

Bonholzer, Michael [Verfasser], Marius [Akademischer Betreuer] Grundmann, Marius [Gutachter] Grundmann, and Georg [Gutachter] Schmidt. "Magnetic Tunnel Junctions based on spinel ZnxFe3-xO4 : Magnetic Tunnel Junctions based onspinel ZnxFe3-xO4 / Michael Bonholzer ; Gutachter: Marius Grundmann, Georg Schmidt ; Betreuer: Marius Grundmann." Leipzig : Universitätsbibliothek Leipzig, 2016. http://d-nb.info/1240629737/34.

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25

Jo, Moon-Ho. "Spin polarised tunnel junctions based on half-metallic manganites." Thesis, University of Cambridge, 2001. https://www.repository.cam.ac.uk/handle/1810/183622.

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26

Guo, Wei. "Compact modeling of magnetic tunnel junctions and design of hybrid CMOS-magnetic integrated circuits." Grenoble INPG, 2010. http://www.theses.fr/2010INPG0126.

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Le but de cette thèse était d’évaluer les performances de circuits logiques combinant des composants CMOS classiques et des composants magnétiques. Les jonctions tunnel magnétiques sont bien connues comme éléments de base des mémoires magnétiques. Mais l’utilisation de ces composants non-volatiles peut également permettre de repousser certaines limites de la microélectronique actuelle, notamment en contribuant à diminuer la consommation, les problèmes de dissipation thermique, en améliorant la fiabilité des circuits et en apportant de nouvelles fonctionnalités. Cette thèse a consisté en deux principaux aspects. Tout d’abord, un modèle électrique équivalent de la jonction tunnel magnétique a été développé afin de pouvoir les utiliser dans les outils standards de la microélectronique. Ensuite, ces modèles ont été utilisés pour concevoir et évaluer différents circuits hybrides CMOS/magnétiques, reprogrammables ou de type ASICs, qui ont été implémentés dans des démonstrateurs
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27

Wang, You. "Analyse de fiabilité de circuits logiques et de mémoire basés sur dispositif spintronique." Thesis, Paris, ENST, 2017. http://www.theses.fr/2017ENST0005/document.

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La jonction tunnel magnétique (JTM) commutée par la couple de transfert de spin (STT) a été considérée comme un candidat prometteur pour la prochaine génération de mémoires non-volatiles et de circuits logiques, car elle fournit une solution pour surmonter le goulet d'étranglement de l'augmentation de puissance statique causée par la mise à l'échelle de la technologie CMOS. Cependant, sa commercialisation est limitée par la fiabilité faible, qui se détériore gravement avec la réduction de la taille du dispositif. Cette thèse porte sur l'étude de la fiabilité des circuits basés sur JTM. Tout d'abord, un modèle compact de JTM incluant les problèmes principaux de fiabilité est proposé et validé par la comparaison avec des données expérimentales. Sur la base de ce modèle précis, la fiabilité des circuits typiques est analysée et une méthodologie d'optimisation de la fiabilité est proposée. Enfin, le comportement de commutation stochastique est utilisé dans certaines nouvelles conceptions d'applications classiques
Spin transfer torque magnetic tunnel junction (STT-MTJ) has been considered as a promising candidate for next generation of non-volatile memories and logic circuits, because it provides a perfect solution to overcome the bottleneck of increasing static power caused by CMOS technology scaling. However, its commercialization is limited by the poor reliability, which deteriorates severely with device scaling down. This thesis focuses on the reliability investigation of MTJ based non-volatile circuits. Firstly, a compact model of MTJ including main reliability issues is proposed and validated by the comparison with experimental data. Based on this accurate model, the reliability of typical circuits is analyzed and reliability optimization methodology is proposed. Finally, the stochastic switching behavior is utilized in some new designs of conventional applications
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Ladak, Sam. "Hot electron transport and barrier oxidation effects in magnetic tunnel junctions." Thesis, University of Exeter, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425319.

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29

Patibandla, Sridhar. "Spin transport studies in nanoscale spin valves and magnetic tunnel junctions." VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/1611.

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Spintronics or electronics that utilizes the spin degree of freedom of a single charge carrier (or an ensemble of charge carriers) to store, process, sense or communicate data and information is a rapidly burgeoning field in electronics. In spintronic devices, information is encoded in the spin polarization of a single carrier (or multiple carriers) and the spin(s) of these carrier(s) are manipulated for device operation. This strategy could lead to devices with low power consumption. This dissertation investigates spin transport in one dimensional and two dimensional semiconductors, with a view to applications in spintronic devices.
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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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31

Urech, Mattias. "Spin-dependant transport in lateral nano-devices based on magnetic tunnel junctions." Doctoral thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3866.

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32

Liu, Huanlong. "Spin Transfer Driven Magnetization Dynamics in Spin Valves and Magnetic Tunnel Junctions." Thesis, New York University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3557012.

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This thesis describes experimental studies of magnetization dynamics in both spin valves (SVs) and magnetic tunnel junctions (MTJs) subject to spin-polarized currents. A spin-polarized electrical current can transfer its angular momentum to a ferromagnet through a spin-transfer torque (STT), resulting in intriguing magnetization dynamics such as the reversal of the magnetization direction, precession and relaxation.

The ferromagnetic systems investigated were nanopillars, tens to hundreds of nanometers in cross section and a few nanometers in thickness, which were further integrated into SV or MTJ structures.

The magnetization switching and relaxation studies were performed on all-perpendicularly magnetized SVs. The switching probabilities were investigated for different pulse conditions at room temperature, where thermal fluctuations can play an important role. The pulse duration was varied over 10 orders of magnitude, from the fundamental timescales of magnetization precessional dynamics, 50 ps, to 1 s. Three switching regimes were found at different timescales. In the short-time regime, the switching probability was mainly determined by the angular momentum transfer between the current and the magnetization. In the long-time regime, the switching becomes thermal activation over an effective energy barrier modified by the STT. In the crossover regime, both spin-transfer and thermal effects are important.

The magnetization relaxation was studied by a two-pulse correlation method, where the relaxation time is measured by the interval between the two pulses. The thermal effects were shown to be important even at nanosecond time scales.

The switching and precession of magnetization were also studied in structures where a perpendicular spin polarizing layer is employed with an in-plane magnetized MTJ. When subject to pulses, the initial STT from the polarizer to the free layer is perpendicular to the free layer plane. For a large enough STT, this tilts the free layer magnetization out of the plane to create a large demagnetization field, typically at tens or hundreds of millitesla. This demagnetization field then becomes the dominant magnetic field acting on the free layer, leading to the precession of its magnetization. This magnetization precession was observed through real-time device resistance measurements, where precessions with hundreds of picoseconds are found from single current pulse stimuli.

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Du, Yuqing. "Film deposition and microfabrication of magnetic tunnel junctions with an MgO barrier." Thesis, University of Plymouth, 2012. http://hdl.handle.net/10026.1/1174.

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Magnetic tunnel junctions (MTJs), which consist of a thin insulation layer sandwiched by two ferromagnetic (FM) layers, are among the key devices of spintronics that have promising technological applications for computer hard disk drives, magnetic random access memory (MRAM) and other future spintronic devices. The work presented here is related to the development of relevant techniques for the preparation and characterization of magnetic films, exchanged biased systems and MTJs. The fabrication and characterization of PtMn/CoFe exchange biased systems and MTJs with Al-O barriers were undertaken when the new Aviza StratIon fxP ion beam deposition tool was developed by the project consortium funded by DTI MNT. After the Nordiko 9550 spintronic deposition tool was installed at Plymouth, the work focused on the development of MTJ multilayer stacks with layer structures of CoFeB/MgO/CoFe/IrMn and IrMn/CoFeB/MgO/CoFeB to achieve coherent tunneling with a crystalline MgO barrier. The film deposition, microfabrication, magnetic field annealing, microstructural and nano-scale characterization, magnetic and magneto-transport measurement for these devices have been systematically studied to achieve smooth interfaces and desired crystallographic textures and magnetic properties of layer stacks. Magnetoresistance (MR) of up to 200% was obtained from MTJs with a layer structure of Ta/CuN/Ta/CoFeB/MgO/CoFe/IrMn/Ta and a CuN bottom electrode. Enhanced exchange anisotropy from the bottom pinned IrMn/CoFeB stacks has been obtained, which demonstrated the possibility of fabricating MTJs with CoFeB as both the top and bottom FM electrodes with strong exchange bias. The origin of the enhanced exchange bias field was studied by employing high resolution transmission electron microscopy (HRTEM) and x-ray magnetic circular dichroism (XMCD) to examine the mmicrostructure properties and element specific magnetic properties of the stacks. Results demonstrate that the enhanced exchange anisotropy in the IrMn/CoFeB system is closely associated with the increased uncompensated interfacial spins. MTJs with layered structures of IrMn/CoFeB/MgO/CoFeB were prepared based on this exchange bias system. However, further work is required for the optimisation of the (001) crystallographic textures of the CoFeB/MgO/CoFeB stack to achieve coherent tunneling.
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34

Meo, Andrea. "Atomistic model of magnetisation dynamics and equilibrium properties of magnetic tunnel junctions." Thesis, University of York, 2018. http://etheses.whiterose.ac.uk/22730/.

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The next generation of portable devices requires random access memories (RAMs) which are characterised by high performance and at the same time low power consumption. A promising candidate as replacement in this sector is magnetic RAM (MRAM) based on CoFeB/MgO magnetic tunnel junctions, since it retains the fast operational capability while reducing the energy requirements due to its non-volatile nature. Despite such outstanding features, a complete understanding of the device operation has not been achieved yet. This limits the scaling of the device below the next technological node (< 20nm). The reduction in the number of atoms constituting these devices is responsible for surface and finite size effects as well as a reduced thermal stability, which affects the dynamic properties. Currently, micromagnetism represents the most used theoretical approach to investigate magnetic materials and their properties. The main limitation of this model is the continuum approach. In this approximation the atomic properties are averaged, which makes it unsuitable to describe interface, surface and finite size effects as well as thermal effects. Do deal with these limitations, in this thesis we use an atomistic spin model to investigate the equilibrium and dynamical properties of CoFeB/MgO-based systems, an approach more appropriate to account for such effects. Our results suggest that CoFeB/MgO systems are characterised by more complex magnetic properties than usually assumed. The reversal mechanism is non-uniform at dimensions and temperatures that are technologically relevant. Moreover, at these time scales thermal effects cause a distribution of the dynamic properties that represent an intrinsic limitation to the device reliability and need to be addressed in order to achieve the desired scaling. The results also show the importance of atomistic models to understand and accurately describe the magnetic properties of devices when they are fabricated on the nano scale.
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Yang, Hongxin. "First-principles study of spintronic phenomena in magnetic tunnel junctions and graphene." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENY054/document.

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Phénomènes de spintronique dans les jonctions tunnel magnétiques et des films minces sont très prometteurs des deux points fondamentaux et l'application de vue. Elles sont basées sur l'exploration de spin d'électron en plus de sa charge et comprennent intercalaire couplage d'échange (CEI), l'anisotropie magnétique perpendiculaire (PMA), géante (GMR) et magnétorésistance tunnel (TMR), Couple de transfert de spin (STT), Spin effet Hall (SHE) et même induire du magnétisme dans les éléments non compris d graphène. Cette thèse comprendra premiers principes des études de phénomènes spintronique qui ont été d'un grand intérêt récemment. La première partie est consacrée à intercalaire couplage d'échange à travers les matériaux isolants dont le MgO, SrTiO3, GaAs et ZnSe. La deuxième partie comprendra des études ab initio d'anisotropie magnétique perpendiculaire au Fe | interfaces MgO et MTJ y compris le mécanisme et sa corrélation avec le spin Bloch symétrie Etat fondé de filtrage. Dans les enquêtes troisième partie de l'anisotropie magnétique et la fonction de travail dans les Co | interfaces graphène seront présentés. Ensuite, il sera montré possibilité d'induire et d'optimiser le magnétisme intrinsèque dans nanomeshes graphène. Dernière partie sera consacrée à l'induction de polarisation de spin et le réglage de Dirac point et ordre magnétique dans le graphène à l'aide d'effets de proximité magnétiques substrat
Spintronic phenomena in magnetic tunnel junctions and thin films are very promising from both fundamental and application points of view. They are based on exploring spin of electron in addition to its charge and include interlayer exchange coupling (IEC), perpendicular magnetic anisotropy (PMA), giant (GMR) and tunnel magnetoresistance (TMR), Spin Transfer Torque (STT), Spin Hall Effect (SHE) and even inducing magnetism in non d elements including graphene. This thesis will include first-principles studies of spintronic phenomena which have been of high interest recently. First part is devoted to interlayer exchange coupling across insulating materials including MgO, SrTiO3, GaAs and ZnSe. The second part will include ab initio studies of perpendicular magnetic anisotropy at Fe|MgO interfaces and MTJs including the mechanism and its correlation to the Bloch state symmetry based spin filtering. In third part investigations of magnetic anisotropy and work function in Co|graphene interfaces will be presented. Next, it will be shown possibility of inducing and optimizing intrinsic magnetism in graphene nanomeshes. Final part will be devoted to inducing spin polarization and tuning Dirac point and magnetic order in graphene by means of magnetic substrate proximity effects
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Schleicher, Filip. "Impact of structural defects on spin-polarized transport across magnetic tunnel junctions." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAE036/document.

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Dans le manuscrit, nous étudions l’impact des défauts sur le transport électronique dépendant du spin dans les jonctions tunnel magnétiques (JTM). Ces études ont été effectuées sur des hétérostructures possédant des barrières tunnel composé de SrTiO3, TiO2 et de MgO. Dans le cas des deux premières structures, nous montrons comment l’oxydation à l’interface induit réduction très prononcée de la magnétorésistance tunnel (TMR). Dans le cas du MgO, des études optiques sur les états induits par les défauts dans la barrière isolante ont été effectué. Nous avons montré qu’il est possible de contrôler la densité de certain type de défaut (lacune d’oxygène) en altérant les conditions de dépôts du MgO. Les études électriques et optiques effectué sur ces échantillons permettent de remonter à l’énergie des défauts au sein de la barrière. Les méthodes d’analyses des mesures électrique Î (I chapeau), qui représente la variation relative ou absolue du courant électrique en fonction de la température, permet de définir différents régime de transport à travers les jonctions CoFeB/MgO/CoFeB. Le régime intrinsèque observé à basse température s’explique par les effets de structure de bande du CoFeB et du MgO (filtrages des électrons de différente symétrie par la barrière de MgO), tandis que le régime « extrinsèque » observé aux températures intermédiaires résulte d’une activation thermique progressive des lacunes d’oxygène et est accompagné d’une réduction de la résistance ainsi que du signal TMR. Nous avons également montré dans des études préliminaires qu’une excitation optique des défauts a un impact sut le magnéto-transport
In the manuscript it is presented how the spin-polarized transport across magnetic tunnel junctions (MTJ) is affected by presence of structural defects within the barrier and at its interfaces. Studies concern structures incorporating SrTiO3, TiO2 and MgO insulators. In case of the first two structures it is shown how interfacial oxidation results in the drastically reduced value of the tunnelmagnetoresistance (TMR). In case of the MgO barrier, extensive studies on defect sites within the crystalline network of the insulator are performed. It is shown that one may control density of certain types of oxygen vacancies by altering growth conditions of the MgO layer. Further electrical and optical studies give insight into energetical positioning of these defect sites. Extension of the Î magnetotransport analysis method from the ‘absolute’ to the ‘relative’ case reveals several regimes of transport across CoFeB/MgO/CoFeB junctions. The low-temperature ‘intrinsic’ regime is attributed exclusively to the band structure effects of the CoFeB electrodes, whereas the mid- to room-temperature ‘extrinsic’ regimes result from the gradual incidence of thermally activated defect sites on the spin-polarized transport, which is accompanied by an increased reduction of both the resistance and the TMR signal. Initial experiments show that optical excitation of the defect sites has a crucial impact on the magnetotransport
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37

Harnchana, Viyada. "Transmission electron microscopy characterisation for development of CoFeB/MgO based magnetic tunnel junctions." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535675.

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38

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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39

Taudul, Beata. "Impact of symmetry of oxygen vacancies on electronic transport in MgO-based magnetic tunnel junctions." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE042/document.

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En spintronique, l’étude des hétérostructures multicouches composées d'une électrode ferromagnétique et d'une couche isolante mince, c'est-à-dire des jonctions tunnel magnétiques (JTM), est particulièrement importante. Le système canonique est le Fe/MgO/Fe où les hautes valeurs du rapport de la magnétoresistance tunnel (TMR) ont été mesurées. Le facteur crucial définissant la performance de la jonction est l’imperfection structurelle dans un dispositif réel. Dans notre travail, nous nous sommes concentrés sur des lacunes d'oxygène dans MgO. Au moyen de la théorie de la fonctionnelle de densité, nous avons étudié les propriétés électroniques de l'état fondamental des lacunes d'oxygène simples et doubles dans MgO massif, appelées respectivement centres F et M. Nous avons ensuite étudié l'impact de ces lacunes sur le transport balistique dans les jonctions magnétiques. Nous avons démontré le rôle supérieur joué par les centres M et nous avons prouvé qu'un transport cohérent, préservant le spin et la symétrie des électrons, est possible en présence de centres M
In sprintronics, the study of multilayer heterostructures composed of a ferromagnetic electrodes and a thin insulating layer, i.e. magnetic tunnel junctions (MTJs), is of special importance. The canonical systems are MTJs made of Fe/MgO/Fe where hight tunneling mangetoresistance ratio (TMR) values were measured. The crucial factor defining the junction performance is the structural imperfection appearing in a real devices. In our work we focused in particular on oxygen vacancies in MgO. By means of density functional theory we studied ground state electronic properties of single and double oxygen vacancies, referred as F and M centers, respectively, in bulk MgO. We then switched to full junctions where we investigated the impact of vacancies on the ballistic transport. We demonstrated that M centers played a superior role and proved that coherent transport, preserving electrons spin and symmetry, is possible in presence of paired vacancies
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Walter, Marvin [Verfasser], Markus [Akademischer Betreuer] Münzenberg, and Christian [Akademischer Betreuer] Jooß. "The tunnel magneto-Seebeck effect in magnetic tunnel junctions / Marvin Walter. Gutachter: Markus Münzenberg ; Christian Jooß. Betreuer: Markus Münzenberg." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2014. http://d-nb.info/1046987240/34.

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41

Newhouse-Illige, T., Y. H. Xu, Y. H. Liu, S. Huang, H. Kato, C. Bi, M. Xu, B. J. LeRoy, and W. G. Wang. "Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdO X barriers." AMER INST PHYSICS, 2018. http://hdl.handle.net/10150/627087.

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Perpendicular magnetic tunnel junctions with GdOX tunneling barriers have shown a unique voltage controllable interlayer magnetic coupling effect. Here, we investigate the quality of the GdOX barrier and the coupling mechanism in these junctions by examining the temperature dependence of the tunneling magnetoresistance and the interlayer coupling from room temperature down to 11 K. The barrier is shown to be of good quality with the spin independent conductance only contributing a small portion, 14%, to the total room temperature conductance, similar to AlOX and MgO barriers. The interlayer coupling, however, shows an anomalously strong temperature dependence including sign changes below 80 K. This non-trivial temperature dependence is not described by previous models of interlayer coupling and may be due to the large induced magnetic moment of the Gd ions in the barrier. Published by AIP Publishing.
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Lei, Zhiqiang, and 雷志强. "Low-frequency noise study of magnetic tunnel junctions and their applications on biomarker immunoassay." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/193413.

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The noise performances of Al2O3-based magnetic tunnel junctions (MTJs) in the low-frequency regime were systematically studied. Conetic alloy Ni77Fe14Cu5Mo4 was deposited as both the MTJ pinned layer and free layer due to its superb magnetically soft properties. The Al2O3-MTJ sensors with Conetic alloy exhibited a linear field response with a relatively small easy-axis coercivity of 3 Oe. A tunneling magneto-resistance (TMR)of 9.5% and Hooge parameter of 3.82 × 〖10〗^(-7)μm^2 were achieved without any hard-axis bias field. The hysteresis was removed by applying an external magnetic field of 8 Oe along the hard axis and the sensor sensitivity was 0.4%/Oe within a linear region at room temperature. The relation between the Hooge parameter and hard-axis field was investigated and the result illustrated that the 1/f noise could be suppressed by an optimized hard-axis bias field. Additionally, a rotating magnetic field was employed to investigate the angular dependence of the MTJ low-frequency noise. Measurement results indicated that the Hooge parameter was angular-dependent and exhibited a linear relation with respect to the angular magneto-resistive susceptibility. Also, it could be inferred that the Hooge parameter possessed a higher value when the Conetic MTJs were in the region of antiparallel state. These studies showed that it was feasible to use Conetic alloy as the soft magnetic layer in MTJ sensor for its small coercivity, and a hard-axis bias field could be used to linearize the sensor response and suppress the 1/f noise induced by the magnetic fluctuation in the MTJ ferromagnetic layers. Besides the study of low-frequency noise in MTJs, the feasibility of biomarker immunoassay with MTJ sensors is investigated. Initially, with the assistance of Al2O3-MTJ sensors with Conetic alloy, 20-nm iron-oxide magnetic nanoparticles (MNPs) with three different concentrations were successfully detected by the shift of the TMR curve. The maximum resistance deviation was 0.16 Ω for an MNP concentration of 20.0 mg/mL. Based on this study, the detection of alpha-fetoprotein (AFP) labeled with 20-nm iron-oxide MNPs together with MTJ sensors by a sandwich-assay configuration was further investigated. AFP is a vital hepatic tumor biomarker and the detection of AFP has significant applications for clinical diagnostics and immunoassay for early-stage liver cancer indication. To further increase the sensitivity, MgO-MTJ sensors with a TMR of 122% and sensitivity of 0.95%/Oe were employed. The target AFP antigens of three concentrations were detected, and experimental data indicated that the resistance variation of the MTJ sensor increased with the AFP concentration ratio proportionally, which was consistent with previous studies. These results conclusively demonstrate that MTJ sensors together with MNPs are a promising bio-sensing platform for biomarker immunoassay.
published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy
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43

Atcheson, Gwénaël Yves Peter. "Integration of oxynitride barriers by reactive RF sputtering for use in magnetic tunnel junctions." Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675949.

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Magnetic field sensors were developed with use of a SFI Shamrock sputtering tool. GMR spin-valve type sensors were developed in CIP geometry requiring no additional processing once deposited, and TMR magnetic tunnel junctions were developed in CPP. This meant the additional development of a photolithographic process in order to produce working devices. The MTJs used MgO as a tunneling barrier in reference devices, and a novel oxynitride barrier in experimental devices deposited by reactive RF sputtering from an elemental target in a variable argon/oxygen/nitrogen atmosphere. Devices produced show potential for further development.
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Jiang, Lai. "Magnetoresistance and electrical noise in silver chalcogenide silver telluride, zigzag-shaped AMR magnetic sensors, and magnetic tunnel junctions." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.40 Mb., 150 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3220789.

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Wimmer, Michael. "Quantum transport in nanostructures : from computational concepts to spintronics in graphene and magnetic tunnel junctions /." Regensburg Univ.-Verl. Regensburg, 2009. http://d-nb.info/99940721X/34.

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46

Franz, Christian [Verfasser]. "An ab initio approach to spin transport in magnetic tunnel junctions with disorder / Christian Franz." Gießen : Universitätsbibliothek, 2016. http://d-nb.info/1088314694/34.

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47

Hughes, Norman David. "The manufacture and testing of magnetic tunnel junctions and a study of their swithching characteristics." Thesis, Brunel University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251203.

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48

Manos, Orestis [Verfasser]. "Perpendicular magnetic tunnel junctions based on CoFeB and MnIr/CoFe with exchange bias / Orestis Manos." Bielefeld : Universitätsbibliothek Bielefeld, 2019. http://d-nb.info/1196642885/34.

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49

Wimmer, Michael. "Quantum transport in nanostructures from computational concepts to spintronics in graphene and magnetic tunnel junctions." Regensburg Univ.-Verl. Regensburg, 2008. http://d-nb.info/99420826X/04.

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50

Rogge, Jan [Verfasser]. "Barium Oxide as novel barrier in Heusler based magnetic tunnel junctions / Jan Rogge. Fakultät für Physik." Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2012. http://d-nb.info/1029455562/34.

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