Review on Spintronics : Principles and Device Applications

Spintronics is one of the emerging fields for the next-generation nanoelectronic devices to reduce their power consumption and to increase their memory and processing capabilities. Such devices utilise the spin degree of freedom of electrons and/or holes, which can also interact with their orbital moments. In these devices, the spin polarisation is controlled either by magnetic layers used as spin-polarisers or analysers or via spin-orbit coupling. Spin waves can also be used to carry spin current. In this review, the fundamental physics of these phenomena is described first with respect to the spin generation methods as detailed in Sections 2 ~ 9. The recent development in their device applications then follows in Sections 10 and 11. Future perspectives are provided at the end

Optical Switching in Tb/Co-Multilayer Based Nanoscale Magnetic Tunnel Junctions

Magnetic tunnel junctions (MTJs) are elementary units of magnetic memory devices. For high-speed and low-power data storage and processing applications, fast reversal by an ultrashort laser pulse is extremely important. We demonstrate optical switching of Tb/Comultilayer-based nanoscale MTJs by combining optical writing and electrical read-out methods. A 90 fs-long laser pulse switches the magnetization of the storage layer (SL). The change in magnetoresistance between the SL and a reference layer (RL) is probed electrically across the tunnel barrier. Single-shot switching is demonstrated by varying the cell diameter from 300 nm to 20 nm. The anisotropy, magnetostatic coupling, and switching probability exhibit cell-size dependence. By suitable association of laser fluence and magnetic field, successive commutation between high-resistance and low-resistance states is achieved. The switching dynamics in a continuous film is probed with the magneto-optical Kerr effect technique. Our experimental findings provide strong support for the growing interest in ultrafast spintronic devices.Comment: total pages 22, Total figure

Configurations de l'aimantation dans des objets magnétiques à dimensionalité réduite. Relation entre magnétisme et transport

Composition du jury Rapporteurs: François GAUTIER, Luc PIRAUX, Jean-Louis PORTESEIL Examinateur: Claude CHAPPERT Directeur de thèse: Kamel OUNADJELA Invités: Emil BURZO, Ursula EBELS, Michel VIRETIn this work, two different aspects of the magnetic properties in systems of small dimensions have been investi-gated. The first aspect concerns the domain wall magnetoresistance in monocristallin cobalt nanowires of rectangular section. These nanowires were fabricated by electron-beam lithography and dry etching from epitaxial cobalt thin films with strong in-plane uniaxial anisotropy. The reduction of the lateral size of the system influences drastically the distribution of the magnetization. Different micromagnetic configurations are obtained in wires, depending on their orientation, parallel or perpendicular, with respect to the easy magnetocristalline axis. These configurations are strongly affected by the magnetic history. The magnetization reversal in the wires was studied by magnetotransport measurements and interpreted in the context of models of domain walls scattering and con-ventional galvanomagnetic effects in ferromagnetic materials. The domain wall magnetoresistance obtained from this study is positive and increases at low temperature. The second part is dedicated to the study of arrays of polycrystalline circular cobalt dots, fabricated by nanoim-print. For the case of widely spaced arrays, where the magnetostatic interactions between dots are negligible, different magnetization reversal mechanisms were identified, as a function of the dot dimensions: a coherent rotation of the magnetization and the formation of one or two vortices. For a dense array, the magnetostatic in-teractions generate collective magnetization reversal phenomena. These interactions lead to the formation, by an avalanche mechanism, of single-domain state chains or vortex-state chains, with identical rotation sense. Fur-thermore, they give rise to a quadratic anisotropy of the reversal process, and namely of the vortex nucleation field.Ce travail de thèse est constitué de deux parties distinctes. La première consiste en l'étude de la magnétorésistance de parois de domaines magnétiques dans des nanofils de cobalt monocristallin. Ces nanofils ont été fabriqués par lithographie électronique et gravure à partir de films minces épitaxiés, à forte anisotropie uniaxiale planaire. Le confinement de l'aimantation qui résulte de la nanos-tructuration affecte fortement sa distribution. Différentes configurations micromagnétiques sont induites dans ces fils selon qu'ils sont découpés parallèlement ou perpendiculairement à l'axe de facile aimantation cristallin. Ces configurations dépendent fortement de l'histoire magnétique. Le retournement de l'aimantation dans ces fils a été étudié en détail, à l'aide de mesures de magnétotransport. Celles ci ont été interprétées dans le cadre des modèles décrivant la magnétorésistance de parois et les effets galvanomagnétiques classiques des matériaux ferromagné-tiques. Il ressort de cette étude que la contribution magnétorésistive des parois est positive et augmente à basse température. La seconde partie de ce travail est consacrée à l'étude du magnétisme des réseaux de plots circulaires de cobalt polycristallin, fabriqués par nano-impression. Dans les réseaux les moins denses, où les interactions magnétosta-tiques entre plots sont négligeables, différents mécanismes de renversement de l'aimantation ont été identifiés en fonction des dimensions des objets: une rotation cohérente de l'aimantation ou la formation d'un, voire de deux vortex. Dans les réseaux les plus denses, les interactions magnétostatiques sont à l'origine de phénomènes de renversement collectif de l'aimantation. Elles entraînent la formation, par un processus d'avalanche, de chaînes de plots monodomaines ou contenant des vortex de sens de circulation identique. Elles imposent au processus de renversement, et notamment au champ de nucléation, d'être anisotrope, de symétrie identique à celle de la maille du réseau

Configurations de l'aimantation dans des objets magnétiques à dimentionalité réduite (Relation entre magnétisme et transport)

Ce travail de thèse est constitué de deux parties distinctes. La première consiste en l'étude de la magnétorésistance de parois de domaines magnétiques dans des nanofils de cobalt monocristallin. Ces nanofils ont été fabriqués par lithographie électronique et gravure à partir de films minces épitaxiés, à forte anisotropie uniaxiale planaire. Le confinement de l'aimantation qui résulte de la nanostructuration affecte fortement sa distribution. Différentes configurations micromagnétiques sont induites dans ces fils selon qu'ils sont découpés parallèlement ou perpendiculairement à l'axe de facile aimantation cristallin. Ces configurations dépendent fortement de l'histoire magnétique. Le retournement de l'aimantation dans ces fils a été étudié en détail, à l'aide de mesures de magnétotransport. Celles ci ont été interprétées dans le cadre des modèles décrivant la magnétorésistance de parois et les effets galvanomagnétiques classiques des matériaux ferromagnétiques. Il ressort de cette étude que la contribution magnétorésistive des parois est positive et augmente à basse température.La seconde partie de ce travail est consacrée à l'étude de réseaux de plots circulaires de cobalt polycristallin, fabriqués par nano-impression. Dans les réseaux les moins denses, où les interactions magnétostatiques entre plots sont négligeables, différents mécanismes de renversement de l'aimantation ont été identifiés en fonction des dimensions des objets: une rotation cohérente de l'aimantation ou la formation d'un, voire de deux vortex. Dans les réseaux les plus denses, les interactions magnétostatiques sont à l'origine de phénomènes de renversement collectif de l'aimantation. Elles entraînent la formation, par un processus d'avalanche, de chaînes de plots monodomaines ou contenant des vortex de sens de circulation identique. Elles imposent au processus de renversement, et notamment au champ de nucléation, d'être anisotrope, de symétrie identique à celle de la maille du réseau.In this work, two different aspects of the magnetic properties in systems of small dimensions have been investigated.The first aspect concerns the domain wall magnetoresistance in monocristallin cobalt nanowires of rectangular section. These nanowires were fabricated by electron-beam lithography and dry etching from epitaxial cobalt thin films with strong in-plane uniaxial anisotropy. The reduction of the lateral size of the system influences drastically the distribution of the magnetization. Different micromagnetic configurations are obtained in wires, depending on their orientation, parallel or perpendicular, with respect to the easy magnetocristalline axis. These configurations are strongly affected by the magnetic history. The magnetization reversal in the wires was studied by magnetotransport measurements and interpreted in the context of models of domain walls scattering and conventional galvanomagnetic effects in ferromagnetic materials. The domain wall magnetoresistance obtained from this study is positive and increases at low temperature. The second part is dedicated to the study of arrays of polycrystalline circular cobalt dots, fabricated by nanoimprint. For the case of widely spaced arrays, where the magnetostatic interactions between dots are negligible, different magnetization reversal mechanisms were identified, as a function of the dot dimensions: a coherent rotation of the magnetization and the formation of one or two vortices. For a dense array, the magnetostatic interactions generate collective magnetization reversal phenomena. These interactions lead to the formation, by an avalanche mechanism, of single-domain state chains or vortex-state chains, with identical rotation sense. Furthermore, they give rise to a quadratic anisotropy of the reversal process, and namely of the vortex nucleation field.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Phase Change and Magnetic Memories for Solid-State Drive Applications

The state-of-the-art solid-state drives (SSDs) now heterogeneously integrate nand Flash and dynamic random access memories (DRAMs) to partially hide the limitation of the nonvolatile memory technology. However, due to the increased request for storage density coupled with performance that positions the storage tier closer to the latency of the processing elements, nand Flash are becoming a serious bottleneck. DRAM as well are a limitation in the SSD reliability due to their vulnerability to the power loss events. Several emerging memory technologies are candidate to replace them, namely the storage class memories. Phase change memories and magnetic memories fall into this category. In this work, we review both technologies from the perspective of their possible application in future disk drives, opening up new computation paradigms as well as improving the storage characteristics in terms of latency and reliability

High speed and high-area efficiency non-volatile look-up table design based on magnetic tunnel junction

International audienceContinual growth in the size and functionality of FPGAs over past few years has resulted in an increasing interest in their use for high speed applications. However, the execution speed is limited by the memory access speed and the whole function is affected due to the great amount of data. This paper introduces a novel high speed and high-area efficiency MRAM-based non-volatile look-up table (nvLUT) to overcome the effect of high resistance introduced by the increasing number of inputs. This nvLUT reduces the sense delay and MTJ count by 55 % and 47%

High density SOT-MRAM memory array based on a single transistor

International audienceSpin Orbit Torque Magnetic RAM (SOT-MRAM) approach represents a new way to overcome over Spin Transfer Torque (STT) memory limitations by separating the reading and the writing paths. It is particularly interesting for high speed applications that do not require very high density because of two transistors per bit cell. This paper presents a high density SOTMRAM memory array based on a single transistor and a unidirectional diode. There are three advantages of this approach. The number of transistors for 32kb memory array is decreased by factor of 45% which leads to an improved cell density by 20% compared to conventional SOT bit cell. Moreover, it requires less control to read operation and finally high endurance, high speed and high density can be achieved. The key challenge going will be to adjust between sense margin and read energ