253 research outputs found
Role of dimensional crossover on spin-orbit torque efficiency in magnetic insulator thin films
Magnetic insulators (MIs) attract tremendous interest for spintronic
applications due to low Gilbert damping and absence of Ohmic loss. Magnetic
order of MIs can be manipulated and even switched by spin-orbit torques (SOTs)
generated through spin Hall effect and Rashba-Edelstein effect in heavy
metal/MI bilayers. SOTs on MIs are more intriguing than magnetic metals since
SOTs cannot be transferred to MIs through direct injection of electron spins.
Understanding of SOTs on MIs remains elusive, especially how SOTs scale with
the film thickness. Here, we observe the critical role of dimensionality on the
SOT efficiency by systematically studying the MI layer thickness dependent SOT
efficiency in tungsten/thulium iron garnet (W/TmIG) bilayers. We first show
that the TmIG thin film evolves from two-dimensional to three-dimensional
magnetic phase transitions as the thickness increases, due to the suppression
of long-wavelength thermal fluctuation. Then, we report the significant
enhancement of the measured SOT efficiency as the thickness increases. We
attribute this effect to the increase of the magnetic moment density in concert
with the suppression of thermal fluctuations. At last, we demonstrate the
current-induced SOT switching in the W/TmIG bilayers with a TmIG thickness up
to 15 nm. The switching current density is comparable with those of heavy
metal/ferromagnetic metal cases. Our findings shed light on the understanding
of SOTs in MIs, which is important for the future development of ultrathin
MI-based low-power spintronics
Thermal Spin Orbit Torque with Dresselhaus Spin Orbit Coupling
Based on the spinor Boltzmann equation, we obtain a temperature dependent
thermal spin-orbit torque in terms of the local equilibrium distribution
function in a two dimensional ferromagnet with Dresselhaus spin-orbit coupling.
We also derive the continuity equation of spin accumulation and spin current,
the spin diffusion equation in Dresselhaus ferromagnet, which contains the
thermal spin orbit torque under local equilibrium assumption. This temperature
dependent thermal spin-orbit torque originates from the temperature gradient
applied to the system. it is also sensitive to temperature due to the local
equilibrium distribution function therein. In the spin diffusion equation, we
can single out the usual spin-orbit torque as well as the spin transfer torque,
which is conceded to our previous results. Finally, we illustrate them by an
example of spin-polarized transport through a ferromagnet with Dresselhaus
spin-orbit coupling driven by temperature gradient, those torques including
thermal spin-orbit torque are demonstrated numerically.Comment: 19pages,6figure
DEMANDS FOR SPIN-BASED NONVOLATILITY IN EMERGING DIGITAL LOGIC AND MEMORY DEVICES FOR LOW POWER COMPUTING
Miniaturization of semiconductor devices is the main driving force to achieve an outstanding performance of modern integrated circuits. As the industry is focusing on the development of the 3nm technology node, it is apparent that transistor scaling shows signs of saturation. At the same time, the critically high power consumption becomes incompatible with the global demands of sustaining and accelerating the vital industrial growth, prompting an introduction of new solutions for energy efficient computations.Probably the only radically new option to reduce power consumption in novel integrated circuits is to introduce nonvolatility. The data retention without power sources eliminates the leakages and refresh cycles. As the necessity to waste time on initializing the data in temporarily unused parts of the circuit is not needed, nonvolatility also supports an instant-on computing paradigm.The electron spin adds additional functionality to digital switches based on field effect transistors. SpinFETs and SpinMOSFETs are promising devices, with the nonvolatility introduced through relative magnetization orientation between the ferromagnetic source and drain. A successful demonstration of such devices requires resolving several fundamental problems including spin injection from metal ferromagnets to a semiconductor, spin propagation and relaxation, as well as spin manipulation by the gate voltage. However, increasing the spin injection efficiency to boost the magnetoresistance ratio as well as an efficient spin control represent the challenges to be resolved before these devices appear on the market. Magnetic tunnel junctions with large magnetoresistance ratio are perfectly suited as key elements of nonvolatile CMOS-compatible magnetoresistive embedded memory. Purely electrically manipulated spin-transfer torque and spin-orbit torque magnetoresistive memories are superior compared to flash and will potentially compete with DRAM and SRAM. All major foundries announced a near-future production of such memories.Two-terminal magnetic tunnel junctions possess a simple structure, long retention time, high endurance, fast operation speed, and they yield a high integration density. Combining nonvolatile elements with CMOS devices allows for efficient power gating. Shifting data processing capabilities into the nonvolatile segment paves the way for a new low power and high-performance computing paradigm based on an in-memory computing architecture, where the same nonvolatile elements are used to store and to process the information
Electrical control of magnetism by electric field and current-induced torques
While early magnetic memory designs relied on magnetization switching by
locally generated magnetic fields, key insights in condensed matter physics
later suggested the possibility to do it electrically. In the 1990s,
Slonczewzki and Berger formulated the concept of current-induced spin torques
in magnetic multilayers through which a spin-polarized current may switch the
magnetization of a ferromagnet. This discovery drove the development of
spin-transfer-torque magnetic random-access memories (STT-MRAMs). More recent
research unveiled spin-orbit-torques (SOTs) and will lead to a new generation
of devices including SOT-MRAMs. Parallel to these advances, multiferroics and
their magnetoelectric coupling experienced a renaissance, leading to novel
device concepts for information and communication technology such as the MESO
transistor. The story of the electrical control of magnetization is that of a
dance between fundamental research (in spintronics, condensed matter physics,
and materials science) and technology (MRAMs, MESO, microwave emitters,
spin-diodes, skyrmion-based devices, components for neuromorphics, etc). This
pas de deux led to major breakthroughs over the last decades (pure spin
currents, magnetic skyrmions, spin-charge interconversion, etc). As a result,
this field has propelled MRAMs into consumer electronics products but also
fueled discoveries in adjacent research areas such as ferroelectrics or
magnonics. Here, we cover recent advances in the control of magnetism by
electric fields and by current-induced torques. We first review fundamental
concepts in these two directions, then discuss their combination, and finally
present various families of devices harnessing the electrical control of
magnetic properties for various application fields. We conclude by giving
perspectives in terms of both emerging fundamental physics concepts and new
directions in materials science.Comment: Final version accepted for publication in Reviews of Modern Physic
Magnetism, symmetry and spin transport in van der Waals layered systems
The discovery of an ever-increasing family of atomic layered magnetic materials, together with the already established vast catalogue of strong spin–orbit coupling and topological systems, calls for some guiding principles to tailor and optimize novel spin transport and optical properties at their interfaces. Here, we focus on the latest developments in both fields that have brought them closer together and make them ripe for future fruitful synergy. After outlining fundamentals on van der Waals magnetism and spin–orbit coupling effects, we discuss how their coexistence, manipulation and competition could ultimately establish new ways to engineer robust spin textures and drive the generation and dynamics of spin current and magnetization switching in 2D-materials-based van der Waals heterostructures. Grounding our analysis on existing experimental results and theoretical considerations, we draw a prospective analysis about how intertwined magnetism and spin–orbit torque phenomena combine at interfaces with well-defined symmetries and how this dictates the nature and figures of merit of spin–orbit torque and angular momentum transfer. This will serve as a guiding role in designing future non-volatile memory devices that utilize the unique properties of 2D materials with the spin degree of freedom
Magnetism, symmetry and spin transport in van der Waals layered systems
The discovery of an ever increasing family of atomic layered magnetic
materials, together with the already established vast catalogue of strong
spin-orbit coupling (SOC) and topological systems, calls for some guiding
principles to tailor and optimize novel spin transport and optical properties
at their interfaces. Here we focus on the latest developments in both fields
that have brought them closer together and make them ripe for future fruitful
synergy. After outlining fundamentals on van der Waals (vdW) magnetism and SOC
effects, we discuss how their coexistence, manipulation and competition could
ultimately establish new ways to engineer robust spin textures and drive the
generation and dynamics of spin current and magnetization switching in 2D
materials-based vdW heterostructures. Grounding our analysis on existing
experimental results and theoretical considerations, we draw a prospective
analysis about how intertwined magnetism and spin-orbit torque (SOT) phenomena
combine at interfaces with well-defined symmetries, and how this dictates the
nature and figures-of-merit of SOT and angular momentum transfer. This will
serve as a guiding role in designing future non-volatile memory devices that
utilize the unique properties of 2D materials with the spin degree of freedom.Comment: 26 pages, 5 figures, 1 table and 1 textbo
Making Atomic-Level Magnetism Tunable with Light at Room Temperature
The capacity to manipulate magnetization in two-dimensional dilute magnetic
semiconductors (2D-DMSs) using light, specifically in magnetically doped
transition metal dichalcogenide (TMD) monolayers (M-doped TX2, where M = V, Fe,
Cr; T = W, Mo; X = S, Se, Te), may lead to innovative applications in
spintronics, spin-caloritronics, valleytronics, and quantum computation. This
Perspective paper explores the mediation of magnetization by light under
ambient conditions in 2D-TMD DMSs and heterostructures. By combining magneto-LC
resonance (MLCR) experiments with density functional theory (DFT) calculations,
we show that the magnetization can be enhanced using light in V-doped TMD
monolayers (e.g., V-WS2, V-WSe2, V-MoS2). This phenomenon is attributed to
excess holes in the conduction and valence bands, as well as carriers trapped
in magnetic doping states, which together mediate the magnetization of the
semiconducting layer. In 2D-TMD heterostructures such as VSe2/WS2 and
VSe2/MoS2, we demonstrate the significance of proximity, charge-transfer, and
confinement effects in amplifying light-mediated magnetism. This effect is
attributed to photon absorption at the TMD layer (e.g., WS2, MoS2) that
generates electron-hole pairs mediating the magnetization of the
heterostructure. These findings will encourage further research in the field of
2D magnetism and establish a novel direction for designing 2D-TMDs and
heterostructures with optically tunable magnetic functionalities, paving the
way for next-generation magneto-optic nanodevices
Spin-orbit torques due to warped topological insulator surface states with an in-plane magnetization
We investigate the extrinsic spin-orbit torque (SOT) on the surface of
topological insulators (TIs), which are characterized by two-dimensional warped
Dirac surface states, in the presence of an in-plane magnetization. The
interplay between extrinsic spin-orbit scattering and the in-plane
magnetization results in a net spin density leading to a SOT. Previous theory
suggested that the SOT could only be generated by an out-of-plane magnetic
field component, and any in-plane magnetic contribution could be gauged away.
However, we demonstrate theoretically that with an in-plane magnetization, the
SOT can be finite in TIs due to extrinsic spin-orbit scattering. In the case of
a TI model with a linear dispersion relation, the skew scattering term is zero,
and the extrinsic spin-orbit scattering influences the side-jump scattering,
leading to a finite SOT in TIs. However, when considering the warping term,
finite intrinsic and skew scattering terms will arise, in addition to
modifications to other scattering terms. We further show that the SOT depends
on the azimuthal angles of the magnetization and an external electric field. By
adjusting the extrinsic spin-orbit strength, Fermi energy, magnetization
strength and warping strength, the resulting SOTs can be maximized. These
findings shed light on the interplay between spin-orbit coupling and
magnetization in TIs, offering insights into the control and manipulation of
spin currents in these systems.Comment: 18 pages, 5 figure
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