This letter introduces a micromagnetic model able to characterize the magnetization dynamics in three terminal magnetic tunnel junctions, where the effects of spin-transfer torque and spin-orbit torque are taken into account. Our results predict that the possibility to separate electrically those two torque sources is very promising from a technological point of view for both next generation of nanoscale spintronic oscillators and microwave detectors. A scalable synchronization scheme based on the parallel connection of those three terminal devices is also proposed.
Iridium is a very promising material for spintronic applications due to its interesting magnetic properties such as large RKKY exchange coupling as well as its large spin-orbit coupling value. Ir is for instance used as a spacer layer for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However, only a few studies of the spintronic parameters of this material have been reported. In this paper, we present inverse spin Hall effect - spin pumping ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the values of the effective spin Hall angle, the spin diffu…
Quantum oxide materials possess a vast range of properties stemming from the interplay between the lattice, charge, spin and orbital degrees of freedom, in which electron correlations often play an important role. Historically, the spin-orbit coupling was rarely a dominant energy scale in oxides. It however recently came to the forefront, unleashing various exotic phenomena connected with real and reciprocal-space topology that may be harnessed in spintronics. In this article, we review the recent advances in the new field of oxide spin-orbitronics with a special focus on spin-charge interconv…
The fast spin dynamics provide many opportunities for the future communication and memory technologies. One of the most promising examples is the domain wall (DW) racetrack memory. To achieve fast device performances, the high-speed motion of DWs is naturally demanded that leaves antiferromagnets (AFMs) and compensated ferrimagnets (FIMs) as the promising materials. While controlling and probing the dynamics of DWs in AFMs remains challenging, the fast motion of DWs with velocities around 1500 m/s has been demonstrated in metallic FIMs. The velocity of DWs in metallic FIMs is, however, suppres…
We have fabricated graphene spin-valve devices utilizing scalable materials made from chemical vapor deposition (CVD). Both the spin-transporting graphene and the tunnel barrier material are CVD-grown. The tunnel barrier is realized by h-BN, used either as a monolayer or bilayer and placed over the graphene. Spin transport experiments were performed using ferromagnetic contacts deposited onto the barrier. We find that spin injection is still greatly suppressed in devices with a monolayer tunneling barrier due to resistance mismatch. This is, however, not the case for devices with bilayer barri…
The spin Hall effect (SHE) is an important spintronics phenomenon, which allows transforming a charge current into a spin current and vice versa without the use of magnetic materials or magnetic fields. To gain new insight into the physics of the SHE and to identify materials with a substantial spin Hall conductivities (SHC), we performed high-precision, high-throughput ab initio electronic structure calculations of the intrinsic SHC for over 20,000 non-magnetic crystals. The calculations reveal a strong and unexpected relation of the magnitude of the SHC with the crystalline symmetry, which w…
This paper reports our Monte Carlo (MC) studies aiming to explain the experimentally observed paramagnetic molecule induced antiferromagnetic coupling between the ferromagnetic (FM) electrodes. Recently developed magnetic tunnel junction based molecular spintronics devices (MTJMSDs), which were prepared by chemically bonding the paramagnetic molecules between the FM electrodes along the exposed side edges of magnetic tunnel junctions, exhibited molecule induced strong antiferromagnetic coupling. Our MC studies focused on the atomic model analogous to the MTJMSD and studied the effect of molecu…
Nonlinear Magnetic Orbital Hall Effect Induced by Spin-Orbit Coupling
Singapore University of Technology and Design（新加坡科技设计大学）；Beihang University（北京航空航天大学）；Yanshan University（燕山大学）；Fudan University（复旦大学）；Lanzhou University（兰州大学）；The Hong Kong Polytechnic University（香港理工大学）
Perpendicular magnetic tunnel junctions are one of the building blocks for spintronic memories, which allow fast nonvolatile data access, offering substantial potentials to revolutionize the mainstream computing architecture. However, conventional switching mechanisms of such devices are fundamentally hindered by spin polarized currents4, either spin transfer torque or spin orbit torque with spin precession time limitation and excessive power dissipation. These physical constraints significantly stimulate the advancement of modern spintronics. Here, we report an optomagnetic tunnel junction us…
Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics driven by the advantages of antiferromagnets producing no stray fields and exhibiting ultrafast magnetization dynamics. The efficient method to detect an AFM order parameter, known as the Néel vector, by electric means is critical to realize concepts of AFM spintronics. Here, we demonstrate that non-collinear AFM metals, such as Mn3Sn, exhibit a momentum dependent spin polarization which can be exploited in AFM tunnel junctions to detect the Néel vector. Using first-principles calculations based on density functional …
Control of magnetism without using magnetic fields enables large-scale integration of spintronic devices for memory, computation and communication in the beyond-CMOS era. Mechanisms including spin torque transfer, spin Hall effect, and electric field or strain assisted switching have been implemented to switch magnetization in various spintronic devices. Their operation speed, however, is fundamentally limited by the spin precession time to be longer than 10-100 picoseconds. Overcoming such a speed constraint is critical for the prospective development of spintronics. Here we report the demons…
Dream of developing molecule-based logic and memory device is more than 70-year-old. Presently, molecule-based devices are also considered for quantum computation hardware. The recent studies have shown the molecule connected to metal leads can perform the qubit-based logic operation. This is an interesting question of why experimental progress is still very slow even when the scope of molecule-based devices may govern the advancement of next-generation logic and memory devices for the highest possible computer technologies. Molecules have the potential to be unmatched device elements as chemi…
We present a circuit design of a spintronic oscillator based on magnetic tunnel junction. In this design, a dc current is passed through a magnetic tunnel junction which is connected to a feed-back wire below it. Any fluctuation in the magnetization direction of the free layer of MTJ, drives a fluctuating current through the feed-back wire, which exerts a magnetic field on the free layer. This in turn can amplify the magnetization fluctuations of the free layer. If the dc current passing through the MTJ is more than a critical value, continuous precessing states of the magnetization are possib…
Molecular bridges covalently bonded to two ferromagnetic electrodes can transform ferromagnetic materials and produce intriguing spin transport characteristics. This paper discusses the impact of molecule induced strong coupling on spin transport. To study the molecular coupling effect organometallic molecular complex (OMC) was bridged between two ferromagnetic electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the exposed side edges. OMCs induced strong iter-ferromagnetic electrode coupling to yield drastic changes in transport properties of the magnetic tunnel junction …
The electrical manipulation of magnetization by current-induced spin torques has given access to realize a plethora of ultralow power and fast spintronic devices such as non-volatile magnetic memories, spin-torque nano-oscillators, and neuromorphic computing devices. Recent advances have led to the notion that relativistic spin-orbit coupling is an efficient source for current-induced torques, opening the field of spin-orbitronics. Despite the significant progress, however, the fundamental mechanism of magnetization manipulation, the requirement of spin currents in generating current-induced t…
Electric currents carrying a net spin polarization are widely used in spintronics, whereas globally spin-neutral currents are expected to play no role in spin-dependent phenomena. Here we show that, in contrast to this common expectation, spin-independent conductance in compensated antiferromagnets and normal metals can be efficiently exploited in spintronics, provided their magnetic space group symmetry supports a non-spin-degenerate Fermi surface. Due to their momentum-dependent spin polarization, such antiferromagnets can be used as active elements in antiferromagnetic tunnel junctions (AFM…
Spin-based electronics or spintronics is an emerging field, in which we try to utilize spin degrees of freedom as well as charge transport in materials and devices. While metal-based spin-devices, such as magnetic-field sensors and magnetoresistive random access memory using giant magnetoresistance and tunneling magnetoresistance, are already put to practical use, semiconductor-based spintronics has greater potential for expansion because of good compatibility with existing semiconductor technology. Many semiconductor-based spintronics devices with useful functionalities have been proposed and…
Magnetic tunnel junctions (MTJs), composed of two ferromagnetic electrodes separated by a thin insulating barrier layer, are currently used in spintronic devices, such as magnetic sensors and magnetic random access memories. Recently, driven by demonstrations of ferroelectricity at the nanoscale, thin-film ferroelectric barriers were proposed to extend the functionality of MTJs. Due to the sensitivity of conductance to the magnetization alignment of the electrodes (tunnelling magnetoresistance) and the polarization orientation in the ferroelectric barrier (tunnelling electroresistance), these …
Spintronics has attracted wide attention by promising novel functionalities derived from both the electron charge and spin. While branching into new areas and creating new themes over the past years, the principal goals remain the spin and magnetic control of the electrical properties, essentially the I-V characteristics, and vice versa. There are great challenges ahead to meet these goals. One challenge is to find niche applications for ferromagnetic semiconductors, such as GaMnAs. Another is to develop further the science of hybrid ferromagnetic metal/semiconductor heterostructures, as alter…
The tunnel magnetoresistance (TMR) effect observed in magnetic tunnel junctions (MTJs) is commonly used in many spintronic applications because the effect can easily convert from local magnetic states to electric signals in a wide range of device resistances. In this study, we demonstrated TMR ratios of up to 631% at room temperature (RT), which is two or more times larger than those used currently for magnetoresistive random access memory (MRAM) devices, using CoFe/MgO/CoFe(001) epitaxial MTJs. The TMR ratio increased up to 1143% at 10 K, which corresponds to an effective tunneling spin polar…
Advancement of molecular devices will critically depend on the approach to establish electrical connections to the functional molecule(s). We produced a molecular device strategy which is based on chemically attaching of molecules between the two magnetic/nonmagnetic metallic electrodes along the multilayer edge(s) of a prefabricated tunnel junction. Here, we present the fabrication methodology for producing these multilayer edge molecular electronics/spintronics devices (MEMEDs/MEMSDs) and details of the associated challenges and their solutions. The key highlight of our MEMED/MEMSD approach …
Magnetoelectric coupling between magnetic and electric dipoles is one of the cornerstones of modern physics towards developing the most energy-efficient magnetic data storage. Conventionally, magnetoelectric coupling is achieved in single-phase multiferroics or in magnetoelectric composite nanostructures consisting of ferromagnetic and ferroelectric/piezoelectric materials. Here, we demonstrate an electric-field-induced strain-mediated magnetoelectric effect in ultrathin CoFeB/MgO magnetic tunnel junction employing non-piezoelectric material, which is a vitally important structure for spintron…
The magnetic tunnel junction (MTJ) is a backbone device for spintronics. Realizing next generation energy efficient MTJs will require operating mechanisms beyond the standard means of applying magnetic fields or large electrical currents. Here, we demonstrate a new concept for programmable MTJ operation via strain control of the magnetic states of CrSBr, a layered antiferromagnetic semiconductor used as the tunnel barrier. Switching the CrSBr from antiferromagnetic to ferromagnetic order generates a giant tunneling magnetoresistance ratio without external magnetic field at temperatures up to ~…
GaAs surface is characterized by a high density of surface states, which preclude the utilization of this semiconducting material for the realization of several advanced devices. Sulfur-based passivation has been found significantly useful in reducing the effect of dangling bonds. In this article first, the problem associated with GaAs surface has been discussed in a tutorial form. Secondly, a brief introduction of a wide variety of surface passivation methods was introduced. Sulfur passivation, the most effective surface state quenching method, has been elaborated. Thirdly, current trends in …
We report on the first integration of an antiferromagnetic Heusler compound acting as a pinning layer into magnetic tunneling junctions. The antiferromagnet Ru$_2$MnGe is used to pin the magnetization direction of a ferromagnetic Fe layer in MgO based thin film tunnelling magnetoresistance stacks. The samples were prepared using magnetron co-sputtering. We investigate the structural properties by X-ray diffraction and reflection, as well as atomic force and high-resolution transmission electron microscopy. We find an excellent crystal growth quality with low interface roughnesses of 1-3 Å, whi…
Over the past few years, intensive studies of ultrathin epitaxial films of perovskite oxides have often revealed exciting properties like giant magnetoresistive tunnelling and electric field effects. Spinel oxides appear as even more versatile due to their more complex structure and the resulting many degrees of freedom. Here we show that the epitaxial growth of nanometric NiFe2O4 films onto perovskite substrates allows the stabilization of novel ferrite phases with properties dramatically differing from bulk ones. Indeed, NiFe2O4 films few nanometres thick have a saturation magnetization at l…
Recently, van der Waals (vdW) magnetic heterostructures have received increasing research attention in spintronics. However, the lack of room-temperature magnetic order of vdW material has largely impedes its development in practical spintronics devices. Inspired by the recently discovered vdW ferromagnet Fe3GaTe2, which has been shown to have magnetic order above room temperature and sizable perpendicular magnetic anisotropy, we investigate the basic electronic structure and magnetic properties of Fe3GaTe2 as well as tunneling magnetoresistance effect in magnetic tunnel junctions (MTJs) with …
Whereas spintronics brings the spin degree of freedom to electronic devices, molecular/organic electronics adds the opportunity to play with the chemical versatility. Here we show how, as a contender to commonly used inorganic materials, organic/molecular based spintronics devices can exhibit very large magnetoresistance and lead to tailored spin polarizations. We report on giant tunnel magnetoresistance of up to 300% in a (La,Sr)MnO3/Alq3/Co nanometer size magnetic tunnel junction. Moreover, we propose a spin dependent transport model giving a new understanding of spin injection into organic …
We report on graphene-passivated ferromagnetic electrodes (GPFE) for spin devices. GPFE are shown to act as spin-polarized oxidation-resistant electrodes. The direct coating of nickel with few layer graphene through a readily scalable chemical vapour deposition (CVD) process allows the preservation of an unoxidized nickel surface upon air exposure. Fabrication and measurement of complete reference tunneling spin valve structures demonstrates that the GPFE is maintained as a spin polarizer and also that the presence of the graphene coating leads to a specific sign reversal of the magneto-resist…
Antiferromagnetic (AF) spintronics is merit on ultra-high operator speed and stability in the presence of magnetic field. To fully use the merit, the device should be pure rather than hybrid with ferromagnet or ferrimagnet. For the magnetism in the antiferromagnet is canceled by that of different sublattices, breaking the symmetry in the material can revive the native magnetism, which can be detected by the magnetoresistance (MR) effect. Achieving noticeable MR effect in the pure AF device is diffcult but essential for the AF spintronic applications. Here, we study the tunnel magnetoresistance…
Ability to tailor the nature of the magnetic coupling between two ferromagnetic electrodes can enable the realization of new spintronics device systems. This paper discusses our finding that deposition of an ultrathin tantalum (Ta) on the NiFe top electrode reversed the nature of inter-ferromagnetic electrode coupling. We observed that the deposition of ~ 5 nm Ta on the top of a magnetic tunnel junction with Ta( 2 nm)/Co(5 nm)/NiFe (5 nm)/AlOx( 2 nm)/NiFe (10-15 nm) configuration changed the magnetic coupling between two ferromagnetic electrodes from antiferromagnetic to ferromagnetic. We inve…
Interface-engineered voltage-driven magnetic tunnel junctions with ultra-low-energy magnetization switching
University of Arizona（亚利桑那大学）；University of Minnesota（明尼苏达大学）；National Institute of Standards and Technology（美国国家标准与技术研究院）；Korea Research Institute of Chemical Technology（韩国化学技术研究所）
Magnetic tunnel junction-based molecular spintronics devices (MTJMSDs) are designed by covalently connecting the paramagnetic molecules across two ferromagnets (FM) electrodes of a magnetic tunnel junction (MTJ). MTJMSD provides opportunities to connect FM electrodes of a vast range of anisotropy properties to a variety of molecules of length scale. Our prior studies showed that the paramagnetic molecules can produce strong antiferromagnetic coupling with FM electrodes. The device properties of MTJMSD depend upon various factors such as anisotropy, spin fluctuation, thermal energy, etc. In thi…
Modern spintronics relies on the generation of spin currents through spin-orbit coupling. The spin-current generation has been believed to be triggered by current-induced orbital dynamics, which governs the angular momentum transfer from the lattice to the electrons in solids. The fundamental role of the orbital response in the angular momentum dynamics suggests the importance of the orbital counterpart of spin currents: orbital currents. However, evidence for its existence has been elusive. Here, we demonstrate the generation of giant orbital currents and uncover fundamental features of the o…
Two-dimensional (2D) van der Waals (vdW) materials provide the possibility of realizing heterostructures with coveted properties. Here, we report a theoretical investigation of the vdW magnetic tunnel junction (MTJ) based on VSe2/MoS2 heterojunction, where the VSe2 monolayer acts as the ferromagnet with the room-temperature ferromagnetism. We propose the concept of spin-orbit torque (SOT) vdW MTJ with reliable reading and efficient writing operations. The non-equilibrium study reveals a large tunneling magnetoresistance (TMR) of 846 % at 300 Kelvin, identifying significantly its parallel and a…
Efficient injection of spin-polarized current into a semiconductor is a basic prerequisite for building semiconductor-based spintronic devices. Here, we use inelastic electron tunneling spectroscopy to show that the efficiency of spin-filter-type spin injectors is limited by spin scattering of the tunneling electrons. By matching the Fermi-surface shapes of the current injection source and target electrode material, spin injection efficiency can be significantly increased in epitaxial ferromagnetic insulator tunnel junctions. Our results demonstrate that not only structural but also Fermi-surf…
A new magnetic logic overcomes the major limitations of field programmable gate arrays while having a 50% smaller unit cell than conventional designs utilizing magnetic tunnel junctions with one Heusler alloy electrode. These show positive and negative TMR values at different bias voltages at room temperature which generally adds an additional degree of freedom to all spintronic devices.
The current research in graphene spintronics strives for achieving a long spin lifetime, and efficient spin injection and detection in graphene. In this article, we review how hexagonal boron nitride (hBN) has evolved as a crucial substrate, as an encapsulation layer, and as a tunnel barrier for manipulation and control of spin lifetimes and spin injection/detection polarizations in graphene spin valve devices. First, we give an overview of the challenges due to conventional SiO$_2$ substrate for spin transport in graphene followed by the progress made in hBN based graphene heterostructures. T…
Spin-filter tunneling is a promising way to generate highly spin-polarized current, a key component for spintronics applications. In this work we explore the tunneling conductance across the spin-filter material CoFe2O4 interfaced with Au electrodes, a geometry which provides nearly perfect lattice matching at the CoFe2O4/Au(001) interface. Using density functional theory calculations we demonstrate that interface states play a decisive role in controlling the transport spin polarization in this tunnel junction. For a realistic CoFe2O4 barrier thickness, we predict a tunneling spin polarizatio…
In recent years, the field of antiferromagnetic spintronics has been substantially advanced. Electric-field control is a promising approach to achieving ultra-low power spintronic devices via suppressing Joule heating. In this article, cutting-edge research, including electric-field modulation of antiferromagnetic spintronic devices using strain, ionic liquids, dielectric materials, and electrochemical ionic migration, are comprehensively reviewed. Various emergent topics such as the Neel spin-orbit torque, chiral spintronics, topological antiferromagnetic spintronics, anisotropic magnetoresis…
Neuromorphic computing uses brain-inspired principles to design circuits that can perform computational tasks with superior power efficiency to conventional computers. Approaches that use traditional electronic devices to create artificial neurons and synapses are, however, currently limited by the energy and area requirements of these components. Spintronic nanodevices, which exploit both the magnetic and electrical properties of electrons, can increase the energy efficiency and decrease the area of these circuits, and magnetic tunnel junctions are of particular interest as neuromorphic compu…
