Spin Transport Behavior Research Articles

Spin Transport Modulation of 2D Fe3O4 Nanosheets Driven by Verwey Phase Transition.

Realizing spin transport between heavy metal and two-dimensional(2D) magnetic materials at high Curie temperature (TC) is crucial to advanced spintronic information storage technology. Here, environmentally stable 2D nonlayered Fe3O4 nanosheets are successfully synthesized using a reproducible process and found that they exhibit vortex magnetic domains at room temperature. A Verwey phase transition temperature (TV) of ≈110 K is identified for ≈3nm thick nanosheet through Raman characterization and spin Hall device measurement of the Pt/Fe3O4 bilayer. The anisotropic magnetoresistance ratio decreases near TV, while both the spin Hall magnetoresistance ratio and spin mixing conductance (Gr) increase at TV. As the temperature approaches 112 K, the anomalous Hall effect ratio tends to become zero. The maximum Gr reaches ≈5 × 1015 Ω-1m-2 due to the clean and flat interface between Pt and 2D nanosheet. The observed spin transport behavior in Pt/Fe3O4 spin Hall devices indicates that 2D Fe3O4 nanosheets possess potential for high-power micro spintronic storage devices applications.

Observation and enhancement of room temperature bilinear magnetoelectric resistance in sputtered topological semimetal Pt3Sn

Topological semimetal materials have attracted a great deal of attention due to their intrinsic strong spin-orbit coupling, which leads to large charge-to-spin conversion efficiency and novel spin transport behaviors. In this work, we have observed a bilinear magnetoelectric resistance (BMER) of up to 0.0034 nm2A−1Oe−1 in a single layer of sputtered semimetal Pt3Sn at room temperature. Being different from previous works, the value of BMER in sputtered Pt3Sn does not change out-of-plane due to the polycrystalline nature of the Pt3Sn layer. The observation of BMER provides strong evidence of the existence of spin-momentum locking in the sputtered polycrystalline Pt3Sn. By adding an adjacent CoFeB magnetic layer, the BMER value of this bilayer system is doubled compared to the single Pt3Sn layer. This work broadens the material system in BMER study, which paves the way for the characterization of topological states and applications for spin memory and logic devices.

Robust chiral spin transport in the antiferromagnetic iron oxide/heavy metal bilayers

We have observed robust chiral spin torques and non-reciprocal charge transport behaviors in the α-Fe2O3/Pt bilayers through a combination of magnetic field and current-dependent second longitudinal harmonic resistance measurements. The interfacial Dzyaloshinskii–Moriya interaction induced magnetic chirality has been predicted to account for the sign reversal characteristic of the second longitudinal harmonic resistance with increasing the current amplitude. A physical model that considers the chirality dependence of both the asymmetric scattering and the giant Rashba spin–orbit coupling has been set up to uncover the microscopic interactions between charge, spin, and magnetic chirality. Our comprehensive approach leverages the semiclassical Boltzmann theory to validate the consistency between this model and our experimental findings. Through our investigation, we have established the pivotal role of interfacial magnetic chirality in determining both charge and spin transport behaviors within antiferromagnetic insulator/heavy metal bilayer systems. Our work not only enhances the comprehension of spin–orbit torques and non-reciprocal charge transport but also contributes to the broader understanding of these phenomena. The outcomes of this study have broader implications for the advancement of spintronics and related fields.

Heusler-alloy-based magnetoresistive sensor with synthetic antiferromagnet

Heusler alloy has been widely utilized in magnetoresistive sensors to enhance the device performance. In this work, we theoretically investigate the performance of Heusler-alloy-based magnetoresistive sensors with a synthetic antiferromagnet (SAF) layer. The atomistic model combined with the spin accumulation model will be used in this work. The former is used to construct the reader stack and investigate the magnetization dynamics in the system. The latter is employed to describe the spin transport behavior at any position of the structure. We first perform simulations of the exchange bias (EB) phenomenon in the IrMn/ (CFS) system providing a high EB field. Then, a realistic reader stack of IrMn/CFS/Ru/CFS/Ag/CFS is constructed via an atomistic model. Subsequently, the resistance–area product (RA) and magnetoresistance (MR) ratio of the reader can be calculated by using the spin accumulation model. As a result of the spin transport behavior in the Heusler-alloy-based reader stack including SAF structure at 0 K, an enhancement of the MR ratio up to 120 and RA can be observed. This study demonstrates the important role of the Heusler alloy and SAF layer in the development of magnetoresistive sensors for the application of readers in hard disk drives with an areal density beyond 2 Tb in−2.

Magnetic field modulated ultrafast spin dynamics at Ni80Fe20/Neodymium interface.

Ultrafast spin dynamics is crucial for the next-generation spintronic devices towards high-speed data processing. Here, we investigate the ultrafast spin dynamics of Neodymium/Ni80Fe20 (Nd/Py) bilayers by the time-resolved magneto-optical Kerr effect. The effective modulation of spin dynamics at Nd/Py interfaces is realized by an external magnetic field. The effective magnetic damping of Py increases with increasing Nd thickness, and a large spin mixing conductance (∼19.35×1015 cm-2) at Nd/Py interface is obtained, representing the robust spin pumping effect by Nd/Py interface. The tuning effects are suppressed at a high magnetic field due to the reduced antiparallel magnetic moments at Nd/Py interface. Our results contribute to understanding ultrafast spin dynamics and spin transport behavior in high-speed spintronic devices.

Multifunctional spin transport behaviors of biphenyl-molecule-based nanodevices

For the development of low-power spin-multifunctional devices, we have explored the spin-dependent transport properties of nanodevices based on zigzag graphene nanoribbons bridged respectively by oblique, horizontal, and vertical connecting biphenyl molecules. Utilizing the first-principles calculations associated with the non-equilibrium Green's function methods, we found the superb transport results demonstrate that almost 100% spin polarization exists for the obliquely connected and horizontally connected biphenyl molecules devices in the parallel state (P). All of the designed devices exhibit excellent dual spin filtering efficiency and rectification effect in the antiparallel state (AP) with the rectification ratios up to 103, 104, and 105 for obliquely, horizontally, and vertically connected model devices, respectively. Simultaneously, a pronounced negative differential resistance effect can be observed in these devices independent of the spin state. Moreover, the thermal spin transport properties of the obliquely connected model device reveal an apparent Seebeck effect. Then, the length effect on the spin-resolved transport properties for the obliquely connected device have been conducted. Results reveal that the current values are highly tunable by changing the length of obliquely connected biphenyl molecules in the P state. Meanwhile, the doual spin filtering effect still remains, but its rectification effect gradually disappears with the increasing length of center scattering region in AP state. This study provides new insights into the design of multifunctional spin carbon-based and low power consumption devices.

Room‐Temperature Spin Transport in Metal Nanocluster‐Based Spin Valves

AbstractAs a new type of inorganic‐organic hybrid semiconductor, quantum‐confined atomically precise metal nanoclusters (MNCs) have been widely applied in the fields of chemical sensing, optical imaging, biomedicine and catalysis. Herein, we successfully design and fabricate the first example of MNC‐based spin valves (SVs) that exhibit remarkable magnetoresistance (MR) value up to 1.6 % even at room temperature (300 K). The concomitant photoresponse of MNC‐based SVs unambiguously confirms that the spin‐polarized electron transmission takes place across the MNC interlayer. Furthermore, the spin‐dependent transport property of MNC‐based SVs is largely varied by changing the atomic structure of MNCs. Both experimental proofs and quantum chemistry calculations reveal that the atomic structure‐discriminative spin transport behavior is attributed to the distinct spin‐orbit coupling (SOC) effect of MNCs.

Room-Temperature Spin Transport in Metal Nanocluster-Based Spin Valves.

As a new type of inorganic-organic hybrid semiconductor, quantum-confined atomically precise metal nanoclusters (MNCs) have been widely applied in the fields of chemical sensing, optical imaging, biomedicine and catalysis. Herein, we successfully design and fabricate the first example of MNC-based spin valves (SVs) that exhibit remarkable magnetoresistance (MR) value up to 1.6 % even at room temperature (300 K). The concomitant photoresponse of MNC-based SVs unambiguously confirms that the spin-polarized electron transmission takes place across the MNC interlayer. Furthermore, the spin-dependent transport property of MNC-based SVs is largely varied by changing the atomic structure of MNCs. Both experimental proofs and quantum chemistry calculations reveal that the atomic structure-discriminative spin transport behavior is attributed to the distinct spin-orbit coupling (SOC) effect of MNCs.

Spin filtering effect in all-van der Waals heterostructures with WSe2 barriers

Exploiting the spin degree of freedom to store and manipulate information provides a paradigm for future microelectronics. The development of van der Waals (vdW) heterostructures has created a fascinating platform for exploring spintronic properties in the two-dimensional (2D) limit. Transition-metal dichalcogenides such as tungsten diselenide (WSe2) have electronic band structures that are ideal for hosting many exotic spin–orbit phenomena. Here, we report the spin-filtering effect in all-vdW heterostructures with WSe2 barrier. Combining 2D-perpendicular magnetic anisotropy Fe3GeTe2 (FGT) with different thicknesses of WSe2, the FGT/WSe2/FGT spin valve shows distinct charge and spin transport behavior. Moreover, the negative magnetoresistance (−4.3%) could be inverted into positive magnetoresistance (up to +25.8%) with decreasing the WSe2 thickness. Furthermore, we proposed a spin-filtering model based on Δ-symmetry electrons tunneling to explain the crossover from negative to positive MR signal through ab initio calculation. These experimental and theoretical results illustrate the rich potential of the families of TMDC materials to control spin currents in 2D spintronic devices.

Peripheral chiral spin textures and topological Hall effect in CoSi nanomagnets

The spin structure and transport behavior of B20-ordered CoSi nanomagnets are investigated experimentally and by theoretical calculations. B20 materials are of interest in spin electronics because their noncentrosymmetric crystal structure favors noncoplanar spin structures that yield a contribution to the Hall effect. However, stoichiometric bulk CoSi is nonmagnetic, and combining magnetic order at and above room temperature with small feature sizes has remained a general challenge. Our CoSi nanoclusters have an average size of 11.6 nm and a magnetic ordering temperature of 330 K. First-principle calculations and x-ray circular dichroism experiments show that the magnetic moment is predominantly confined to the shells of the clusters. The CoSi nanocluster ensemble exhibits a topological Hall effect, which is explained by an analytical model and by micromagnetic simulations on the basis of competing Dzyaloshinskii-Moriya and intra- and intercluster exchange interactions. The topological Hall effect is caused by formation of chiral spin textures in the shells of the clusters, which exhibit fractional skyrmion number and are therefore termed as paraskyrmions (closely related to skyrmion spin structures). This research shows how nanostructuring of a chiral atomic structure can create a spin-textured material with a topological Hall effect and a magnetic ordering temperature above room temperature.

Gate-Voltage-Modulated Spin Precession in Graphene/WS2 Field-Effect Transistors

Transition metal dichalcogenide materials are studied to investigate unexplored research avenues, such as spin transport behavior in 2-dimensional materials due to their strong spin-orbital interaction (SOI) and the proximity effect in van der Waals (vdW) heterostructures. Interfacial interactions between bilayer graphene (BLG) and multilayer tungsten disulfide (ML-WS2) give rise to fascinating properties for the realization of advanced spintronic devices. In this study, a BLG/ML-WS2 vdW heterostructure spin field-effect transistor (FET) was fabricated to demonstrate the gate modulation of Rashba-type SOI and spin precession angle. The gate modulation of Rashba-type SOI and spin precession has been confirmed using the Hanle measurement. The change in spin precession angle agrees well with the local and non-local signals of the BLG/ML-WS2 spin FET. The operation of a spin FET in the absence of a magnetic field at room temperature is successfully demonstrated.

Temperature dependence of spin-transport properties and spin torque in a magnetic nanostructure

The study and understanding of spin-transport mechanisms including thermal fluctuation are required for the development and design of spintronic devices. In this paper, we present an approach to investigate the temperature dependence of spin-transport behavior within the magnetic structure by using the generalized spin accumulation model. The temperature affects not only the magnetization orientation, but also the spin-transport properties. Its effect on transport parameters can be taken into account by considering the spin-dependent resistivity at any finite temperature. This leads to the calculation of temperature-dependent spin-transport parameters and eventually allows the calculation of the thermal effects on spin accumulation, spin current, and spin torque. It is observed that increasing temperature is likely to decrease the value of key transport parameters relevant to the magnitude of spin torque. This study demonstrates the importance of thermal effects on spin-transport behavior which needs to be considered for spin-transfer torque based device design with high performance.

Magneto-electronic and spin transport properties of transition metal doped antimonene nanoribbons

Abstract Recently, how to induce magnetism for two-dimensional materials have become one of research hot topics. Here, we study geometrical stability and magneto-electronic properties for antimonene nanoribbons doped with low-concentration transition metal(TM) atom (Mn, Fe, Cr and Co). It is found that these structures are stable by the formation energy calculation and molecular dynamics simulation. In particular, results show that these doped nanoribbons possess interesting magnetic phases, such as magnetic half-metal, magnetic half-semiconductor, and bipolar magnetic semiconductor, depending on the type of TM atoms. Furthermore, Mn-doped ribbon based magnetic device is constructed and the spin transport behaviors are investigated in details. The perfect double spin-filtering effect, excellent dual spin diode performance and giant magnetoresistance up to 109% are observed in this device. These findings might make a significant contribution for designing multi-function spintronic devices.

Large spin Hall effect in Si at room temperature

Silicon's weak intrinsic spin-orbit coupling and centrosymmetric crystal structure are a critical bottleneck to the development of Si spintronics, because they lead to an insignificant spin-Hall effect (spin current generation) and inverse spin-Hall effect (spin current detection). Here, we undertake current, magnetic field, crystallography dependent magnetoresistance and magneto thermal transport measurements to study the spin transport behavior in freestanding Si thin films. We observe a large spin-Hall magnetoresistance in both p-Si and n-Si at room temperature and it is an order of magnitude larger than that of Pt. One explanation of the unexpectedly large and efficient spin-Hall effect is spin-phonon coupling instead of spin-orbit coupling. The macroscopic origin of the spin-phonon coupling can be large strain gradients that can exist in the freestanding Si films. This discovery in a light, earth abundant and centrosymmetric material opens a new path of strain engineering to achieve spin dependent properties in technologically highly-developed materials.

Imaging antiferromagnetic domains in nickel oxide thin films by optical birefringence effect

Recent demonstrations of electrical detection and manipulation of antiferromagnets (AFMs) have opened new opportunities towards robust and ultrafast spintronics devices. However, it is difficult to establish the connection between the spin-transport behavior and the microscopic AFM domain states due to the lack of the real-time AFM domain imaging technique under the electric field. Here we report a significant Voigt rotation up to 60 mdeg in thin NiO(001) films at room temperature. Such large Voigt rotation allows us to directly observe AFM domains in thin-film NiO by utilizing a wide-field optical microscope. Further complementary XMLD-PEEM measurement confirms that the Voigt contrast originates from the NiO AFM order. We examine the domain pattern evolution at a wide range of temperature and with the application of external magnetic field. Comparing to large-scale-facility techniques such as the X-ray photoemission electron microscopy, the use with a wide-field, tabletop optical imaging method enables straightforward access to domain configurations of single-layer AFMs.

Atomic‐Scale Manipulation and In Situ Characterization with Scanning Tunneling Microscopy

AbstractScanning tunneling microscope (STM) has presented a revolutionary methodology to nanoscience and nanotechnology. It enables imaging of the topography of surfaces, mapping the distribution of electronic density of states, and manipulating individual atoms and molecules, all at atomic resolutions. In particular, atom manipulation capability has evolved from fabricating individual nanostructures toward the scalable production of the atomic‐sized devices bottom‐up. The combination of precision synthesis and in situ characterization has enabled direct visualization of many quantum phenomena and fast proof‐of‐principle testing of quantum device functions with immediate feedback to guide improved synthesis. Several representative examples are reviewed to demonstrate the recent development of atomic‐scale manipulation, focusing on progress that addresses quantum properties by design in several technologically relevant materials systems. Integration of several atomically precisely controlled probes in a multiprobe STM system vastly extends the capability of in situ characterization to a new dimension where the charge and spin transport behaviors can be examined from mesoscopic to atomic length scale. The automation of atomic‐scale manipulation and the integration with well‐established lithographic processes further push this bottom‐up approach to a new level that combines reproducible fabrication, extraordinary programmability, and the ability to produce large‐scale arrays of quantum structures.

First Principle Study of Temperature-Dependent Magnetoresistance and Spin Filtration Effect in WS2 Nanoribbon.

An applicable use of density functional theory (DFT) along with nonequilibrium Green's function (NEGF) is done for exploring the temperature-dependent spin electron transport nature in a ferromagnetic tungsten disulfide (WS2) nanoribbon. To demonstrate the effect of temperature on spin filtration and spin Seebeck effect, we evaluated vital parameters such as spin-polarized current and spin filtration efficiency. Spin filtration efficiency of around ∼95% is obtained in the high-temperature difference range. The high temperature (TL) of the left electrode in comparison to the high temperature (TR) of the right electrode results in higher and lower spin filtration efficiency in parallel magnetization (PM) and antiparallel magnetization (APM), respectively. Transmission spectrum plots at equilibrium are also calculated in PM and APM to justify the temperature-dependent spin transport behavior in the WS2 nanoribbon. Giant thermal magnetoresistance around 1.934 × 103% is achieved. The temperature-dependent negative differential resistance behavior of the current plot has been observed. Huge value of thermal magnetoresistance (MR) and excellent spin filtration obtained for WS2 nanoribbon suggests the potential application of this material in spin caloritronic devices.

Calculation of domain wall resistance in magnetic nanowire

The enhancement of domain wall resistance (DWR) in spintronic devices containing the domain wall is required for a full understanding since it represents the efficiency of spin transport and contributes to magnetoresistance phenomena. In this work, we theoretically investigate the effect of the domain wall width, injected current density, and temperature on DWR in magnetic nanowire by using the generalized spin accumulation model based on the Zhang, Levy, and Fert approach. The proposed model allows us to deal with a multilayer system with arbitrary orientation of magnetization. In addition, the temperature effect can be taken into account by considering the spin-dependent resistivity of the ferromagnet at any finite temperature. This leads to the calculation of temperature variation of spin transport parameters, and it eventually allows us to calculate the thermal effect on spin accumulation. The spin transport behavior and DWR can be calculated directly from the gradient of spin accumulation and spin current within the wall. The results show the increase in DWR with temperature as the thermal effect causes the reduction of transport parameters.

Spin-orbit coupling induced robust spin-Seebeck effect and pure thermal spin currents in achiral molecule systems

Spin-Seebeck effect (SSE) is an effective route to realize pure spin current by using spin-polarized electrons or spin-wave transport in magnetic systems. Here we propose a route, i.e., by using spin-orbit coupling (SOC), to achieve robust SSE characterized by pure thermal spin current. The material examples are constructed on achiral nanotubes, and the theoretical results reveal that (i) as temperature gradient is applied along the nanotubes, thermal spin-up and spin-down currents with opposite flow directions are produced without any accompanying charge current, (ii) the SSE is robust against decoherence and nonuniform interchain SOC, (iii) the thermal spin currents display a multioscillation feature with increasing device temperatures, supporting their potential device applications in thermal spin-current multiswitcher, and (vi) strain engineering in the radical direction of nanotubes is an effective way to improve SSE and to control pure thermal spin current. These inspiring spin transport behaviors in achiral molecular systems put forward a mechanism to realize the robust SSE characterized by pure spin current and develop the research field of spin-orbito-caloritronics, which focuses on the interplay of electrons' spin and orbital degrees of freedom in the presence of temperature gradient.

Enhanced Anomalous Hall Effect in Pt/CoO Heterostructures by Ferrimagnetic Insulator Gating

Interfacial spin current phenomena in multilayer hybrid structures consisting of heavy metal Pt and a ferrimagnetic insulator have recently drawn a great deal of attention. Here, we demonstrate the uncompensated spins of an insulator CoO surface can induce a square anomalous Hall effect (AHE) in a Pt/CoO device, where the AHE will change sign at 200 K for the thickness of CoO tCoO = 3.5 nm. More importantly, for a Pt/CoO bilayer grown on ferrimagnetic insulating Y3Fe5O12 (YIG) substrates, the ferrimagnetic gate can enhance the AHE resistance about three times and the Hall sign change temperature can be increased about 100 K compared to that of the Pt/CoO/SiO2/Si sample. Systematic study of the thickness of CoO-dependent AHE of Pt/CoO/YIG heterostructures reveals that the AHE resistance, coercive field, and Hall sign change temperature of Pt/CoO/YIG trilayers reach a maximum at tCoO = 3.5 nm. Our results highlight the key role of the antiferromagnetic material in the spin transport behavior of the magnetic multilayer structure, providing a possible pathway to detect the antiferromagnetic moment by electrical measurements, which will be great of importance for antiferromagnetic spintronics.