Spin Anomalous Hall Effect Research Articles

Highly efficient field-free switching of perpendicular yttrium iron garnet with collinear spin current

Yttrium iron garnet, a material possessing ultralow magnetic damping and extraordinarily long magnon diffusion length, is the most widely studied magnetic insulator in spintronics and magnonics. Field-free electrical control of perpendicular yttrium iron garnet magnetization with considerable efficiency is highly desired for excellent device performance. Here, we demonstrate such an accomplishment with a collinear spin current, whose spin polarization and propagation direction are both perpendicular to the interface. Remarkably, the field-free magnetization switching is achieved not only with a heavy-metal-free material, Permalloy, but also with a higher efficiency as compared with a typical heavy metal, Pt. Combined with the direct and inverse effect measurements, we ascribe the collinear spin current to the anomalous spin Hall effect in Permalloy. Our findings provide a new insight into spin current generation in Permalloy and open an avenue in spintronic devices.

Anomalous and inverse spin Hall effects in Pt1-xBix/(YLuBiCa)3(FeGa)5O12 heterojunction

A garnet film with spatial magnetic moment distribution has been grown on gadolinium gallium garnet wafer (111) crystal plane, by regulating liquid phase epitaxial growth parameters and sub-lattice ions substitution, then 10 nm Pt1-xBix (x = 2% – 8%) alloy film was deposited on the surface of the garnet films. A new spin heterojunction Pt1-xBix/(YLuBiCa)3(FeGa)5O12 with both inverse spin Hall effect (ISHE) and anomalous spin Hall effect (ASHE) was designed and fabricated. The spatial magnetic moment distribution of the heterojunction has been found, which lays the foundation of the spin heterojunction for multiple spin injection with both spin electron reverse injection and anomalous injection. Because Bi ions doping and substitution increases the spin–orbit torque and the mixed conductance of the heterojunction, an oblique ASHE voltage curve and an enhanced ISHE voltage curve with double resonance peak were observed. It was confirmed that the injection of spinning electron into the heterojunction can be enhanced with both the ISHE and ASHE effect by adjusting the spatial magnetic moment distribution, which is a foundation for the future application of spin wave 3D antenna and other devices.

Carbon-induced magnetic properties and anomalous Hall effect in Co2Mn2C thin films with L10 -like structures

${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$ thin films were synthesized via vacuum carburization of the host CoMn alloy films based on a conventional gas-solid reaction to demonstrate the effect of C, a common light element, on the magnetic and spintronic materials. The crystal structure transitioned from the disordered face-centered-cubic CoMn to the $L{1}_{0}$-like ${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$, for which the lattice constant increased from 0.356 to 0.378 nm. The C $1s$ x-ray photoemission spectra of the ${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$ film indicated hybridization in C-Co and C-Mn and a homogeneous concentration of C in the film. The enhancement of both the saturation magnetization and the anomalous Hall conductivity (${\ensuremath{\sigma}}_{xy}$) was induced by C, attributing to the magnetic transition to the ferrimagnetic spin order. The surface flatness and high ${\ensuremath{\sigma}}_{xy}$ are promising characteristics for spintronic applications such as the spin-anomalous Hall effect. The atom- and spin-resolved density of states (DOS) via first-principles calculations revealed that face-centered Mn(II) and Co could be significantly influenced by C because of p-d hybridization, resulting in enhanced spin polarization of the DOS at the Fermi level of \ensuremath{\sim}0.82. These results demonstrate that the use of C could be an essential way to boost material properties in the future.

Spin-flop transition in the quasi-two-dimensional antiferromagnet MnPS3 detected via thermally generated magnon transport

We present the detection of the spin-flop transition in the antiferromagnetic van der Waals material ${\mathrm{MnPS}}_{3}$ via thermally generated nonlocal magnon transport using permalloy (Py) detector strips. Py detector strips possess the inverse anomalous spin Hall effect, which has the unique power to detect an out-of-plane spin accumulation [Das et al., Nano Lett. 18, 5633 (2018)]. This enables us to detect magnons with an out-of-plane spin polarization, in contrast to strips of high-spin-orbit materials such as Pt which possess only the spin Hall effect and are sensitive to only an in-plane spin polarization of the spin accumulation. We show that nonlocal magnon transport is able to measure the spin-flop transition in the absence of spurious magnetoresistance effects. Our measurements show the detection of magnons generated by the spin Seebeck effect before and after the spin-flop transition. We observe a signal reversal of the magnon spin accumulation which agrees with the out-of-plane spin polarization carried by magnon modes before and after the spin-flop transition.

Intrinsic anomalous spin Hall effect

Charge-spin interconversion in magnetic materials is investigated by using the first-principles calculations. In addition to the conventional spin Hall effect (SHE) that requires mutual orthogonality of the charge current, spin-flow direction, and spin polarization, the recently proposed anomalous SHE (ASHE) is confirmed in Mn2Au and WTe2. The interaction of the order parameter with conduction electrons leads to sizeable non-zero spin Berry curvatures that give rise to anomalous spin Hall conductivity (ASHC). Our calculations show that the ASHE is intrinsic and originates from the order-parameter-controlled spin-orbit interaction, which generates an extra anomalous effective field. A useful relationship among the order parameter, the spin Berry curvature, and the ASHC is revealed. Our findings provide a new avenue for generating and detecting arbitrary types of spin currents.

Spin-orbit-derived giant magnetoresistance in a layered magnetic semiconductor AgCrSe2

Two-dimensional magnetic materials have recently attracted great interest due to their unique functions as the electric field control of a magnetic phase and the anomalous spin Hall effect. For such remarkable functions, a spin-orbit coupling (SOC) serves as an essential ingredient. Here we report a giant positive magnetoresistance in a layered magnetic semiconductor AgCrSe2, which is a manifestation of the subtle combination of the SOC and Zeeman-type spin splitting. When the carrier concentration approaches the critical value of 2.5\times10^18 cm^-3, a sizable positive magnetoresistance of ~400 % emerges upon the application of magnetic fields normal to the conducting layers. Based on the magneto-Seebeck effect and the first-principles calculations, the unconventional magnetoresistance is ascribable to the enhancement of effective carrier mass in the SOC induced J = 3/2 state, which is tuned to the Fermi level through the Zeeman splitting enhanced by the p-d coupling. This study demonstrates a new aspect of the SOC-derived magnetotransport in two-dimensional magnetic semiconductors, paving the way to novel spintronic functions.

Spin anomalous-Hall unidirectional magnetoresistance

We predict a spin anomalous-Hall unidirectional magnetoresistance (AH-UMR) in conducting bilayers composed of a ferromagnetic layer and a nonmagnetic layer, which does not rely on the spin Hall effect in the normal metal layer---in stark contrast to the well-studied unidirectional spin-Hall magnetoresistance---but instead arises from the spin anomalous Hall effect in the ferromagnetic layer. Physically, it is the charge-spin conversion induced by the spin anomalous Hall effect that conspires with the structural inversion asymmetry to generate a net nonequilibrium spin density in the ferromagnetic layer, which, in turn, modulates the resistance of the bilayer when the direction of the applied current or the magnetization is reversed. The dependencies of the spin AH-UMR effect on materials and geometric parameters are analyzed and compared with other nonlinear magnetoresistances. In particular, we show that, in magnetic bilayers where spin anomalous Hall and spin Hall effects are comparable, the overall UMR may undergo a sign change when the thickness of either layer is varied, suggesting a scheme to quantify the spin Hall or spin anomalous Hall angle via a nonlinear transport measurement.

Ferrimagnet GdFeCo Characterization for Spin‐Orbitronics: Large Field‐Like and Damping‐Like Torques

Spintronics is showing promising results in the search for new materials and effects to reduce energy consumption in information technology. Among these materials, ferrimagnets are of special interest because they can produce large spin currents that trigger the magnetization dynamics of adjacent layers or even their own magnetization. Herein, a study of the generation of spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice magnetization is dominant at room temperature is presented. Magnetic properties such as the saturation magnetization are deduced from magnetometry measurements while damping constant is estimated from spin‐torque ferromagnetic resonance (ST‐FMR). It is shown that the overall damping‐like (DL) and field‐like (FL) effective fields as well as the associated spin Hall angles can be reliably obtained by performing the dependence of ST‐FMR by an added dc current. The sum of the spin Hall angles for both the spin Hall effect (SHE) and the spin anomalous Hall effect (SAHE) symmetries is: and . From the symmetry of ST‐FMR signals, it is found that is positive and dominated by the negative . The present study paves the way for tuning the different symmetries in spin conversion in highly efficient ferrimagnetic systems.

Impact of Magnetic Field on Magnetic States in Kagome Magnets

Impact of magnetic field on the magnetic states in kagome magnets is studied. The magnetic field is patterned in such a way that it can generally maintain the most prominent magnetic states in kagome magnets, such as the out-of-plane ferromagnetism and the in-plane antiferromagnetism. The tight-binding model with the spin-orbit coupling and the magnetic field on the kagome lattice is exactly solved. In both the out-of-plane ferromagnetic and the in-plane antiferromagnetic states the magnetic field opens a gap at half filling. In the out-of-plane ferromagnetic state both the half topological state, where only one spin component is topologically nontrivial, and the quantum spin anomalous Hall effect, where both spin components are topologically nontrivial, can be observed. The in-plane antiferromagnetic state may be insulating, but it is topologically trivial. The quantum anomalous Hall effect may also be observed in canted \(\sqrt{3} \times \sqrt{3}\) antiferromagnetic state.

Abnormal optical response of PAMAM dendrimer-based silver nanocomposite metamaterials

Optical metamaterials present opportunities and challenges for manipulation of light. However, metamaterials with visible and near infrared responses are still particularly challenging to fabricate due to the complex preparation process and high loss. Here, a visible light poly(amidoamine) (PAMAM)-Ag metamaterial is prepared with the assistance of fifth-generation PAMAM (5G PAMAM), based on the dendritic structure. The large area of metamaterials, where Ag nanoparticles are spherical with diameters of ∼ 9 nm and distributed in a multilevel netlike sphere, results in broadband resonance. The negative Goos–Hänchen shift and anomalous spin Hall effect of light generated by 5G PAMAM-Ag in visible broadband are observed, and a strong slab focusing effect at 750–1050 nm is demonstrated. In addition, the simulation shows possible application of the dendritic structure in topological photonics. The results offer advances in the preparation of large-scale visible light metamaterials, showing the potential for subwavelength super-resolution imaging and quantum optical information fields.

Controllable spin current in van der Waals ferromagnet Fe3GeTe2

The control of spin current is pivotal for spintronic applications, especially for spin-orbit torque devices. Spin Hall effect (SHE) is a prevalent method to generate spin current. However, it is difficult to manipulate its spin polarization in nonmagnet. Recently, the discovery of spin current in ferromagnet offers opportunity to realize the manipulation. In the present work, the spin current in van der Waals ferromagnet Fe3GeTe2 (FGT) with varying magnetization is theoretically investigated. It has been observed that the spin current in FGT presents the nonlinear behavior with respect to magnetization. The in-plane and out-of-plane spin polarization emerges simultaneously, and the bilayer FGT can even exhibit arbitrary spin polarization thanks to the reduced symmetry. More intriguingly, the correlation between anomalous Hall effect (AHE) and spin anomalous Hall effect (SAHE) has been interpreted from the aspect of Berry curvature. This work illustrates that the interplay of symmetry and magnetism can effectively control the magnitude and spin polarization of the spin current, providing a practical method to realize exotic spin-orbit torques.

First-principles calculations on the spin anomalous Hall effect of ferromagnetic alloys

The spin anomalous Hall effect (SAHE) in ferromagnetic metals, which can generate a spin-orbit torque to rotate the magnetization of another ferromagnetic layer through a nonmagnetic spacer in magnetic junctions, has attracted much attention. We theoretically investigated the spin anomalous Hall conductivity (SAHC) of the $L{1}_{0}$-type alloys $X\mathrm{Pt}$ ($X=\mathrm{Fe},\mathrm{Co},\mathrm{Ni}$) on the basis of first-principles density functional theory and linear response theory. We found that the SAHC of FePt is much smaller than the anomalous Hall conductivity (AHC), leading to very small polarization for the anomalous Hall effect $\ensuremath{\zeta}=\mathrm{SAHC}/\mathrm{AHC}$ of around 0.1. On the other hand, the SAHC increases with an increasing number of valence electrons (${N}_{\mathrm{v}}$), and CoPt and NiPt show relatively large values of $|\ensuremath{\zeta}|$, greater than 1. The negative contribution of the spin-down-down component of AHC is the origin of the large SAHC and $\ensuremath{\zeta}$ in CoPt and NiPt, which is due to the antibonding states of Pt around the Fermi level in the minority-spin states.

Anomalous spin Hall and inverse spin Hall effects in magnetic systems

Spin current is a very important tensor quantity in spintronics. However, the well-known spin-Hall effect (SHE) can only generate a few of its components whose propagating and polarization directions are perpendicular with each other and to an applied charge current. It is highly desirable in applications to generate spin currents whose polarization can be in any possible direction. Here anomalous SHE and inverse spin-Hall effect (ISHE) in magnetic systems are predicted. Spin currents, whose polarisation and propagation are collinear or orthogonal with each other and along or perpendicular to the charge current, can be generated, depending on whether the applied charge current is along or perpendicular to the order parameter. In anomalous ISHEs, charge currents proportional to the order parameter can be along or perpendicular to the propagating or polarization directions of the spin current.

Efficient Modulation of Magnon Conductivity in Y3Fe5O12 Using Anomalous Spin Hall Effect of a Permalloy Gate Electrode

We report the control of the modulation efficiency of the magnon conductivity in yttrium iron garnet (YIG) using magnon spin injection from a ferromagnetic metal permalloy (Py) used as a modulator in a three-terminal magnon transistor geometry. The modulation efficiency is estimated by means of nonlocal spin-transport measurements between platinum injector and detector strips. A charge current is sent through the Py modulator to create a spin accumulation at the YIG-Py interface via the spin Hall effect and the anomalous spin Hall effect (ASHE). We observe an enhancement of the modulation efficiency for the electrically generated magnons from 2.5%/mA at 10 mT to 4.7%/mA for magnetic fields higher than 50 mT. That enhancement is attributed to the ASHE, which is maximized when the Py magnetization is perpendicular to the charge current. However, the modulation efficiency of the thermally generated magnons exhibits an opposite behavior, 12.0%/mA at 10 mT to 6.6%/mA at 50 mT, which disagrees with what we expect from the ASHE contribution to the modulation.

Tunneling Transistor by Quantum Anomalous Spin Hall Effect of Phase Isolator

Tunneling Transistor by Quantum Anomalous Spin Hall Effect of Phase Isolator

Composition dependence of the spin-anomalous Hall effect in a ferromagnetic Fe–Co alloy

We investigated the spin-anomalous Hall effect (SAHE) in ferromagnetic Fe–Co binary alloys with different compositions. The ferromagnetic resonance (FMR) measurement in Fe1−xCox/Ti/Py trilayer structures was performed to detect the SAHE in Fe1−xCox. The modulation of FMR linewidth in the Py layer due to the SAHE was observed. The effective spin-anomalous Hall angle changed from a positive value (+0.027 at x = 0.15) to a negative value (−0.012 at x = 0.65) with increasing Co composition. This study provides a deeper understanding of the SAHE.

Large spin anomalous Hall effect in L10−FePt : Symmetry and magnetization switching

We quantitatively evaluate a spin anomalous Hall effect (SAHE), generating spin angular momentum flow (spin current, $J_{\rm s}$), in an L1$\rm_{0}$-FePt ferromagnet by exploiting giant magnetoresistance devices with L1$\rm_{0}$-FePt / Cu / Ni$\rm_{81}$Fe$\rm_{19}$ . From the ferromagnetic resonance linewidth modulated by the charge current ($J_{\rm c}$) injection, the spin anomalous Hall angle ($ \alpha_{\rm SAH} $) is obtained to be 0.25 $ \pm $ 0.03. The evaluation of $ \alpha_{\rm SAH} $ at different configurations between $J_{\rm c}$ and magnetization enables us to discuss the symmetry of SAHE and gives the unambiguous evidence that SAHE is the source of $J_{\rm s}$. Thanks to the large $ \alpha_{\rm SAH} $, we demonstrate the SAHE-induced magnetization switching.

Visible Light Metasurfaces Assembled by Quasiperiodic Dendritic Cluster Sets

AbstractPeriodic metasurfaces have achieved various light manipulations. However, the preparation of those responding in visible waveband still encounters many constraints. Inspired by the idea of the Gerchberg–Saxton algorithm, a quasiperiodic dendritic cluster set metasurface is proposed where the cluster is used as the unit instead of cell that is used as the unit in the periodic metasurface. By gradually changing the theoretical model from periodic to quasiperiodic structure and the dendritic cluster sets prepared through a bottom‐up electrochemical deposition method from disordered to quasiperiodic distribution, the simulation and experimental results show that, when the two both resonate in visible light, the quasiperiodic cluster set metasurface can produce nearly the same abnormal optical responses as those produced by the periodic metasurfaces, and this metasurface is isotropic. The experiments show that the sample can generate an anomalous spin Hall effect of light in a red light band. This anomalous manipulation of angular momentum of light enables the metasurface to be applicable to the fields of quantum optics and information. This method establishes a new means for developing optical metasurfaces.

Efficient Injection and Detection of Out-of-Plane Spins via the Anomalous Spin Hall Effect in Permalloy Nanowires.

We report a novel mechanism for the electrical injection and detection of out-of-plane spin accumulation via the anomalous spin Hall effect (ASHE), where the direction of the spin accumulation can be controlled by manipulating the magnetization of the ferromagnet. This mechanism is distinct from the spin Hall effect (SHE), where the spin accumulation is created along a fixed direction parallel to an interface. We demonstrate this unique property of the ASHE in nanowires made of permalloy (Py) to inject and detect out-of-plane spin accumulation in a magnetic insulator, yttrium iron garnet (YIG). We show that the efficiency for the injection/detection of out-of-plane spins can be up to 50% of that of in-plane spins. We further report the possibility to detect spin currents parallel to the Py/YIG interface for spins fully oriented in the out-of-plane direction, resulting in a sign reversal of the nonlocal magnon spin signal. The new mechanisms that we have demonstrated are highly relevant for spin torque devices and applications.

Spin-transfer torque induced by the spin anomalous Hall effect

The anomalous Hall effect in ferromagnets is a well-known phenomenon in which electromotive force is generated in the direction perpendicular to both the electric current and the magnetization. With nonmagnetic heavy metals, the generation of spin current by the spin Hall effect, as well as excitation of magnetization dynamics in an adjacent ferromagnet by spin-transfer torque, has been reported. However, the generation of a spin current in ferromagnets by the anomalous Hall effect has so far not been measured. Here we report the observation of spin current generation by the anomalous Hall effect through spin-transfer torque excitation in CoFeB/Cu/NiFe trilayer films. In this spin anomalous Hall effect, a spin current generated in the CoFeB by the anomalous Hall effect is injected into the NiFe and excites spin-transfer torque in the NiFe. This leads to a measurable modulation in the ferromagnetic resonance linewidth of the NiFe. The spin anomalous Hall angle in the CoFeB is estimated to be −0.14 ± 0.05, which is comparable to the spin Hall angle reported in heavy metals. The generation of a spin current by the anomalous Hall effect is observed by measuring the modulation in the ferromagnetic resonance linewidth of CoFeB/Cu/NiFe trilayer films.