Jiang Wanjun

Toward low-energy-consumption spintronic devices, magnetic multilayers that host chiral spin textures, as well as efficient spin-torques, are highly promising. As compared with resistive materials, superconducting materials are optimal for constructing dissipationless electronic devices, in which the electricity is conducted without producing Joule heating. In this regard, magnetic multilayers containing superconductors are well suited for building ultra-low power spintronic devices. Following this motivation, we study the possible existence of chiral spin textures in the two-dimensional (2D) high temperature superconductor/ferrimagnet heterostructures of stacking order Bi2Sr2CaCu2O8þd/Fe1ÀxTbx and stacking order Bi2Sr2CaCu2O8þd/Co1ÀxTbx. Through x-ray photon-emission electron microscopy, we observe bubble-like spin textures in a wide temperature range. Based on the first-principles calculations, the …

Electrical control of magnetism is highly desirable for energy-efficient spintronic applications. Realizing electric-field-driven perpendicular magnetization switching has been a long-standing goal, which, however, remains a major challenge. Here, electric-field control of perpendicularly magnetized ferrimagnetic order via strain-mediated magnetoelectric coupling is reported. We show that the gate voltages isothermally toggle the dominant magnetic sublattice of the compensated ferrimagnet FeTb at room temperature, showing high reversibility and good endurance under ambient conditions. By implementing this strategy in FeTb/Pt/Co spin valves with giant magnetoresistance (GMR), we demonstrate that the distinct high and low resistance states can be selectively controlled by the gate voltages with assisting magnetic fields. Our results provide a promising route to use ferrimagnets for developing electric-field …

Electrical switching of topological antiferromagnetic states in Mn3Sn thin films has been a subject of active investigation. However, dependences of switching behaviors on the film thickness, external field, and crystal orientation remain to be fully explored, which motivate the present study. In this work,(1120)-orientated Mn3Sn thin films are fabricated on sapphire substrates, in which a large anomalous Hall effect over a wide temperature range (270–400 K) can be identified. The current-induced spin–orbit torques (SOTs) are utilized to electrically manipulate the topological antiferromagnetic states in Mn3Sn/Pt bilayers. The robust SOT switching can be realized in Mn3Sn films with thicknesses up to 100 nm and with in-plane fields up to 1200 mT. Furthermore, SOT switching behaviors that are independent of the choice of crystal orientations are clearly revealed. Our results could be useful for implementing Mn3Sn …

A leading nonlinear effect in magnonics is the interaction that splits a high-frequency magnon into two low-frequency magnons with conserved linear momentum. Here, we report experimental observation of nonlocal three-magnon scattering between spatially separated magnetic systems, viz. a CoFeB nanowire and a yttrium iron garnet (YIG) thin film. Above a certain threshold power of an applied microwave field, a CoFeB Kittel magnon splits into a pair of counterpropagating YIG magnons that induce voltage signals in Pt electrodes on each side, in excellent agreement with model calculations based on the interlayer dipolar interaction. The excited YIG magnon pairs reside mainly in the first excited (n= 1) perpendicular standing spin-wave mode. With increasing power, the n= 1 magnons successively scatter into nodeless (n= 0) magnons through a four-magnon process. Our results demonstrate nonlocal detection …

Magnetic skyrmions are real-space topological spin textures, which have attracted increasing attention from the nanospintronics community. Toward functional skyrmionics, the efficient manipulation of skyrmions is a prerequisite, which has been successfully demonstrated through electrical, thermal, optical, and other means. Here, through integrating an interfacially asymmetric Ta/CoFeB/MgO multilayer with an on-chip wire that induces Oersted fields and their gradients, we show experimentally the generation and topology-dependent motion of Néel type skyrmions at room temperature. In particular, an opposite longitudinal motion for skyrmions with opposite topological charges along the gradient direction is observed. Through comparing with the well-known Stern–Gerlach experiment, in which the splitting of atomic spins under magnetic field gradients was observed, our work identifies another interesting aspect of …

Anomalous Nernst effect in compensated ferrimagnetic Mn₂Ru<i>_x</i>Ga Toggle navigation J-STAGE home 資料・記事を探す 資料を探す:資料タイトルから 資料を探す:分野 から 資料を探す:発行機関から 記事を探す データを探す(J-STAGE Data) J-STAGEについて J-STAGEの 概要 各種サービス・機能 公開データ 利用規約・ポリシー 新規登載の申し込み ニュース&PR お知らせ一覧 リリースノート メンテナンス情報 イベント情報 J-STAGEニュース 特集コンテンツ 各種 広報媒体 サポート J-STAGE登載機関用コンテンツ 登載ガイドライン・マニュアル 閲覧者向け ヘルプ 動作確認済みブラウザ FAQ お問い合わせ サイトマップ サインイン カート JA English 日本 語 資料・記事を探す 資料を探す:資料タイトルから 資料を探す:分野から 資料を探す:発行機関から 記事を探す データを探す(J-STAGE Data) J-STAGEについて J-STAGEの概要 各種サービス・機能 公開データ 利用規約・ポリシー 新規登載の申し込み ニュース&PR お知らせ一覧 リリースノート …

The dynamical properties of skyrmions can be exploited to build devices with new functionalities. Here, we first investigate a skyrmion-based ring-shaped device by means of micromagnetic simulations and Thiele’s equation. We subsequently show three application scenarios:(1) a clock with tunable frequency that is biased with an electrical current having a radial spatial distribution,(2) an alternator, where the skyrmion circular motion driven by an engineered anisotropy gradient is converted into an electrical signal, and (3) an energy harvester, where the skyrmion motion driven by a thermal gradient is converted into an electrical signal, thus providing a heat recovery operation. We also show how to precisely tune the frequency and amplitude of the output electrical signals by varying material parameters, geometrical parameters, and number and velocity of skyrmions, and we further prove the correct device …

Electrically manipulating the magnetization of insulators presents exciting opportunities for fast and energy‐efficient spintronic devices. However, the existing approaches, which rely on spin‐orbit torque (SOT), invariably require an auxiliary field. Here field‐free current‐induced magnetization switching in perpendicularly magnetized Tm3Fe5O12 films is demonstrated. This is achieved through a magnetic hybrid structure, Tm3Fe5O12/Co40Fe40B20/Cu/SiO2, where the Cu layer acts as the source of orbital current, and the in‐plane magnetized Co40Fe40B20 layer functions as the converter of orbital‐to‐spin current. The interplay between the insulating and metallic magnetic layers not only yields a significant anomalous Hall signal for monitoring the Tm3Fe5O12 magnetization states, but also enables field‐free switching that is immune to the magnetic history of the structure. It also observes similar Tm3Fe5O12 …

Magnetic skyrmions are topological spin textures that can be used as memory and logic components for advancing the next generation spintronics. In this regard, control of nanoscale skyrmions, including their sizes and densities, is of particular importance for enhancing the storage capacity of skyrmionic devices. Here, we propose a viable route for engineering ferrimagnetic skyrmions via tuning the magnetic properties of the involved ferrimagnets Fe1–xTbx. Via tuning the composition of Fe1–xTbx that alters the magnetic anisotropy and the saturation magnetization, the size of the ferrimagnetic skyrmion (ds) and the average density (ηs) can be effectively tailored in [Pt/Fe1–xTbx/Ta]10 multilayers. In particular, a stabilization of sub-50 nm skyrmions with a high density is demonstrated at room temperature. Our work provides an effective approach for designing ferrimagnetic skyrmions with the desired size and density …

Rare-earth iron garnets (ReIGs) are attracting considerable attention because they could enable many intriguing spintronic phenomena. Material choices of these garnets are, however, limited to rather simple compositions, such as Y 3 Fe 5 O 12, Tm 3 Fe 5 O 12, and Gd 3 Fe 5 O 12, among many others. The magnetic properties of these garnets, including saturation magnetization, anisotropy, and damping parameter, are accordingly limited within a narrow parameter space. In this study, we will first grow a series of substituted ReIGs of composition Gd 3− x Ho x Fe 5 O 12 (x Ho= 0− 3). Subsequently, a continuous tuning of magnetic parameters, including the net saturation magnetization (M S), the magnetization compensation temperature (T M), and the damping parameter (α), are also demonstrated through linearly changing the Ho concentration. The present method could be useful for designing garnets with …

Compensated ferrimagnets (FIMs) made of rare-earth transition-metal compounds have stimulated increasing interest for enabling fast spin dynamics. Taking Fe-Tb compounds as an example, substantial efforts have been made on the study of compensated magnetism and its potential spintronic applications. Current-induced spin-orbit torque (SOT) switching and its evolution with compensated ferrimagnetism in these compounds, however, remain to be systematically explored, which motivates the present study. By combining magnetometry and anomalous Hall effect measurements, a compositional magnetization compensation point (x c= 0.25) is determined for Fe 1− x Tb x films of a fixed thickness of 6.5 nm. The antiferromagnetic coupling between Fe and Tb sublattices is directly revealed by conducting element-specific x-ray magnetic circular dichroism measurements. The evolution of SOT switching as a …

Current induced spin-orbit torque (SOT) holds great promise for next generation magnetic-memory technology. Field-free SOT switching of perpendicular magnetization requires the breaking of in-plane symmetry, which can be artificially introduced by external magnetic field, exchange coupling or device asymmetry. Recently it has been shown that the exploitation of inherent crystal symmetry offers a simple and potentially efficient route towards field-free switching. However, applying this approach to the benchmark SOT materials such as ferromagnets and heavy metals is challenging. Here, we present a strategy to break the in-plane symmetry of Pt/Co heterostructures by designing the orientation of Burgers vectors of dislocations. We show that the lattice of Pt/Co is tilted by about 1.2° when the Burgers vector has an out-of-plane component. Consequently, a tilted magnetic easy axis is induced and can be tuned …

The anomalous Hall effect (AHE) is a quantum coherent transport phenomenon that conventionally vanishes at elevated temperatures because of thermal dephasing. Therefore, it is puzzling that the AHE can survive in heavy metal (HM)/antiferromagnetic (AFM) insulator (AFMI) heterostructures at high temperatures yet disappears at low temperatures. In this paper, an unconventional high‐temperature AHE in HM/AFMI is observed only around the Néel temperature of AFM, with large anomalous Hall resistivity up to 40 nΩ cm is reported. This mechanism is attributed to the emergence of a noncollinear AFM spin texture with a non‐zero net topological charge. Atomistic spin dynamics simulation shows that such a unique spin texture can be stabilized by the subtle interplay among the collinear AFM exchange coupling, interfacial Dyzaloshinski–Moriya interaction, thermal fluctuation, and bias magnetic field.

Crystal geometry can greatly influence the emergent properties of quantum materials. As an example, the kagome lattice is an ideal platform to study the rich interplay between topology, magnetism, and electronic correlation. In this work, combining high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we systematically investigate the electronic structure of X Mn 6 Sn 6 (X= Dy, Tb, Gd, Y) family compounds. We observe the Dirac fermion and the flat band arising from the magnetic kagome lattice of Mn atoms. Interestingly, the flat band locates in the same energy region in all compounds studied, regardless of their different magnetic ground states and 4 f electronic configurations. These observations suggest a robust Mn magnetic kagome lattice across the X Mn 6 Sn 6 family, thus providing an ideal platform for the search for, and investigation of, new emergent phenomena in magnetic …

The interlayer exchange coupling (IEC) in synthetic antiferromagnets (SAFs) is attracting considerable attention in the spintronics community. While exciting physics is revealed, systematic control of the IEC via tuning the thickness of the magnetic layer is yet to be adequately addressed in SAFs with perpendicular magnetic anisotropy (PMA). In this work, we experimentally investigate this aspect in Pt/Co/Ru/Fe 0.55 Tb 0.45 [ferromagnet (FM)/Ru/ferrimagnet (FIM)] multilayers with PMA, which possess a broader material-parameter space beyond what can be achieved with traditional SAFs. More importantly, the incorporation of the Fe− Tb FIM layer into the SAF multilayers allows us to directly probe the layer-resolved magnetization reversal by utilizing the anomalous Hall effect and standard magnetometry measurements. Our findings are further verified by x-ray magnetic circular dichroism measurements by providing …

Magnetic domain walls (DWs) in rare-earth-transition-metal (RE-TM) ferrimagnetic alloys can be used as information carriers in nonvolatile spintronic devices. Due to the rich combinations of RE-TM elements (such as CoGd, FeGd, CoTb, and FeTb in our case), it is intriguing to reveal the characteristics of DW dynamics in these wide choices of RE-TM compounds. Through a systematic study of the DW motion in thin films with different compositions of stacking order Pt(3 nm)/(Fe,Co)1−x(Gd,Tb)x(∼8 nm)/Ta(3 nm), we show that the partially compensated ferrimagnets CoGd and FeGd can exhibit a faster DW motion under various (in-plane and out-of-plane) magnetic fields driven by current-induced spin–orbit torques. In stark contrast with the fast motion of domain walls in Gd-based ferrimagnets, we find that the CoTb system exhibits much slower DW dynamics, and the FeTb system shows no motion, but evolved into a …

Rashba spin–orbit coupling (SOC) could facilitate an efficient interconversion between spin and charge currents. Among various systems, BiTeI holds one of the largest Rashba-type spin splittings. Unlike other Rashba systems (e.g., Bi/Ag and Bi2Se3), an experimental investigation of the spin-to-charge interconversion in BiTeI remains to be explored. Through performing an angle-resolved photoemission spectroscopy (ARPES) measurement, such a large Rashba-type spin splitting with a Rashba parameter αR = 3.68 eV Å is directly identified. By studying the spin pumping effect in the BiTeI/NiFe bilayer, we reveal a very large inverse Rashba–Edelstein length λIREE ≈ 1.92 nm of BiTeI at room temperature. Furthermore, the λIREE monotonously increases to 5.00 nm at 60 K, indicating an enhanced Rashba SOC at low temperature. These results suggest that BiTeI films with the giant Rashba SOC are promising for …

Complex oxides hosting 4d and 5d cations with significant spin–orbit coupling have recently been shown as promising materials for efficient spin‐charge interconversion. Through interfacing 4d and 5d oxides with magnet layers, a large spin–orbit torque (SOT) is reported. However, a room‐temperature SOT switching of perpendicular magnetization by using these oxides, which is essential for spintronic devices, is not demonstrated. Here, this is addressed yet missing aspect by studying heterostructures comprised of two representative complex oxides (4d SrRuO3 and 5d SrIrO3) and a compensated ferrimagnet FeGd with perpendicular magnetic anisotropy. A room temperature current‐induced SOT switching of perpendicular magnetization in both SrRuO3/FeGd and SrIrO3/FeGd bilayers, with the critical switching current density on the order of 106 A cm−2 is demonstrated. The SOT efficiencies of SrRuO3 and …

Van der Waals materials are attracting great attention in the field of spintronics due to their novel physical properties. For example, they are utilized as spin‐current generating materials in spin–orbit torque (SOT) devices, which offers an electrical way to control the magnetic state and is promising for future low‐power electronics. However, SOTs have mostly been demonstrated in vdW materials with strong spin–orbit coupling (SOC). Here, the observation of a current‐induced SOT in the h‐BN/SrRuO3 bilayer structure is reported, where the vdW material (h‐BN) is an insulator with negligible SOC. Importantly, this SOT is strong enough to induce the switching of the perpendicular magnetization in SrRuO3. First‐principles calculations suggest a giant Rashba effect at the interface between vdW material and SrRuO3 (110)pc thin film, which leads to the observed SOT based on a simplified tight‐binding model …

The discovery of magnetic skyrmions provides a promising pathway for developing functional spintronic memory and logic devices. Towards the future high-density memory application, nanoscale skyrmions with miniaturized diameters, ideally down to 20 nm are required. Using x-ray magnetic circular dichroism transmission microscopy, nanoscale skyrmions are observed in the [Pt/Co/Ir] 15 multilayer at room temperature. In particular, small skyrmions with minimum diameters approaching 20 nm could be generated by the current-induced spin-orbit torques. Through implementing material specific parameters, the dynamic process of skyrmion generation is further investigated by performing micromagnetic simulations. According to the simulation results, we find that both the tube-like Néel-type skyrmions and the bobber-like Néel-type skyrmions can be electrically generated. In particular, the size of the bobber-like …

The static and dynamic properties of skyrmions have recently received increased attention due to the potential application of skyrmions as information carriers and for unconventional computing. While the current-driven dynamics has been explored deeply, both theoretically and experimentally, the theory of temperature gradient-induced dynamics—skyrmion caloritronics—is still at its early stages of development. Here, we move the topic forward by identifying the role of entropic torques due to the temperature dependence of magnetic parameters. Our results show that skyrmions move towards higher temperatures in single-layer ferromagnets with interfacial Dzyaloshinski-Moriya interactions, whereas, in multilayers, they move to lower temperatures. We analytically and numerically demonstrate that the opposite behaviors are due to different scaling relations of the material parameters as well as a non-negligible …

Magnetic skyrmions have great potential for developing novel spintronic devices. The electrical manipulation of skyrmions has mainly relied on current-induced spin-orbit torques. Recently, it was suggested that the skyrmions could be more efficiently manipulated by surface acoustic waves (SAWs), an elastic wave that can couple with magnetic moment via the magnetoelastic effect. Here, by designing on-chip piezoelectric transducers that produce propagating SAW pulses, we experimentally demonstrate the directional motion of Néel-type skyrmions in Ta/CoFeB/MgO/Ta multilayers. We find that the shear horizontal wave effectively drives the motion of skyrmions, whereas the elastic wave with longitudinal and shear vertical displacements (Rayleigh wave) cannot produce the motion of skyrmions. A longitudinal motion along the SAW propagation direction and a transverse motion due to topological charge are …

Spintronic devices are considered a possible solution for the hardware implementation of artificial synapses and neurons, as a result of their non‐volatility, high scalability, complementary metal‐oxide‐semiconductor transistor compatibility, and low power consumption. As compared to ferromagnets, ferrimagnet‐based spintronics exhibits equivalently fascinating properties that have been witnessed in ultrafast spin dynamics, together with efficient electrical or optical manipulation. Their applications in neuromorphic computing, however, have still not been revealed, which motivates the present experimental study. Here, by using compensated ferrimagnets containing Co0.80Gd0.20 with perpendicular magnetic anisotropy, it is demonstrated that the behavior of spin‐orbit torque switching in compensated ferrimagnets could be used to mimic biological synapses and neurons. In particular, by using the anomalous Hall …

A broken interfacial inversion symmetry in ultrathin ferromagnet/heavy metal (FM/HM) bilayers is generally believed to be a prerequisite for accommodating the Dzyaloshinskii-Moriya interaction (DMI) and for stabilizing chiral spin textures. In these bilayers, the strength of the DMI decays as the thickness of the FM layer increases and vanishes around a few nanometers. In the present study, through synthesizing relatively thick films of compositions CoPt or FePt, CoCu or FeCu, FeGd and FeNi, contributions to DMI from the composition gradient-induced bulk magnetic asymmetry (BMA) and spin-orbit coupling (SOC) are systematically examined. Using Brillouin light scattering spectroscopy, both the sign and amplitude of DMI in films with controllable direction and strength of BMA, in the presence and absence of SOC, are experimentally studied. In particular, we show that a sizable amplitude of DMI (±0.15 mJ/m 2) can …

Magnetic skyrmions are mobile topological spin textures that can be manipulated by different means. Their applications have been frequently discussed in the context of information carriers for racetrack memory devices, which on the other hand, exhibit a skyrmion Hall effect as a result of the nontrivial real-space topology. While the skyrmion Hall effect is believed to be detrimental for constructing racetrack devices, we show here that it can be implemented for realizing a three-terminal skyrmion circulator. In analogy to the microwave circulator, nonreciprocal transportation and circulation of skyrmions are studied both numerically and experimentally. In particular, successful control of the circulating direction of being either clockwise or counterclockwise is demonstrated, simply by changing the sign of the topological charge. Our studies suggest that the topological property of skyrmions can be incorporated for enabling …

Compensated ferrimagnetic insulators are particularly interesting for enabling functional spintronic, optical, and microwave devices. Among many different garnets, Gd 3 Fe 5 O 12 (GdIG) is a representative compensated ferrimagnetic insulator. In this paper, we will study the evolution of the surface morphology, the magnetic properties, and the magnetization compensation through changing the following parameters: the annealing temperature, the growth temperature, the annealing duration, and the choice of different single crystalline garnet substrates. Our objective is to find the optimized growth condition of the GdIG films, for the purpose of achieving a strong perpendicular magnetic anisotropy (PMA) and a flat surface, together with a small effective damping parameter. Through our experiments, we have found that the surface roughness approaching 0.15 nm can be obtained by choosing the growth temperature …

Two-dimensional (2D) magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices. The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism. Here, we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe 3 GeTe 2 (FGT) with a thickness range of 11.2–112 nm. Three types of domain structures and their corresponding hysteresis loops can be obtained. The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness, which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields. These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated …

Spin valve effect driven by current-induced spin–orbit torques can help to realize electrically controllable and miniaturized two terminal spintronic devices. Here, we show that in a perpendicularly magnetized Fe1Àx1 Tbx1/Pt/Fe1Àx2 Tbx2 spin-valve multilayer, spin currents from dual surfaces of the inserted Pt layer can be used to generate spin torques that can separately switch the adjacent ferrimagnetic Fe1ÀxTbx layers. In a two-terminal device, we further show that the accompanied parallel and anti-parallel magnetization configurations between the two Fe1ÀxTbx layers can lead to the observation of the current-in-plane giant magnetoresistance (CIP-GMR). Our results demonstrate that the current-induced spin–orbit torques can be implemented into two-terminal spin-torque devices, which can be electrically read out by the CIP-GMR. The present study could be important for designing miniaturized spintronic …

The spin–orbit torques (SOTs) induced by spin currents in the heavy metal/ferromagnet (HM/FM) bilayer are of great importance for enabling nonvolatile, low power consumption spintronics. In the standard HM/FM bilayers, only the spin current at the interface is employed for implementing SOTs. Another part of the spin current with the opposite spin polarization, which is generated at the opposite side of the HM layer, is supposably not put into action. Here, we will show the experimental feasibility of utilizing spin currents from the dual surfaces of the HM Pt layer. In particular, through synthesizing perpendicularly magnetized Fe 1− x 1 Tb x 1/Pt/Fe 1− x 2 Tb x 2 trilayers, we demonstrate that spin currents at the dual surfaces of the Pt layer can be simultaneously used to deterministically switch the perpendicular magnetization vectors of the neighboring Fe 1-x Tb x layers, through the current-induced SOTs. Based on the …

The explosive demands of storage capacity and the von Neumann bottleneck of modern computer architectures trigger many innovations in information technology. Amongst them, nonvolatile spintronics attract considerable attentions for which can embed the computation capability into memory, enable neuromorphic, and probabilistic computing. These exciting progresses typically rely on the manipulation of the relative magnetization orientations of two magnetic layers. By extending to 3D spintronic architectures made of multiple magnetic layers (n), the exponentially increased 2n magnetic states can provide ample opportunities for implementing novel spintronic functionalities. Here, through building perpendicularly magnetized 3D spin‐orbitronic architectures – [Pt/Fe1−xTbx/Si3N4]n multilayers, it is demonstrated the electrical programing of 2n memory states via current‐induced spin–orbit torques (SOTs), and …

Interfacially asymmetric magnetic multilayers made of heavy metal/ferromagnet have attracted considerable attention in the spintronics community for accommodating spin‐orbit torques (SOTs) and meanwhile for hosting chiral spin textures. In these multilayers, the accompanied interfacial Dzyaloshinskii–Moriya interaction (iDMI) permits the formation of Néel‐type spin textures. While significant progresses have been made in Co, CoFeB, Co2FeAl, CoFeGd based multilayers, it would be intriguing to identify new magnetic multilayers that could enable spin‐torque controllability and meanwhile host nanoscale skyrmions. In this report, first, thin films made of permanent magnet SmCo5 with perpendicular magnetic anisotropy are synthesized, in which the deterministic SOT switching, enabled by the spin Hall effect, in Pt/SmCo5/Ta trilayer is demonstrated. Further, the stabilization of room‐temperature skyrmions with …

Bismuth and rare earth elements have been identified as effective substituent elements in the iron garnet structure, allowing an enhancement in magneto-optical response by several orders of magnitude in the visible and near-infrared region. Various mechanisms have been proposed to account for such enhancement, but testing of these ideas is hampered by a lack of suitable experimental data, where information is required not only regarding the lattice sites where substituent atoms are located but also how these atoms affect various order parameters. Here, we show for a Bi-substituted lutetium iron garnet how a suite of advanced electron microscopy techniques, combined with theoretical calculations, can be used to determine the interactions between a range of quantum-order parameters, including lattice, charge, spin, orbital, and crystal field splitting energy. In particular, we determine how the Bi distribution …

We report the realization of fully compensated synthetic antiferromagnets (SAFs) in Pt/Co/Ru/Fe 1− x Tb x multilayers with perpendicular magnetic anisotropy, pronounced anomalous Hall resistances and magneto-optical responses. In particular, the properties of SAFs are systematically investigated through optimizing the thicknesses of the Co layer, the Ru spacer, and the concentration (x) of the ferrimagnet (FIM) Fe 1− x Tb x layers. The incorporation of the FIM Fe 1− x Tb x films into SAFs accelerates the search for a magnetic multilayer with fully compensated magnetism and exhibiting pronounced anomalous Hall resistance and magneto-optical signals. These advantages enable spin-orbit-torque switching and magneto-optical Kerr effect imaging experiments on the fully compensated SAFs to be readily investigated. Through incorporating FIMs into SAFs, we believe that the present material system could provide …

We report transport measurements on Josephson junctions consisting of Bi 2 Te 3 topological insulator (TI) thin films contacted by superconducting Nb electrodes. For a device with junction length L= 134 nm, the critical supercurrent I c can be modulated by an electrical gate which tunes the carrier type and density of the TI film. I c can reach a minimum when the TI is near the charge neutrality regime with the Fermi energy lying close to the Dirac point of the surface state. In the p-type regime the Josephson current can be well described by a short ballistic junction model. In the n-type regime the junction is ballistic at 0.7 K< T< 3.8 K while for T< 0.7 K the diffusive bulk modes emerge and contribute a larger I c than the ballistic model. We attribute the lack of diffusive bulk modes in the p-type regime to the formation of p–n junctions. Our work provides new clues for search of Majorana zero mode in TI-based …

Room-temperature skyrmions in magnetic multilayers are considered to be promising candidates for the next-generation spintronic devices. Several approaches have been developed to control skyrmions, but they either cause significant heat dissipation or require ultrahigh electric fields near the breakdown threshold. Here, we demonstrate electric-field control of skyrmions through strain-mediated magnetoelectric coupling in ferromagnetic/ferroelectric multiferroic heterostructures. We show the process of non-volatile creation of multiple skyrmions, reversible deformation and annihilation of a single skyrmion by performing magnetic force microscopy with in situ electric fields. Strain-induced changes in perpendicular magnetic anisotropy and interfacial Dzyaloshinskii–Moriya interaction strength are characterized experimentally. These experimental results, together with micromagnetic simulations, demonstrate that …

Magnetic skyrmions, topological‐chiral spin textures, have potential applications in next‐generation high‐density and energy‐efficient spintronic devices for information storage and logic technologies. Tailoring the detailed spin textures of skyrmions is of pivotal importance for tuning skyrmion dynamics, which is one of the key factors for the design of skyrmionic devices. Here, the direct observation of parallel aligned elliptical magnetic skyrmions in Pt/Co/Ta multilayers with an oblique‐angle deposited Co layer is reported. Domain wall velocity and spin–orbit‐torque‐induced out‐of‐plane effective field analysis demonstrate that the formation of unusual elliptical skyrmions is correlated to the anisotropic effective perpendicular magnetic anisotropy energy density (Keffu) and Dzyaloshinskii–Moriya interaction (DMI) in the film plane. Structural analysis and first‐principles calculations further show that the anisotropic Keff …

We have systematically studied the magnetoresistance effect in Pt/(CoNi) n multilayers featured with perpendicular magnetic anisotropy and fcc (111) texture. Angular dependence of the magnetoresistance, including high-order cosine terms, was found in the plane perpendicular to the electrical current, which can be attributed to the geometrical size effects and the anisotropic interface magnetoresistance effect. However, the contribution from spin Hall magnetoresistance (SMR) is absent. The spin Hall angle of Pt was evaluated by spin-torque ferromagnetic resonance measurements, and the theoretical magnitude of SMR in our samples was estimated to be one order higher than the accuracy of our experiments. The absence of SMR in our multilayers indicates that the Elliott-Yafet spin relaxation of itinerant electrons in the ferromagnetic metal is crucial when studying the spin transport in all-metallic heterostructures.

Conventional spintronics exploit predominately the properties of ferromagnets (FM). The functionalities of the related devices suffer from two detrimental aspects including the stray fields and the gigahertz (GHz) spin dynamics. These intrinsic limits of FMs can be overcome in antiferromagnets (AFMs), resulting from their vanished stray field, and the faster dynamics in the terahertz (THz) range. On the other hand, AFMs are typically inert to the external magnetic fields. A reliable writing, and more importantly, an accurate read-out of these AFM states are often experimentally challenging, which impede their technological applications. By contrast, ferrimagnets (FIMs) exhibit two antiparallel lattices, and the magnetism of these two sublattices can be fully compensated that manifests as AFM-like dynamics. Unlike the weak resistive response of AFMs, the spin transport properties in FIMs is dominated by one particular …

In this paper, the growth of rare‐earth‐free compensated ferrimagnet (C‐FIM) Mn4N single crystalline films is reported, with perpendicular magnetic anisotropy (PMA) on the MgO(001) substrates by reactive magnetron sputtering. Subsequently, the current‐induced spin‐orbit torque (SOT) switching is experimentally demonstrated through passing currents in the Hall bar device made of Mn4N/Pt bilayer, with the thickness of Mn4N approaching 60 nm. Furthermore, the accompanied SOT efficiencies are characterized by employing the harmonic Hall voltage measurements. In particular, an enhanced effective SOT efficiency with the increased thickness of Mn4N films is observed, suggesting the existence of a bulk‐like spin torque in the present material system. The results demonstrate that the perpendicularly magnetized C‐FIM Mn4N films can provide a promising material platform for developing the rare‐earth‐free …

Spin-orbit torque (SOT) has been widely used in data writing of spintronic memory devices by current-induced magnetization switching. The typical structure of SOT-induced magnetization switching of ferromagnetic multilayers with perpendicular magnetic anisotropy such as Ta/CoFeB/MgO allowed the ferromagnetic and adjacent nonmagnetic layer to be patterned independently. In this letter, we study the role of device geometry in the manipulation of magnetization switching by placing two separated CoFeB magnetic bits at different locations on a Ta layer with trapezoid shape. Manipulation of the magnetization states of the magnetic bits was achieved simply by applying different write current. Both memory writing and Boolean logic functions and/nand with large logic output ratio have been demonstrated experimentally.

Néel skyrmions are generally realized in asymmetric multilayers made of heavy metals (HMs) and ultrathin ferromagnets possessing strong interfacial Dzyaloshinskii-Moriya interactions (iDMIs). Depending on the relative strengths of iDMIs at the interfaces, various types of Néel skyrmions have been suggested, which are typified with characteristically different topological properties and current-driven dynamics. This suggests the importance of a precise quantification of their spin chiralities. In this paper, we explore the possibility of realizing Néel skyrmions in magnetic multilayers without the direct usage of standard HMs. Specifically, through depositing a thin layer of ferrimagnetic (FIM) CoTb layer on top of an antiferromagnetic (AFM) quantum material of composition Mn 3 Sn, the AFM exchange interaction at the asymmetric interface provides an equivalent iDMI for stabilizing FIM Néel skyrmions. Secondly, through …

Van der Waals (vdW) ferromagnetic materials have attracted considerable attention in the nanomaterial community, which could provide a unique platform to study magnetism at the nanoscale. Along this direction, many interesting results have been reported, including the electric field control of magnetism and topological spin textures. In this report, we present a rapid and spatially resolved imaging method to study the dimensionality-dependent magnetic properties of Fe 3 GeTe 2 (FGT) nanoflakes. Our method is named as polar magneto-optical Kerr imaging microscopy magnetometry (p-MIMM), which is made possible by analyzing the intensity evolution of wide-field polar magneto-optical Kerr effect (MOKE) images that were collected by varying magnetic fields, thicknesses, and temperatures. In particular, spatially resolved MOKE hysteresis loops can be acquired in the FGT nanoflakes with a submicrometer …

The efficient generation, manipulation and detection of magnetic skyrmions are important for the development of future spintronic devices. One approach is to use electric-current-induced spin torques. Recently, thermally induced skyrmion motion has also been observed, but wider experimental evidence and its capabilities remain limited. Here we report the thermal generation, manipulation and thermoelectric detection of nanoscale skyrmions in microstructured metallic multilayers integrated with on-chip heaters. The local application of heat can facilitate a domain morphological transition and the formation of skyrmions at the device edge, where a low energy barrier exists. We observe the unidirectional diffusion of skyrmions from hot regions to cold regions, which is due to the interplay among the repulsive forces between skyrmions, thermal spin–orbit torques, entropic forces and magnonic spin torques. The …

We demonstrate spin-orbit torque (SOT) switching of amorphous CoTb single-layer films with perpendicular magnetic anisotropy (PMA). The switching sustains even the film thickness is above 10 nm, where the critical switching current density stays almost constant. Without the need of overcoming the strong interfacial Dzyaloshinskii-Moriya interaction caused by the heavy metal, a quite low assistant field of∼ 20 Oe is sufficient to realize the full switching. The SOT effective field decreases and undergoes a sign change with the decrease of the Tb concentration, implying that a combination of the spin Hall effect from both Co and Tb as well as an asymmetric spin current absorption accounts for the SOT switching mechanism. Our findings advance the use of magnetic materials with bulk PMA for energy-efficient and thermally stable nonvolatile memories, and add a different dimension for understanding the ordering …

Manipulation of magnetization by electric‐current‐induced spin–orbit torque (SOT) is of great importance for spintronic applications because of its merits in energy‐efficient and high‐speed operation. An ideal material for SOT applications should possess high charge‐spin conversion efficiency and high electrical conductivity. Recently, transition metal dichalcogenides (TMDs) emerge as intriguing platforms for SOT study because of their controllability in spin–orbit coupling, conductivity, and energy band topology. Although TMDs show great potentials in SOT applications, the present study is restricted to the mechanically exfoliated samples with small sizes and relatively low conductivities. Here, a manufacturable recipe is developed to fabricate large‐area thin films of PtTe2, a type‐II Dirac semimetal, to study their capability of generating SOT. Large SOT efficiency together with high conductivity results in a giant …

We report the study of current-induced magnetization switching in the Ta/CoFeB heterostructures by simultaneous magneto-electrical transport and magneto-optical Kerr effect (MOKE) microscopy measurements. Although the anomalous Hall hysteresis loop summarizes the general switching behaviors, the supplementary MOKE data can provide spatial and temporal information to visualize the magnetic domain evolution as functions of the applied current and the in-plane magnetic field. More importantly, when the initial magnetic field is not sufficient enough, the interfacial Dzyaloshinskii-Moriya interaction (DMI) would modulate the spin-orbit torque (SOT) current switching dynamics and lead to the formation of the intermediate Hall resistance plateau with meta-stable tilted domain texture. Our work elucidates the importance of the applied in-plane field and unveils an effective approach to investigate the SOT/DMI …