Antiferromagnets (AFs) attract much attention due to potential applications in spintronics. Both the electric current and the electric field are considered as tools suitable to control properties and the Néel vector direction of AFs. Among AFs, CuMnAs has been shown to exhibit specific properties that result in the existence of the current-induced spin-orbit torques commensurate with spin directions and topological Dirac quasiparticles. Here, we report on the observation of a reversible effect of an electric field on the resistivity of CuMnAs thin films, employing ionic liquid as a gate insulator. The data allow to determine the carrier type, concentration, and mobility independently of the Hall effect that may be affected by an anomalous component.
CuMnAs with perpendicular magnetic anisotropy is proposed as an active material for antiferromagnetic memory. Information can be stored in the antiferromagnetic domain state, while writing and readout can rely on the existence of the surface magnetization. It is predicted, based on first-principles calculations, that easy-axis anisotropy can be achieved in bulk CuMnAs by substituting a few percent of As atoms by Ge, Si, Al, or B. This effect is attributed to the changing occupation of certain electronic bands near the Fermi level induced by the hole doping. The calculated temperature dependenc…
The recently discovered electrical-induced switching of antiferromagnetic (AF) materials that have spatial inversion asymmetry has enriched the field of spintronics immensely and opened the door for the concept of antiferromagnetic MRAM. CuMnAs is one promising AF material that exhibits such electrical switching ability, and has been studied to switch using electrical pulses of length millisecond down to picosecond, but with little focus on nanosecond regime. We demonstrate here switching of CuMnAs/GaP using nanosecond pulses. Our results showed that in the nanosecond regime low-energy switchi…
Recent studies have demonstrated the potential of antiferromagnets as the active component in spintronic devices. This is in contrast to their current passive role as pinning layers in hard disk read heads and magnetic memories. Here we report the epitaxial growth of a new high-temperature antiferromagnetic material, tetragonal CuMnAs, which exhibits excellent crystal quality, chemical order and compatibility with existing semiconductor technologies. We demonstrate its growth on the III-V semiconductors GaAs and GaP, and show that the structure is also lattice matched to Si. Neutron diffractio…
Antiferromagnetic spintronics allows us to explore storing and processing information in magnetic crystals with vanishing magnetization. In this manuscript, we investigate magnetoresistance effects in antiferromagnetic CuMnAs upon switching into high-resistive states using electrical pulses. By employing magnetic field sweeps up to 14 T and magnetic field pulses up to $\sim$ 60 T, we reveal hysteretic phenomena and changes in the magnetoresistance, as well as the resilience of the switching signal in CuMnAs to the high magnetic field. These properties of the switched state are discussed in the…
We describe measurements of the uniaxial magnetic anisotropy and spin-flop rotation of the Néel vector in antiferromagnetic CuMnAs thin films using neutron diffraction. The suppression of the magnetic (100) peak under magnetic fields is observed for films as thin as 20 nm indicating that they undergo a spin-flop transition. Good agreement is found between neutron diffraction and electron transport measurements of the spin-flop rotation in the same layer, with a similar shape and hysteresis of the obtained curves, while the neutron measurements provide a quantitative determination of the spin f…
Detecting the orientation of the Néel vector is a major research topic in antiferromagnetic spintronics. Here we recognize the intrinsic nonlinear Hall effect, which is independent of the relaxation time, as a prominent contribution to the time-reversal-odd second order conductivity and can be used to detect the flipping of the Néel vector. In contrast, the Berry-curvature-dipole-induced nonlinear Hall effect depends linear on relaxation time and is time-reversal-even. We study the intrinsic nonlinear Hall effect in an antiferromagnetic metal: tetragonal CuMnAs, and show that its nonlinear Hal…
The effect of Cu substitution on the stability of the CuMnAs tetragonal phase was studied both experimentally and by ab initio calculations. Polycrystalline samples with various compositions Cu$_{1+x}$Mn$_{1-x}$As $(x = 0 - 0.5)$ were synthetized. The tetragonal phase of CuMnAs is found to be stabilized by substituting Mn by Cu in the amount of $x$ ~ 0.1 or higher. This observation is supported by ab initio calculations of the total energy of the tetragonal and orthorhombic phases; with increasing Cu content the tetragonal phase is favoured. Small variations of composition thus allow to grow s…
Recent research works have shown that the magnetic order in some antiferromagnetic materials can be manipulated and detected electrically, due to two physical mechanisms: Neel-order spin-orbit torques and anisotropic magnetoresistance. While these observations open up opportunities to use antiferromagnets for magnetic memory devices, different physical characterization methods are required for a better understanding of those mechanisms. Here we report a magnetic field induced rotation of the antiferromagnetic Neel vector in epitaxial tetragonal CuMnAs thin films. Using soft x-ray magnetic line…
We present a detailed study of the growth of the tetragonal polymorph of antiferromagnetic CuMnAs by the molecular beam epitaxy technique. We explore the parameter space of growth conditions and their effect on the microstructural and transport properties of the material. We identify its typical structural defects and compare the properties of epitaxial CuMnAs layers grown on GaP, GaAs and Si substrates. Finally, we investigate the correlation between the crystalline quality of CuMnAs and its performance in terms of electrically induced resistance switching.
Efficient manipulation of antiferromagnetic (AF) domains and domain walls has opened up new avenues of research towards ultrafast, high-density spintronic devices. AF domain structures are known to be sensitive to magnetoelastic effects, but the microscopic interplay of crystalline defects, strain and magnetic ordering remains largely unknown. Here, we reveal, using photoemission electron microscopy combined with scanning X-ray diffraction imaging and micromagnetic simulations, that the AF domain structure in CuMnAs thin films is dominated by nanoscale structural twin defects. We demonstrate t…
Recent breakthroughs in electrical detection and manipulation of antiferromagnets have opened a new avenue in the research of non-volatile spintronic devices. Antiparallel spin sublattices in antiferromagnets, producing zero dipolar fields, lead to the insensitivity to magnetic field perturbations, multi-level stability, ultra-fast spin dynamics and other favorable characteristics which may find utility in fields ranging from magnetic memories to optical signal processing. However, the absence of a net magnetic moment and the ultra-short magnetization dynamics timescales make antiferromagnets …
Noncollinear magnetic moments in antiferromagnets (AFM) lead to a complex behavior of electrical transport, even to a decreasing resistivity due to an increasing temperature. Proper treatment of such phenomena is required for understanding AFM systems at finite temperatures; however first-principles description of these effects is complicated. With ab initio techniques, we investigate three models of spin fluctuations (magnons) influencing the transport in AFM CuMnAs; the models are numerically feasible and easily implementable to other studies. We numerically justified a fully relativistic co…
Electrical and optical pulsing allow for manipulating the order parameter and magnetoresistance of antiferromagnets, opening novel prospects for digital and analog data storage in spintronic devices. Recent experiments in CuMnAs have demonstrated giant resistive switching signals in single-layer antiferromagnetic films together with analog switching and relaxation characteristics relevant for neuromorphic computing. Here we report simultaneous electrical pulsing and scanning NV magnetometry of antiferromagnetic domains in CuMnAs performed using a pump-probe scheme. We observe a nano-scale frag…
Antiferromagnetic materials as active components in spintronic devices promise insensitivity against external magnetic fields, the absence of own magnetic stray fields, and ultrafast dynamics at the picosecond time scale. Materials with certain crystal-symmetry show an intrinsic Néel-order spin-orbit torque that can efficiently switch the magnetic order of an antiferromagnet. The tetragonal variant of CuMnAs was shown to be electrically switchable by this intrinsic spin-orbit effect and its use in memory cells with memristive properties has been recently demonstrated for high-quality films gro…
Temperature-dependent resistivity and magnetoresistance are measured in bulk tetragonal phase of antiferromagnetic CuMnAs and the latter is found to be anisotropic both due to structure and magnetic order. We compare these findings to model calculations with chemical disorder and finite-temperature phenomena included. The finite-temperature ab initio calculations are based on the alloy analogy model implemented within the coherent potential approximation and the results are in fair agreement with experimental data. Regarding the anisotropic magnetoresistance (AMR) which reaches a modest magnit…
Electronic, magnetic, and transport properties of the antiferromagnetic (AFM) CuMnAs alloy with tetragonal structure, promising for the AFM spintronics, are studied from first principles using the Vienna ab-initio simulation package. We investigate the site-occupation of sublattices and the lattice parameters of three competing phases. We analyze the factors that determine which of the three conceivable structures will prevail. We then estimate formation energies of possible defects for the experimentally prepared lattice structure. Mn$_{\rm Cu}$- and Cu$_{\rm Mn}$-antisites as well as Mn$\lef…
We report the physical properties of orthorhombic o-CuMnAs single crystal, which is predicted to be a topological Dirac semimetal with magnetic ground state and inversion symmetry broken. o-CuMnAs exhibits an antiferromagnetic transition with TN ~ 312 K. Further characterizations of magnetic properties suggest that the AFM order may be canted with the spin orientation in the bc plane. Small isotropic MR and linearly field-dependent Hall resistivity with positive slope indicate that single hole-type carries with high density and low mobility dominate the transport properties of o-CuMnAs. Furthe…
Orthorhombic CuMnAs has been proposed as an antiferromagnetic semimetal hosting nodal line and Dirac points around the Fermi level. We investigate relations between the topological bands and transport phenomena, i.e. spin Hall effect and anomalous Hall effect, in orthorhombic CuMnAs with first-principles calculations combined with symmetry analysis of magnetic structures and of (spin) Berry curvature. We show the nodal line gapped with spin-orbit coupling in CuMnAs dominantly generates large spin Hall conductivity in the ground state. Although the magnetic symmetry in the ground state of CuMnA…
Electrical switching and readout of antiferromagnets allows to exploit the unique properties of antiferromagnetic materials in nanoscopic electronic devices. Here we report experiments on the spin-orbit torque induced electrical switching of a polycrystalline, metallic antiferromagnet with low anisotropy and high Néel temperature. We demonstrate the switching in a Ta / MnN / Pt trilayer system, deposited by (reactive) magnetron sputtering. The dependence of switching amplitude, efficiency, and relaxation are studied with respect to the MnN film thickness, sample temperature, and current densit…
Antiferromagnets offer spintronic device characteristics unparalleled in ferromagnets owing to their lack of stray fields, THz spin dynamics, and rich materials landscape. Microscopic imaging of aniferromagnetic domains is one of the key prerequisites for understading physical principles of the device operation. However, adapting common magnetometry techniques to the dipolar-field-free antiferromagnets has been a major challenge. Here we demonstrate in a collinear antiferromagnet a thermoelectric detection method by combining the magneto-Seebeck effect with local heat gradients generated by sc…
Antiferromagnets have a number of favourable properties as active elements in spintronic devices, including ultra-fast dynamics, zero stray fields and insensitivity to external magnetic fields . Tetragonal CuMnAs is a testbed system in which the antiferromagnetic order parameter can be switched reversibly at ambient conditions using electrical currents . In previous experiments, orthogonal in-plane current pulses were used to induce 90 degree rotations of antiferromagnetic domains and demonstrate the operation of all-electrical memory bits in a multi-terminal geometry . Here, we demonstrate th…
Electrical detection of the 180 deg spin reversal, which is the basis of the operation of ferromagnetic memories, is among the outstanding challenges in the research of antiferromagnetic spintronics. Analogous effects to the ferromagnetic giant or tunneling magnetoresistance have not yet been realized in antiferromagnetic multilayers. Anomalous Hall effect (AHE), which has been recently employed for spin reversal detection in non-collinear antiferromagnets, is limited to materials that crystalize in ferromagnetic symmetry groups. Here we demonstrate electrical detection of the 180 deg Néel vec…
Antiferromagnets are magnetically ordered materials which exhibit no net moment and thus are insensitive to magnetic fields. Antiferromagnetic spintronics aims to take advantage of this insensitivity for enhanced stability, while at the same time active manipulation up to the natural THz dynamic speeds of antiferromagnets is possible, thus combining exceptional storage density and ultra-fast switching. However, the active manipulation and read-out of the Néel vector (staggered moment) orientation is challenging. Recent predictions have opened up a path based on a new spin-orbit torque, which c…
Antiferromagnets (AFs) are remarkable magnetically ordered materials that due to the absence of a net magnetic moment do not generate dipolar fields and are insensitive to external magnetic field perturbations. However, it has been notoriously difficult to control antiferromagnetic moments by any practical means suitable for device applications. This has left AFs over their hundred years history virtually unexploited and only poorly explored, in striking contrast to the thousands of years of fascination and utility of ferromagnetism. Very recently it has been predicted and experimentally confi…
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）
Motivated by the existence of superconductivity in pyrite-structure CuS$_2$, we explore the possibility of ionic-liquid-gating-induced superconductivity in the proximal antiferromagnetic Mott insulator NiS$_2$. A clear gating-induced transition from a two-dimensional insulating state to a three-dimensional metallic state is observed at positive gate bias on single crystal surfaces. No evidence for superconductivity is observed down to the lowest measured temperature of 0.45 K, however. Based on transport, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, atomic force micr…
The topological quantum field-effect transition in buckled 2D-Xenes can potentially be engineered to enable sub-thermionic transistor operation coupled with dissipationless ON-state conduction. Substantive device design strategies to harness this will necessitate delving into the physics of the quantum field effect transition between the dissipationless topological phase and the band insulator phase. Investigating workable device structures, we uncover fundamental sub-threshold limits posed by the gating mechanism that effectuates such a transition, thereby emphasizing the need for innovations…
Electrical manipulation of magnetization is essential for integration of magnetic functionalities such as magnetic memories and magnetic logic devices into electronic circuits. The current induced spin-orbit torque (SOT) in heavy metal/ferromagnet (HM/FM) bilayers via the spin Hall effect in the HM and/or the Rashba effect at the interfaces provides an efficient way to switch the magnetization. In the meantime, current induced SOT has also been used to switch the in-plane magnetization in single layers such as ferromagnetic semiconductor (Ga,Mn)As and antiferromagnetic metal CuMnAs with global…
Magnetic anisotropy in an antiferromagnet (AFM) with inversion symmetry breaking (ISB) is investigated. The magnetic anisotropy energy (MAE) resulting from the Rashba spin-orbit and s-d type exchange interactions is determined for two different models of AFMs. The global ISB model, representing the effect of a surface, an interface, or a gating electric field, results in an easy-plane magnetic anisotropy. In contrast, for a local ISB model, i.e., for a noncentrosymmetric AFM, perpendicular magnetic anisotropy (PMA) arises. Both results differ from the ferromagnetic case, in which the result fo…
Recent advances in tuning electronic, magnetic, and topological properties of two-dimensional (2D) magnets have opened a new frontier in the study of quantum physics and promised exciting possibilities for future quantum technologies. In this study, we find that the dual-gate technology can well tune the electronic and topological properties of antiferromagnetic (AFM) even septuple-layer (SL) MnBi$_2$Te$_4$ thin films. Under an out-of-plane electric field that breaks $\mathcal{PT}$ symmetry, the Berry curvature of the thin film could be engineered efficiently, resulting in a huge change of ano…
We recently demonstrated that the superconductor-to-insulator transition induced by ionic liquid gating of the high temperature superconductor YBa2Cu3O7 (YBCO) is accompanied by a deoxygenation of the sample [Perez-Munoz et al., PNAS 114, 215 (2017)]. DFT calculations helped establish that the pronounced changes in the spectral features of the Cu K-edge absorption spectra measured in situ during the gating experiment arise from a decrease of the Cu coordination within the CuO chains. In this work, we provide a detailed analysis of the electronic structure origin of the changes in the spectra r…
Theoretical studies have shown that Majorana bound states can be induced at the ends of a one dimensional wire, a phenomenon possible due to the interplay between s-wave superconductivity, spin-orbit coupling, and an external magnetic field. These states have been observed in superconductor-semiconductor hybrid nanostructures in the presence of a Zeeman field, and in the limit of a low density of particles. In this paper, we demonstrate and discuss the possibility of the emergence of Majorana bound states in a superconducting Rashba nanowire deposited on an antiferromagnetically ordered surfac…
Ferromagnetism above 200 K in organic-ion intercalated CrSBr
CIC nanoGUNE（纳米技术联合研究中心）；UPV/EHU（巴斯克地区理工大学）；CSIC-UPV/EHU（西班牙国家科研委员会-巴斯克地区理工大学）；Izmir Institute of Technology（伊兹密尔理工大学）；IKERBASQUE（伊克尔巴斯基奎基金会）；Universitat de València（瓦伦西亚大学）
The concept of electronic topology and the associated topological protection brings excellent opportunities for developing next-generation devices. Ideally, magnetic topological materials (MTM) should have their Dirac/Weyl points and/or associated mass gaps at the Fermi energy (EF) or be readily tunable such that they can be placed at EF via external perturbations such as electric field gating, chemical substitutions, or doping. Three-dimensional antiferromagnetic (AFM) materials like Mn$Bi_{2}$$X_{4}$ (X=Se, Te) that have strong spin-orbit coupling (SOC) and broken time-reversal symmetry (TRS…
Anomalous Hall effect (AHE) is an important transport signature revealing topological properties of magnetic materials and their spin textures. Recently, antiferromagnetic MnBi2Te4 has been demonstrated to be an intrinsic magnetic topological insulator that exhibits quantum AHE in exfoliated nanoflakes. However, its complicated AHE behaviors may offer an opportunity for the unexplored correlation between magnetism and band structure. Here, we show the Berry curvature dominated intrinsic AHE in wafer-scale MnBi2Te4 thin films. By utilizing a high-dielectric SrTiO3 as the back-gate, we unveil an…
Materials that crystalize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneoulsy, the two atomic sites in the unit cell of these crystals form inversion partners which gives rise to relativistic non-equilibrium spin phenomena highly relevant for magnetic memories and other spintronic devices. When the inversion-partner sites are occupied by the same atomic species, electrical current can generate local spin polarization with the same magnitude and opposite sign on the two inversion-partner sites. In CuMnAs, which share…
Spin transistors (whose on-off operation is achieved by electric-field-controlled spin orientation 1), if realized, can revolutionize modern electronics through the implementation of a faster and a more energy-efficient performance as well as non-volatile data storage 2, 3. The original proposal by Datta and Das 1 that relies on electric-field-controlled spin precession in a semiconductor channel faces significant challenges including inefficient spin injection, spin relaxation and spread of the spin precession angle 4, 5. Recent demonstration of electric-field switching of magnetic order 6-8 …
