We study in this paper the parallel spin current in an antiferromagnetic semiconductor thin film where we take into account the interaction between itinerant spins and lattice spins. The spin model is an anisotropic Heisenberg model. We use here the Boltzmann's equation with numerical data on cluster distribution obtained by Monte Carlo simulations and cluster-construction algorithms. We study the cases of degenerate and non-degenerate semiconductors. The spin resistivity in both cases is shown to depend on the temperature with a broad maximum at the transition temperature of the lattice spin system. The shape of the maximum depends on the spin anisotropy and on the magnetic field. It shows however no sharp peak in contrast to ferromagnetic materials. Our method is applied to MnTe. Comparison to experimental data is given.
A ternary ferrimagnetic half-metal, constructed through substituting 25% Fe for Mn in zincblende semiconductor MnTe, is predicted in terms of accurate first-principles calculations. It has a large half-metallic (HM) gap of 0.54eV and its ferrimagnetic order is very stable against other magnetic fluctuations. The HM ferrimagnetism is formed because the complete moment compensation in the antiferromagnetic MnTe is replaced by an uncomplete one in the Fe-substituted MnTe. This should make a novel approach to new HM materials. The half-metal could be fabricated because Fe has good affinity with Mn…
Antiferromagnetic hexagonal MnTe is a promising material for spintronic devices relying on the control of antiferromagnetic domain orientations. Here we report on neutron diffraction, magnetotransport, and magnetometry experiments on semiconducting epitaxial MnTe thin films together with density functional theory (DFT) calculations of the magnetic anisotropies. The easy axes of the magnetic moments within the hexagonal basal plane are determined to be along $\left<1\bar100\right>$ directions. The spin-flop transition and concomitant repopulation of domains in strong magnetic fields is observed…
We show that the spin-orbit coupling (SOC) in alpha-MnTe impacts the transport behavior by generating an anisotropic valence-band splitting, resulting in four spin-polarized pockets near Gamma. A minimal k-dot-p model is constructed to capture this splitting by group theory analysis, a tight-binding model and ab initio calculations. The model is shown to describe the rotation symmetry of the zero-field planer Hall effect (PHE). The upper limit of the PHE percentage is shown to be fundamentally determined by the band shape, and is quantitatively estimated to be roughly 31% by first principles.
A common perception assumes that magnetic memories require ferromagnetic materials with a non-zero net magnetic moment. However, it has been recently proposed that compensated antiferromagnets with a zero net moment may represent a viable alternative to ferromagnets. So far, experimental research has focused on bistable memories in antiferromagnetic metals. In the present work we demonstrate a multiple-stable memory device in epitaxial manganese telluride (MnTe) which is an antiferromagnetic counterpart of common II-VI semiconductors. Favorable micromagnetic characteristics of MnTe allow us to…
Investigation of transport and magnetic properties of MnTe at low temperatures sInvestigation of transport and magnetic properties of MnTe at low temperatures showed anomalies like negative coefficient of resistance below 100K and a sharp rise in susceptibility at around 83K similar to a ferromagnetic transition. Low temperature powder neutron diffraction experiments were therefore carried out to understand the underlying phenomena responsible for such anomalous behavior. Our study indicates that the rise in susceptibility at low temperatures is due to strengthening of ferromagnetic interactio…
Conductivity scaling of the anomalous Hall effect in the altermagnetic semiconductor α-MnTe
University of Notre Dame（圣母大学）；U.S. Naval Research Laboratory（美国海军研究实验室）；Stavropoulos Center for Quantum Matter, University of Notre Dame（圣母大学斯塔夫罗普洛斯量子物质中心）；Northeastern University（东北大学）；Quantum Materials and Sensing Institute, Northeastern University Innovation Campus（东北大学创新校区量子材料与传感研究所）；Synchrotron SOLEIL（SOLEIL同步辐射光源）；AGH University of Krakow（克拉科夫AGH科技大学）；Oak Ridge National Laboratory（橡树岭国家实验室）
Plaid-Like Spin Splitting and Chirality of Magnon Bands in Antiferromagnetic MnTe$_2$
Sejong University（世宗大学）；Korea Advanced Institute of Science and Technology (KAIST)（韩国科学技术院）；Sungkyunkwan University（成均馆大学）；Institute of Physics, Academia Sinica（中央研究院物理研究所）
Quantized spin-wave known as magnon, a bosonic quasiparticle, can drag electrons or holes via sd exchange interaction and boost the thermopower over the conventional diffusive thermopower. P-type magnon-drag thermopower has been observed in both ferromagnetic and antiferromagnetic metallic and degenerate semiconductors. However, it has been less reported for intrinsic or n-type magnetic semiconductors; therefore, the impact of magnon-bipolar carrier drag on thermopower has remained unexplored. Here, a theoretical model for magnon-bipolar carrier drag thermopower is derived based on the magnon-…
We investigate in this paper properties of the spin resistivity in the magnetic semiconducting MnTe of NiAs structure. MnTe is a crossroad semiconductor with a large band gap. It is an antiferromagnet with the Néel temperature around 310K. Due to this high Néel temperature, there are many applications using its magnetic properties. The method we use here is the Monte Carlo simulation in which we take into account the interaction between itinerant spins and lattice Mn spins. Our results show a very good agreement with experiments on the shape of the spin resistivity near the Néel temperature.
We report studies of the magnetic properties of a staggered stacked triangular lattice Ba$_2$MnTeO$_6$ using magnetic susceptibility, specific heat, neutron powder diffraction and inelastic neutron scattering measurements, as well as first principles density functional theory calculations. Neutron diffraction measurements reveal an antiferromagnetic order with a propagated vector $\textbf{\emph{k}}=(0.5, 0.5, 0)$ and N{é}el transition temperature of $T_\text{N}\approx20$ K. The dominant interaction derived from the Curie-Weiss fitting to the inverse DC susceptibility is antiferromagnetic. Thro…
Néel-order-dependent transverse transport in noncoplanar antiferromagnet $\text{MnTe}_{2}$
Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology（北京理工大学 光电量子架构与测量教育部重点实验室 物理学院）；International Center for Quantum Materials, Beijing Institute of Technology（北京理工大学 国际量子材料中心）
Unlocking Doping Effects on Altermagnetism in MnTe: Emergence of Quasi-altermagnetism
Indian Institute of Technology Madras（印度马德拉斯理工学院）；Indian Institute of Science, Bangalore（印度科学研究所班加罗尔分校）；Scuola Internazionale Superiore di Studi Avanzati (SISSA)（国际高等研究院）
Emergent Magnetic Structures at the 2D Limit of the Altermagnet MnTe
Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia（马德里高级研究所，IMDEA纳米科学研究所）；Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST（加泰罗尼亚纳米科学与技术研究所（ICN2），西班牙国家研究委员会和巴塞罗那自治大学）；Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU)（材料物理中心 CFM/MPC（西班牙国家研究委员会-巴斯克国立理工大学/巴斯克大学））；Departamento de Física de la Materia Condensada Universidad Autónoma de Madrid（马德里自治大学凝聚态物理系）；Condensed Matter Physics Center (IFIMAC) Universidad Autónoma de Madrid（马德里自治大学凝聚态物理中心（IFIMAC））；School of Physics and Astronomy - Monash University（莫纳什大学物理与天文学学院）；Instituto Nicolás Cabrera, Universidad Autónoma de Madrid（马德里自治大学尼古拉斯·卡布雷拉研究所）
We present experimental evidence for the simultaneous existence of the magnons and spin-state transition contributions to the heat capacity in ferromagnetic (FM) Cr-doped MnTe (Tc~280K), where the magnon heat capacity is attributed to the observed magnon-bipolar carrier-drag thermopower. The pristine antiferromagnetic (AFM) MnTe shows only a magnon-induced peak in the heat capacity near the Neel temperature, TN~307K. However, Cr-doped MnTe shows a magnon-contributed heat capacity peak at ~293K with an additional peak in the deep paramagnetic domain near 780K. Temperature-dependent magnetic sus…
The possibility of half-metallic antiferromagnetism, a special case of ferrimagnetism with a compensated magnetization, in the diluted magnetic semiconductors is highlighted on the basis of the first principles electronic structure calculation. As typical examples, the electrical and magnetic properties of II-VI compound semiconductors doped with 3d transition metal ion pairs--(V, Co) and (Fe, Cr)--are discussed.
Two-dimensional intrinsic antiferromagnetic semiconductors are expected to stand out in the spintronic field. The present work finds the monolayer T'-MoTeI is intrinsically an antiferromagnetic semiconductor by using first-principles calculation. Firstly, the dimerized distortion of the Mo atoms causes T'-MoTeI to have dynamic stability, which is different from the small imaginary frequency in the phonon spectrum of T-MoTeI. Secondly, T'-MoTeI is an indirect-bandgap semiconductor with 1.35 eV. Finally, in the systematic study of strain effects, there are significant changes in the electronic s…
Proximity Magnetism in Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3/MnTe Natural Heterostructures
DEVCOM Army Research Laboratory（DEVCOM陆军研究实验室）；Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology（麻省理工学院等离子体科学与聚变中心弗朗西斯·比特磁实验室）；Department of Electrical Engineering, National Cheng Kung University（国立成功大学电气工程系）；Department of Physics, University of Ottawa（渥太华大学物理系）；Department of Materials Science and Engineering, North Carolina State University（北卡罗来纳州立大学材料科学与工程系）
Discovering new antiferromagnetic compounds is at the forefront of developing future spintronic devices without fringing magnetic fields. The antiferromagnetic gapless semiconducting D03 phase of V3Al was successfully synthesized via arc-melting and annealing. The antiferromagnetic properties were established through synchrotron measurements of the atom-specific magnetic moments, where the magnetic dichroism reveals large and oppositely-oriented moments on individual V atoms. Density functional theory calculations confirmed the stability of a type G antiferromagnetism involving only two-third …
Short-range magnetic correlations can significantly increase the thermopower of magnetic semiconductors, representing a noteworthy development in the decades-long effort to develop high-performance thermoelectric materials. Here, we reveal the nature of the thermopower-enhancing magnetic correlations in the antiferromagnetic semiconductor MnTe. Using magnetic pair distribution function analysis of neutron scattering data, we obtain a detailed, real-space view of robust, nanometer-scale, antiferromagnetic correlations that persist into the paramagnetic phase above the Néel temperature $T_{\math…
The electronic band structures of orthorhombic (oP28) and monoclinic (mC28) MnSb_2S_4 were investigated with ab initio calculations in the local spin density approximation (LSDA) to the density functional theory (DFT). An analysis of the electronic properties and of the chemical bonding is provided using the augmented spherical wave (ASW) method considering nonmagnetic, ferromagnetic, ferrimagnetic and antiferromagnetic model orderings. In agreement with experimental results both modifications of MnSb_2S_4 are predicted to be antiferromagnetic. While the experimental band gap is missed for the…
After decades of research, the low Curie temperature of ferromagnetic semiconductors remains the key problem in the development of magnetic semiconductor spintronic technologies. Removing this roadblock might require a change of the field's basic materials paradigm by looking beyond ferromagnets. Recent studies of relativistic magnetic and magnetotransport anisotropy effects, which in principle are equally well present in materials with ferromagnetically and antiferromagnetically ordered spins, have inspired our search for antiferromagnetic semiconductors suitable for high-temperature spintron…
Two-dimensional (2D) Janus semiconductors with mirror asymmetry can introduce novel properties, such as large spin-orbit coupling (SOC) and normal piezoelectric polarization, which have attracted a great interest for their potential applications. Inspired by the recently fabricated 2D ferromagnetic (FM) semiconductor CrI3, a stable 2D (in x-y plane) antiferromagnetic (AFM) Janus semiconductor Fe2Cl3I3 with normal sublattice magnetization (m//z) is obtained by density functional theory calculations. By applying a tensile strain, the four magnetic states sequentially occur: AFM with m//z of subl…
Towards the First Realization of Weyl Magnons in the Non-Coplanar Antiferromagnet MnTe$_2$
The Ohio State University（俄亥俄州立大学）；National Institute of Standards and Technology（美国国家标准与技术研究院）；Oak Ridge National Laboratory（橡树岭国家实验室）；Duke University（杜克大学）
Searching for novel antiferromagnetic materials with large magnetotransport response is highly demanded for constructing future spintronic devices with high stability, fast switching speed, and high density. Here we report a colossal anisotropic magnetoresistance effect in an antiferromagnetic binary compound with layered structure rare-earth dichalcogenide EuTe2. The AMR reaches 40000%, which is 4 orders of magnitude larger than that in conventional antiferromagnetic alloys. Combined magnetization, resistivity, and theoretical analysis reveal that the colossal AMR effect is attributed to a no…
Structure-property relationships have always been guiding principles in discovering new materials. Here we explore the relationships to discover novel two-dimensional (2D) materials with the goal of identifying 2D magnetic semiconductors for spintronics applications. In particular, we report a density functional theory + $U$ study of single-layer antiferromagnetic (AFM) semiconductor CoS$_2$ with the pentagonal structure forming the so-called Cairo Tessellation. We find that this single-layer magnet exhibits an indirect bandgap of 1.06 eV with light electron and hole effective masses of 0.03 a…
Motivated by the fact that septuple-atomic-layer MnBi$_2$Te$_4$ can be structurally viewed as the combination of double-atomic-layer MnTe intercalating into quintuple-atomic-layer Bi$_2$Te$_3$, we present a general approach of constructing twelve septuple-atomic-layer $α_i$- and $β_i$-$MA_2Z_4$ monolayer family (\emph{i} = 1 to 6) by intercalating MoS$_2$-type $MZ$$_2$ monolayer into InSe-type A$_2$Z$_2$ monolayer. Besides reproducing the experimentally synthesized $α_1$-MoSi$_2$N$_4$, $α_1$-WSi$_2$N$_4$ and $β_5$-MnBi$_2$Te$_4$ monolayer materials, another 66 thermodynamically and dynamically…
Evidence for Magnon-Assisted Exciton Radiation in a Layered Antiferromagnetic Semiconductor
State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University（厦门大学化学化工学院固体表面物理化学国家重点实验室）；Department of Physics, Xiamen University（厦门大学物理系）；Fujian Provincial Key Laboratory of Advanced Materials Oriented Chemical Engineering, Fujian Normal University（福建师范大学面向化学工程的先进材料福建省重点实验室）
It has been proposed that antiferromagnetic Fe adatom spins on semiconductor Cu-N surfaces can be used to store information [S. Loth {\it et al}, Science \textbf{335}, 196 (2012)]. Here, we investigate spin dynamics of such antiferromagnetic systems through Monte Carlo simulations. We find out the temperature and size laws of switching rates of Néel states and show that the Néel states can become stable enough for the information storage when the number of spins reaches to one or two dozens of the Fe spins. We also explore promising methods for manipulating the Néel states. These could help re…
We report electrical and thermal transport properties of Mn-based material BaMn$_2$Bi$_2$ with ThCr$_2$Si$_2$ structure. The resistivity of the antiferromagnetic BaMn$_2$Bi$_2$ shows a metal-semiconductor transition at $\sim 80$ K with decreasing temperature. Correspondingly, the thermopower $S$ shows a peak at the same temperature, approaching ~150 $μ$V/K. With increasing temperature $S$ decreases to about 125 $μ$V/K at the room temperature. The magnetic field enhances the peak value to 210 $μ$V/K. The Hall resistivity reveals an abrupt change of the carrier density close to the metal-semicon…
Lord Kelvin with his discovery of the anisotropic magnetoresistance (AMR) phenomenon in Ni and Fe was 70 years ahead of the formulation of relativistic quantum mechanics the effect stems from, and almost one and a half century ahead of spintronics whose first commercial applications relied on the AMR. Despite the long history and importance in magnetic sensing and memory technologies, the microscopic understanding of the AMR has struggled to go far beyond the basic notion of a relativistic magnetotransport phenomenon arising from combined effects on diffusing carriers of spin-orbit coupling an…
We provide an overview of progress on the exchange biasing of a ferromagnetic semiconductor (Ga1-xMnxAs) by proximity to an antiferromagnetic oxide layer (MnO). We present a detailed characterization study of the antiferromagnetic layer using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, transmission electron microscopy, and x-ray reflection. In addition, we describe the variation of the exchange and coercive fields with temperature and cooling field for multiple samples.
The samples of Ga doped Cr2O3 oxide have been prepared using chemical co-precipitation route. X-ray diffraction pattern and Raman spectra have confirmed rhombohedral crystal structure with space group R3-C. Magnetic measurement has indicated the dilution of antiferromagnetic (AFM) spin order in Ga doped alpha-Cr2O3 system oxide, where the AFM transition temperature of bulk alpha-Cr2O3 oxide at about 320 K has been suppressed and ferrimagnetic behavior is observed from the analysis of the temperature dependence of magnetization data below 350 K. Apart from Ga doping effect, the spin freezing (5…
Centrosymmetric antiferromagnetic semiconductors, although abundant in nature, seem less promising than ferromagnets and ferroelectrics for practical applications in semiconductor spintronics. As a matter of fact, the lack of spontaneous polarization and magnetization hinders the efficient utilization of electronic spin in these materials. Here, we propose a paradigm to harness electronic spin in centrosymmetric antiferromagnets via Zeeman spin splittings of electronic energy levels -- termed as spin Zeeman effect -- which is controlled by electric field.By symmetry analysis, we identify twent…
The contribution of bulk and surface to the electrical resistance along crystallographic \textit{b}- and \textit{c}-axes as a function of crystal thickness gives evidence for a temperature independent surface states in an antiferromagnetic narrow-gap semiconductor CrSb$_{2}$. ARPES shows a clear electron-like pocket at $Γ$-$Z$ direction which is absent in the bulk band structure. First-principles calculations also confirm the existence of metallic surface states inside the bulk gap. Whereas combined experimental probes point to enhanced surface conduction similar to topological insulators, sur…
We investigated low-frequency current fluctuations, i.e. noise, in the quasi-two-dimensional (2D) van der Waals antiferromagnetic semiconductor FePS3 with the electronic bandgap of 1.5 eV. The electrical and noise characteristics of the p-type, highly resistive, thin films of FePS3 were measured at different temperatures. The noise spectral density was of the 1/f - type over most of the examined temperature range but revealed well-defined Lorentzian bulges, and increased strongly near the Neel temperature of 118 K (f is the frequency). Intriguingly, the noise spectral density attained its mini…
A two-dimensional double-metal oxide MnCoO4 was predicted to be an intrinsic ferromagnetic semiconductor by using density functional theory. The low cleavage energy 0.36 Jm-2, which is similar to that of graphene, indicates that it can be easily exfoliated. The bulk structure has an antiferromagnetic ground state while the ferromagnetic configuration is the ground state against two antiferromagnetic and three ferrimagnetic configurations in the two-dimensional structure. The spin flip gaps for valence and conduction bands are 0.41 and 0.10 eV calculated with the HSE06 density functional, which…
We use neutron reflectometry to investigate the interlayer exchange coupling between Ga$_{0.97}$Mn$_{0.03}$As ferromagnetic semiconductor layers separated by non-magnetic Be-doped GaAs spacers. Polarized neutron reflectivity measured below the Curie temperature of Ga$_{0.97}$Mn$_{0.03}$As reveals a characteristic splitting at the wave vector corresponding to twice the multilayer period, indicating that the coupling between the ferromagnetic layers are antiferromagnetic (AFM). When the applied field is increased to above the saturation field, this AFM coupling is suppressed. This behavior is no…
Changes of the electronic structure accompanied by charge localization and a transition to an antiferromagnetic ground state were observed in the (DOEO)$_4$[HgBr$_4$]TCE organic semiconductor. Localization starts in the region of about 150 K and the antiferromagnetic state occurs below 60 K. The magnetic moment of the crystal contains contributions of antiferromagnetic inclusions (droplets), individual paramagnetic centers formed by localized holes and free charge carriers at 2 K. Two types of inclusions of 100-400 nm and 2-5 nm sizes were revealed by transmission electron microscopy. Studying…
Antiferromagnetic interlayer coupling in dilute magnetic semiconductor superlattices could result in the realisation of large magnetoresistance effects analogous to the giant magnetoresistance seen in metallic multilayer structures. In this paper we use a mean-field theory of carrier induced ferromagnetism to explore the multidimensional parameter space available in (Ga,Mn)As based superlattice systems. Based on these investigations we examine the feasibility of creating a superlattice that exhibits antiferromagnetic coupling and suggest potentially viable recipes.
The seeking of room temperature ferromagnetic semiconductors, which take advantages of both the charge and spin degrees of freedom of electrons to realize a variety of functionalities in devices integrated with electronic, optical, and magnetic storage properties, has been a long-term goal of scientists and engineers. Here, by using the spin-polarized density functional theory calculations, we predict a new series of high temperature ferromagnetic semiconductors based on the melilite-type oxysulfide Sr$_2$MnGe$_2$S$_6$O through hole (K) and electron (La) doping. Due to the lack of strong antif…
The interlayer spin correlations in the magnetic/non-magnetic semiconductor superlattices are reviewed. The experimental evidences of interlayer exchange coupling in different all-semiconductor structures, based on neutronographic and magnetic studies, are presented. A tight-binding model is used to explain interaction transfer across the non-magnetic block without the assistance of carriers in ferromagnetic EuS/PbS and antiferromagnetic EuTe/PbTe systems.
Various types of magnetism can appear in emerging quantum materials such as van der Waals layered ones. Here, we report the successful doping of manganese atoms into a post-transition metal dichalcogenide semiconductor: SnSe$_2$. We synthesized a single crystal Sn$_{1-x}$Mn$_x$Se$_{2}$ with $\textit{x}$ = 0.04 by the chemical vapor transport (CVT) method and characterized it by x-ray diffraction (XRD) and energy-dispersive x-ray spectroscopy (EDS). The magnetic properties indicated a competition between coexisting ferromagnetic and antiferromagnetic interactions, from the temperature dependenc…
Van der Waals (vdW) heterostructures have attracted great interest because of their rich material combinations.The discovery of two-dimensional magnets has provided a new platform for magnetic vdW heterointerfaces; however, research on magnetic vdW heterointerfaces has been limited to those with ferromagnetic surfaces. Here we report a magnetic vdW heterointerface using layered intralayer-antiferromagnetic MPSe3 (M=Mn, Fe) and monolayer transition metal dichalcogenides (TMDs). We found an anomalous upshift of the excitonic peak in monolayer TMDs below the antiferromagnetic transition temperatu…
