Possible Applications In Spintronics Research Articles

Hidden Valley Polarization, Piezoelectricity, and Dzyaloshinskii-Moriya Interactions of Janus Vanadium Dichalcogenides.

Due to the lack of inversion symmetry and the discovery of room-temperature ferromagnetism, two-dimensional semiconducting vanadium-based van der Waals transition-metal dichalcogenides (V-TMDs) are drawing attention for their possible application in spintronics and valleytronics. Here, we show the functional properties enriched by the broken inversion, out-of-plane mirror, and time-reversal symmetries of Janus H-VXY TMDs (X, Y = S, Se, Te). By first-principles calculations, we reveal the intrinsic xy easy-plane magnetism of the Janus vanadium-based TMD monolayers and systematically study their hidden valley polarization and giant magneto band structure. Their strong nearest-neighbor exchange strengths lead to near-room-temperature magnetic phase transitions. The Janus H-VXY system also exhibits piezoelectricity with nonzero e31 and e21. Interestingly, it is found that the right-handed Dzyaloshinskii-Moriya interaction has nonzero in-plane components in our Janus system, with fluctuating magnitudes determined by competence between relaxed bond-angle and atomic index of ligands.

Band splitting induced Berry flux and intrinsic anomalous Hall conductivity in the NiCoMnGa quaternary Heusler compound

The anomalous transport properties of Heusler compounds become a hotspot of research in recent years due to their unique band structure and possible application in spintronics. In this paper, we report the anomalous Hall effect in polycrystalline NiCoMnGa quaternary Heusler compound by experimental means and theoretical calculations. The experimental anomalous Hall conductivity (AHC) was found at about 256 S/cm at 10K with an intrinsic contribution of ~ 121 S/cm. The analysis of Hall data reveals the presence of both extrinsic and intrinsic contributions in AHE. Our theoretical calculations show that a pair of spin-orbit coupled band formed by the band splitting due to spin-orbit interaction (SOI) at the Fermi level produces a finite Berry flux in the system that provides the intrinsic AHC about 100 S/cm, which is in good agreement with the experiment.

Growth of \u03b1-Sn on silicon by a reversed \u03b2-Sn to \u03b1-Sn phase transformation for quantum material integration

α-Sn and SnGe alloys are attracting attention as a new family of topological quantum materials. However, bulk α-Sn is thermodynamically stable only below 13∘C. Moreover, scalable integration of α-Sn quantum materials and devices on silicon is hindered by their large lattice mismatch. Here, we grow compressively strained α-Sn doped with 2-4 at.% germanium on a native oxide layer on a silicon substrate at 300–500∘C. Growth is found to occur by a reversed β-Sn to α-Sn phase transformation without relying on epitaxy, with germanium-rich GeSn nanoclusters in the as-deposited material acting as seeds. The size of α-Sn microdots reaches up to 200 nm, which is approximately ten times larger than the upper size limit for α-Sn formation reported previously. Furthermore, the compressive strain makes it a candidate 3D topological Dirac semimetal with possible applications in spintronics. This process can be further optimized to achieve optically tunable SnGe quantum material and device integration on silicon.

Antiferromagnetic coupling in the initial stages of the MnN epitaxial growth on the CrN (0 0 1) surface

Spin polarized first principles calculations have been performed to study the structural and electronic properties, and spin coupling of the MnN deposit on the CrN (001) surface. Results indicate that Mn may transform from a paramagnetic to a ferromagnetic system, when adsorbed on a surface. Also, the first CrN layer switches from antiferromagnetic to ferromagnetic alignment. Surface formation energies show that epitaxial growth of θ-MnN on the CrN (001)-(1x1) surface is favorable for N-rich conditions and intermediate conditions. The double MnN layer exhibits an antiferromagnetic behavior, with the magnetic moments coupled parallel and alternating along c. Moreover, the exchange bias effect is manifested in the first CrN layer. The calculated projected densities of states spectra show a half metallic character in the first CrN layer. The Mn magnetic moments are in the range of 2.8–3.3 μB. This work identifies an antiferromagnetic system for possible applications in spintronics.

Strain effect on topological and thermoelectric properties of half Heusler compounds XPtS (X = Sr, Ba)

In this article, we report theoretical investigations of topological and thermoelectric (TE) properties of non-centrosymmetric half Heusler compounds XPtS (X = Sr, Ba) using first principles calculations. In addition, we also investigated the effect of static strain (up to 10%) on its topological and TE properties. Our detailed investigations show that the XPtS compounds are topological insulators (TIs) and continue as TIs up to a strain of 10%. However, the band gap becomes a maximum of 0.213 eV under a strain of 3% for SrPtS and 0.164 eV at a strain of 5% for BaPtS. TE investigations show that the figure of merit (a measure of TE performance) ZT becomes maximum (0.222) at room temperature for BaPtS under a strain of 1%. The detailed theoretical investigations of XPtS with and without strain provide a theoretical platform for experiments and its possible applications in spintronics and thermoelectricity.

Novel half-metallicity in Y-type equiatomic quaternary Heusler alloys XFeCrAl (X = Rh, Pd, and Pt)

In the present study, we performed theoretical investigations to understand the origin of the half-metallic properties of new types of equiatomic quaternary Heusler compounds XFeCrAl (X = Rh, Pd, and Pt) and their possible applications in spintronics. These compounds crystallize in the Y-type structure with the F-43m space group, where the constitutive atoms are located in their non-equivalent positions in Type-I. Furthermore, we verified the thermodynamic, chemical, mechanical, and dynamical stabilities of these alloys. The results showed that they are stable in the magnetic phase where the optimized lattice constants are X-dependent. Among the three sample alloys, PdFeCrAl was shown to be the hardest with a brittle nature, whereas the others were found to be ductile. Analyses of the energy bands and magnetic profiles indicated the 100% spin-polarized, half-metallic, ferromagnetic natures of PdFeCrAl and PtFeCrAl, with EHM values of 0.09 eV and 0.03 eV, respectively, whereas RhFeCrAl is a nearly half-metallic ferrimagnet with 91% spin-polarization and it tends to act as a half-metal under the effect of uniform pressure. Their half-metallic nature can be expected because of the wide range of uniform strain due to their high bulk moduli. Thus, they have novel characteristics with lattice constants in the ranges of 5.55–5.64 Å, 5.53–6.04 Å, and 5.55–5.99 Å for RhFeCrAl, PdFeCrAl, and PtFeCrAl, respectively. The total magnetic moments of 1.98 μB, 2.99 μB, and 3.0 μB per formula unit obtained for RhFeCrAl, PdFeCrAl, and PtFeCrAl follow the Slater–Pauling rule. The highest Curie temperature (1113 K) obtained for PtFeCrAl demonstrates its feasible applications in spintronics with a high temperature limit.

Room temperature d0 ferromagnetism, zero dielectric loss and ac-conductivity enhancement in p-type Ag-doped SnO2 compounds

d0 Ferromagnetic oxide materials have emerged as a promising material for possible application in spintronics. The recent theoretical calculation has predicted d0 ferromagnetism in Ag-doped SnO2 compounds. In this work, we have undertaken an investigation into structural, micro-structural, optical, magnetic, and electrical properties of Ag doped SnO2 compounds. Crystal structure study by the XRD pattern analysis confirms polycrystalline rutile phase with tetragonal structure. The SEM micrographs reveal the formation of uniform spherical nanoparticle morphology. The optical property study by UV/VIS spectrophotometer indicates the band-gap narrowing. A p-type conductivity was observed by Hall effect measurement and the hole concentration was found to increase with the increase in Ag doping. Ferromagnetism with Curie temperature ranging from 304 to 359 K is observed in all Ag-doped compounds, along-with a coercivity value of 240–1310 Oe, whereas un-doped SnO2 exhibited diamagnetism. The magnitude of dielectric constant and ac conductivity was observed to enhance with an increase in Ag concentration, which implies that the charge carriers' hopping is responsible for this transport. The observed ferromagnetism can be ascribed to a p–d hybridization between O and Ag ions.

Magnetic Properties of Electrospun Magnetic Nanofiber Mats after Stabilization and Carbonization.

Magnetic nanofibers are of great interest in basic research, as well as for possible applications in spintronics and neuromorphic computing. Here we report on the preparation of magnetic nanofiber mats by electrospinning polyacrylonitrile (PAN)/nanoparticle solutions, creating a network of arbitrarily oriented nanofibers with a high aspect ratio. Since PAN is a typical precursor for carbon, the magnetic nanofiber mats were stabilized and carbonized after electrospinning. The magnetic properties of nanofiber mats containing magnetite or nickel ferrite nanoparticles were found to depend on the nanoparticle diameters and the potential after-treatment, as compared with raw nanofiber mats. Micromagnetic simulations underlined the different properties of both magnetic materials. Atomic force microscopy and scanning electron microscopy images revealed nearly unchanged morphologies after stabilization without mechanical fixation, which is in strong contrast to pure PAN nanofiber mats. While carbonization at 500 °C left the morphology unaltered, as compared with the stabilized samples, stronger connections between adjacent fibers were formed during carbonization at 800 °C, which may be supportive of magnetic data transmission.

Mn-Doped Sr/Si(111)-(3 × 2) HCC Surfaces: Antiferromagnetic Semiconductors for Spintronic Applications.

Manganese and manganese silicide as promising candidates for spintronic applications have attracted great interest in recent years. Here, we adopt Sr-induced Si(111)-(3 × 2) honeycomb-chain channel (HCC) surface as a template and perform a systematical study on the structural stability and magnetic and electronic properties of Mn-doped Sr/Si(111)-(3 × 2) HCC surfaces by ab initio calculations. Our energetic and kinetic results show two robust inserting structures M6 and H4, where Mn atoms are located below the honeycomb Si chain and on the top or hollow site of the Si(111) surface. Their high structural stabilities are attributed to the doped Mn atoms that saturate all the dangling bonds of Si(111) surface. In these two structures, Mn atoms prefer antiferromagnetic coupling with the same local magnetic moment of 3 μB. Electronic band structures and band-decomposed charge density distributions reveal that these two stable surface structures have a semiconducting characteristic with a surface band gap of 0.21-0.28 eV. This work provides an antiferromagnetic system for the possible application in spintronics.

Theoretical investigation of the applicability of the Meservey–Tedrow technique to the surface states of topological insulators

The spin polarization of topological surface states is of high interest for possible applications in spintronics. At present, the only technique capable to measure the surface state spin texture is spin and angle resolved photoemission spectroscopy (SARPES). However, values reported by SARPES differed strongly. An established technique to measure the spin polarization of ferromagnetic materials is the so-called Meservey–Tedrow technique, which is based on spin dependent tunneling from a superconducting electrode to a ferromagnet. Here, we theoretically investigate how the Meservey–Tedrow technique can be adapted to topological insulators. We demonstrate that with a specific device geometry it is possible to determine the in-plane component of the spin polarization of topological surface states. More complex device geometries can access the full momentum dependence of the spin polarization. We also show that it is possible to extract the spin-flip scattering rate of surface electrons with the same devices.

Electronic and magnetic control in fully-hydrogenated boron nitride

We investigate the effects of vacancies on the electronic and magnetic properties in fully-hydrogenated boron nitride sheet by performing first-principles calculation. Our results reveal that this sheet fosters magnetic materials with finite magnetic moment under certain vacancies. This phenomenon can be explained by the charge redistribution in which the unpaired electrons in bands determine the magnitude of magnetic moment and thus the ground state of the systems. The magnetic moment can be tuned from 0 to 2 by introducing different vacancies. This picture explicitly demonstrates that the type of vacancy plays an important role in determining nonmagnetic or magnetic materials of fully-hydrogenated boron nitride sheet, indicating their functionalities and possible applications in spintronics.

Complex magnetic orders in small cobalt-benzene molecules.

Organometallic clusters based on transition metal atoms are interesting because of their possible applications in spintronics and quantum information processing. In addition to the enhanced magnetism at the nanoscale, the organic ligands may provide a natural shield against unwanted magnetic interactions with the matrices required for applications. Here we show that the organic ligands may lead to non-collinear magnetic order as well as the expected quenching of the magnetic moments. We use different density functional theory (DFT) methods to study the experimentally relevant three cobalt atoms surrounded by benzene rings (Co3Bz3). We found that the benzene rings induce a ground state with non-collinear magnetization, with the magnetic moments localized on the cobalt centers and lying on the plane formed by the three cobalt atoms. We further analyze the magnetism of such a cluster using an anisotropic Heisenberg model where the involved parameters are obtained by a comparison with the DFT results. These results may also explain the recent observation of the null magnetic moment of Co3Bz3+. Moreover, we propose an additional experimental verification based on electron paramagnetic resonance.

Preparation, Characterization, Electrical and Magnetic Properties of Mn-Doped Dilute Magnetic Semiconductors

Nanoparticle dilute magnetic semiconductors (DMS) are becoming increasingly important due to their possible applications in spintronics, an emerging field where the conduction process in the materials is a spin-based process. Nanoparticles of Mn-doped ZnO (DMS) material with general formula Zn[Formula: see text]MnxO ([Formula: see text]) were prepared by opting single stage combustion synthesis process. The samples characterized, exhibited formation of monophasic nanoparticles of the sample with average particle size ranging between 17 nm to 23 nm. The calculations of energy bandgap made from UV absorption spectra showed variation of the bandgap from 2.18 eV to 2.32 eV. The magnetic measurements (VSM) made on the samples confirmed formation of a single diamagnetic (Zn[Formula: see text]Mn[Formula: see text]) and two namely (Zn[Formula: see text]Mn[Formula: see text]) (Zn[Formula: see text]Mn[Formula: see text]) paramagnetic samples. It is interesting to see that all the three magnetic profiles exhibit hysteresis type behavior both in diamagnetic form and paramagnetic form. The resistivity of the samples was of the order of 10[Formula: see text] Ohm-cm ([Formula: see text]-cm) at lower temperatures. Temperature-dependent resistivity curves exhibited peaking behavior for all the three samples which is very interesting. Temperature-dependent thermo-power profiles give an indication of [Formula: see text]-type semiconductor behavior with significantly deep and broad minima around 100[Formula: see text] which becomes sharper for sample with higher Mn concentration.

Graphene-multiferroic interfaces for spintronics applications

Graphene and magnetoelectric multiferroics are promising materials for spintronic devices with high performance and low energy consumption. A very long spin diffusion length and high carrier mobility make graphene attractive for spintronics. The coupling between ferroelectricity and magnetism, which characterises magnetoelectrics, opens the way towards unique device architectures. In this work, we combine the features of both materials by investigating the interface between graphene and BaMnO3, a magnetoelectric multiferroic. We show that electron charge is transferred across the interface and magnetization is induced in the graphene sheet due to the strong interaction between C and Mn. Depending on the relative orientation of graphene and BaMnO3, a quasi-half-metal or a magnetic semiconductor can be obtained. A remarkably large proximity induced spin splitting of the Dirac cones (~300 meV) is achieved. We also show how doping with acceptors can make the high-mobility region of the electronic bands experimentally accessible. This suggests a series of possible applications in spintronics (e.g. spin filters, spin injectors) for hybrid organic-multiferroic materials and reveals hybrid organic-multiferroics as a new class of materials that may exhibit exotic phenomena such as the quantum anomalous Hall effect and a Rashba spin-orbit induced topological gap.

ChemInform Abstract: Boron Nitride Nanotubes for Spintronics

AbstractReview: 224 refs.

Vectorial mapping of noncollinear antiferromagnetic structure of semiconducting FeSe surface with spin-polarized scanning tunneling microscopy

Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations.

Magnon-phonon interconversion in a dynamically reconfigurable magnetic material

The ferrimagnetic insulator yttrium iron garnet (YIG) is an important material in the field of magnon spintronics, mainly because of its low magnetic losses. YIG also has very low acoustic losses, and for this reason the conversion of a state of magnetic excitation (magnons) into a state of lattice vibration (phonons), or vice versa, broadens its possible applications in spintronics. Since the magnetic parameters can be varied by some external action, the magnon-phonon interconversion can be tuned to perform a desired function. We present a quantum theory of the interaction between magnons and phonons in a ferromagnetic material subject to a dynamic variation of the applied magnetic field. It is shown that when the field gradient at the magnetoelastic crossover region is much smaller than a critical value, an initial elastic excitation can be completely converted into a magnetic excitation, or vice versa. This occurs with conservation of linear momentum and spin angular momentum, implying that phonons created by the conversion of magnons have spin angular momentum and carry spin current. It is shown further that if the system is initially in a quantum coherent state, its coherence properties are maintained regardless of the time dependence of the field.

Exchange Bias Effect Determined by Anisotropic Magnetoresistance in CoxNi1−xO/Ni0.8Fe0.2 Bilayer System

Exchange bias effect is the unidirectional anisotropy induced by the interface between ferromagnetic (FM) and antiferromagnetic (AFM) layers below the Neel temperature of antiferromagnetic materials, leading to a shift of hysteresis loop. The effect of exchange bias has been studied for many years because of its possible application in spintronics, especially in spin valves for magnetic recording and sensor devices [1]. The essentials of exchange bias effect are not fully understood yet. It is generally accepted that the uncompensated moments in the AFM layer play an important role in pinning the spins at the interface and determine the strength of exchange bias field [2]. We prepared bilayer systems composed of the FM layer Ni 0.8 Fe 0.2 and the AFM layer Co x Ni 1−x O (x = 0.3, 0.4, 0.5, and 0.6) by using the DC/RF magnetron sputtering method. Exchange bias field H EB , the shift field in hysteresis loop, was observed in all the Ni 0.8 Fe 0.2 /Co Ni 1−x O bilayer systems. The changes of H EB were explicitly studied for various parameters such as the composition of AFM material x, the measured temperature T, and the angle θ of applied magnetic field. We measured anisotropic magnetoresistance (AMR) and analyzed the AMR data to extract the H EB , since the peak structure in AMR is not exactly same to the coercive field H C , unlike the magnetization data. We propose a new approach to analysis for AMR in determining H EB and H C along the field angle θ with respect to the field-cooling direction. The results were compared with the variations of H EB and H C simulated by Mauri model and spin-glass model [3].

Cycloid manipulation by electric field inBiFeO3films: Coupling between polarization, octahedral rotation, and antiferromagnetic order

The room temperature multiferroic ${\mathrm{BiFeO}}_{3}$, by far the most studied experimentally, exhibits outstanding ferroelectric properties with a cycloidal magnetic order in the bulk and many unexpected advantages for possible applications in spintronics, sensor techniques, and photovoltaics. To consider ferroelectric and magnetic phase transitions in multiferroic ${\mathrm{BiFeO}}_{3}$ under electric field, we suggest the Ginsburg-Landau-like approach based on the symmetry and $\mathbf{P}\ensuremath{-}\ensuremath{\omega}\ensuremath{-}\mathbf{L}$ coupling, where the order parameters are: $\mathbf{P}$ is the electric polarization, $\ensuremath{\omega}$ is the axial vector of antidistorsion (describing a rotation of the oxygen octahedrons), and $\mathbf{L}$ is the antiferromagnetic vector. The theoretical model is consistent with experiment and ab initio calculations data. We give the complete set of numerical coefficients of the model and explore the behavior of $\mathbf{P}$ and $\ensuremath{\omega}$ vectors in strong electric field. The proposed approach is particularly promising for the analysis of magnetoelectric phenomena whose length scale is significantly larger than the length of the cell used in ab initio calculations. The considered cycloid problem is the clear example of such a system. Electric field-induced transformations of cycloid are exemplified on an epitaxial ${\mathrm{BiFeO}}_{3}$ film grown on the (001)-oriented substrate. We show that the jump of vectors $\mathbf{P}$ and $\ensuremath{\omega}$ in the field $E=6$ MV/m is accompanied by a jump of a cycloid spin rotation plane. This effect is of particular interest for spintronics and nanoelectronics.

Quantum dot as spin current generator and energy harvester

The thermoelectric transport in the device composed of a central nanoscopic system in contact with two electrodes and subject to the external magnetic field of Zeeman type has been studied. The device can support pure spin current in the electrodes and may serve as a source of the temperature induced spin currents with possible applications in spintronics. The system may also be used as an energy harvester. We calculate its thermodynamic efficiency η and the power output P. The maximal efficiency of the device reaches the Carnot value when the device works reversibly but with the vanishing power. The interactions between carriers diminish the maximal efficiency of the device, which under the constant load drops well below the Carnot limit but may exceed the Curzon-Ahlborn limit. While the effect of intradot Coulomb repulsion on η depends on the parameters, the interdot/interlevel interaction strongly diminishes the device efficiency.