Spin density in frustrated magnets under mechanical stress: Mn-based antiperovskites

In this paper we present results of our calculations of the non-collinear spin density distribution in the systems with frustrated triangular magnetic structure (Mn-based antiperovskite compounds, Mn_{3}AN (A=Ga, Zn)) in the ground state and under external mechanical strain. We show that the spin density in the (111)-plane of the unit cell forms a "domain" structure around each atomic site but it has a more complex structure than the uniform distribution of the rigid spin model, i.e. Mn atoms in the (111)-plane form non-uniform "spin clouds", with the shape and size of these "domains" being function of strain. We show that both magnitude and direction of the spin density change under compressive and tensile strains, and the orientation of "spin domains" correlates with the reversal of the strain, i.e. switching compressive to tensile strain (and vice versa) results in "reversal" of the domains. We present analysis for the intra-atomic spin-exchange interaction and the way it affects the spin density distribution. In particular, we show that the spin density inside the atomic sphere in the system under mechanical stress depends on the degree of localization of electronic states

Effect of Fe substitution on structural, magnetic and electron-transport properties of half-metallic Co2TiSi

In recent years, research on magnetic materials has been one of the most technologically appealing developments in materials science. Among other applications, magnetic materials are essential components of data storage and information processing in computer hardware elements, such as hard drives and random access memories. Here, we present a theoretical study of structural, magnetic and electronic properties of ferrimagnetic Co2Ti1−xFexSi (x = 0, 0.25, 0.5), using density functional calculations. We show that the magnetic moment of Co2Ti1−xFexSi increases when Ti is substituted with Fe, consistent with experimental findings. Calculations also indicate that Co2Ti1−xFexSi remains nearly half-metallic for x ≤ 0.5. The Curie temperature is enhanced due to Fe substitution from 340 K for Co2TiSi to 780 K for Co2Ti0.5Fe0.5Si. The change in Fe concentration is also found to affect the lattice constant. The predicted large band gaps and high Curie temperatures make these materials promising for room temperature spin-based electronics

First Principles Study of Surface States and Tetragonal Distortion in Half Metals

Magnetic materials have been an increasingly popular area of research over the past decade. Half-metallic materials, in particular, are of specific interest due to their high degree of spin-polarization. One application of these materials that is of interest is spintronics. Electronics utilize the electric charge of electrons, while spintronics utilizes the spin of these electrons instead. Half-metals are very promising for this application, as they generally hold their magnetic properties up to high temperatures, and are relatively cheap compared to other metals. The following research has two goals for two different half metals. Firstly, identify the so called ‘surface properties’ of Ti2MnAl0.5Sn0.5,. Second, determine the crystal structure of Mn2PtSn

Out-of-plane electron transport in finite layer MoS2

Ballistic electron emission microscopy (BEEM) has been used to study the processes affecting electron transport along the [0001] direction of finite layer MoS2 flakes deposited onto the surface of Au/Si(001) Schottky diodes. Prominent features present in the differential spectra from the MoS2 flakes are consistent with the density of states of finite layer MoS2 calculated using density functional theory. The ability to observe the electronic structure of the MoS2 appears to be due to the relatively smooth density of states of Si in this energy range and a substantial amount of elastic or quasi-elastic scattering along the MoS2/Au/Si(001) path. Demonstration of these measurements using BEEM suggests that this technique could potentially be used to study electron transport through van der Waals heterostructures, with applications in a number of electronic devices

Electronic, Magnetic, and Structural Properties of CoMnVSb

Background Spin degree of freedom in electronic devices. Ideal candidate – room temperature half-metal. Heusler compounds attractive because of high Curie temperature Various mechanisms altering degree of spin polarization – mechanical strain, structural disorder, temperature, termination surface/interface, etc. CoMnVSb: nearly a spin gapless semiconductor

Atomic disorder induced modification of magnetization in MnCrVAl

We have investigated the physical mechanism behind magnetization reduction in a potential spingapless semiconducting compound MnCrVAl by analyzing various atomic disorder schemes. In particular, we show that depending on the degree of disorder, exchanging atomic positions between Mn/Cr and V/Al leads to reduced total magnetization due to either spin flip, or vanishing spin magnetic moments. The latter is attributed to the itinerant character of magnetism in Cr-, Mn-, and V-containing Heusler alloys, and to the frustration of antiferromagnetic exchange interactions, and is accompanied by a tetragonal distortion, but such distortion alone (i.e., in a fully ordered crystal, with no atomic disorder) is not sufficient for a transition to zero magnetization. Besides, we demonstrate that in certain disordered structures the spin polarization of MnCrVAl significantly increases, reaching the half-metallic state. Our calculations indicate that exchange of atomic positions of Mn with Cr, and V with Al has no significant effect on electronic and magnetic properties of MnCrVAl. We also show that antisite disorder does not result in significant reduction of magnetization. At the same time, some types of antisite disorder result in essentially 100% spin-polarized structures. These findings may contribute to understanding the role of atomic disorder on magnetic properties of materials with potential applications in spin-based electronics

Model of orbital populations for voltage-controlled magnetic anisotropy in transition-metal thin films

Voltage-controlled magnetic anisotropy (VCMA) is an efficient way to manipulate the magnetization states in nanomagnets and is promising for low-power spintronic applications. The underlying physical mechanism for VCMA is known to involve a change in the d orbital occupation on the transition-metal interface atoms with an applied electric field. However, a simple qualitative picture of how this occupation controls the magnetocrystalline anisotropy (MCA) and even why in certain cases the MCA has the opposite sign remains elusive. In this paper, we exploit a simple model of orbital populations to elucidate a number of features typical for the interface MCA, and the effect of the electric field on it, for 3d transition-metal thin films used in magnetic tunnel junctions. We find that in all considered cases, including the Fe(001) surface, clean Fe1−xCox (001)/MgO interface, and oxidized Fe(001)/MgO interface, the effects of alloying and the electric field enhance the MCA energy with electron depletion, which is largely explained by the occupancy of the minority-spin dxz,yz orbitals. However, the hole-doped Fe(001) exhibits an inverse VCMA in which the MCA enhancement is achieved when electrons are accumulated at the Fe (001)/MgO interface with the applied electric field. In this regime, we predict a significantly enhanced VCMA that exceeds 1 pJ/Vm. Realizing this regime experimentally may be favorable for the practical purpose of voltage-driven magnetization reversal

Model of orbital populations for voltage-controlled magnetic anisotropy in transition-metal thin films

Voltage-controlled magnetic anisotropy (VCMA) is an efficient way to manipulate the magnetization states in nanomagnets and is promising for low-power spintronic applications. The underlying physical mechanism for VCMA is known to involve a change in the d orbital occupation on the transition-metal interface atoms with an applied electric field. However, a simple qualitative picture of how this occupation controls the magnetocrystalline anisotropy (MCA) and even why in certain cases the MCA has the opposite sign remains elusive. In this paper, we exploit a simple model of orbital populations to elucidate a number of features typical for the interface MCA, and the effect of the electric field on it, for 3d transition-metal thin films used in magnetic tunnel junctions. We find that in all considered cases, including the Fe(001) surface, clean Fe1−xCox (001)/MgO interface, and oxidized Fe(001)/MgO interface, the effects of alloying and the electric field enhance the MCA energy with electron depletion, which is largely explained by the occupancy of the minority-spin dxz,yz orbitals. However, the hole-doped Fe(001) exhibits an inverse VCMA in which the MCA enhancement is achieved when electrons are accumulated at the Fe (001)/MgO interface with the applied electric field. In this regime, we predict a significantly enhanced VCMA that exceeds 1 pJ/Vm. Realizing this regime experimentally may be favorable for the practical purpose of voltage-driven magnetization reversal