Extrinsic and Intrinsic Contributions to the Spin Hall Effect of Alloys

A fully relativistic description of the spin-orbit induced spin Hall effect is presented that is based on Kubo’s linear response formalism. Using an appropriate operator for the spin-current density a Kubo-Středa-like equation for the spin Hall conductivity (SHC) is obtained. An implementation using the Korringa-Kohn-Rostoker band structure method in combination with the coherent potential approximation allow detailed investigations on various alloy systems. A decomposition of the SHC into intrinsic and extrinsic contributions is suggested. Accompanying calculations for the skew-scattering contribution of the SHC using the Boltzmann equation demonstrate the equivalence to the Kubo formalism in the dilute alloy regime and support the suggested decomposition scheme

Electronic transport properties of electron- and hole-doped semiconducting C1b Heusler compounds: NiTi1−xMxSn (M=Sc, V)

The substitutional series of Heusler compounds NiTi1−xMxSn (where M=Sc,V and 0<x≤0.2) were synthesized and investigated with respect to their electronic structure and transport properties. The results show the possibility to create n-type and p-type thermoelectrics within one Heusler compound. The electronic structure and transport properties were calculated by all-electron ab initio methods and compared to the measurements. Hard x-ray photoelectron spectroscopy was carried out and the results are compared to the calculated electronic structure. Pure NiTiSn exhibits massive “in gap” states containing about 0.1 electrons per cell. The comparison of calculations, x-ray diffraction, and photoemission reveals that Ti atoms swapped into the vacant site are responsible for these states. The carrier concentration and temperature dependence of electrical conductivity, Seebeck coefficient, and thermal conductivity were investigated in the range from 10 to 300 K. The experimentally determined electronic structure and transport measurements agree well with the calculations. The sign of the Seebeck coefficient changes from negative for V to positive for Sc substitution. The high n-type and low p-type power factors are explained by differences in the chemical-disorder scattering-induced electric resistivity. Major differences appear because p-type doping (Sc) creates holes in the triply degenerate valence band at Γ whereas n-type doping (V) fills electrons in the single conduction band above the indirect gap at X what is typical for all semiconducting transition-metal-based Heusler compounds with C1b structure

Galvanomagnetic and thermogalvanomagnetic transport effects in ferromagnetic fcc Cox_xPd1−x_{1-x} alloys from first principles

The galvanomagnetic and thermogalvanomagnetic transport of the prototypical ferromagnetic transition-metal alloy system fcc CoxPd1−x has been investigated on the basis of Kubo's linear response formalism. The results for the full electric conductivity tensor allow discussing the spin-orbit-induced anisotropic magnetoresistance and the anomalous Hall effect. These are complemented by results for the corresponding thermogalvanomagnetic transport properties anisotropy of the Seebeck effect and anomalous Nernst effect. The relation between the respective response coefficients is discussed with the underlying electronic structure calculated relativistically within the Korringa-Kohn-Rostoker coherent potential approximation band structure method for disordered alloys

Calculating condensed matter properties using the KKR-Green's function method—recent developments and applications

The modern version of the KKR (Korringa–Kohn–Rostoker) method represents the electronic structure of a system directly and efficiently in terms of its single-particle Green's function (GF). This is in contrast to its original version and many other traditional wave-function-based all-electron band structure methods dealing with periodically ordered solids. Direct access to the GF results in several appealing features. In addition, a wide applicability of the method is achieved by employing multiple scattering theory. The basic ideas behind the resulting KKR-GF method are outlined and the different techniques to deal with the underlying multiple scattering problem are reviewed. Furthermore, various applications of the KKR-GF method are reviewed in some detail to demonstrate the remarkable flexibility of the approach. Special attention is devoted to the numerous developments of the KKR-GF method, that have been contributed in recent years by a number of work groups, in particular in the following fields: embedding schemes for atoms, clusters and surfaces, magnetic response functions and anisotropy, electronic and spin-dependent transport, dynamical mean field theory, various kinds of spectroscopies, as well as first-principles determination of model parameters

Skyrmion magnetic structure of an ordered FePt monolayer deposited on Pt(111)

The effect of the Dzyaloshinsky-Moriya interaction on the magnetic structure of an ordered FePt monolayer deposited on the Pt(111) surface has been investigated. In the ground state, the pronounced anisotropic geometry of the FePt layer with alternating Fe and Pt chains gives rise to a helimagnetic structure with a strong difference in the helicity period along the chains and perpendicular to them. In the presence of an external magnetic field, the region of stable Skyrmion magnetic structures in the B-T phase diagram has been demonstrated via Monte Carlo simulations using the parameters obtained within first-principles electronic structure calculations. The present study demonstrates clearly that the ratio of the exchange coupling parameters J/D for a deposited magnetic film—being of central importance for the formation of Skyrmions—can be manipulated by growing an overlayer of 2-dimensional compounds with the atoms carrying spontaneous magnetic moments separated by the atoms of nonmagnetic elements

Subatomic resolution force microscopy reveals internal structure and adsorption sites of small iron clusters

Clusters built from individual iron atoms adsorbed on surfaces (adatoms) were investigated by atomic force microscopy (AFM) with subatomic resolution. Single copper and iron adatoms appeared as toroidal structures and multiatom clusters as connected structures, showing each individual atom as a torus. For single adatoms, the toroidal shape of the AFM image depends on the bonding symmetry of the adatom to the underlying structure [twofold for copper on copper(110) and threefold for iron on copper(111)]. Density functional theory calculations support the experimental data. The findings correct our previous work, in which multiple minima in the AFM signal were interpreted as a reflection of the orientation of a single front atom, and suggest that dual and triple minima in the force signal are caused by dimer and trimer tips, respectively