A. Vernes

Relativistic bandstructure of disordered magnetic alloys

Abstract The concept of the Bloch spectral function (BSF) has been extended to deal with disordered magnetic alloys with their electronic structure described using the spin polarized relativistic Korringa-Kohn-Rostoker Coherent Potential Approximation (SPR-KKR-CPA) formalism. Applications are presented for the alloy system fcc-Fe x Ni 1− x that shows a rather well defined dispersion relation and Fermi surface. Additional spin decomposition of the BSF clearly reveals the spin hybridisation due to spin-orbit coupling as well as its anisotropy in k -space.

Crystal structure, electrical properties and electronic band structure of tantalum ditelluride

Motivated by the unexpectedly strong influence of the Te atoms on the structural and bonding properties of the transition metal tellurides, we have performed a detailed study of . Experimentally, this comprises a crystal structure determination as well as electrical resistivity measurements. The former analysis leads to an accurate update of the structural data reported in the 1960s, while the latter provides evidence for the mainly electronic character of scattering processes leading to the electrical conductivity. In addition, the electronic properties of have been calculated using the TB-LMTO method. The partial density of states reflects the close connection of the Ta zigzag chains and the Te-Te network. This finding explains the charge transfer in the system in a rather simple way. The orthogonal-orbital character of the bands proved the existence of -bonds. The Fermi-surface study supports the interpretation of the experimental resistivity measurements.

Spin-orbit interaction and spontaneous galvanomagnetic effects in ferromagnetic alloys

Abstract The dependency of the isotropic residual resistivity and of the galvano-magnetic effects on the various relativistic effects has been studied for permalloy Fe 0.2 Ni 0.8 . For the isotropic resistivity the two-current model was found to break down because of the influence of the spin-orbit coupling. While the so-called scalar relativistic effects were found to have a small influence on the isotropic resistivity they are unimportant for the spontaneous magnetoresistance anisotropy and anomalous Hall resistivity. These spin-orbit induced effects turned out to vary roughly quadratically with the spin-orbit coupling strength.

The influence of spin-orbit coupling and a current dependent potential on the residual resistivity of disordered magnetic alloys

Abstract It has been shown recently, for a number of various magnetic disordered alloy systems, that the spin–orbit coupling (SOC) may have an important influence on the isotropic residual resistivity and that it is the primary source of the galvano-magnetic properties spontaneous magnetoresistance anisotropy (SMA) and anomalous Hall resistivity (AHR). Here it is demonstrated that—in contrast to many other spin–orbit induced phenomena—all these findings stem from the part of the spin–orbit coupling that gives rise to a mixing of the two spin sub-systems. In line with this result it is shown that inclusion of a current dependent potential within a calculation of the underlying electronic structure hardly affects the transport properties if the corresponding magnetic vector potential does not lead to a mixing of the spin sub-systems.

On the validity of two-current model for systems with strongly spin-dependent disorder

The resistivities of the ferromagnetic alloy systems Fe-Ni and Co-Ni were studied in detail by application of the Kubo-Greenwood formalism. The electronic structure of the randomly disordered ferromagnetic alloys was computed by use of the spin-polarized Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method. Two sets of calculations were carried out: one fully relativistic and another one based on the two-current model. The former one will judge whether the two, not directly coupled spin-subsystems, could lead to the spontaneous magnetoresistance anisotropy, as it is supposed within the two-current model. Furthermore, all the results obtained are compared with the experimental data. We found that the two-current model calculations yield spin-resolved resistivities more polarized than could be expected from the experiments. Finally they lead to a much lower total resistivity than the relativistic calculations, showing that the scattering processes between the spin-systems are of crucial importance.

Investigation of Galvano-Magnetic Properties of Transition Metal Alloy Systems Using the Kubo-Greenwood Equation

The galvano-magnetic effects, i.e. the spontaneous magnetoresistance anisotropy (SMA) and the anomalous Hall resistivity (AHR) observed in spontaneously magnetized materials are used since decades in sensor technology [1]. Although it has been pointed out more than 40 years ago that these effects are caused by spin-orbit coupling, i.e. are of intrinsic origin and not due to an external magnetic field [2], a thorough theoretical description for them could be given only very recently by Banhart and Ebert [3]. Since then detailed theoretical investigations of the residual (T = 0 K) resistivity properties of disordered FexNi1_x [3], CoxPd1_x and CoxPt1_x [4] alloys have been performed. The theoretical approach of Banhart and Ebert is based on the KuboGreenwood-formalism with the underlying electronic structure described within the Dirac-formalism for magnetic solids. This ensures that the sources of galvano-magnetic effects — spin-orbit coupling and magnetization — are accounted for on the same level. As will be shown, additional insight into the mechanism giving rise to the SMA and AHR can be obtained by model calculations for which relativistic effects are manipulated. Furthermore it is demonstrated that performing scalar and fully relativistic calculations in parallel, it is possible to check the two-current model [2, 5, 6] that has been used so far to deal with the galvano-magnetic effects in magnetic solids.