Publications by Year: 2015

Gayles J, Freimuth F, Schena T, Lani G, Mavropoulos P, Duine RA, Blügel S, Sinova J, Mokrousov Y. Dzyaloshinskii-Moriya Interaction and Hall Effects in the Skyrmion Phase of Mn1-xFexGe. PHYSICAL REVIEW LETTERS. 2015;115:036602.Abstract
We carry out density functional theory calculations which demonstrate that the electron dynamics in the Skyrmion phase of Fe-rich Mn1-xFexGe alloys is governed by Berry phase physics. We observe that the magnitude of the Dzyaloshinskii-Moriya interaction directly related to the mixed space-momentum Berry phases, changes sign and magnitude with concentration x in direct correlation with the data of Shibata et al. {[}Nat. Nanotechnol. 8, 723 (2013)]. The computed anomalous and topological Hall effects in FeGe are also in good agreement with available experiments. We further develop a simple tight-binding model able to explain these findings. Finally, we show that the adiabatic Berry phase picture is violated in the Mn-rich limit of the alloys.
Jakobsson A, Mavropoulos P, Sasioglu E, Blügel S, Lezaic M, Sanyal B, Galanakis I. First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors. PHYSICAL REVIEW B. 2015;91:174439.Abstract
Employing first-principles electronic-structure calculations in conjunction with the frozen-magnon method, we calculate exchange interactions, spin-wave dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin gapless semiconductor (SGS) compounds Mn2CoAl, Ti2MnAl, Cr2ZnSi, Ti2CoSi, and Ti2VAs. We find that their magnetic behavior is similar to the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice exchange interactions play an essential role in the formation of the magnetic ground state and in determining the Curie temperature T-c. All compounds, except Ti2CoSi, possess a ferrimagnetic ground state. Due to the finite energy gap in one spin channel, the exchange interactions decay sharply with the distance, and hence magnetism of these SGSs can be described considering only nearest-and next-nearest-neighbor exchange interactions. The calculated spin-wave dispersion curves are typical for ferrimagnets and ferromagnets. The spin-wave stiffness constants turn out to be larger than those of the elementary 3d ferromagnets. Calculated exchange parameters are used as input to determine the temperature dependence of the magnetization and Tc of the SGSs. We find that the Tc of all compounds is much above the room temperature. The calculated magnetization curve for Mn2CoAl as well as the Curie temperature are in very good agreement with available experimental data. This study is expected to pave the way for a deeper understanding of the magnetic properties of the inverse-Heusler-based SGSs and enhance the interest in these materials for application in spintronic and magnetoelectronic devices.
Kovacik R, Mavropoulos P, Blügel S. Spin transport and spin-caloric effects in (Cr,Zn) Te half-metallic nanostructures: Effect of spin disorder at elevated temperatures from first principles. PHYSICAL REVIEW B. 2015;91:014421.Abstract
An important contribution to the thermoelectric and spin-caloric transport properties in magnetic materials at elevated temperatures is the formation of a spin-disordered state due to local moment fluctuations. This effect has not been largely investigated so far. We focus on various magnetic nanostructures of CrTe in the form of thin layers or nanowires embedded in ZnTe matrix, motivated by the miniaturization of spintronics devices and by recent suggestions that magnetic nanostructures can lead to extraordinary thermoelectric effects due to quantum confinement. The electronic structure of the studied systems is calculated within the multiple scattering screened Korringa-Kohn-Rostoker Green function (KKR-GF) framework. The Monte Carlo method is used to simulate the magnetization in the temperature induced spin disorder. The transport properties are evaluated from the transmission probability obtained using the Baranger-Stone approach within the KKR-GF framework. We find qualitative and quantitative changes in the thermoelectric and spin-caloric coefficients when spin disorder is included in the calculation. Furthermore, we show that substitutional impurities in CrTe nanowires could considerably enhance the Seebeck coefficient and the thermoelectric figure of merit.