Dresden 2017 – scientific programme
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MA: Fachverband Magnetismus
MA 34: Spin Dynamics and Transport: Magnonics
MA 34.10: Talk
Wednesday, March 22, 2017, 12:00–12:15, HSZ 04
Interatomic Exchange Interactions for Finite-Temperature Magnetism and Nonequilibrium Spin Dynamics — •Attila Szilva1, Marcio Costa1,2,3, Anders Bergman1, Laszlo Szunyogh4, Lars Nordström1, and Olle Eriksson1 — 1Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, SE-75120 Uppsala, Sweden — 2Instituto de Fisica, Universidade Federal Fluminense, 24210-346 Niteroi, Rio de Janeiro, Brazil — 3Department of Physics and Astronomy, University of California, Irvine, California 92697, USA — 4Department of Theoretical Physics and Condensed Matter Research Group of Hungarian Academy of Sciences, Budapest University of Technology and Economics, Budafoki ut 8., H1111 Budapest, Hungary
We derive ab inito exchange parameters for general noncollinear magnetic configurations, in terms of a multiple scattering formalism. We show that the general exchange formula has an anisotropiclike term even in the absence of spin-orbit coupling, and that this term is large, for instance, for collinear configuration in bcc Fe, whereas for fcc Ni it is quite small. We demonstrate that keeping this term leads to what one should consider a biquadratic effective spin Hamiltonian even in the case of collinear arrangement. To illustrate our results in practice, we calculate for bcc Fe magnon spectra obtained from configuration- dependent exchange parameters, where the configurations are determined by finite-temperature effects. Our theory results in the same quantitative results as the finite-temperature neutron scattering experiments.