Berlin 2018 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 38: Theory of strongly correlated systems

MA 38.10: Vortrag

Donnerstag, 15. März 2018, 12:15–12:30, H 0110

Comparison of different approaches to ab-initio calculations of the spin wave stiffness — •Ondřej Šipr¹, Sergey Mankovsky², and Hubert Ebert² — ¹Institute of Physics, Czech Acadademy of Sciences, Praha, Czech Republic — ²Ludwig-Maximilians-Universität München, Germany

The spin waves stiffness constant D is one of the basic quantities characterizing magnetism in solids. Ab-initio calculations of spin wave stiffness reported in the literature have been performed within the scalar relativistic approximation. Usually D is evaluated either (i) in real space as a weighted sum of exchange coupling constants or (ii) in reciprocal space by fitting the spin-wave dispersion in the long-wave limit to a parabola. Even though both approaches look conceptually simple, theoretical values of D obtained for Fe and Ni by different groups show considerable spread of 50–100 %. We present results for the spin waves stiffness constant D of Fe, Ni, and permalloy Fe_0.2Ni_0.8 obtained by explicit summation of weighted exchange coupling constants as well as by fitting the spin-wave dispersion. We demonstrate that both procedures yield similar values when properly converged and we discuss which issues are crucial in this respect (especially concerning the summation of weighted exchange coupling constants and its extrapolation to the limit of zero damping). We inspect to what extent the energies of spin spirals can be described within the magnetic force theorem. In addition, we show how the spin waves stiffness changes if spin-orbit coupling is taken into account.