Exchange interactions, spin waves, and transition temperatures in itinerant magnets

Abstract

This contribution reviews an ab initio two-step procedure to determine exchange interactions, spin-wave spectra, and thermodynamic properties of itinerant magnets. In the first step, the self-consistent electronic structure of a system is calculated for a collinear spin structure at zero temperature. In the second step, parameters of an effective classical Heisenberg Hamiltonian are determined using the magnetic force theorem and the one-electron Green functions. The Heisenberg Hamiltonian and methods of statistical physics are employed in subsequent evaluation of magnon dispersion laws, spin-wave stiffness constants, and Curie/Néel temperatures. The applicability of the developed scheme is illustrated by selected properties of various systems such as transition and rare-earth metals, disordered alloys including diluted magnetic semiconductors, ultrathin films, and surfaces. A comparison to other ab initio approaches is presented as well.

Acknowledgements

We are grateful to L. Bergqvist, G. Bihlmayer, S. Blügel, G. Bouzerar, M. Divi[sbreve], P. Franek, F. Máca, O. Eriksson, M. Pajda, J. Rusz and P. Weinberger for collaboration at various stages of the project, and to P. Dederichs, B. Gyorffy, P. Levy, A. Liechtenstein, L. Sandratskii, A. Shick, L. Szunyogh and L. Udvardi for helpful discussions.

We acknowledge the financial support provided by the Academy of Sciences of the Czech Republic (A1010203, S2041105, AVOZ20410507, AVOZ10100520), the Ministry of Education of the Czech Republic (MSM0021620834), the Czech Science Foundation (202/04/0583, 202/05/2111), and the Center for Computational Materials Science in Vienna (GZ 45.547).