Dresden 2011 – scientific programme
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MA: Fachverband Magnetismus
MA 60: Spin Structures and Magnetic Phase Transitions
MA 60.7: Talk
Thursday, March 17, 2011, 19:00–19:15, HSZ 103
Effective magnetic Hamiltonians — •Vaclav Drchal1, Josef Kudrnovsky1, and Ilja Turek2 — 1Institute of Physics, AS CR, Praha, Czech Republic — 2Institute of Physics of Materials, AS CR, Brno, Czech Republic
The effective magnetic Hamiltonian which can be used to derive magnetic structure of a solid or a nanostructure, consists of: (i) Local exchange part that describes formation of local moments on individual atoms. This part can be calculated using the fixed spin moment method. (ii) Isotropic Heisenberg Hamiltonian that describes interactions between spin moments on different atoms. It is responsible for ordering of magnetic moments. The isotropic exchange interactions are calculated from the Liechtenstein formula. (iii) Anisotropic part which includes relativistic effects and dipole-dipole interactions. These terms determine the orientation of magnetic moments with respect to crystallographic axes. The methods of statistical mechanics can be applied to the effective magnetic Hamiltonian in order to predict properties (such as the size and orientation of magnetic moments, the Curie/Néel temperature, magnon spectra, etc.) of complex magnetic systems. Simultaneous treatment of local exchange interactions and the interatomic exchange interactions makes possible to correctly describe the varying values of magnetic moments and origin of induced moments. We will show in some detail how to construct the effective magnetic Hamiltonian for 3d and 4d metals and their alloys from first principles, and the importance of anisotropic interactions for determination of the magnetic structure of magnetic monolayers on non-magnetic substrates.