Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 30: Electron Theory

MA 30.14: Vortrag

Donnerstag, 28. Februar 2008, 18:00–18:15, H 1028

Parametrization of the adiabatic magnetic energy on the atomic level: spin-cluster expansion technique vs. Heisenberg modeling — •Reinhard Singer, Frank Dietermann, and Manfred Fähnle — Max-Planck-Institut für Metallforschung, Heisenbergstr. 3, 70569 Stuttgart

A widely adopted analytic representation of the adiabatic magnetic energy on the atomic level is the family of Heisenberg models. There the basic configurational dependence of the adiabatic magnetic energy is assumed to be a sum of pair interactions, e_i·e_j, with e_i being the unit vector of the atomic magnetic moment located at site i. The recently introduced spin-cluster expansion (SCE) [1] breaks this limitation and takes account of all possible multi-site spin clusters and of a complete set of site basis functions Y_lm(e_i) which are the spherical harmonics. Under the symmetry restrictions of the Heisenberg model, i.e., time-reversal and rotational invariance, a complete set of SCE basis functions were obtained [2] which contain the Heisenberg interactions as a subset. Practically the interaction parameters of a truncated SCE are obtained by fitting to energies calculated with the ab-initio electron theory for a set of reference configurations. We show how the SCE is constructed and how it offers a more efficient and flexible way of parametrizing the complex adiabatic magnetic energy landscape of fcc-Fe and fcc-Ni. Furthermore we present how the SCE helps to identify new magnetic groundstate candidates in fcc-Fe.

[1] R. Drautz and M. Fähnle, Phys. Rev. B 69, 104404 (2004).

[2] R. Singer and M. Fähnle, J. Math. Phys. 47, 113503 (2006).