Regensburg 2007 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 4: Electron Theory of Magnetism

MA 4.10: Vortrag

Montag, 26. März 2007, 12:30–12:45, H23

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

The adiabatic magnetic energy on an atomic level may be represented in principle exactly within the spin-cluster expansion (SCE) [1] by contributions arising from all possible spin clusters. The basis functions for this representation thereby are constructed from a complete set of one-spin basis functions (like, e.g. spherical harmonics Y_lm(e_i)) of the unit vector e_i describing the orientation of the atomic magnetic moment at site i. The complete set of cluster basis functions is then obtained by reducing each corresponding direct product of one-spin functions according to the symmetry restrictions of the magnetic system under consideration, i.e., time-reversal and rotational invariance in the case of isotropic magnets.[2] The expansion coefficients corresponding to the cluster basis functions can be practically obtained by carefully fitting to reference configurations calculated with the ab-initio electron theory. The so constructed SCE of the magnetic energy comprises ab-initio accuracy and thus lends itself to quickly find the true magnetic ground state in complicated systems, to thermo-statistical methods like Monte-Carlo simulations, or to large scale spin dynamics simulations. First results for the SCE of fcc Fe and fcc Ni are presented.

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

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