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MA: Fachverband Magnetismus

MA 30: Electron Theory

MA 30.15: Vortrag

Donnerstag, 28. Februar 2008, 18:15–18:30, H 1028

Spin-mixing in noncollinear ferromagnetic metals as basis of femtosecond magnetization dynamics — •Daniel Steiauf and Manfred Fähnle — Max-Planck-Institut für Metallforschung, Heisenbergstr. 3, 70569 Stuttgart

A simple phenomenological model for the ultrafast demagnetization of a system after laser pulse irradiation is presented. The basic ideas are very similar to those of the Elliott-Yafet mechanism. If the spinor-field wavefunctions of the electrons are mixtures of spin-up and spin-down states depending on the wave vector, the transitions between states with different wave vectors due to scattering at defects or phonons change the spin polarization of the electrons, whereby angular momentum is transferred to the lattice via spin-orbit coupling. In collinear magnetic configurations the spin-mixing arises exclusively from spin-orbit coupling and thus it is very small, requiring very many scattering events for a considerable change of the magnetic moment of the system. In noncollinear magnetic systems there is an additional and much stronger spin-mixing arising from the much larger exchange couplings. For systems like Ni which are ferromagnetic in the ground state a noncollinearity arises at nonzero temperatures due to thermal disordering. The degree of spin-mixing due to spin-orbit coupling on the one hand and due to the noncollinearity on the other hand is calculated quantitatively by the ab-initio density functional electron theory.