Theory of excitation and relaxation of magnetic systems in the femto-second range

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Finding and understanding the fundamental time limits for the magnetization reversal in a solid state system is currently one of the most inspiring questions in magnetism. Theoretical physics has currently no clear cut procedure or concept at hand to answer this question. Instead concepts have to be developed. We will address the physical origin of the change of the magnetization after a local excitation of a magnetic system by femto-second laser pulse. As neither the laser field nor internal Coulomb interactions are able to alter the magnetization, apparently a mechanism breaking the spin conservation is necessary. The discussion concentrates on the two most obvious candidates: the spin-orbit interaction and the spin-lattice relaxation. We want to study their influence on the magnetisation during the excitation via a time-dependent Schrödinger equation and in the period of relaxation afterwards via a Boltzmann equation for the two spin channels.