# Berlin 2015 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 40: Electronic Structure of Magnetism, Micromagnetism, Computational Magnetism (organized by MA)

### TT 40.5: Vortrag

### Dienstag, 17. März 2015, 10:30–10:45, H 0112

**Real-time dynamics of a classical spin exchange coupled to a Fermi sea** — •Mohammad Sayad and Michael Potthoff — I. Institut für Theoretische Physik , University of Hamburg, Germany

Using a numerical time-step propagation technique, we study the real-time dynamics of a single classical spin locally coupled via an antiferromagnetic exchange J to a system of non-interacting electrons. The dynamics is initiated by suddenly switching a local magnetic field B. In the regime of weak J and B, linear-response theory and the separation of time scales can be employed to derive the Landau-Lifshitz-Gilbert equation. We show, however, that this theory must break down and that the Gilbert damping becomes ill-defined in the case of one-dimensional systems. The reversal time of the spin is systematically calculated in the entire parameter regime. For strong J we find an incomplete relaxation on a short time scale followed by a slow drift towards saturation. Retardation effects and deviations from adiabatic spin dynamics are discussed for systems with a single and with two classical spins.