Regensburg 2010 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 26: Spin Dynamics / Spin Torque IV

MA 26.4: Vortrag

Donnerstag, 25. März 2010, 15:15–15:30, H10

Parametric resonance and the kinetics of magnons in Yttrium Iron Garnet — •Thomas Kloss, Andreas Kreisel, and Peter Kopietz — Goethe-Universität, Frankfurt, Deutschland

The time evolution of magnon gases subject to an external time-dependent microwave field is usually described within the so-called “S-theory”, which amounts to deriving self-consistent kinetic equations for the distribution function within the time-dependent Hartree-Fock approximation. For the theoretical description of the recently observed “Bose-Einstein condensation of magnons” under external microwave pumping the “S-theory” should be generalized to include the Gross-Pitaevskii equation for the time-dependent expectation value of the magnon creation and annihilation operator. We explicitly solve the resulting coupled equations within a simple approximation where only the condensed mode and its fluctuations are retained. We also re-examine the usual derivation of time-dependent effective boson models from a realistic spin model for Yttrium-Iron-Garnet films and argue that for strictly parallel pumping (where the time-dependent part of the magnetic field is parallel to its static component) the magnons should condense.