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MA: Fachverband Magnetismus

MA 43: Magnetization Dynamics III

MA 43.7: Vortrag

Donnerstag, 3. April 2014, 16:45–17:00, HSZ 401

Condensation of mixed magnon-phonon states below the bottom of the magnon spectrum — •Dmytro A. Bozhko¹, Alexander A. Serga¹, Peter Clausen¹, Vitaliy I. Vasyuchka¹, Andrii V. Chumak¹, Gennadii A. Melkov², and Burkard Hillebrands¹ — ¹Fachbereich Physik and Landesforschungszentrum OPTIMAS, TU Kaiserslautern, Germany — ²Faculty of Radiophysics, Taras Shevchenko National University of Kyiv, Ukraine

The Brillouin light scattering technique is used to measure the distribution of a parametrically driven magnon gas in frequency and wavevector spaces. The experiment is performed utilizing an in-plane magnetized 6.7 µm thick single-crystal yttrium iron garnet film. A magnetizing field is tuned to excite the parametric magnons at the ferromagnetic resonance frequency of 6.8 GHz. In the case of a quasi-uniform pumping field, we are able to detect a strong magnon density peak around the bottom of the spin waves spectrum (4.8 GHz) at the hybridization area (8·10⁴ rad/cm) between a backward volume magnetostatic wave and a transverse acoustic wave. This peak is understood as the condensation of magnon-phonon quasi-particles at a virtual energy minimum, whose frequency position is determined by magnon-phonon interaction. It is remarkable that no condensation is observed in the spatially localized pumping field: The magnon-phonon quasi-particles have a very high group velocity, and thus leave the thermalization area. Financial support by the DFG within the SFB/TR 49 is gratefully acknowledged.