Regensburg 2016 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 36: Magnetization and Demagnetization Dynamics III

MA 36.10: Vortrag

Mittwoch, 9. März 2016, 17:30–17:45, H34

Nonlinear spin-wave excitations at low magnetic bias fields — Hans G. Bauer¹, Peter Majchrak¹, Torsten Kachel³, Christian H. Back¹, and •Georg Woltersdorf^1,2 — ¹Department of Physics, University of Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany — ²Institute of Physics, Martin Luther University Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle, Germany — ³Institut for Methods and Instrumentation in Synchrotron Radiation Research, Helmholtz-Center Berlin for Materials und Energy, Albert-Einstein-Str. 15, 12489 Berlin, Germany

We investigate experimentally and theoretically the nonlinear magnetization dynamics in magnetic films at low magnetic bias fields. In the experiments we use X-ray magnetic circular dichroism to determine the number density of excited magnons in magnetically soft NiFe thin films. Our data show that the common Suhl instability model of nonlinear ferromagnetic resonance is not adequate for the description of the nonlinear behavior in the low magnetic field limit. Here we derive a model of parametric spin-wave excitation, which correctly predicts nonlinear threshold amplitudes and decay rates at high and at low magnetic bias fields. In fact, a series of critical spin-wave modes with fast oscillations of the amplitude and phase is found, generalizing the theory of parametric spin-wave excitation to large modulation amplitudes. Our results also show that it is not required to invoke a wave vector-dependent damping parameter in the interpretation of nonlinear magnetic resonance experiments performed at low bias fields.