title: Nonlinear spin-wave excitations at low magnetic bias fields.
abstract: Nonlinear magnetization dynamics is essential for the operation of numerous spintronic devices ranging from magnetic memory to spin torque microwave generators. Examples are microwave-assisted switching of magnetic structures and the generation of spin currents at low bias fields by high-amplitude ferromagnetic resonance. Here we use X-ray magnetic circular dichroism to determine the number density of excited magnons in magnetically soft Ni80Fe20 thin films. Our data show that the common model of nonlinear ferromagnetic resonance is not adequate for the description of the nonlinear behaviour 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.
authors.affiliation: Department of Physics, University of Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany.
authors.forename: Hans G
authors.initials: HG
authors.lastname: Bauer
authors.affiliation: Department of Physics, University of Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Majchrak
authors.affiliation: Institut for Methods and Instrumentation in Synchrotron Radiation Research, Helmholtz-Center Berlin for Materials und Energy, Albert-Einstein-Str. 15, 12489 Berlin, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Kachel
authors.affiliation: Department of Physics, University of Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany.
authors.forename: Christian H
authors.initials: CH
authors.lastname: Back
authors.affiliation: Department of Physics, University of Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany.|Institute of Physics, Martin Luther University Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Woltersdorf