Regensburg 2010 – scientific programme

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MA: Fachverband Magnetismus

MA 26: Spin Dynamics / Spin Torque IV

MA 26.7: Talk

Thursday, March 25, 2010, 16:00–16:15, H10

Splitting of the homogeneous mode in high power ferromagnetic resonance experiment — •Peter Majchrak¹, Georg Woltersdorf¹, Thorsten Kachel², Christian Stamm², Hermann Dürr², and Christian Back¹ — ¹Institut für Exp. und Angewandte Physik, Uni Regensburg, 93040 Regensburg — ²BESSY II, Albert-Einstein-Straße 15, 12489 Berlin, Germany

Utilizing X-ray magnetic circular dichroism (XMCD) we measured the transversal components of the precessing magnetization in a thin film under cw microwave excitation (phase locked to the X-ray pulses) in a coplanar waveguide structure. From the signal calibrated by XMCD hysteresis loops we directly evaluated the absolute values of precessing magnetization. At large microwave fields the susceptibility becomes nonlinear due to the decrease of the effective magnetization and the excitation of parametric spin waves (Suhl instability). The measured amplitude of the excursion saturates above the critical field and at the same time the resonance line of the uniform mode is splitting. The split of the line increases with growth of the pumping field and that results in an effective linewidth broadening. The measurement of both components of the complex susceptibility allows for evaluation of the phase of the two modes with respect to the exciting field and then to reconstruct their lineshapes. This way we distinguished two separate uniform precession modes, which appeared in nonlinear regime and characterized their phase and the resonance field for various microwave excitation amplitudes. Support by the BMBF (05 ES3XBA/5) is gratefully acknowledged.