Dresden 2009 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
MA: Fachverband Magnetismus
MA 35: Spin-Dynamics / Spin-Torque IV
MA 35.4: Vortrag
Donnerstag, 26. März 2009, 16:00–16:15, HSZ 04
Absolute measurements of the excitation amplitude at ferromagnetic resonance — •P. Majchrak1, G. Woltersdorf1, T. Martin1, T. Kachel2, C. Stamm2, H. Dürr2, and C. H. Back1 — 1Institut für Exp. und Angewandte Physik, Uni Regensburg, 93040 Regensburg — 2BESSY, Albert-Einstein-Straße 15, 12489 Berlin
Using X-ray magnetic circular dichroism (XMCD) we directly measure the transversal components of the precessing magnetization in a thin film under cw microwave excitation (phase locked to the X-ray flashes). The real and imaginary parts of the rf-magnetic susceptibility are obtained by adjusting the phase between exciting microwave signal and the X-ray flashes to 0∘ and 90∘, respectively. Measurements at different angles between the sample plane and the X-ray beam allow to determine the in and out-of-plane rf magnetization components and thereby the ellipticity of the precession. Since the signal is calibrated by XMCD hysteresis loops the excursion angle can be evaluated. 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). We measure the precession angle and the ellipticity as function of rf power up to the nonlinear regime. XMCD also allows for an element specific and therefore layer sensitive investigation of the magnetization dynamics. Optic and acoustic modes are observed in an interlayer exchange coupled sample Co90Fe10/Ru/Ni80Fe20. From the phase difference between the precessing magnetizations of both layers the coupling energy is determined.