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MA: Fachverband Magnetismus

MA 24: Spindynamics / Switching II

MA 24.5: Vortrag

Donnerstag, 29. März 2007, 11:15–11:30, H23

Critical damping of precessional magnetization dynamics in microscopic spin valve elements — •Hans-Joachim Elmers¹, Frederik Wegelin¹, Dimitri Valdaitsev¹, Alexander Krasyuk¹, Sergei Nepijko¹, Gerd Schönhense¹, Ingo Krug², and Claus M. Schneider² — ¹Institut für Physik, Johannes Gutenberg-Universität, D-55099 Mainz, Germany — ²Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany

We have studied ultrafast magnetization processes in micropatterned spin valve structures using time-resolved x-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism (XMCD-PEEM). Exciting the magnetodynamics with ultrafast field pulses of 250 ps width, we find the dynamic response of the free layer to strongly depend on the amplitude and repetition rate (0.5 - 1 GHz) of the exciting field pulses. This response can be only roughly described by a single spin model using an unexpectedly high damping constant of α=0.025, which is 2-3 times higher than reported for single ferromagnetic layers and results in a critical damping of the magnetization oscillations. A pulse repetition rate of 1 GHz leads to an oscillatory response thus limiting the available bandwidth of the sensor. Time resolved microscopy reveals that the magnetodynamics does not follow a phase coherent precessional motion. The observed deviations from the single spin model are attributed to the excitation of additional short wavelength standing spin wave modes.