Berlin 2008 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 26: Spin Dynamics / Spin -Torque II
MA 26.15: Vortrag
Donnerstag, 28. Februar 2008, 18:15–18:30, EB 301
Photo-Induced Magnetization Dynamics of FeRh Thin Films Investigated by Time-Resolved X-ray Magnetic Circular Dichroism — •Ilie Radu1,2, Christian Stamm2, Torsten Kachel2, Niko Pontius2, Paul Ramm1, Jan Thiele3, Hermann Dürr2, and Christian Back1 — 1Institut für Experimentelle Physik, Universität Regensburg — 2BESSY GmbH, Berlin — 3Hitachi GST, San Jose Research Center, USA
For close to equiatomic composition the FeRh alloy undergoes a first-order phase transition from the antiferromagnetic (AFM) to ferromagnetic (FM) state upon heating above room temperature. We trigger the magnetic phase transition by femtosecond laser excitation and study the subsequent dynamics of the Fe and Rh magnetic moments in an element specific manner using X-ray magnetic circular dichroism (XMCD) as a probing tool. For both elements we observe a gradual growth of ferromagnetic ordering that takes place on a ~200 ps time scale after optical excitation. On the other hand, once in the FM state, FeRh can be demagnetized on a few picoseconds time interval, the observed dynamics being limited by the width of the X-ray probing pulse (here ~10 ps). By comparison to the demagnetization dynamics measured on Ni under similar conditions, we retrieve the lower limit of the demagnetization process that evolves on a sub-picosecond time scale. Hence, the AFM-FM phase transition in conjunction with time-resolved XMCD allow us to study at a microscopic level the elementary processes involved in the magnetization growth, demagnetization and re-magnetization phenomena.