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MA: Fachverband Magnetismus
MA 26: Spin Dynamics / Spin -Torque II
MA 26.12: Talk
Thursday, February 28, 2008, 17:30–17:45, EB 301
Ultrafast magnetization dynamics in Gd studied by time-resolved XMCD — •Marko Wietstruk1, Torsten Kachel1, Niko Pontius1, Christian Stamm1, Hermann A. Dürr1, Wolfgang Eberhardt1, Alexey Melnikov2, Uwe Bovensiepen2, Cornelius Gahl3, and Martin Weinelt2,3 — 1BESSY GmbH, Berlin — 2FU Berlin, FB Physik — 3MBI Berlin
In order to improve heat assisted magnetic recording techniques, the understanding of ultrafast magnetization processes especially the flow of energy and angular momentum is essential. The demagnetization of a thin gadolinium film has been investigated in the .1 to 100 ps regime after excitation of the 5d6s valence electrons by a 100 fs IR laser pulse.
The measurements were done at the fs-slicing facility at BESSY in low-α and slicing mode. Using circularly polarized synchrotron radiation we measured X-ray magnetic circular dichroism (XMCD) at the Gd M4,5 absorption edges, a method which provides access to the 4f spin and orbital momentum.
The measurements show that the demagnetization process is divided into two steps. First, a ’fast’ demagnetization occurs with a reduction of the sample magnetization by 20% within the first ps after excitation. This is followed by a further magnetization decrease within 100ps. While the latter time scale corroborates earlier observations [1] and is assigned to spin-lattice relaxation, the sub-ps component suggests ultrafast demagnetization via the exchange interaction between the 5d6s valence and the 4f core electrons.
[1] A. Vaterlaus et.al., Phys. Rev. Lett. 67, 3314 - 3317 (1991)