Stroboscopic XMCD-PEEM Using Synchrotron Radiation
D. Neeb, A. Krasyuk, F. Wegelin, S. A. Nepijko, H. J. Elmers,G. Schönhense
Picosecond magnetization dynamics is measured using stroboscopic photoemission electron microscopy at Synchrotron sources. We started these experiments in 2002, a typical set-up is shown in Fig.1. PEEM detects the spatial distribution of the X-ray absorption via the electron yield of secondary electrons. When the energy of circularly polarized (polarization vector P) photons is tuned to the relevant (e.g. Ni, Co or Fe-L3) absorption edge the electron yield varies with the relative orientation of magnetization M and P. Time resolved experiments are performed by stroboscopic illumination of the sample by X-ray pulses produced by electron bunches in the synchrotron ring (tFWHM about 50 ps in normal multibunch mode) with a repetition rate of 500 MHz. The AC driving current and the probe pulses are synchronized via a variable electronic delay t. The sample is thus excited and probed every 2 ns. To acquire an image we typically integrate the signal for 30 s, thus averaging over 1.5 x 1010 pump-probe cycles.
Fig. 1: Schematic set-up for strocoscopic PEEM (a), photo of FOCUS IS-PEEM (b) and photo of UHV exchangeable sample holder with high-frequency current leads (c).
Snapshots of the time evolution of the magnetization M in a permalloy ring are shown in Fig. 2. Here, a rather long field pulse acts on the magnetization, so that the behavior at the leading and the trailing edge can be observed separately.
Fig. 2: Snapshots of XMCD-PEEM images revealing the magnetization dynamics in a permalloy ring.
Funded by BMBF (03 N 6500 „Nanocentre“) and by Stiftung Rheinland-Pfalz für Innovation (project 535). The early stage of the experiment was funded via Verbundforschung Synchrotronstrahlung (BMBF 05KS1 UM1/5).
Sub-nanosecond resolution XMCD-PEEM of magnetization processes in a Permalloy ring
First results have been presented in:
Imaging sub-nanosecond processes using photoemission electron microscopy
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