Stroboscopic XMCD-PEEM Using Synchrotron Radiation

D. Neeb, A. Krasyuk, F. Wegelin, S. A. Nepijko, H. J. Elmers,G. Schönhense
Johannes Gutenberg-Universität, Institut für Physik, D-55128 Mainz, Germany
C. M. Schneider
Institut für Festkörperforschung IFF-6, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany

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.


       (a)Schematic set-up

              (b)     FOCUS IS-PEEM (c)  sample holder

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
D. Neeb, A. Krasyuk, A. Oelsner, S. Nepijko, H. J. Elmers, A. Kuksov, C. M. Schneider, G. Schönhense, J. Phys.: Condens. Mat.  17 (2005) S1381.

First results have been presented in:

Imaging sub-nanosecond processes using photoemission electron microscopy
G. Schönhense, A. Oelsner, A. Krasyuk, C.M. Schneider, M. Bauer, M. Aeschlimann
in: Recent Trends in Charged Particle Optics, Brno 2002 (ISBN 80-238-8986-9), p. 87-90





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