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Magnetismus Vortrag: Fr., 10:00–10:20 F-V53
A View on Fast Magnetization Dynamics: Studies by XPEEM
C. M. Schneider 1 , M. Bolte 2 , A. Krasyuk 3 , A. Oelsner 3 , S. A. Nepijko 3 , H.-J.
Elmers 3 , G. Schönhense 3
1 IFF, FZ Jülich GmbH, D-52425 Jülich, Germany – 2 Inst. f. Ang. Physik u. Zentrum
f. Mikrostrukturforschung, Univ. Hamburg, D-20355 Hamburg, Germany – 3 Inst. f.
Physik, Univ. Mainz, Staudinger Weg 7, D-55099 Mainz, Germany
Understanding the microscopic mechanisms governing fast magnetic switching processes
is of high fundamental interest as well as of vital technological importance. A
macrospin picture often fails to adequately describe the situation in extended systems.
A detailed study of the magnetization dynamics in complex magnetic materials thus
requires a real-space mapping of the magnetization distribution in the ground state and
of its time evolution. Imaging these transient magnetization distributions on a subnanosecond
time scale is an experimental challenge, which can be successfully addressed
by time-resolved x-ray photoemission microscopy (XPEEM). XPEEM is known as an
extremely versatile tool to image static domain patterns, combining element selectivity
with strong magnetic contrast and high lateral resolution. The choice of different magnetic
contrast modes with circularly or linearly polarized light provides access to both
ferro- and antiferromagnetically ordered structures. The technique can be extended
into the sub-nanosecond time-domain by exploiting the intrinsic time structure of the
synchrotron light [1-3].
We investigated the magnetodynamic behavior of small Permalloy platelets using a
stroboscopic approach with synchronized magnetic field pulses (pump) via coplanar
waveguides. The time resolution is limited by the width of the soft x-ray pulse (probe)
and can be varied via the operation mode of the storage ring between 10 and 70
ps. Starting from well-defined Landau ground state domain patterns we observed a
variety of reversal modes and magnetodynamic phenomena, depending on the timescale
and -structure of the magnetic field pulse. For nanosecond field pulses we mainly
found coherent and incoherent rotation events [4, 5]. Incoherent magnetization rotation
occurs, if the exciting pulse field Hp points opposite to the sample magnetization
M. It is associated with sizable magnetic stray fields, proving the importance of the
magnetization torque in these fast processes. The picture changes, if we apply sub-ns
magnetic field pulses. In addition to domain wall motion and rotation events, we find
also collective excitations of the magnetization. These modes have frequencies in the
GHz regime and are determined by the shape of the platelets. Exciting the magnetic
system close to the resonance frequency of one of these modes leads to an interesting
self-trapping process of the modes [6].
[1] A. Krasyuk et al., Appl. Phys. A 76 (2003) 836. [2] J. Vogel et al., Appl. Phys.
Lett. 82 (2003) 2299. [3] S.-B. Choe et al., Science 304 (2004) 420. [4] C. M. Schneider
et al., Appl. Phys. Lett. 85 (2004) 2562. [5] G. Schönhense et al., Adv. Imaging Elec.
Phys. 142 (2006) 157. [6] A. Krasyuk et al., Phys. Rev. Lett. 95 (2005) 207201.