Plenarvorträge - DPG-Tagungen

Magnetismus Montag
a local magnetic moment. The local density of the state, N(E), at the
Fermi level at impurity site and the Stoner parameter, I, play a decisive
role for the onset of a magnetic moment. Theoretical calculations show
that the Stoner criteria, N(E) ·I > 1 for the development of Fe moments
are fulfilled in the Cd host. The magnetic properties of Fe impurities in
Cd are of particular interest as theoretical calculations predict a large
magnetic moment for Fe atoms in the Cd host on the other hand there
is no experimental information available about the magnetic moment of
Fe in Cd. The aim of the present work is to clarify the magnetic properties
of nanoscale Fe atoms in a Cd. Diluted Fe in Cd can be prepared
by co-evaporation of Fe and Cd under ultra high vacuum (UHV) conditions.
Of special interest is the determination of the internal magnetic
hyperfine field which is correlated to the magnetic moment of Fe. In the
CdFe system magnetic clusters have an average size of about 5 atoms;
this means that the Fe atoms are surrounded by Cd atoms and can therefore
be treated effectively as surface atoms. Such ferromagnetic clusters
with surface properties offer a new kind of material for which detailed
theoretical and experimental investigations are desirable.
MA 6.12 Mo 18:00 H10
Remagnetization dynamics in Permalloy microparticles
observed on the nanosecond time scale. — •Andrew Kuksov 1 ,
Aleksander Krasyuk 2 , Andreas Oelsner 2 , Daniel Neeb 2 ,
Gerd Schoenhense 2 , and Claus Schneider 3 — 1 IFW, Helmholz
str.20, 01069 Dresden — 2 Universitat Mainz, Staudingerweg 7, 55128
Mainz — 3 Forschungszentrum Juelich Institut fur Festkoerperforschung,
D-52425 Juelich
We have investigated the time evolution of the magnetization distribution
in Permalloy microparticles with time-resolved X-Ray Photo Emission
Electron Microscopy. The stroboscopic pump-probe experiments
with sub-nanosecond time resolution have been carried out at the synchrotron
facilities BESSY II and ESRF using soft X-ray magnetic circular
dichroism as magnetic contrast mechanism. The particles had a thickness
of 30 nm and the following shapes with linear dimensions of 40 microm-
MA 7 Magnetische Abbildungsverfahren
eters: rings, squares and diamonds (square rotated by 45 degree). As
the static domain patterns are dominated by the shape anisotropy, the
local magnetization M has well-defined directions (parallel, antiparallel,
orthogonal, 45 degree) with respect to the external magnetic field H generated
by a current pulse through the micro stripline. Depending on the
orientation between M and H the magnetization dynamics varies significantly.
The best time resolution achieved in these measurements was in
the range of 130ps.
MA 6.13 Mo 18:15 H10
Theoretical study of magnetic and spectroscopic properties of
supported transition metal clusters — •Ján Minár 1 , H. Ebert 1 ,
V. Popescu 1 , I. Cabria 2 , R. Zeller 2 und P. H. Dederichs 2 für die
ABRA-Kollaboration — 1 Department Chemie / Physikalische Chemie,
Universität München, Butenandstr. 5-13, D-81377 München, Germany
— 2 Inst. für Festkörperforschung, Forschungszentrum Jülich, Postfach
1913, D-52425 Jülich, Germany
Magnetic clusters receive recently a lot of attention in academic but
also in technological research. On the one hand side, the interest is caused
by the fact that clusters provide a bridge between atoms and bulk
material often showing quite peculiar properties. On the other hand, the
ongoing need for miniaturizing, in particular in data storage technology,
leads to smaller and smaller functional units leading finally to small clusters.
In this work the fully relativistic spin-polarized KKR method has
been used to study the magnetic and spectroscopic properties for supported
clusters. For clusters supported on a transition metal substrate it is
shown that the magnetic properties depend on many different parameters
as substrate type, cluster size and shape and so on. This applies especially
if one considers properties that are caused by spin-orbit coupling
as the X-ray circular dichroism. In line with recent experimental findings
a very pronounced magnetic circular dichroism in X-ray absorption is
found for Co-clusters on Pt(111). The results for the MCXD spectra and
their connection with the spin, orbital and spin dipolar moments will be
discussed on the basis of the so-called sum rules.
Zeit: Montag 15:15–15:45 Raum: H22
MA 7.1 Mo 15:15 H22
Stroboscopic wide-field Kerr microscopy with ps time resolution
— •Andreas Neudert, Jeffrey McCord, Rudolf Schäfer, and
Ludwig Schultz — Leibniz-Institut für Festkörper- und Werkstoffforschung
Dresden, P.O. Box 270016, D-01171 Dresden, Germany
We have extended a standard wide-field Kerr microscope with a pulsed
solid-state laser as illumination source to investigate magnetization processes
with a temporal resolution of about 30 ps. This is achieved by stroboscopic
imaging, thus limiting the observation to repeatable processes.
The repetition frequency of the laser pulses is 23 MHz, thus limiting the
time frame of the observation to 43 ns. The spatial resolution is about
0.3 µm. Due to the good SNR ratio, integration times for the pictures
are down to 50 ms/frame. The magnetic samples are excited by using
standard pulse generators with rise-times down to 100 ps, which are directly
triggered by the pulsed laser source. First results, demonstrating
the capabilities of the experimental setup, on the vortex movement in
structured Permalloy elements will be shown. A clearly different behavior
of the motion of a vortex compared to quasistatic remagnetization
processes is observed. The vortex structure first broadens and then restores
some µm away in a new equilibrium state.
This work is funded by the DFG Schwerpunktprogramm 1133 ”Ultrafast
magnetization processes”.
MA 7.2 Mo 15:30 H22
Noise and artifact suppression for near-field magneto-optical
microscopy through improved data preprocessing and piloted
wavelet analysis — •Fabian Kiendl and Gernot Güntherodt —
II. Physikalisches Institut der RWTH Aachen, D-52056 Aachen, Germany
The extraction of information about a sample from the raw data acquired
by our magneto-optical SNOM set-up [1,2] needs to be improved.
We propose a refined pre-processing of raw data into a raw image and a
wavelet de-noising that is tailored to SNOM images.
We make the pre-processing more resilient to outliers, base it additionally
on previously unused portions of the raw data, and refine the
suppression of low-frequency noise. Image features are pronounced much
more clearly in the resulting raw image, and the previously present stripelike
artifacts are removed. To tackle high-frequency noise, we adjust the
parameters of wavelet de-noising [3,4] to a given noisy SNOM image by
de-noising a superposition of this SNOM image with a known pilot image.
Additionally, we overcome the tendency of wavelet de-noising to produce
directional artifacts.
We find that images are de-noised well enough for our recently proposed
deconvolution method [5] to further enhance them. Yet we find
de-noising not to be restricted to SNOM images.
[1] G. Eggers, PhD thesis, Aachen University, ISBN 3-89825-065-2 (1999)
[2] A. Rosenberger, PhD thesis, Aachen University (2000)
[3] F. Kiendl, G. Güntherodt, 269th WE-Heraeus seminar (2002)
[4] W. Bäni, Wavelets, ISBN 3-486-25427-8, Oldenbourg (2002)
[5] F. Kiendl, G. Güntherodt, Verh. DPG (VI) 37, 1/215 (2002)