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Magnetismus Vortrag: Fr., 09:40–10:00 F-V52
Exchange bias instability in a bi-layer with an ion beam imprinted stripe
pattern of FM/AFM interfaces
K. Theis-Bröhl 1 , B.P. Toperverg 1 , M. Wolff 1 , H. Zabel 1 , U. Rücker 2
1 Department of Physics, Ruhr-University Bochum, D-44780 Bochum – 2 Institut für
Festkörperforschung, Forschungszentrum Jülich GmbH, D-52425 Jülich
We have investigated the magnetization arrangement in an in-plane stripe pattern with
alternating exchange bias domains. The stripe pattern was produced by ion bombardment
induced magnetic patterning, which changed locally the exchange bias direction
at the ferromagnet/ antiferromagnet interface, but not the ferro- or antiferromagnetic
properties of the Co70Fe30 and Mn83Ir17 layers, respectively. For the analysis of the
magnetic domain structure evolution along the hysteresis loop we used a combination
of experimental techniques: magneto-optical Kerr effect (MOKE), Kerr microscopy,
polarized neutron reflectometry (PNR), and off-specular scattering of polarized neutrons
with polarization analysis. Instead of a perfect antiparallel alignment we found
that the magnetization in neighboring stripes is periodically canted with respect to
the stripe axis so that the net magnetization of the ferromagnetic film turns almost
perpendicular to the stripes. At the same time the projection of the magnetization
vector onto the stripe axis has a periodically alternating sign. In Fig.1 the longitudinal
MOKE hysteresis loop and in Fig. 2 specular PNR curves are displayed. In
this measurements the non-spin-flip-reflectivities are almost degenerate and the spin
asymmetry is SA≈0. The experimental observations are explained and quantitatively
described within the frame of a phenomenological model. The model defines conditions
which can be used for tailoring nano- and micro-patterned EB systems with different
types of magnetic order. We gratefully acknowledge financial support by the DFG via
SFB 491 and BMBF 03ZA6BC1.
Fig. 1: MOKE hysteresis loop (line)
and results of fits to the PNR data (symbols).
Fig. 2: PNR measurements taken in the
antiparallel state of the sample.