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Magnetismus Poster: Do., 13:00–15:30 D-P245
Photons, neutrons and ions reveal epxitaxy, reversal mechanism and stoichiometry
dependence of the blocking temperature of CoO/Fe exchange
bias bilayers
Gregor Nowak 1 , Arndt Remhof 1 , Florin Radu 1 , Alexei Nefedov 1 , Hans
Werner Becker 2 , Kurt Westerholt 1 , Hartmut Zabel 1
1 Institut für Experimentalphysik/Festkörperphysik, Ruhr-Universität Bochum, Germany
– 2 Physik mit Ionenstrahlen, Ruhr-Universität Bochum, Germany
The magnetic properties of CoO/Fe blayers are strongly influenced by the stoichiometry
of the antiferromagnetic (AFM) CoO layer. We prepared stoichiometric and single
crystalline CoO-films by an annealing step in UHV and compared them to as prepared
samples. Especially the blocking temperature TB is sensitive to the oxygen concentration
as shown by SQUID magnetometry (Fig. 1). While TB of stoichiometric, epitaxial
CoO equals the Neel temperture of the bulk material, it is reduced by 40K in the superstoichiometric
case. The annealed CoO films serve as a seed layer for the growth of
epitaxial Fe films. The epitaxial relation between CoO and Fe was found to be of the
Nishiyama-Wassermann [1,2] type (Fig. 2). Polarized neutron reflectometry (PNR)
reveals the magnetic reversal mechanism. We observe a transition from domain wall
movement to domain rotation within the first hysteresis after field cooling indicated by
an strong increase of spin-flip scattering in the second half of the hysteresis loop [3].
This work was supported by the DFG via SFB 491.
[1] Z. Nishiyama, Sci. Rep. Tohoku Univ. 23, (1934) 638.
[2] G. Wassermann, Arch. Eisenhüttenwesen 126 (1933) 647.
[3] Florin Radu, Dissertation, Bochum 2005.
Fig. 1: Stochiometry dependence of the
exchange bias field.
Fig. 2: In-plane rocking scans reveal the
epitaxial relation between Fe and CoO.