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Magnetismus Vortrag: Fr., 10:20–10:40 F-V54
Antiferromagnetic coupling between the oxide layers in Fe/Fe-oxide superlattices
Thomas Diederich 1 , Sebastien Couet 1 , Ralf Röhlsberger 1
1 Hasylab am DESY, Notkestr. 85, 22607 Hamburg
We have studied the magnetic structure of multilayer systems consisting of Fe and
native Fe-oxide. The Fe layers have been produced by magnetron sputtering. Native
oxide layers on the Fe were prepared by subsequent dosage of oxygen into the chamber.
The samples have been analysed in-situ by nuclear resonant scattering (NRS) of
synchrotron radiation. Ultrathin layers of 57 Fe are used to probe the magnetic structure
of the Fe and the Fe-oxide layers with very high depth resolution. Surface oxide
layers coupled to the metallic Fe appeared to be non-magnetic at room temperature.
After deposition of another Fe layer one observes a magnetically ordered component
in the Fe-oxide layer that increases with growing thickness of the iron capping layer.
This results in a relatively high magnetization of these buried oxide layers [1]. In an
Fe/Fe-oxide superlattice we discovered an antiferromagnetic (AFM) alignment of the
oxide layers [2]. This became evident by a strong superstructure (half-order) Bragg
peak in the nuclear resonant reflectivty of a Fe/ 57 Fe-oxide multilayer. If an external
magnetic field of 1 T is applied this peak vanishes. These observations point to a pure
magnetic origin of the superstructure and hence to an antiferromagnetically ordered
spin arrangement within the lattice of the Fe-oxide layers. Quite remarkably, the coupling
angle between the metallic iron and the component in the oxide that participates
in the AFM order is about 90 ◦ . This suggests the existence of a spin-flop phase that is
stabilized by the magnetization of the metallic Fe layers. The spin-flop transition, i. e.,
a sudden reorientation of the layer moments upon application of an external field has
in fact been found. Such an antiferromagnetic coupling has so far only been observed
for multilayers consisiting of ferromagnetic layers separated by non-magnetic spacer
layers that mediated the interaction between the neighbouring ferromagnetic layers.
This is in contrast to our system where the metallic iron layers seem to mediate the
coupling between the oxide layers.
[1] G.S.D. Beach et al. Phys. Rev. Lett. 91 (2003) 267201.
[2] Th. Diederich et al., in preparation