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Magnetismus Poster: Do., 13:00–15:30 D-P254
Magnetic short-range order in CaBaCo3AlO7 and CaBaCo3ZnO7
Yvonne Sanders 1 , Werner Schweika 1 , Martin Valldor 2 , Thomas Brückel 1
1 Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, D-52425 Jülich,
Germany – 2 IPKM, TU-Braunschweig, D-38106 Braunschweig, Germany
The new cobaltates CaBaCo3AlO7 and CaBaCo3ZnO7 have a common structure, in
which Co-ions form kagomé layers leading to high geometrical frustration among the
strongly antiferromagnetically coupled Co-spins. The different ions Al and Zn in both
compounds choose different sites; Zn prefers sites within the kagomé layers, while Al
occupies sites in between the kagomé layers.
We have performed neutron scattering experiments with polarization analysis to separate
the diffuse magnetic scattering, which shows an asymmetric peak, indicating lowdimensional
spin correlations. Despite the strong antiferromagnetic coupling between
the Co-ions, evidenced from the large negative Curie-Weiss constant, both materials
do not exhibit magnetic long-range order down to T=1.2K. The diffuse scattering is
similar to predictions for the classical Heisenberg antiferromagnet on the kagomé lattice,
which is supposed to select a ground state of staggered chirality, the so-called
√ 3x √ 3 structure. For CaBaCo3ZnO7 the non-magnetic Zn-ions cause spin dilution in
the kagomé layers, resulting in spin disorder among the Co-spins. The non-magnetic
Al-ions on the interlayer sites cause a magnetic decoupling of the kagomé layers and
prohibit 3D spin order to take place.
[1] M. Valldor, Solid State Sciences 6, 251 (2004); M. Valldor, J. Phys.: Condens.
Matter 16, 9209 (2004).