Regensburg 2007 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 3: Magnetic Materials I

MA 3.10: Vortrag

Montag, 26. März 2007, 12:30–12:45, H22

The antiferromagnetic ground state on 2D kagomé lattices in Y0.5Ca0.5BaCo4O7 — •Martin Valldor¹ and Werner Schweika² — ¹II. Phys. Inst., Zülpicher Str. 77, D-50937 Köln — ²Institut für Festkörperforschung, FZ Jülich, D-52425 Jülich

The compound Y0.5Ca0.5BaCo4O7 contains a net of tetrahedrally coordinated Co, similar to that in the wurtzite type structure. The transition metal sublattice forms perfect kagomé type layers and the intra-layer coupling is much stronger than any inter-layer interaction, giving low-dimensional magnetism. Frustration and an unusual spin state of the inter-layers Co cause the layers to magnetically decouple. The susceptibility measurements indicate strong antiferromagnetic coupling between spins [1], but the magnetic part of neutron diffraction data, separated through polarization, shows no long-range order down to 1.2 K [2]. The observed diffuse peak indicates an ordering tendency towards a staggered chiral ground state, a spin structure of Heisenberg spins in layers called V3xV3. This coplanar spin structure exhibits a degeneracy with local chiral disorder even at very low temperatures. Studies of this complex, highly frustrated magnetic state give clues to unique spin ordering effects close to their ground state.

[1] M.Valldor Solid State Sciences 8 (2006) 1272-1280

[2] W.Schweika, M.Valldor, P. Lemmens submitted to PRL (2006)