Dresden 2011 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 60: Spin Structures and Magnetic Phase Transitions
MA 60.2: Vortrag
Donnerstag, 17. März 2011, 17:45–18:00, HSZ 103
Magnetic ordering and spin dynamics in the Swedenborgite CaBaCo2Fe2O7 — •Johannes Reim1, Werner Schweika1, Erik Rosén1, Martin Valldor2, and Enrico Faulhaber3 — 1IFF-4, Forschungszentrum Jülich GmbH — 2II. Phys. Institut, Universität zu Köln — 3FRM II, Garching
The Swedenborgites [1] represent a new type of highly frustrated magnets with antiferro-magnetically coupled spins on staggered kagome layers. Geometrical frustration suppresses long-range magnetic order to evolve in many compounds that we have studied so far by polarised neutron diffraction on powder samples. However, a few chemical compositions do enter a Néel state at lower temperatures [2], for example CaBaCo2Fe2O7.
By using neutron single crystal diffraction and diffuse neutron scattering we observed magnetic long-range order below 160 K exhibiting a √3 × √3 superstructure and a weak anisotropy as evidenced by polarisation analysis. Modelling a Heisenberg nearest neighbour Hamiltonian for different in- and out-of-plane coupling constants with Monte Carlo simulations we determine the phase diagram in dependence on these coupling constants. Neutron measurements of the spin dispersion exhibits unusually broad excitations indicating strongly damped spin vectors.
[1] M. Valldor, M. Andersson, Solid State Sciences 4 (2002) 923-931; [2] M. Valldor, Y. Sanders, W. Schweika, Journal of Physics: Conference Series 145, 012076 (2009)