Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 11: Magnetic Materials

MA 11.14: Vortrag

Montag, 23. März 2009, 18:45–19:00, HSZ 103

Polarized neutron scattering on geometrically frustrated magnets with Swedenborgite structure — •Martin Valldor¹, Yvonne Sanders², and Werner Schweika² — ¹II. Physikalisches Institut, Universität Köln, 50937 Köln, Germany — ²Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany

Diffuse scattering of polarized neutrons on cobaltate polycrystalline samples with Swedenborgite structure, ABaCo3BO7 (A = Y, Ca, and B = Co, Fe, Al, Zn) was used to study the change in magnetic order depending on chemical composition. The atomic structure contains alternate stacking of kagome and triangular layers of metal ions, all in tetrahedral oxygen coordination. Geometrical frustration of antiferromagnetically coupled spins should suppress long-range order even at low temperatures despite strong spin-spin coupling in the Swedenborgites. The diffuse magnetic scattering in Y0.5Ca0.5BaCo4O7 reveals two dimensional (2D) spin correlations on the kagome sublattices towards the entropically favoured V3*V3 structure and suggests a decoupling of layers on triangular sites. Co-substitution by Al and Zn yields similar diffuse magnetic scattering, however, spin dilution results in even more disordered spin liquid or spin glass states. With B = Fe or Co, differences in the magnetic scattering evolve, indicating the onset of spin correlations perpendicular to the kagome layers.