| dc.description |
The spin correlations in a series of cobaltate polycrystalline samples with Swedenborgite structure, ABaCo<sub>3</sub>BO<sub>7</sub> (A Y, Ca, and B Co, Fe, Al, Zn), were studied by means of diffuse polarized neutron scattering. The alternate stacking of kagome and triangular Co layers forms a tetrahedral Co-network with geometrical frustration of antiferromagnetically (AF) coupled spins, which typically suppresses long-range order even at low temperatures (~1K) despite Curie-Weiss temperatures in the order of 1000 K. The generic diffuse magnetic scattering as found in Y<sub>0.5</sub>Ca<sub>0.5</sub>BaCo<sub>4</sub>O<sub>7</sub> reveals two dimensional (2D) spin correlations on the kagome sublattices towards the entropically favoured × structure and suggests a decoupling of layers by low spin states S 0 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 and non-vanishing spin states on the triangular sites. Geometrical frustration prohibits any 3D long-range order when the characteristic 2D spin correlations with the × motif is present. We observe long-range order only in YBaCo<sub>4</sub>O<sub>7</sub> and CaBaCo<sub>3</sub>FeO<sub>7</sub> showing rather distinct ordering wave-vectors. |
