Structural chemistry and magnetic properties of Y2CoGe4O12

•Co2+ and Y3+ occupy the same site in a disordered manner.•Distorted coordination geometry around Co2+ results in an unusually large effective magnetic moment.•Use of neutron diffraction and EXAFS to probe average structure and local structure, respectively.

Polycrystalline Y2CoGe4O12 has been prepared by standard ceramic methods. The crystal structure (space group P4/nbm; a=9.8465(2), c=4.92986(9) Å) consists of metal-rich layers separated from each other by Ge4O12 groups comprised of four corner-sharing GeO4 tetrahedra. Two cation sites lie within the layers; an eight-coordinate site occupied by yttrium and a six-coordinate site occupied by a 1:1 disordered distribution of yttrium and cobalt. Neutron diffraction revealed two-fold disorder on the oxide sublattice; this has been elucidated using Co K-edge EXAFS spectroscopy. The availability of two sites allows each oxide ion to accommodate the coordination preferences of its single Co/Y neighbour; the GeO4 tetrahedra distort to absorb any consequent strain. The octahedron of anions around each Co2+ cation shows a pseudo-tetragonal distortion with a strain (Co–O)eq–(Co–O)ax/(Co–O)eq=−0.173. This results in an unusually large effective magnetic moment of 6.05 µB per Co2+ cation.

Graphical abstractA distorted coordination environment leads to an unusually large effective magnetic moment of Co2+ in Y2CoGe4O12.Figure optionsDownload full-size imageDownload as PowerPoint slide