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Spin-ordered structures of monoclinic brannerite-type CoV206 have been determined from neutron diffraction data recorded at 2 ? in applied magnetic fields of 0,2.5, and 5.0 T. Three collinear magnetic phases were observed as field increases: an antiferromagnetic state with propagation vector (0 1 ½). a ferrimagnetic (−⅓ 1 ⅓) phase, and a (0 0 0) ferromagnetic order. Co2+ moments of 4.4-5.0 µ? have a large orbital component and are aligned close to the c-axis direction in all cases. Spin-lattice coupling leads to a magnetostriction and volume expansion as field increases. The ferrimagnetic phase accounts for the previously reported 1 /3-magnetization plateau, and demonstrates that monoclinic CoV206 behaves as an accidental triangular antiferromagnetic lattice in which further frustrated orders may be accessible. [ABSTRACT FROM AUTHOR]

Abstract: A variable-temperature powder neutron diffraction study of the monoclinic brannerite-type CoV2O6 (space group C2/m, a=9.2531(2), b=3.5040(1), c=6.6201(1) Å and β=111.617(1)° at 300K) is reported. No structural transition is observed down to 4K, but a magnetostriction accompanying antiferromagnetic order at T N =15K is discovered. Antiferromagnetic order observed below T N has an a×b×2c supercell in which Co2+ moments of magnitude 4.77(4)μB at 4K lie in the ac plane and are ferromagnetically coupled within chains of edge-sharing CoO6 octahedra parallel to b. Ferromagnetic chains are coupled antiferromagnetically to neighbouring chains in the a and c directions, and a model for the interchain order in the reported 1/3 magnetization plateau region is proposed. [Copyright &y& Elsevier]