Neutron powder diffraction study on the crystal and magnetic structures of BiCoO

Belik, A. A.*; Iikubo, Satoshi; Kodama, Katsuaki   ; Igawa, Naoki   ; Shamoto, Shinichi  ; Niitaka, Seiji*; Azuma, Masaki*; Shimakawa, Yuichi*; Takano, Mikio*; Izumi, Fujio*; Muromachi, Eiji*

The crystal and magnetic structures of polycrystalline BiCoO have been determined by the Rietveldmethod from neutron diffraction data measured at temperatures from 5 to 520 K. BiCoO (space groupP4mm; Z=1; a=3.72937(7) and c=4.72382(15) at room temperature; tetragonality c/a=1.267) is isotypic with BaTiO and PbTiO in the whole temperature range. BiCoO is an insulator with a Neeltemperature of 470 K. A possible model for antiferromagnetic order is proposed with a propagationvector of k=(1/2, 1/2, 0). In this model, magnetic moments of Co ions are parallel to the c directionand align antiferromagnetically in the ab plane. The antiferromagnetic ab layers stack ferromagneticallyalong the c axis, forming a C-type antiferromagnetic structure. Refined magnetic moments at 5 and 300K are 3.24(2) and 2.93(2), respectively. The structure refinements revealed no deviation fromstoichiometry in BiCoO. BiCoO decomposed in air above 720 K to give CoO and sillenite-like BiCoO.