Neutron diffraction study in spinel GeCoO in magnetic field

Matsuda, Masaaki; Hoshi, Takemichi*; Katori, Hiroko*; Kosaka, Masashi*; Takagi, Hidenori*

GeCoO has the spinel structure, in which the Co moments with =3/2 are located at the corners of the tetrahedron. It shows an antiferromagnetic ordering with a characteristic wave vector of =(1/2, 1/2, 1/2) below 21 K accompanied by a structural phase transition from cubic to tetragonal symmetry. This compound also exhibits a magnetic phase transition at 4 T. Magnetic field dependence of some magnetic Bragg peak intensities was measured. For example, the (1/2, 1/2, 1/2) Bragg intensity increases with increasing magnetic field up to 4 T and gradually decreases above 4 T. This characteristic field is consistent with Hc. The field dependence of the intensity probably originates from the combined effects of the redistribution of the magnetic domains and a magnetic phase transition.