Magnetic ordering of planar spins in Ge-doped CoTiO 3, a crystalline random anisotropy system

Abstract

Ge substitutions at non-magnetic Ti sites in CoTiO 3 lower the symmetry at the Co sites and hence favour certain ordering directions of Co spins. Random anisotropy effects should therefore arise without additional complexities due to magnetic dilution or structural disorder. Antiferromagnetic ordering in polycrystalline CoGe x Ti 1- x O 3 samples was examined by neutron diffraction to search for random anisotropy behaviour. In a sample with 30% Ge, diffuse magnetic scattering appeared near 38 K whose intensity grew slowly down to 30 K. A magnetic Bragg peak appeared near 31 K and grew rapidly at lower temperatures. The magnetic spectra appeared to equilibrate rapidly above 20 K but not below. These features are similar to those observed in an analogous rare-earth system, and are qualitatively consistent with theoretical predictions for planar spins in a d=3 random anisotropy system.