Structural and magnetic properties of the M2Ga2Fe2O9 (M=In, Sc) oxides

We report on the structural and magnetic properties of In2Ga2Fe2O9 and Sc2Ga2Fe2O9. X-ray diffraction measurements confirmed the presence of a single orthorhombic phase, corresponding to the expected structure for M2Ga2Fe2O9 (M=In, Sc). Neutron diffraction measurements show considerable cation disorder at different lattice sites, and suggest that there is no long range magnetic ordering down to T=10 K. Temperature dependent magnetization measurements show a separation between field-cooled and zero-field-cooled curves near Tf≈19 K. Below this temperature the M(H) curves also exhibit history dependent behavior. The temperature dependent ac susceptibility shows a peak in the magnetic dissipation, with the temperature of the peak varying systematically with frequency suggesting that this feature may be associated with a glassy relaxation. Zero-field specific heat measurements down to 4 K do not reveal any long range magnetic ordering of these compounds, nor is there any transition to an ordered state under the application of a 7 T field.