Structural and magnetic properties of the M 2 Ga 2 Fe 2 O 9 ( 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=10K. Temperature dependent magnetization measurements show a separation between field-cooled and zero-field-cooled curves near Tf≈19K. 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 4K 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 7T field.