Interplay Between Cation Distribution and Magnetic Properties in MgM0.5Mn1.5O4 (M = Al, Ga) and Al1.5Mn1.5O4 Spinels

Abstract

The polycrystalline samples of Al1.5Mn1.5O4, MgAl0.5Mn1.5O4 and MgGa0.5Mn1.5O4 were prepared using a standard ceramic method and characterized by X-ray diffraction and magnetic measurements. The cationic distributions were determined by the combination of the Rietveld refinement and the tabulated cation-oxygen distances in spinel compounds. The results obtained were compared with those calculated using a thermodynamic calculation according to the O’Neill model. The Al1.5Mn1.5O4 compound is characterized by its cationic distribution with a high occupancy rate of the magnetic ions Mn2+ in the A sites, in agreement with the experimental magnetic moment. This compound presents a ferrimagnetic behavior at T < 23.5 K. The MgAl0.5Mn1.5O4 and MgGa0.5Mn1.5O4 compounds have almost the same distribution of magnetic manganese cations in both A and B sites, with a weak presence of the magnetic ions Mn2+ in the A sites, justified by the refinement Rietveld, thermodynamic calculation and the hyperbolic form of the inverse magnetic susceptibility above 23.2 K. Both compounds have almost the same magnetic behavior at low temperature T < 23.2 K, typical of a spin glass. This behavior is attributed to the strong presence of diamagnetic ions on the A sites and the magnetic disorder in B sites.