Abstract
The structural, magnetic and electrical properties of the Al3+-substituted disordered spinel system Mg(Fe2−xAlx)O4 have been investigated by X-ray diffraction, magnetization, a.c. susceptibility and electrical resistivity measurements. The cation distribution derived from the X-ray diffractometry data was found to agree very well with the cation distribution obtained through Mossbauer spectroscopy. The variation of saturation magnetization per formula unit as a function of aluminium context, x, has been satisfactorily explained on the basis of Neel's collinear spin model and the slight discrepancy between the observed and calculated nB values can be explained in terms of a random canting model. The Neel temperatures calculated theoretically by applying molecular field theory agreed well with the experimentally determined values from thermal variation of susceptibility and electrical resistivity. An unusual metal-like thermo-electric behaviour was found for the compositions with x⩾ 0.3 which was attributed to the decrease in the Fe-Fe separation distance arising from aluminium substitution.
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