Magnetic properties of copper ferrite aluminates

The Al-substituted disordered spinel series CuFe2-xAlxO4 (x = 0.0-1.6) has been synthesized and studied by X-ray diffraction, magnetization, ac susceptibility and Mossbauer effect measurements. The lattice constants are determined and the applicability of Vegard's law has been tested. The variation of the saturation magnetic moment per formula unit measured at 77 and 300 K with the Al content is satisfactorily explained on the basis of Neel's collinear spin ordering model for x = 0.0-1.0. The Mossbauer spectra at 300 K have been fitted with two sextets in the ferrimagnetic state corresponding to Fe3+ at the tetrahedral (A) and octahedral (B) sites for x less than or equal to 0.8. Mossbauer results confirm a collinear ferrimagnetic structure for x = 0.0-0.6 and suggest non-collinear behaviour for x greater than or equal to 0.8. The Curie temperature decreases nearly linear with increase of Al concentration from x = 0.0 to 1.2.