Structural and magnetic properties of aluminium and chromium co-substituted cobalt ferrite

Polycrystalline cobalt aluminium chromium ferrites (CoAlxCrxFe2-2xO4) with varying Al-Cr substitution (0 < x < 0.5) have been prepared in pellet form by standard double sintering technique and studied by X-ray diffraction (XRD), magnetization and ac susceptibility measurements. The lattice constants are determined and the applicability of Vegard's law has been verified. The saturation magnetization (sigma(s)) decreases with Al-Cr content (x), indicating reduction in ferrimagnetic behaviour. The variation of the saturation magnetic moment per formula unit measured at 300 K with AI-Cr content is satisfactorily explained on the basis of Neel's colinear spin ordering model for x = 0.0-0.3. Thermal variation of low field ac susceptibility measurements from room temperature to 860 K exhibits almost normal ferrimagnetic behaviour and the Neel temperature (TN) decreases with increasing A1-Cr content x, which is consistent with the observed decrease in sigma(s) with x. (C) 2000 Elsevier Science B.V. All rights reserved.