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

Abstract

Polycrystalline cobalt aluminium chromium ferrites (CoAl x Cr x Fe 2−2 x O 4) 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 ( σ 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 Al–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 ( T N) decreases with increasing Al–Cr content x, which is consistent with the observed decrease in σ s with x.