Influence of Al3+ion concentration on the crystal structure and magnetic anisotropy of nanocrystalline spinel cobalt ferrite

Aluminium substituted cobalt ferrite nanocrystalline materials with chemical formula CoFe2−xAlxO4 (x  =0.0−0.4) have been synthesised by citrate precursor method. The crystal structure and phase purity were studied by powder X-ray diffraction (XRD). All the XRD patterns have been analysed by Rietveld refinement technique using the Fd3¯m space group. The unit cell volume, average crystallite size, effective bond lengths and lattice parameters decrease with Al3+ concentration. Magnetic hysteresis loop measurements were carried out at room temperature using a vibrating sample magnetometer over a field range of ±2 T. The saturation magnetisation, coercivity and Remanent magnetisation decrease with Al3+ concentration. The magnetic data in saturation have been analysed by employing the law of approach technique. The anisotropy constants are found to decrease with Al concentration. The saturation magnetisation, coercivity, remanent magnetisation and anisotropy constant increase with crystallite size.

► Nanocrystalline CoFe2−xAlxO4 materials have been synthesised by citrate method. ► The samples are mixed cubic-spinel structure. ► Lattice constant and unit cell volume decrease with the increasing Al3+ concentration. ► Saturation magnetization and coercivity decrease with the Al3+ concentration. ► The magnetic anisotropy constant increases with crystallite size.