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 Fd (3) over barm 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. (C) 2011 Elsevier B.V. All rights reserved.