Effect of Al3+ substitution on structural, cation distribution, electrical and magnetic properties of CoFe2O4

•Rietveld refinement of CoAlxFe2−xO4 samples shows single-phase cubic spinel structure.•The cation distribution reveals that the bond lengths and edge lengths decrease with increasing Al3+ substitution.•Non-Debye-type relaxation behaviour is confirmed from the stretched exponent and Cole–Cole plots.•The alternating current (AC) conduction mechanism is dominated by small polarons.•The overall strength of magnetic interactions is found to decrease with Al3+ substitution.

We present the structural, cation distribution, electrical and magnetic studies of CoAlxFe2−xO4 (x   = 0.0, 0.2, 0.4, 0.6, 0.8) ferrites. The Rietveld-fitted X-ray diffraction (XRD) patterns confirm the formation of single-phase cubic spinel structures with Fd3¯m space group for all the samples. A comprehensive analysis of XRD-based cation distribution has been performed to see the effect of Al3+ ions substitution on various structural parameters such as site ionic radii, edge length, bond length and interionic distances. The dielectric constant and direct current (DC) conductivity decreases with increasing Al3+ substitution up to x = 0.4. However, with further increase in Al3+ substitution, both the dielectric constant and the DC conductivity increase. The presentation of dielectric data in the complex electric modulus form reveals the presence of a non-Debye-type relaxation behaviour in the considered ferrites. The power law behaviour of alternating current (AC) conductivity indicates a strong correlation among electrons in these systems. The isothermal magnetisation versus applied field curves with high-field slope and significant coercivity suggest that the studied materials are highly anisotropic with canted spin structures. The samples exhibit ferrimagnetic behaviour at 300 K and the magnetisation decreases with increasing Al3+ concentration. The as-prepared samples are promising candidates for various industrial applications.