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.