Correlating cation distribution with the structural and magnetic properties of Co0.5Zn0.5AlxFe2–xO4 nanoferrites

Abstract

Unprecedented analysis of the impact of high-level Al3+ substitution on the structural and magnetic properties of low-coercivity Co0.5Zn0.5AlxFe2−xO4 (0.3 ≤ x ≤ 0.8) nanoferrites prepared via autocombustion method is presented. Single-phase cubic structure has been assured for all samples using XRD patterns and FTIR spectra. Due to the notable difference in the ionic radii of Fe3+ and Al3+, structural defects are created for high substitution levels, which is to be balanced by cation redistribution and/or the appearance of Fe2+ and Co3+ cations. Rietveld analysis and size-strain plots were used to explain the non-monotonic change of the lattice parameter, microstrain and crystallite size. For the as-prepared samples, the estimated size ranged from 9 to 19 nm, which was confirmed by HRTEM images. Magnetic properties were deduced from M–H loops traced at room temperature. Saturation magnetization (MS) decreased with increasing Al3+ content while coercivity (Hc) was fluctuating. Based on the experimental data of XRD, FTIR, and VSM, a cation distribution has been proposed and tightly correlated with the structural and magnetic properties. The significant reduction of the lattice parameter and coercivity for the sample with x = 0.8 upon sintering process has been explained in the light of the cation distribution.