Influence of Al3+ Ion Doping on the Microstructure and Magnetic Properties of CoFe2O4 Spinel Ferrite

In this work, Al x Co 1-x Fe 2 O 4 nanoferrites (x = 0, 0.05, 0.10, 0.15, and 0.20) were synthesized from metal nitrates using the sol-gel method.The objective of this study was to investigate how replacing cobalt ions (Co 2+ ) with non-magnetic aluminum ions (Al 3+ ) would affect the structural, morphological, and magnetic properties of this ferrite.The X-ray diffraction (XRD) results indicated that pure cubic spinel could be obtained in all samples.At the same time, the values of the crystal lattice constant and grain size varied slightly and irregularly with aluminum content.Field emission scanning electron microscopy (FESEM) images indicated a uniform distribution of grains in the undoped sample (x = 0) and that the incorporation of (Al 3+ ) led to a small increase in average grain size as well as broadened grain size distribution.The purity of the samples and successful substitution were additionally verified by energy-dispersive X-ray spectroscopy (EDX) analysis.Vibrating Sample Magnetometry (VSM) measurements demonstrated that the saturation magnetization and remanence decreased with increasing Al 3+ content, which was attributed to magnetic relaxation caused by substituting ferromagnetic Co 2+ ions for non-magnetic Al 3+ ions.Values of the remanent-to-saturation magnetization ratio (M r /M s ) also indicate the presence of single-domain magnetic particles.The coercive field (H c ) showed a non-monotonic dependence, increasing with the low concentrations of aluminum but decreasing weakly, and hence is an effect of the competition between internal stresses and a decrease in crystal anisotropy.This work has shown that the magnetic properties of cobalt ferrite can be modulated by substitution with aluminum.