Effects of Al3+ Substitution on Structural and Magnetic Behavior of CoFe2O4 Ferrite Nanomaterials

Abstract

A sol-gel autocombustion method was used to synthesize Al³⁺ ion-substituted cobalt ferrite CoAl<i>_x</i>Fe_2-<i>x</i>O₄ (<i>x</i> = 0⁻1.5). According to X-ray diffraction analysis (XRD), cobalt ferrite was in a single cubic phase after being calcined at 1000 °C for 3 h. Moreover, the lattice constant decreased with increase in aluminum substituents. When the sample was analyzed by Scanning Electron Microscopy (SEM), we found that uniformly sized, well-crystallized grains were distributed in the sample. Furthermore, we confirmed that Al³⁺ ion-substituted cobalt ferrite underwent a transition from ferrimagnetic to superparamagnetic behavior; the superparamagnetic behavior was completely correlated with the increase in Al³⁺ ion concentration at room temperature. All these findings were observed in Mössbauer spectra. For the cobalt ferrite CoAl<i>_x</i>Fe_2-<i>x</i>O₄, the coercivity and saturation magnetization decrease with an increase in aluminum content. When the annealing temperature of CoAl_0.1Fe_1.9O₄ was steadily increased, the coercivity and saturation magnetization initially increased and then decreased.