Effects of Al(3+) Substitution on Structural and Magnetic Behavior of CoFe(2)O(4) Ferrite Nanomaterials

A sol-gel autocombustion method was used to synthesize Al(3+) ion-substituted cobalt ferrite CoAl(x)Fe(2−x)O(4) (x = 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 Al(3+) ion-substituted cobalt ferrite underwent a transition from ferrimagnetic to superparamagnetic behavior; the superparamagnetic behavior was completely correlated with the increase in Al(3+) ion concentration at room temperature. All these findings were observed in Mössbauer spectra. For the cobalt ferrite CoAl(x)Fe(2−x)O(4), the coercivity and saturation magnetization decrease with an increase in aluminum content. When the annealing temperature of CoAl(0.1)Fe(1.9)O(4) was steadily increased, the coercivity and saturation magnetization initially increased and then decreased.