Cation distribution and magnetic properties of CoAlxFe2−xO4/SiO2 nanocomposites

CoAlxFe2−xO4/SiO2 (x=0.0–1.0) nanocomposites have been prepared by the sol–gel method. Cation distribution and magnetic properties are studied by X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and vibrating sample magnetometer (VSM). The morphology and size are measured by transmission electron microscope (TEM). Cation distribution obtained indicates that Al3+ besides preferring octahedral (B) sites, also have a small tendency to occupy tetragonal (A) sites. And the ratio of Al3+(B)/Al3+(A) is not a constant, but a variable with increasing Al content. Mössbauer spectra show that the samples transfer from the completely magnetic order to mixed state of superparamagnetic and magnetic order with increasing x. Otherwise, both calculated from MS and VSM values of the magnetic moment per formula unit decrease with increasing Al content, indicating a collinear ferrimagnetic structure.