Effect of Co2+ion on the magnetic properties of sol–gel cobalt ferrite thin films

Abstract

The effect of Co2+ ion on the magnetic properties of the sol–gel derived cobalt ferrite thin films (400 nm thickness) was studied. Films with different solution composition ([Co2+]/[Fe3+] = 0.5–1.0) were deposited on a Si substrate from the precursor containing an aqueous solution of FeCl3·6H2O and CoCl2·6H2O. Deposited films were heat treated at different temperatures (700–1100 °C) and were characterized by X-ray diffraction using Cu Kα radiation. The films containing a nonstoichiometric α-(Fe1−xCox)2O3 phase were obtained in addition to a small amount of CoO at relatively lower temperatures. With increasing heat treatment temperature, nonstoichiometric α-(Fe1−xCox)2O3 was decomposed to stoichiometric α-Fe2O3 and the CoFe2O4 phase was intensified. Only the films obtained from the solution enriched with Co showed the single phase of CoFe2O4, though the Co to Fe content ratio analyzed by inductive coupled plasma spectroscopy (ICP) and energy dispersive X-ray spectroscopy (EDX) was nearly consistent with that of the starting solutions. The study of surface morphology of the films by using field emission scanning electron microscope (FESEM) showed that films were homogeneously distributed throughout the surface of the substrate and the grain sizes were in the range of 60 to 140 nm. Magnetic properties of the films, including the Curie temperature, were studied by using a vibrating sample magnetometer (VSM) and conversion electron Mossbauer spectroscopy (CEMS). The Curie temperature and the magnetic hyperfine fields of the films slightly decreased with increasing molar ratio of the Co2+ and Fe3+ ions while the saturation magnetization reached a maximum value with the film composition of x = 0.28.