Substrate Temperature Dependent Anomalous Magnetic Behavior in $\hbox {CoFe}_{2}\hbox {O}_{4}$ Thin Film

Co-ferrite (CoFe₂O₄) thin films were pulsed laser deposited on fused quartz substrate at different substrate temperatures (T_S) ranging from room temperature (RT) to 750°C in oxygen pressure of 0.16 mbar. All the deposited films were ex-situ annealed at different temperatures (T_A) between 350 and 1100°C in air for 2 h and were furnace cooled. The spontaneous magnetization (4πM_S) of the as deposited film shows an expected increase as T_S goes up, but always remains smaller than the bulk target value. For the annealed films deposited at different T_S, we observed that 4πM_S of the films deposited at lower T_S increases at a faster rate with the increase in T_A than the films deposited at higher T_S. The 4πM_S values higher than the Co-ferrite bulk value (5300G) were observed in the annealed films deposited at lower T_S . The highest value of 6550G has been observed for the RT deposited film annealed at 1000°C, which is 24% higher than the bulk value. These results are explained on the basis of grain growth and the cation distribution in the films.