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

Co-ferrite (CoFe
₂
O
₄
) 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.