High coercive cobalt ferrite Co$_{x}Fe$_(3-x)$O$_{4}$ nano-composite thin films prepared by spin-on process

Spin coating technique have been employed to synthesize Co$_{x}$Fe$_{3-x}$O$_{4}$ (0.5 $\le $ x $\le $ 1.9) nano-composite thin films of $\sim $10 nm crystalline size on sapphire, glass, and aluminum substrates. The films were annealed in various environments such as air, H$_{2}$/Ar, and vacuum. The structural properties were characterized by XRD and Raman Spectroscopy. The magnetic hysteresis measurements of the films exhibit a large coercivity H$_{C }$(15 - 17 kOe) at 5 K. Low temperature processed films demonstrate supermagnetic characteristics with H$_{C}$ = $\sim $150 Oe and reduced remanence M$_{r}$/M$_{s}=\sim $ 0.05 at 300K. These films show a spin-glass behavior with the blocking temperature T$_{B}$ $\propto $ H$^{2 }$for low fields and T$_{B} \quad \propto $ H$^{2/3}$ for high fields. High temperature processed films with various annealing conditions demonstrate H$_{C}$ as high as 1.8 kOe at 300K. Estimated magnetic anisotropy value of the films is in the range of 0.8 -- 2.4 x 10$^{6}$ erg/cm$^{3}$. Optical absorption spectra exhibit band gaps in the visible range of 1.4 -1.7 eV and in the IR range (1.0 eV and 0.7 eV). Annealing in hydrogen shows a reduction of resistivity. Further details of the structural, electrical and magnetic properties of the films will be presented.