Preparation of Cobalt Ferrite Thick Films and Their Magnetic and Electrical Properties

Hybridized sol–gel processing has been adopted to fabricate magnetic CoFe2O4 composite thick films onto Pt/Ti/SiO2/Si substrate by the spin coating technique. The process includes the chemical synthesis of CoFe2O4 sol–gel solution, the modified CoFe2O4 particles via high-energy ball milling, and the synthesis of uniform CoFe2O4 hybrid slurry. Thermogravimetric analysis/differential thermal analysis studies indicate the baking and pyrolysis temperatures of 140° and 300°C, respectively. After annealing from 550° to 700°C in air, pure CoFe2O4 spinel phase was observed above 600°C by X-ray diffraction and Raman spectra. The resulting thick films were measured to be 10 μm thick by a surface profiler and verified by a cross-sectional scanning electronic microscope. The increasing annealing temperature increases the grain size of CoFe2O4 composite thick films, confirming the increasing magnetic coercivity and saturation magnetization. Furthermore, electric measurement indicates an annealing temperature-dependent impedance relaxation behavior in the frequency range of 10 Hz–10 kHz. Above 10 kHz, impedance curves merge together; while below 10 Hz, diffusion phenomenon is observed in impedance spectroscopy. This behavior has not been reported in CoFe2O4 bulks or thin films. Further investigation of ac conductivity spectra used by “universal dynamic response” law demonstrates the ion motion nature in the composite thick films. Optimized annealing temperature of 650°C was concluded for the fabrication of CoFe2O4 composite thick films with promising electric properties.