Structural and Magnetic Properties of CoAl0.1Fe1.9O4 Thin Films Prepared by a Sol–Gel Method

Thin films of Al substituted cobalt ferrite layers on thermally oxidized silicon wafers were fabricated by a sol-gel method with various annealing temperatures. The structural and magnetic properties of the films were investigated with a X-ray diffractometer, a vibrating sample magnetometer (VSM) and atomic force microscopy (AFM). The crystallization temperature for CoAl 0.1 Fe 1.9 O 4 powder was determined to be 390 °C by using thermogravimetry analysis (TGA) and differential thermal analysis (DTA). The crystal structure is found to be a single cubic spinel structure without any preferred crystallite orientation. Lattice constants monotonically decreased from 8.379 to 8.362 A with increasing annealing temperature from 400 to 800 °C. Increasing the annealing temperature from 300 up to 800 °C, the grain size increased from 80 up to 250 A, while the surface roughness was minimized at 700 °C to a value of 2.0 nm. Parallel and perpendicular coercivity at room temperature showed maximum value in the sample annealed at 600 °C and their values were 3300 and 2700 Oe, respectively. Coercivity is strongly dependent on not only annealing temperature but also surface roughness.