Structural and magnetic properties of CoAl0.1Fe1.9O4 thin films prepared by a sol-gel method

Thin films of At substituted cobalt ferrite layers on thermally oxidized silicon wafers were fabricated by a sot-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 CoAl0.1Fe1.9O4 powder was determined to be 390 degreesC by using thermogravimetry analysis (TGA) and differential thermal analysis (DTA). The crystal structure is found to be a single cubic spinet structure without any preferred crystallite orientation. Lattice constants monotonically decreased from 8.379 to 8.362 Angstrom with increasing annealing temperature from 400 to 800 degreesC. Increasing the annealing temperature from 300 up to 800 degreesC, the grain size increased from 80 up to 250 Angstrom. while the surface roughness was minimized at 700 degreesC to a value of 2.0 urn. Parallel and perpendicular coercivity at room temperature showed maximum value in the sample annealed at 600 degreesC and their values were 3300 and 2700 Oe, respectively. Coercivity is strongly dependent on not only annealing temperature but also surface roughness.