Perpendicular magnetic anisotropy in 70 nm CoFe2O4 thin films fabricated on SiO2/Si(1 0 0) by the sol–gel method

Cobalt ferrite CoFe2O4 films were fabricated on SiO2/Si(1 0 0) by the sol–gel method. Films crystallized at/above 600 °C are stoichiometric as expected. With increase of the annealing temperature from 600 °C to 750 °C, the columnar grain size of CoFe2O4 film increases from 13 nm to 50 nm, resulting in surface roughness increasing from 0.46 nm to 2.55 nm. Magnetic hysteresis loops in both in-plane and out-of-plane directions, at different annealing temperatures, indicate that the films annealed at 750 °C exhibit obvious perpendicular magnetic anisotropy. Simultaneously, with the annealing temperature increasing from 600 °C to 750 °C, the out of plane coercivity increases from 1 kOe to 2.4 kOe and the corresponding saturation magnetization increases from 200 emu/cm3 to 283 emu/cm3. In addition, all crystallized films exhibit cluster-like structured magnetic domains.

► 70 nm CoFe2O4 films with the spinel phase are obtained by annealing at/above 600 °C. The grain size and the RMS roughness (lower than 3.00 nm for all the films) increase with the annealing temperature from 600 °C to 750 °C.
► By using the thermal stress arising from the difference in the thermal expansion coefficients of the substrate and the films, the crystallized CoFe2O4 films show perpendicular magnetic anisotropy.
► CoFe2O4 thin films prepared by sol–gel method show cluster-like magnetic domain structure with the domain length of about 150 nm.