Blueshifted Kerr effects and enhanced reflectivity in nanocrystalline $CoFe2−xAlxO4$ thin films

The doping effects of $Al3+$ on the microstructure, magnetism, polar magneto-optical Kerr effects, and optical property of the sol-gel derived nanocrystalline $CoFe2−xAlxO4$ $(x=0–1.0)$ thin films on silicon substrate were investigated. Doping of $Al3+$ not only led to the existence of two Kerr rotation peaks at 620 and 550 nm associated with the crystal-field transition, but also aroused the blueshifting of another peak at 540 nm correlated with the intervalence charge transfer transition. On the other hand, the reflectivity of as-deposited films increased with the $Al3+$ content $x$ (except $x=0.2)$ due to the decreased light scatter and absorptivity of $Al3+$ in substitution of $Fe3+.$ Both the blueshifted Kerr effects and enhanced reflectivity in these films are of much benefit to magneto-optical recording.