The magnetization of epitaxial nanometric CoFe2O4(001) layers

We have studied the magnetic anisotropy of nanometric CoFe2O4 (CFO) thin films grown on (100)SrTiO3 (STO) substrates. It has been found that epitaxial substrate-induced compressive strain makes the normal-to-film axis harder than the in-plane directions. In agreement with some previous reports, the magnetization loops are found to display a characteristic shrinking at low fields. Detailed structural and microstructural analyses, together with a modeling of the magnetization loops, revealed that the microstructure of the films, namely, the coexistence of a continuous CFO and a distribution of pyramidal CFO huts emerging from the surface, are responsible for this peculiar feature. We argue that this behavior, which significantly impacts the magnetic properties, could be a general trend of spinel films grow on (001)STO substrates.