Magnetic anisotropy of epitaxial cobalt ferrite thin films

We have fabricated epitaxial single crystalline cobalt ferrite (CoFe₂O₄) thin films on CoCr₂O₄ buffered SrTiO₃ and MgAl₂O₄ substrates. Structural characterization by X-ray diffraction, Rutherford backscattering spectroscopy and atomic force microscopy indicates excellent crystallinity. Magnetic anisotropy measurements in the in-plane and perpendicular directions as a function of film thickness provide strong evidence for the dominant role of strain in the magnetic anisotropy. Cobalt ferrite (1 0 0) films grown under compression have an easy [0 0 1] and hard [0 1 1] direction in the plane and [1 0 0] direction out of the plane of the film. Cobalt ferrite (1 1 0) films grown under compression give rise to an easy [0 0 1] and a hard [1 1̄ 0] directions in the plane of the film and a hard axis perpendicular to the film. Films grown under tension give rise to an easy axis perpendicular to the film. These observations are explained using magneto-elastic theory.