Reorientation of magnetic anisotropy in epitaxial cobalt ferrite thin films

Abstract

Spin reorientation has been observed in $\mathrm{Co}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ thin single crystalline films epitaxially grown on (100) MgO substrate upon varying the film thickness. The critical thickness for such a spin-reorientation transition was estimated to be $300\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The reorientation is driven by a structural transition in the film from a tetragonal to cubic symmetry. At low thickness, the in-plane tensile stress induces a tetragonal distortion of the lattice that generates a perpendicular anisotropy, large enough to overcome the shape anisotropy and to stabilize the magnetization easy axis out of plane. However, in thicker films, the lattice relaxation toward the cubic structure of the bulk allows the shape anisotropy to force the magnetization to be in plane aligned.