Anisotropic lattice disorder and enhanced magnetic anisotropy in Fe₃O₄ films on (1 1 0) SrTiO₃

Epitaxial Fe₃O₄ films on (1 1 0)-oriented SrTiO₃ and MgAl₂O₄ were prepared to investigate the in-plane-direction dependence of the interfacial lattice disorder and its effect on the magnetic property. Transmission electron microscopy images of (1 1 0) Fe₃O₄/SrTiO₃ showed that lattice spots at the interface along the in-plane [−1 1 0] direction were quite regular, but those along the in-plane [0 0 1] direction exhibited a distinctive lattice disorder. In contrast, the (1 1 0) Fe₃O₄/MgAl₂O₄ exhibited quite regular and smooth interfaces along both in-plane directions. The (1 1 0) Fe₃O₄/SrTiO₃, which keeps structural symmetry across the interface along the in-plane [−1 1 0] direction but not across the interface along the in-plane [0 0 1] direction, exhibited improved properties: The in-plane uniaxial magnetic anisotropy was about five times larger than those in the previous reports, and the maximum magnetoresistance was about twice that of the Fe₃O₄/MgAl₂O₄. This suggests that the microscopically anisotropic lattice disorder at the interface can be used to control the uniaxial magnetic anisotropy and the magnetoresistance of a magnetic film for spintronic applications.