Magnetic anisotropy modulation of magnetite in Fe$_3$O$_4$/BaTiO$_3$(100) epitaxial structures

Temperature dependent magnetometry and transport measurements on epitaxial Fe3O4 films grown on BaTiO$_3$(100) single crystals by molecular beam epitaxy show a series of discontinuities that are attributed to changes in the magnetic anisotropy induced by strain in the different crystal phases of BaTiO$_3$. High resolution x-ray diffraction measurements show that the magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO$_3$ at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magnetic anisotropy is determined and compared with numerical estimates for the magnetoelastic anisotropies. In particular, the tensile strain in the Fe$_3$O$_4$ films is shown to give rise to a strong perpendicular magnetic anisotropy, as observed experimentally. These results demonstrate the possibility of using the piezoelectric response of BaTiO$_3$ to modulate the magnetic anisotropy of magnetite films.