Mechanical Regulation of the Magnetic Properties of Uniaxial Anisotropic Hexaferrite Thin Films

Flexible oxide thin films with uniaxial magnetocrystalline anisotropy $({K}_{u})$ not only have many applications in flexible electronics, but also provide an ideal low-crystal-symmetry material for a fundamental understanding of the competitive interplay among magnetocrystalline anisotropy, shape anisotropy, and stress anisotropy. However, an understanding of the mechanical tuning of magnetic parameters in flexible oxide films with ${K}_{u}$ has not been realized up to now. In this work, epitaxial flexible hexaferrite ${\mathrm{Ba}\mathrm{Fe}}_{12}{\mathrm{O}}_{19}$ thin films with a room temperature out-of-plane ${K}_{u}$ of 1.1 \ifmmode\times\else\texttimes\fi{} ${10}^{5}$ J/m${}^{3}$ are fabricated. The continuous and controllable tuning of magnetic parameters is found to be realizable by different bending radii of the film. The changes in magnetic parameters are symmetrical under tensile and compressive bending due to the dominance of film geometry and bending-stress directions, which are perpendicular to the easy axis of ${K}_{u}$. The micromagnetic simulations further show that the magnitude of ${K}_{u}$ plays a critical role in the mechanical tuning performance of the film, where high ${K}_{u}$ drastically reduces the role of stress anisotropy and increases the magnetic bending repeatability of the film by suppressing bending-defect-related anisotropy degradation. This work not only provides an understanding of the role of the direction and magnitude of ${K}_{u}$ in the flexible thin films, but also demonstrates that the flexible hexaferrite film is one of the best materials for mechanical tunable devices up to the millimeter-wave region.