Strain Engineering of Magnetic Anisotropy in Epitaxial Films of Cobalt Ferrite

Abstract Perpendicular magnetic anisotropy (PMA) energy up to K u = 6.1 ± 0.8 MJm −3 is demonstrated in this study by inducing large lattice distortion exceeding 3% at room temperature in epitaxially distorted cobalt ferrite Co 0.73 Fe 2.18 O 4 (001) thin films. Although the thin film materials include no rare‐earth elements or noble metals, the observed K u is larger than that of the neodymium‐iron‐boron compounds for high‐performance permanent magnets. The large PMA is attributed to the significantly enhanced magneto‐elastic effects, which are pronounced in distorted films with epitaxial lattice structures upon introducing a distortion control layer of composition Mg 2− x Sn 1+ x O 4 . Surprisingly, the induced K u can be quantitatively explained in terms of the agreement between the local crystal field of Co 2+ and the phenomenological magneto‐elastic model, indicating that the linear response of induced K u is sufficiently valid even under lattice distortions as large as 3.2%. Controlling tetragonal lattice deformation using a non‐magnetic spinel layer for ferrites could be a promising protocol for developing materials with large magnetic anisotropies.