  Perpendicular magnetic anisotropy (PMA) energy up to
$K_{\mathrm{u}}=6.1\pm0.8$ MJ m$^{-3}$ is demonstrated in this study by
inducing large lattice-distortion exceeding 3% at room temperature in
epitaxially distorted cobalt ferrite Co$ _{x} $Fe$ _{3-x} $O$ _{4} $ (x = 0.72)
(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.
