Strain Engineering of Magnetic Anisotropy in Epitaxial Films of Cobalt Ferrite

TL;DR

This study demonstrates large perpendicular magnetic anisotropy in epitaxially distorted cobalt ferrite films, achieved through strain engineering, with potential applications in high-performance magnetic devices.

Contribution

It introduces a method to induce significant magnetic anisotropy in cobalt ferrite films via epitaxial lattice distortion and strain control layers, surpassing traditional rare-earth based magnets.

Findings

Achieved up to 6.1 MJ/m^3 PMA energy at room temperature.

Large lattice distortion (>3%) enhances magneto-elastic effects.

Quantitative agreement with phenomenological magneto-elastic model.

Abstract

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.