Magnetic anisotropy in epitaxial CoV 2 O 4 thin films under strain

Epitaxial ${\mathrm{CoV}}₂{\mathrm{O}}₄$ (CVO) thin films were fabricated on different substrates, and strain-induced magnetic anisotropy is observed in the films. The magnetic easy axis of CVO thin film under compressive strain changes from out-of-plane to in-plane $<83$ K, while under a small tensile strain, the spin direction orientates from in-plane to out-of-plane $<75$ K. It is found that, under compressive strain, above the reorientation temperature, Co-V exhibits strong antiferromagnetic interaction. Due to a significant out-of-plane anisotropy of ${\mathrm{V}}³⁺$, the total spin of CVO tends to be out-of-plane oriented. Below the reorientation temperature, the V-V interaction is prominent, leading to an itinerancy of ${\mathrm{V}}³⁺ 3d$ electrons and thereby weakening the magnetocrystalline anisotropy of the sample. Dominated by the shape anisotropy, the total spin of CVO epitaxial film changes to the in-plane orientation. When CVO film is subjected to a small tensile strain, the magnetocrystalline anisotropy is relatively weak. The change in the easy magnetization direction cannot be explained by the single-ion anisotropy of ${\mathrm{Co}}²⁺$ or ${\mathrm{V}}³⁺$ and shape anisotropy but can be understood by the strain-induced anisotropy related to the magnetostriction coefficient.