Strain-Induced Magnetic Anisotropy in Epitaxial Thin Films of the Spinel CoCr$_2$O$_4$

TL;DR

This study demonstrates how strain influences magnetic anisotropy in CoCr₂O₄ thin films, showing opposite behavior to similar compounds, and uses theoretical calculations to explain the phenomena.

Contribution

It provides a detailed theoretical analysis of strain-dependent magnetic anisotropy in CoCr₂O₄, extending understanding to various Co²⁺ ion arrangements in spinels.

Findings

Compressive strain induces out-of-plane easy axis.

Tensile strain induces in-plane easy axis.

Theoretical calculations match experimental observations.

Abstract

We show that the magnetic anisotropy in spinel-structure CoCr$_2$O$_4$ thin films exhibits a strain dependence in which compressive strain induces an out-of-plane magnetic easy axis and tensile strain an in-plane easy axis, exactly opposite to the behavior reported for the related compound CoFe$_2$O$_4$. We use density functional theory calculations within the LSDA+U approximation to reproduce and explain the observed behavior. Using second-order perturbation theory, we analyse the anisotropy tensor of the Co$^{2+}$ ions in both octahedral and tetrahedral coordination, allowing us to extend our results to spinels with general arrangements of Co$^{2+}$ ions.