Tunable magnetic interactions in mono-transition metal spinels MgCr2X4 (X=O,S,Se) and ACr2S4 (A=Ca,Sr,Ba)

Abstract

We investigate the electronic and magnetic properties of the spinel materials $\mathrm{Mg}{\mathrm{Cr}}_{2}{X}_{4}$ ($X$ = O, S, Se) and $A{\mathrm{Cr}}_{2}{\mathrm{S}}_{4}$ ($A$ = Ca, Sr, Ba), a special type of mono-transition metal spinel material. The magnetic properties of these materials are understood by inspecting the competition between the ${90}^{\ensuremath{\circ}}$ ferromagnetic superexchange interactions and the antiferromagnetic direct exchange interactions. We found the direct exchange interaction is extremely sensitive to the distance between the Cr ions, ${d}_{\text{Cr-Cr}}$. The overall magnetic interaction can be transformed from antiferromagnetic at short ${d}_{\text{Cr-Cr}}$ to ferromagnetic at larger ${d}_{\text{Cr-Cr}}$. Therefore, we can realize different magnetic states in the same material by controlling the ${d}_{\text{Cr-Cr}}$ with external strain. Furthermore, the ferromagnetism is strengthened as tensile strain is employed, and a strategy to improve the Curie temperature, which is essential for spintronics devices, is proposed.