Epitaxial strain-mediated spin-state transitions: can we switch off magnetism?

We use first-principles density functional theory calculations to explore spin-state transitions in epitaxially strained LaCoO$_3$. While high-spin to low-spin state transitions in minerals are common in geophysics, where pressures can reach over 200~GPa, we explore whether heteroepitaxial strain can achieve similar transitions with moderate strain in thin films. LaCoO$_3$ is known to undergo a low-spin ($S$=0, t$_{2g}^6e_g^0$) to intermediate-spin ($S$=1, t$_{2g}^5e_g^1$) or high-spin ($S$=2, t$_{2g}^4e_g^2$) state transition with increasing temperature, and thus makes it a promising candidate material for strain-mediated spin transitions. Here we discuss the physics of the low-spin transition and changes in the electronic structure of LaCoO$_3$, most notably, the metal-insulator transition that accompanies the spin-state transitions with epitaxial strain. As thin film growth techniques continue to reach atomic-level precision, we suggest this is another approach for controlling magnetism in complex oxide heterostructures.