Switchable orbital polarization and magnetization in strained LaCoO3 films

Abstract

Strain engineering of epitaxial heterostructures offers opportunities to control the orbital degree of freedom by lifting the degeneracy of ${e}_{g}$ states. Here, we show that the orbital occupation in $\mathrm{LaCo}{\mathrm{O}}_{3}$ (LCO) films can be switched between two degenerate ${e}_{g}$ bands with epitaxial strain. The orbital polarization of nearly \ensuremath{-}100% (or 100%) is controlled by depleting occupation of the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}\phantom{\rule{4pt}{0ex}}(\mathrm{or}\phantom{\rule{0.16em}{0ex}}{d}_{3{z}^{2}\ensuremath{-}{r}^{2}})$ orbital entirely in LCO for large compressive (or moderate tensile) strain. The change of electronic configuration associated with the spin-state transition modulates the magnetization of strained LCO films. Under compressive strain, LCO films exhibit a small magnetization without long-range ferromagnetic ordering. With tensile-strain increases, the magnetization of LCO films increases and reaches the maximum value when the bonding angle (Co--O--Co) is close to ${180}^{\ensuremath{\circ}}$ and the in-plane bond length (Co--O) is unstretched. Our results highlight the role of octahedral distortion and spin-state crossover in tailoring the magnetic properties of cobaltite thin films, suggesting an attractive route to deliberately control the orbital polarization that can be tuned to maximize the functionality of oxide heterostructures.