Manipulating the metal-to-insulator transition and magnetic properties in manganite thin films via epitaxial strain

Abstract

Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of ${\mathrm{La}}_{0.9}{\mathrm{Ba}}_{0.1}{\mathrm{MnO}}_{3}$ thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn ${e}_{g}$ orbitals can be switched from the ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital to the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital by varying the strain from compressive to tensile. The change of orbital occupancy associated with Mn $3d$-O $2p$ hybridization leads to dramatic modulation of the magnetic and electronic properties of strained ${\mathrm{La}}_{0.9}{\mathrm{Ba}}_{0.1}{\mathrm{MnO}}_{3}$ thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the ${\mathrm{La}}_{0.9}{\mathrm{Ba}}_{0.1}{\mathrm{MnO}}_{3}$ system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.