Orbital polarization change and magnetic enhancement in rutile MnO2-δ epitaxial films

Effectively manipulating the orbital configuration is an emerging method to design quantum functional materials with novel electronic ground states. Here, we report the realization of orbital polarization change in rutile MnO2-δ epitaxial thin films by reductive treatments such as CaH2 coating annealing and hydrogen atmosphere annealing. These treated samples show significant lattice expansion due to the generation of oxygen vacancies and incorporation of H, and the mixed valence states of Mn2+ and Mn3+ are formed with the decrease in the Mn valence state. The X-ray linear dichroism results show that the electron occupied state of Mn in the treated film samples changes from 3d3z2-r2 to 3dx2-y2, which means that the deprivation of oxygen atoms in the oxygen octahedron of MnO6 causes a change of orbital polarization. The resulting high spin state in the treated MnO2-δ films greatly enhances the magnetic properties of the films. This work not only demonstrates how the oxygen atoms in the edge-shared oxygen octahedron of rutile structures are replaced by reduction but also extends the study of orbital polarization and magnetic ground state control in oxide epitaxial films.