Magnetic and electronic properties at the γ−Al2O3/SrTiO3 interface

The magnetic and electronic nature of the $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}/{\mathrm{SrTiO}}_{3}$ spinel/perovskite interface is explored by means of x-ray absorption spectroscopy. Polarized x-ray techniques combined with atomic multiplet calculations reveal localized magnetic moments assigned to ${\mathrm{Ti}}^{3+}$ at the interface with equivalent size for in- and out-of-plane magnetic field directions. Although magnetic fingerprints are revealed, the ${\mathrm{Ti}}^{3+}$ magnetism can be explained by a paramagnetic response at low temperature under applied magnetic fields. Modeling the x-ray linear dichroism results in a ${\mathrm{\ensuremath{\Delta}}}_{0}\ensuremath{\sim}1.9$ eV splitting between the ${t}_{2g}$ and ${e}_{g}$ states for the ${\mathrm{Ti}}^{4+}\phantom{\rule{4pt}{0ex}}3{d}^{0}$ orbitals. In addition these results indicate that the lowest energy states have the out-of-plane ${d}_{xz}/{d}_{yz}$ symmetry. The isotropic magnetic moment behavior and the lowest energy ${d}_{xz}/{d}_{yz}$ states are in contrast to the observations for the two-dimensional electron gas at the perovskite/perovskite interface of ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ that exhibits an anisotropic magnetic ${d}_{xy}$ ground state.