Formation of ilmenite-type single-crystalline MgTiO₃ thin films by pulsed-laser deposition

Ilmenite structure is a good playground to explore magnetism in honeycomb lattices owing to the existence of an intriguing variety of magnetism in 3d transition metal compounds. Because of the absence of magnetic ions, ilmenite-type MgTiO₃ is a promising candidate for d⁰ transparent insulators to reveal general features of TiO₆ honeycomb layers. In this study, we found an optimum growth condition to synthesize ilmenite-type single-crystalline MgTiO₃ thin films on Al₂O₃(0001) substrates by pulsed-laser deposition. By increasing oxygen pressure from roughly 10⁻⁶ to 10⁻¹ Torr, we obtained (0001)-oriented MgTiO₃ thin films with suppression of segregation of a Mg₂TiO₄ phase. On the triangular lattice of Al₂O₃, twin-domain formation is suppressed with decreasing deposition rate, resulting in the synthesis of single-crystalline MgTiO₃ thin films. The bandgap of the MgTiO₃ film was evaluated to be about 4.4 eV by optical absorption spectra, which implies d⁰ transparent insulator.