Stable metal–insulator transition in epitaxial SmNiO₃ thin films

Samarium nickelate (SmNiO₃) is a correlated oxide that exhibits a metal–insulator transition (MIT) above room temperature and is of interest for advanced electronics and optoelectronics. However, studies on SmNiO₃ thin films have been limited to date, in part due to well-known difficulties in stabilizing the Ni³⁺ valence state during growth, which are manifested in non-reproducible electrical characteristics. In this work, we show that stable epitaxial SmNiO₃ thin films can be grown by rf magnetron sputtering without extreme post-deposition annealing conditions using relatively high growth pressure (>200 mTorr). At low growth pressure, SmNiO₃ is insulating and undergoes an irreversible MIT at ∼430 K. As pressure is increased, films become metallic across a large temperature range from 100 to 420 K. At high pressure, films are insulating again but with a reversible and stable MIT at ∼400 K. Phase transition properties can be continuously tuned by control of the sputtering pressure.