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.