Electronic phase diagram of oxygen-deficient SmNiO_3-δ epitaxial thin films

Epitaxial SmNiO_3-δ thin films were fabricated under various oxygen partial pressures (P_o2) on (0 0 1)-oriented LaAlO₃ substrates by using the pulsed laser deposition method. Continuous control of the metal-insulator transition temperature (T _MI) from 350 K to 85 K was achieved by varying P_o2 from 26 Pa to 0.5 Pa. The reduction of T _MI can be attributed to the straightening-out of the out-of-plane Ni-O-Ni bond angle due to the elongation of unit cell volume with decreasing P_o2. When P_o2 > 3 Pa, resistivity anomalies around 200 K are observed in the insulating phase of strained SmNiO_3-δ films, suggesting the onset of antiferromagnetic ordering of the Ni sublattices. An electronic phase diagram of the oxygen-deficient SmNiO_3-δ films has been established in this work based on the results of the transport measurements.