Study of the phase transitions in SmNiO3

SmNiO3 has been synthesized under high oxygen pressure from a precursor prepared by means of a sol-gel method. The material obtained is of single phase and has an orthorhombic crystal structure at room temperature. The magnetic, electrical and thermal properties have been measured over a wide temperature range. This compound exhibits a metal-insulator and a paramagnetic-antiferromagnetic transition at 400 K and at 220 K, respectively. The metal-insulator transition is of first order while the magnetic ordering is a second order transition as can be inferred from calorimetric measurements. In addition, we observe an anomaly in the resistivity near the Neel temperature indicating a change in the conduction mechanism at this temperature. Our results support local antiferromagnetic correlations above the Neel temperature for this compound.