Negative magnetoresistance in epitaxial films of neodymium nickelate

A significant increase in conductivity under an applied magnetic field or large negative magnetoresistance up to several percent is observed at low temperatures in epitaxial perovskite NdNiO₃ films. The (20–100 nm) strained films are grown on compressive (001)LaAlO₃ and tensile (001)(La₀.₃Sr₀.₇)(Al₀.₆₅Ta₀.₃₅)O₃ substrates. The negative magnetoresistance is found in the insulating phase, where the hopping mechanism of conductivity is revealed. It is shown that the presence and Zeeman splitting of localized states are responsible for conductivity and magnetoresistance. The localized states are suggested to emerge due to thermally induced local disorder in the Ni-O bond disproportionation. Such disorder can also lead to a phase coexistence in a broad temperature range.