Metal-insulator-metal transition in NdNiO3 films capped by CoFe2O4

Abstract

Metal-insulator transition features as a transformation from a highly charge conductive state to another state where the charge conductivity is greatly suppressed when decreasing the temperature. Here, we demonstrate two consecutive transitions in NdNiO3 films with CoFe2O4 capping, in which the metal-insulator transition occurs at ∼85 K, followed by an unprecedented insulator-metal transition below 40 K. The emerging insulator-metal transition associated with a weak antiferromagnetic behavior is observed in 20 unit cell-thick NdNiO3 with more than 5 unit cell CoFe2O4 capping. Differently, the NdNiO3 films with thinner CoFe2O4 capping only exhibit metal-insulator transition at ∼85 K, accompanied by a strong antiferromagnetic state below 40 K. Charge transfer from Co to Ni, instead of from Fe to Ni, formulates the ferromagnetic interaction between Ni–Ni and Ni–Co atoms, thus suppressing the antiferromagnetic feature and producing a metallic conductive behavior. Furthermore, a phase diagram for the metal-insulator-metal transition in this system is drawn.