  Metal-insulator transition features as a transformation, from a highly charge
conductive state to another state where 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 metallic conductive behavior.
Furthermore, a phase diagram for the metal-insulator-metal transition in this
system is drawn.
