Insulator–Metal Transition in the Nd<sub>2</sub>CoFeO<sub>6</sub> Disordered Double Perovskite
Leonardo Soares de Oliveira, Fernando P. Sabino, Daniel Zanetti de Florio, Anderson Janotti, Gustavo M. Dalpian, J. A. Souza
Abstract
A comprehensive study on the correlations of structural, magnetic, and electronic properties of a new disordered Nd2CoFeO6 double perovskite has been conducted. The lack of strong divergence of the magnetic susceptibility suggests competition between magnetic interactions at the magnetic phase transition TN = 246 K, which is confirmed by the absence of a heat capacity peak. The magnetic susceptibility results indicate that the Fe/Co spins form a classical noninteracting paramagnetic state above T ≈ 2.2TN, while deviations are found at intermediate temperatures indicating the presence of strong short-range magnetic interactions. AC and DC electrical resistivity results reveal a melting of insulating polaronic behavior to a metallic-like conductivity, establishing an electronic crossover closely related to both local magnetic moment and lattice-parameter evolution. We show from density functional calculations that the magnetic configurations have a strict relation to this crossover, being associated to a transition from low to high spin states of Co3+ ions. This insulator–metal transition has its origin driven by a local increase in the magnetic moment of Co3+ ions. Our results point to a scenario in which a continuous spin-state transition triggers a crossover between distinct electronic states from the insulating polaronic behavior to permanent metallic states.