Insulator–Metal Transition in the Nd₂CoFeO₆ Disordered Double Perovskite

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 T N = 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 ≈ 2.2T N, 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.

Enhancing Trifunctional Electrocatalytic Activities via Lanthanide Modulation in Fe–Co-Based Double Perovskite Oxides

“…62) for the sample Nd 2 CoFeO 6 and Pbnm for all the other compositions. 40,41 In this configuration, the simultaneous presence of Fe and Co ions at the 4b Wyckoff sites, along with the lack of superstructure reflections, serves as distinctive features indicative of a disordered double perovskite structure. Therefore, to account for this, the occupancy factor was maintained consistently with both transition metals occupying half of the sites.…”