Unveiling Exsolution-Induced Giant Electronic and Magnetic Property Changes in Non-Stoichiometric Titanate Perovskite Thin Films.

Abstract

Exsolution of nanoparticles, which forms socketed nanostructures partially submerged into a host metal-oxide surface under in-situ reducing conditions, has attracted considerable attention because of its exceptionally high stability against particle coarsening compared with conventionally deposited nanoparticles. Consequently, exsolution-based systems have been widely explored for catalytic and energy-related applications. However, the electronic and magnetic property changes induced by the exsolution process, in particular their physical origins, remain largely unexplored. Here, a giant insulator-to-metal transformation accompanied by the emergence of room-temperature superparamagnetism is reported, driven by nanoparticle exsolution. By combining comprehensive experimental characterization with density functional theory calculations, it is revealed that the A-site- and oxygen-deficient perovskite oxide La_0.2Sr_0.7Ni_0.1Ti_0.9O_3-δ, designed to promote B-site cation exsolution, exhibits a charge-compensated insulating behavior in its pristine state. Upon reduction, the lattice evolves toward a La-doped SrTiO₃-like phase, resulting in a heavily electron-doped, degenerate metallic state, leading to the giant insulator-to-metal transition with a resistivity change exceeding three orders of magnitude. Furthermore, the exsolution process induces a pronounced magnetic transition from diamagnetism in the pristine lattice to room-temperature superparamagnetism arising from thermally fluctuating exsolved Ni nanoparticles. This work provides new insights into the coupled electronic and magnetic evolution induced by exsolution and highlights its potential for the development of functional electronic and spintronic devices.