Nanoparticle exsolution opens a new route to functional oxide electronics and spintronics

A research team has developed a new strategy to simultaneously control the electronic and magnetic properties of oxide thin films through a process known as exsolution. The team was led by Professor Hyeon Han and Professor Donghwa Lee from the Department of Materials Science and Engineering at Pohang University of Science and Technology (POSTECH), together with Professor Sang Ho Oh's group at Korea Institute of Energy Technology (KENTECH). The findings are published in the journal Advanced Materials.

Exsolution is a process in which metal ions embedded within an oxide crystal migrate to the surface under reducing conditions and precipitate as metallic nanoparticles. Because these nanoparticles are partially anchored in the oxide lattice, they are more thermally and chemically stable than those deposited by conventional methods. For this reason, exsolution has attracted significant attention in energy-related applications such as catalysis, fuel cells and electrolysis. However, how exsolution affects the intrinsic electronic and magnetic properties of oxide materials has remained insufficiently understood.

To address this question, the research team focused on La0.2Sr0.7Ni0.1Ti0.9O₃-δ, a well-known A-site-deficient perovskite titanate composition known to promote B-site cation exsolution into metallic nanoparticles. By combining comprehensive experimental characterization with density functional theory calculations, the team revealed that this material contains multiple types of defects, including strontium vacancies, oxygen vacancies, lanthanum substitution and nickel substitution. In the pristine state, these defects electrically compensate for one another, resulting in a charge-compensated insulating state.

After exsolution, however, nickel nanoparticles form both within and on the surface of the film, and the resulting defect reconstruction in the oxide lattice drives a marked change in the electronic structure. The lattice evolves toward a La-doped SrTiO3-like phase, resulting in a heavily electron-doped, degenerate metallic state. This transformation leads to a giant insulator-to-metal transition with a resistivity change exceeding three orders of magnitude. These results show that exsolution is not merely a method for generating metal nanoparticles; it can also fundamentally modify the electronic structure of the host oxide lattice.

The team also observed a striking change in magnetic properties. While the pristine film exhibited nearly diamagnetic behavior, the exsolved film showed room-temperature superparamagnetism, arising from interactions among the newly formed Ni nanoparticles. This demonstrates that exsolution can simultaneously tune both the electrical behavior of the perovskite oxide matrix and the magnetic response of embedded metallic nanoparticles.

"This study shows that exsolution can go beyond nanoparticle formation and act as a versatile route to simultaneously control electronic and magnetic properties in oxide thin films," said Professor Han. "By combining defect engineering with nanoparticle formation, this approach could open new design strategies for functional electronic and spintronic devices."

Sungil Kim et al, Unveiling Exsolution‐Induced Giant Electronic and Magnetic Property Changes in Non‐Stoichiometric Titanate Perovskite Thin Films, Advanced Materials (2026). DOI: 10.1002/adma.202600031

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