Defect-Rich Dopant-Free ZrO₂ Nanoclusters and Their Size-Dependent Ferromagnetism

Area of Science:

• Materials Science
• Nanotechnology
• Condensed Matter Physics

Background:

• Nanoclusters (NCs) bridge the gap between single atoms and bulk materials, exhibiting unique properties due to high surface area-to-volume ratios.
• Their distinct physical and electronic structures make them promising for advanced applications like spintronics and magnetic tunneling junctions.

Purpose of the Study:

• To develop a method for producing size-specific zirconium dioxide (ZrO2) nanoclusters.
• To investigate the size-dependent electronic and magnetic properties of these nanoclusters.
• To propose a model explaining the observed ferromagnetism.

Main Methods:

• Large-area deposition of monosized ZrO2 nanoclusters using gas-phase aggregation.
• In situ size selection of nanoclusters via a quadrupole mass filter.
• Characterization of photoemission features and magnetic properties.

Main Results:

• Size-specific ZrO2 nanoclusters (3-9 nm) displayed sub-oxide photoemission features with binding energies dependent on cluster size.
• These features were attributed to varying oxygen vacancy defect states.
• Dopant-free ZrO2 nanoclusters exhibited strong, size-dependent ferromagnetism, outperforming traditional dilute magnetic semiconductors in solubility and magnetic homogeneity.

Conclusions:

• A novel protocol for manipulating magnetization through size control of nanoclusters was demonstrated.
• A defect-band hybridization-induced magnetic polaron model was proposed to explain the size-dependent ferromagnetism.
• These defect-rich, size-selected nanoclusters hold potential for future device applications.