Thermal annealing and grain boundary effects on ferromagnetism in Y2O3:Co diluted magnetic oxide nanocrystals

Abstract

Structures and magnetic properties of ${\text{Y}}_2{\text{O}}_3:\text{Co}$ nanocrystals were investigated using high resolution transmission electron microscopy, x-ray diffraction, x-ray absorption fine structures, and superconducting quantum interference device. Cobalt atoms were found to be driven by thermal annealing from interstitial locations inside the ${\text{Y}}_2{\text{O}}_3$ nanoparticles toward particle surface, where increased O vacancies surrounding Co atoms led to increased saturation magnetization. Our results strongly support a bound magnetic polaron model for ferromagnetism in diluted magnetic oxides mostly due to magnetic dopants located on the grain boundaries.