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

Structures and magnetic properties of Y2O3: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 Y2O3 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.