Ferromagnetism as a universal feature of nanoparticles of the otherwise nonmagnetic oxides

TL;DR

This study reports room-temperature ferromagnetism in nanoparticles of nonmagnetic oxides, suggesting that ferromagnetism is a universal feature of metal oxide nanoparticles due to surface oxygen vacancies, unlike their bulk counterparts.

Contribution

It demonstrates that nonmagnetic oxide nanoparticles exhibit ferromagnetism at room temperature, a phenomenon absent in their bulk forms, indicating a surface-related magnetic origin.

Findings

Nanoparticles show ferromagnetism at room temperature.

Bulk samples are diamagnetic, unlike nanoparticles.

Ferromagnetism likely due to surface oxygen vacancies.

Abstract

Room-temperature ferromagnetism has been observed in the nanoparticles (7 - 30 nm dia) of nonmagnetic oxides such as CeO2, Al2O3, ZnO, In2O3 and SnO2. The saturated magnetic moments in CeO_2 and Al_2O_3 nanoparticles are comparable to those observed in transition metal doped wide band semiconducting oxides. The other oxide nanoparticles show somewhat lower values of magnetization but with a clear hysteretic behavior. Conversely, the bulk samples obtained by sintering the nanoparticles at high temperatures in air or oxygen became diamagnetic. As there were no magnetic impurities present, we assume that the origin of ferromagnetism may be due to the exchange interactions between localized electron spin moments resulting from oxygen vacancies at the surfaces of nanoparticles. We suggest that ferromagnetism may be a universal characteristic of nanopartilces of metal oxides