Enhanced Room-Temperature Ferromagnetism Observed in SiO₂-Coated CuO Nanostructures

In this paper, the magnetic properties of pure CuO and SiO₂-coated CuO nanocrystals were reported. Strongly enhanced room-temperature ferromagnetism was observed in SiO₂-coated CuO nanocrystals, whose saturation magnetization is two orders of magnitude enhanced compared to that of the uncoated CuO nanocrystals. The mechanism of this enhancement was investigated. It points out the main origin of ferromagnetism in these CuO nanocrystals is the uncompensated surface state, so that the coating of SiO₂ can effectively protect the surface state to improve the ferromagnetism in these CuO nanocrystals.