Synthesis of room-temperature ferromagnetic Co-doped ZnO nanocrystals under a high magnetic field

Transitional-metal cobalt-doped ZnO nanocrystals were synthesized under an external magnetic field. The growth behavior of cobalt-doped ZnO nanocrystals was greatly affected by the high magnetic field. The growth rate of the nanocrystals along (001) direction was significantly suppressed because of the magnetization energy differences in a, b, and c-axis. Robust room-temperature ferromagnetism of Co-doped ZnO nanocrystals can be activated by the external magnetic field. The characterization of the annealed samples combined with the analysis of Raman scattering suggested that the appearance of ferromagnetism cannot be contributed to the presence of oxygen vacancies but to the ferromagnetic coupling of Co2+ under an external magnetic field.