Room temperature ferromagnetism in two-step-prepared Co-doped ZnO bulks

We have prepared Co-doped ZnO bulks with a two-step method. The bulk samples are sintered at the temperature above 1000°C to get pure single phase and then treated by Zn vapor in a vacuum. Based on such two-step preparation, clear carrier induced ferromagnetism is found in Zn treated Co-doped ZnO bulks, which suggests that the magnetism mechanism can be of codoping effect. The onset of ferromagnetism is associated with the further increase of the hybridization of the impurity band with 3d states near the Fermi level when additional carrier induced to let the Stoner criterion for ferromagnetism to be satisfied.