The effect of substitution of Zn by transition metal atoms Co and Mn (5%) in the host diamagnetic ZnO matrix was investigated using X-ray diffraction, magnetization and photoelectron spectroscopy. The dopant atoms incorporate at the Zn site in the hexagonal wurtzite structure without forming any impurity phases or cluster formation. The Mn atoms induce weak room temperature ferromagnetism in ZnO while the Co doping could drive it to only a paramagnetic status. However, the injection of H ions causes a giant ferromagnetism in Co-doped ZnO, on the contrary, the Mn doped ZnO does not respond to hydrogenation. Interestingly, the re-heating causes the H-induced magnetism to vanish in Co-doped ZnO, however, the Mn doped ZnO shows only a marginal sensitiveness towards re-heating. The switching action between ferromagnetic and paramagnetic states in ZnO:Co, by hydrogenation and heating, respectively, is a significant finding of this work. The experimental findings strongly suggest that the ferromagnetism in doped bulk ZnO might be associated with the O vacancies.
H-induced ferromagnetism in Co-doped ZnO vanishes upon its re-heating/ long storage. “Switch” action of ferromagnetism between hydrogenation and re-heating in ZnO:CO. ZnO:Co shows giant ferromagnetism on H-injection, in contrast, the ZnO:Mn does not! Ferromagnetism show close relation with oxygen vacancies in magnetic semiconductors.
Keywords: Magnetic semiconductors; X-ray spectroscopy; Zinc oxide; Doping effects