Ferromagnetism induced by hydrogen in polycrystalline nonmagnetic $Zn0.95Co0.05O$

Polycrystalline $Zn0.95Co0.05O$ is found to be paramagnetic at room temperature and down to $12K$⁠. Optical measurements prove the incorporation of $Co2+$ ions inside the ZnO lattice in the tetrahedral site. When the paramagnetic sample is heated in $Ar∕H2$ at $1125K$ for $2h$⁠, ferromagnetism with a very high value of magnetization is observed at room temperature. Hydrogen reduction does not affect the substituted $Co2+$ ions inside the wurtzite crystal lattice as evidenced from optical studies. X-ray diffraction studies show the presence of Co metal after the reduction process which is the origin of room temperature ferromagnetism.