Magnetism in Co doped ZnO (ZnO:Co) was strongly affected by the presence of ZnO extrinsic impurities, such as unintentional hydrogen dopants. This ab initio investigation revealed that, in ZnO:Co, the formation of substitutional H (HO) with four-fold hydrogenic bonds was favoured over interstitial hydrogen (HI) by 0.4eV. It was found that HO was trapped by Co ions to form highly stable Co–HO–Co complexes. HO also mediated a strong short-ranged ferromagnetic interaction between Co dopants via short-range exchange interaction which induces room temperature ferromagnetism.

Hydrogen Multicenter Bond Mediated Magnetism in Co Doped ZnO. M.H.N.Assadi, Y.B.Zhang, S.Li: Journal of Physics - Condensed Matter, 2010, 22[15], 156001