Hydrogen multicenter bond mediated magnetism in Co doped ZnO

Magnetism in Co doped ZnO (ZnO:Co) is strongly affected by the presence of the ZnO's extrinsic impurities, such as unintentional hydrogen dopants. Our ab initio investigation reveals that in ZnO: Co the formation of substitutional H (H-O) with four-fold hydrogenic bonds is favored over interstitial hydrogen (H-I) by 0.4 eV. It is found that H-O is trapped by Co ions to form highly stable Co-H-O-Co complexes. H-O also mediates a strong short-ranged ferromagnetic interaction between Co dopants via short-range exchange interaction which induces room temperature ferromagnetism.