The electronic structures, binding energies and magnetic properties of Ni-containing vacancies and vacancy-H complexes were studied by using a first-principles all-electron self-consistent embedded-cluster model which was based upon local spin-density functional theory. It was found that the results correctly described the properties of ferromagnetic Ni. The calculated local-spin magnetic moment at the nearest-neighbor site of a mono-vacancy was found to be 30% higher than the bulk value. This magnetic moment was significantly reduced when H occupied the vacancy center. Calculations of the binding energies of six H atoms, moving along octahedral directions from the vacancy center, revealed that the magnetic moments at the nearest-neighbor Ni site continually decreased and eventually coupled antiferromagnetically with the bulk moment. This occurred when H atoms were displaced, from the vacancy center, by a distance that was equal to half of the lattice constant. This was considered to be analogous to antiferromagnetic coupling in NiO. The trapping of a 6-H atom complex within a vacancy was found to be energetically favored.

H.Zheng, B.K.Rao, S.N.Khanna, P.Jena: Physical Review B, 1997, 55[7], 4174-81