Hydrogen in laves phase ZrX2 (X=V, Cr, Mn, Fe, Co, Ni) compounds:: Binding energies and electronic and magnetic structure -: art. no. 094109

The effects of hydrogen on the ground-state electronic and magnetic structures of AB(2) (A=Zr; B=V, Cr, Mn, Fe, Co, Ni) Laves phase compounds were investigated by first-principles local-density-functional calculations. We calculated the relative stability of atomic hydrogen at various interstitial tetrahedral sites formed by two A atoms and two B atoms (2A2B site), one A atom and three B atoms (1A3B site), and four B atoms (4B site). We find that (i) for ZrV2 and ZrCr2, hydrogen prefers the site with the largest interstitial hole size (i.e., 2A2B site); (ii) for ZrMn2, ZrFe2, and ZrCo2, the hydrogen binding energies at the 1A3B site become comparable to or even lower than those at the 2A2B site once the antibonding states of B atoms become progressively occupied. In H-free ZrFe2, we found a large magnetic moment (0.5mu(B)) at the Zr site, which is coupled antiparallel to the moment at the Fe site (1.9mu(B)). The hydrogen absorption does not have a strong effect in suppressing the magnetic moments of atoms closest to the absorbed hydrogen but increases the magnetic moments of atoms not having hydrogen as the nearest neighbor. This increase in the moment is partly due to the H-induced lattice expansion.