EFFECT OF HYDROGEN ON SUB-LATTICE MAGNETIZATION OF LAVES-PHASE RARE-EARTH IRON COMPOUNDS

We have used elastic neutron scattering to examine the effect of hydriding on the sublattice magnetization of the Laves-phase compounds RFe2 for R=Ho and Er. On addition of hydrogen or deuterium a stable phase of composition about RFe2D3.5 is formed. The pure compounds RFe 2 are ferrimagnetic, with the R moment equal to the free ion value and Fe moment of ∼1.6 μB. The bulk Curie temperatures T c of the hydrides and deuterides are considerably lower than the corresponding RFe2 values (e.g., 440 K for ErFe2D 3.5 versus 574 K for ErFe2). The 10 K R moment is also significantly reduced in the deuterides (4.4 and 5.2 μB versus 9 and 10 μB for Er and Ho in RFe2) and drops steadily with increased temperature, reaching zero below Tc in the case of Er. The Fe moment remains nearly constant with temperature until just below T c where it drops rapidly to zero; in ErFe2D3.5 and HoFe2D3.5 its magnitude is 1.6 μB, and 1.9 μB, respectively. These results indicate that the exchange interactions involving the R atoms are markedly weakened in the hydrides. The distortion of the local anisotropy field due to random site occupancy of H and the weak exchange coupling of R produces a fanning" of the R moment which reduces the spatially averaged moment measured in the neutron experiment."