Effect of hydrogen on sublattice magnetization of Laves-phase rare earth iron compounds

Abstract

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 RFe₂D_3.5 is formed. The pure compounds RFe₂ are ferrimagnetic, with the R moment equal to the free ion value and Fe moment of ∼1.6 μ_B. 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 μ_B versus 9 and 10 μ_B for Er and Ho in RFe₂) and drops steadily with increased temperature, reaching zero below T_c 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 ErFe₂D_3.5 and HoFe₂D_3.5 its magnitude is 1.6 μ_B, and 1.9 μ_B, 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.