Mössbauer Study of Two Pd-Fe Alloys Containing Absorbed Hydrogen

The temperature dependence of hyperfine fields and isomer shifts in the system Pd-Fe-H (2 and 5% Fe) has been investigated by means of the Fe⁵⁷ M\"ossbauer effect. We observe hyperfine fields indicating that an ordered magnetic structure exists in the β phase at H concentrations high enough to cause filling of the Pd4d band (H/Pd{≥}0.59 for 2% Fe). The β-phase transition temperature Tc(β) is considerably lower than the corresponding α-phase transition temperature. For the 2%-Fe alloy, Tc(β)=(3±1)^∘K and H(1.8^∘K)≈240 kOe; for the 5%-Fe alloy, Tc(β)=(10±3)^∘K and H(1.8^∘K)≈310 kOe. The distribution of measured hyperfine fields has been correlated with the H near-neighbor configuration. Above Tc(α) and also below Tc(β), we observe an isomer shift of +0.045±{}0.003 mm/sec in going from the α to the β phase.