Mechanical and magnetic relaxation of H and D in dilute PdGdFe

The relaxation of H and D in Pd90Gd5Fe5 was investigated over a wide temperature range by means of internal friction (IF) using a vibrating reed apparatus (frequencies 450 Hz..2100 Hz) and an inverted torsion pendulum (1 Hz..12 Hz) and by means of magnetic after-effect (MAE) (relaxation times corresponding to frequencies of 0.005 Hz..0.17 Hz). After charging with H, Pd90Gd5Fe5H5.65 shows a relaxation maximum in the MAE at 68 K (=0.005 Hz) and a maximum of the IF at 108 K (f=4.7 Hz). The activation parameters were determined independently by both methods to τ0H=4.10-12±0.5 s and HaH=(0.19±0.02) eV. With decreasing H or D content this maximum shifts to higher temperatures, similar to the shift in the binary alloy Pd100-xGdx. Owing to this concentration dependence, together with the similar activation parameters, the relaxation maximum can be attributed to the reorientation of H-Gd complexes. For identical concentrations, the IF relaxation maximum shows an isotope shift of about 5 K to lower temperatures for deuterium with respect to hydrogen. For a concentration of 3.85 at.%, activation parameters of τ0H=6.10-12±0.5 s, HaH=(0.21±0.01) eV and τ0D=6.10-13±0.5 s, HaD=(0.23±0.01) eV were obtained. (orig.)