Mechanical and magnetic relaxation of H and D in dilute PdGdFe

The relaxation of H and D in Pd90Gd5Fe5 was investigated over a wide temper ature range by means of internal friction (IF) using a vibrating reed appar atus (frequencies 450 Hz ... 2100 Hz) and an inverted torsion pendulum (1 H z ... 12 Hz) and by means of magnetic after-effect (MAE) (relaxation times corresponding to frequencies of 0.005 Hz ... 0.17 I-it). After charging wit h H, Pd90Gd5Fe5H5.65 shows a relaxation maximum in the MAE at 68 K (< f >=0 .005 Hz) and a maximum of the IF at 108 It (f=4.7 Hz). The activation param eters were determined independently by both methods to tau(0)(H)=4.10-12+/- 0.5 s and H-a(H)=(0.19+/-0.02) eV.With decreasing H or D content this maxim um shifts to higher temperatures, similar to the shift in the binary alloy Pd100-xGdx. Owing to this concentration dependence, together with the simil ar activation parameters, the relaxation maximum can be attributed to the r eorientation of H-Gd complexes. For identical concentrations, the IF relaxa tion 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.%, activ ation parameters of tau(0)(H)=6.10(-12+/-0.5) s, H-a(H)=(0.21+/-0.01) eV an d tau(0)(D)=6.10(-13+/-0.5) s, H-a(D)=(0.23+/-0.01) eV were obtained. (C) 1 999 Elsevier Science S.A. All rights reserved.