MUON SPIN RELAXATION IN HYDROGEN-LOADED AMORPHOUS NI-TI ALLOYS

Muon spin relaxation in the amorphous alloy Ni35Ti65 containing inters titial hydrogen has been measured in longitudinal geometry at zero app lied magnetic field, at temperatures in the range 18-340 K. The relaxa tion profiles at all temperatures were consistent with time-dependent magnetic fields at the muon site and were analysed by means of a dynam ic form of the Kubo-Toyabe relaxation theory. The correlation time of the local field at the muon below 80 K was found to be about 6 mus and to vary only slowly with temperature. Above approximately 250 K, wher e the diffusion hopping rate of the hydrogen atoms is about 10(7)-10(8 ) s-1, as measured by nuclear magnetic relaxation methods, the activat ion energy of the correlation time is similar to the activation energy of the hydrogen diffusion. The relaxation of the muon spin at these t emperatures is ascribed to the highly correlated motion of the muon an d the hydrogen atoms. Some Monte Carlo calculations of the fluctuation rates of the local fields under such conditions are reported. Accordi ng to the outcome of these calculations the experimental data are cons istent with the muon having an intrinsically lower diffusion rate than the hydrogen atoms,