Muon spin relaxation in amorphous samples which contained interstitial H was measured in a longitudinal geometry, in a zero applied magnetic field, at 18 to 340K. The relaxation profiles at all temperatures were consistent with the presence of time-dependent magnetic fields at the muon site. They were analyzed by using a dynamic form of Kubo-Toyabe relaxation theory. The correlation time of the local field at the muon, below 80K, was found to be about 6s and varied only slowly with temperature. At temperatures above about 250K, where the diffusion hopping rate of the H atoms was 107 to 108/s (as measured by using nuclear magnetic relaxation methods), the activation energy of the correlation time was similar to the activation energy for H diffusion. The relaxation of the muon spin at these temperatures was attributed to a highly correlated motion of the muon and the H atoms. Monte Carlo calculations were made of the fluctuation rates of the local fields under such conditions. According to those results, the experimental data were consistent with the muon having an intrinsically lower diffusion rate than that of H atoms.

Muon Spin Relaxation in Hydrogen-Loaded Amorphous Ni-Ti Alloys. M.Asif, R.L.Havill, J.M.Titman: Journal of Physics - Condensed Matter, 1994, 6[39], 8077-86