MUON SPIN RELAXATION AND HYDROGEN DIFFUSION IN THE HFV2 LAVES PHASE

Muon spin relaxation has been measured using the zero-magnetic-field t echnique in the HfV2 Laves compound containing interstitial hydrogen. At low temperatures the relaxation profiles have the characteristic fo rm associated with fluctuating local fields. The correlation time is a lmost;independent of temperature. As the temperature is raised above a bout 100 K, motional narrowing takes place in which the correlation ti me of the local field decreases rapidly. Comparison with the hopping r ate of the hydrogen atoms, as measured by means of nuclear magnetic re laxation, shows that the change in the correlation time is consistent with an increasingly rapid motion of the hydrogen atoms. If the sample is then cooled, hysteresis occurs, in which the motional narrowing is retained to lower temperatures. The hysteresis in the muon relaxation rate together with parallel effects present in the nuclear magnetic r elaxation are discussed in relation to the phase changes that are know n to occur in this alloy.