DYNAMICS OF MU(+) IN SC AND SCHX

Muon spin rotation (mu SR) experiments on single-crystal samples of Sc Hx, with x = 0, 0.05, 0.10 and 0.25, were performed in order to invest igate the muon location and possible systematic variations in muon dyn amics in these systems. The angular and magnetic field dependence of t he mu SR relaxation rates shows that at temperatures below 50 K the mu on is localized at the interstitial tetrahedral (T) sites. The results for pure Sc, covering a wide range of high and low fields, are cohere nt with the picture that the muon performs fast tunnelling between two adjacent T sites, separated by 2z = 0.18c, above and below the a-b pl ane. This value for the muon position along the c axis is remarkably n ear the 2z = 0.194c found for D in Sc by neutron diffraction. The anis otropy of the relaxation rate at low magnetic fields varies sensitivel y with the H concentration, indicating a change in the ratio of the ra dial, muon-induced and the partly inherent, uniaxial electric field gr adients at the position of the Sc nuclei.