Hyperfine Interactions 31 (1986) 433-437 433 /z+KNIGHT SHIFTS AND TRAPPING IN DILUTE SbSn ALLOYS J.H. BREWER, D.R. HARSHMAN, E. KOSTER, S.R. KREITZMAN, D.R. NOAKES., M. SENBA and D.LI. WILLIAMS Dept. of Physics, University of British Columbia and TRIUMF, Vancouver, RC., Canada, V6T 2A3 E.J. ANSALDO Dept. of Physics, Univ, of Saskatchewan, Saskatoon, Sask., Canada, S7N OWO Giant ~+ Knight shifts K have been studied previously in Sb and SbB~ alloys. Here we report ~+SR measurements on ~ with dilute heterovalent Sn impurities. A dramatic concentration dependence is observed: K is increased slightly (relative to the value in pu~e Sb) by Sn concentrations of ( 0.1%, whereas larger concentrations cause a drastic reduction of K . One concern could be that K values in the alloy m~ght reflect local band structure in trap sites near Sn impurities rather than the bulk "host" band structure of the alloy. This is indeed the case in both __SbSn(0"03%) and SbSn(0.06%), where a second, lower frequency TF-~SR signal begins to appear for T > 60K. The amplitude of the low K signal grows with increasing T at the expense o~ the amplitude of the high-K , low-T signal, suggesting + that the ~ migrates through the host lattice to trap sites. A simple trapping model correctly describes the observed T-dependence of the amplitudes, phases a,%d celaxation rates of the two signals. We conclude that the low-T Knight shift is truly characteristic of the host band structure while the much lower K value of the high-T site is characteristic of a specific trap site, presumably adjacent to a Sn impurity. Hartmann et al /i/ first discovered that the positive muon in antimony metal exhibited an unusually large, anisotropic, and temperature dependent Knight shift. Subsequently this effect was studied in detail by Brewer et al /2/ who also examined the effect of alloying with the homovalent impurity, bismuth, in order to investigate its sensitivity to electronic structure. Specifically it was found that the addition of bismuth reduced the Knight shift progressively so that the J.C. Baltzer A.G., Scientific Publishing Company