μ+SR knight shift in single crystal PrNi5—Evidence for muon-induced distortion of crystal-field levels

New transverse field measurements on single crystal PrNi5 have been carried out. The angular dependence of the Knight shift indicatesμ+ at f-sites of the hexagonal unit cell [(1/2 0 0), (0 1/2 0), (1/2 1/2 0)] in apparent contrast to previous conclusions. It is confirmed that the temperature dependence of the Knight shift does not scale with the bulk susceptibility. While the latter shows a distinct maximum around 15 K and Van Vleck behaviour for T→0 K, the Knight shift does not exhibit any saturation down to 2 K. This peculiar behaviour is explained by aμ+-induced change of the crystal field level scheme of the nearest-neighbour Pr3+-ions that significantly reduces the splitting between the lowest lying levels.