Muon spin rotation measurements were made of the temperature dependence and anisotropy of the + Knight shift in monocrystals. This revealed pronounced deviations from linearity, of the Knight shift as a function of the bulk magnetic susceptibility, at temperatures below 50K. These were explained in terms of a +-induced modification of the atomic susceptibility of neighboring Pr3+ ions. From the Knight-shift anisotropy at temperatures above 50K, it was deduced that the implanted + occupied a single interstitial site. This was the 6i site (0.5,0,0.21). By using this site information, a good fit to the measured data was obtained by assuming a +-induced perturbation of the crystal electric field at Pr3+ ions which were next to +. It appeared that the presence of + led to a lowering of the local symmetry; thus causing a lifting of the degeneracy and a marked rearrangement of the low-lying crystal electric field levels for these ions.

R.Feyerherm, A.Amato, A.Grayevsky, F.N.Gygax, N.Kaplan, A.Schenck: Zeitschrift für Physik B, 1995, 99[1], 3-13