Muon spin-rotation measurements of the temperature dependence and anisotropy of the Knight shift in monocrystalline material revealed pronounced deviations from a linear scaling of the Knight shift with the bulk magnetic susceptibility at temperatures below 50K. These were explained in terms of a +-induced modification of the 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; at least below the diffusion onset temperature of about 150K. By using the site information, good model fits to the experimental data were obtained by assuming the occurrence of a +-induced perturbation of the crystal electric field at the Pr3+ ions next to the +. It was proposed that the presence of the + led to a decrease in local symmetry; thus causing a lifting of the degeneracy and to 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: Journal of Alloys and Compounds, 1995, 231, 164-9