Muon-spin-rotation study of Ce7Ni3: muon-related and intrinsic properties of the paramagnetic phase

We report on transverse-field (0.6 T) muon-spin-rotation (mu SR) measuremen ts between 3 K and 300 K on single crystals of the hexagonal heavy-fermion compound Ce7Ni3 with the primary goal of determining the mu (+) lattice sit e(s). The mu SR spectrum consists in each case of two components which are distinguished by their anisotropic, axially symmetric Knight shifts and whi ch can be associated with two types of tetrahedrally coordinated b site (in Wyckoff notation). The relative occupation of the two sites varies with te mperature and, surprisingly, depends also on the orientation of the crystal s with respect to the applied field B-ext. We find that below 80 K the muon Knight shift follows a perfect Curie-Weiss behaviour down to 3 K, exhibiti ng Curie temperatures of approximately +/-l K in striking contrast to the b ehaviour of the bulk susceptibility. Above 100 K the Knight shift scales wi th the bulk susceptibility. In the transitional range 60 K-100 K muon diffu sion sets in, probably proceeding by jumps via the two types of b site. Bel ow 50 K an increasing part of the mu SR signal appears to be wiped out (sim ilar to 30% at 3 K), signalling the presence of an internal static field sp read above 1 kG, perhaps related to a persisting magnetic order above T-N = 1.9 K in part of the sample volume.