Evidence for ordered moments on the Rh sites in (formula presented)

The magnetic structure of the tetragonal heavy fermion compound (formula presented) (formula presented) has been studied by zero-field muon spin rotation (formula presented) in the range 1.8-4.3 K in a single crystal. In addition, the anisotropic muon (formula presented) Knight shift has been measured in the paramagnetic regime with the aim to determine the (formula presented) site or sites. It is found that about 70% of the implanted (formula presented) are located at the a site (formula presented) The site of the other 30% is not unambigeously determined but may be the f sites (formula presented) and (formula presented) The data also imply that a small negative moment is induced on the Rh sites. Below (formula presented) we find five components in the (formula presented) signal reflecting spontaneous, relatively sharp internal fields of zero, 13, 37, 69, and 98 G at (formula presented) which are confined to the surface of cones oriented along the c axis with apertures ranging from (formula presented) to (formula presented) These results are not reproducible by the known incommensurate helical magnetic structure of the Ce sublattice but can be explained if, in addition, a small moment order of unusual type on the Rh sublattice is assumed.