Evidence for ordered moments on the Rh sites inCeRhIn5

Abstract

The magnetic structure of the tetragonal heavy fermion compound ${\mathrm{CeRhIn}}_{5}$ ${(T}_{N}=3.8\mathrm{K})$ has been studied by zero-field muon spin rotation $(\ensuremath{\mu}\mathrm{SR})$ in the range 1.8--4.3 K in a single crystal. In addition, the anisotropic muon $({\ensuremath{\mu}}^{+})$ Knight shift has been measured in the paramagnetic regime with the aim to determine the ${\ensuremath{\mu}}^{+}$ site or sites. It is found that about 70% of the implanted ${\ensuremath{\mu}}^{+}$ are located at the a site $(\frac{1}{2},\frac{1}{2},\frac{1}{2}).$ The site of the other 30% is not unambigeously determined but may be the f sites $(0,\frac{1}{2},0)$ and $(\frac{1}{2},0,0).$ The data also imply that a small negative moment is induced on the Rh sites. Below ${T}_{N}$ we find five components in the $\ensuremath{\mu}\mathrm{SR}$ signal reflecting spontaneous, relatively sharp internal fields of zero, 13, 37, 69, and 98 G at $T=0\mathrm{K},$ which are confined to the surface of cones oriented along the c axis with apertures ranging from $14\ifmmode^\circ\else\textdegree\fi{}$ to $90\ifmmode^\circ\else\textdegree\fi{}.$ 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.