COEXISTENCE OF MAGNETIC ORDER AND HEAVY-FERMION PARAMAGNETISM IN CE5SN3

We report resistivity, magnetic, thermodynamic, and neutron-diffraction data for the heavy-fermion compound Ce5Sn3. These data indicate an antiferromagnetic phase transition at T(N) = 17.5 K, but at lower temperatures the linear coefficient of specific heat gamma(T) = C(T)/T rises to 1.6 J/f.u. mol K2, characteristic of a moderately-heavy-fermion compound. Only a small amount of entropy is liberated by the phase transition (<< R 1n2), whereas most of the entropy [(3-4)R 1n2] is liberated by heavy-fermion processes. This implies a small ordered moment. Further, neutron diffraction implies a rather complicated magnetic order. We discuss two alternatives: (a) that ordering occurs on the Ce site of higher symmetry, while heavy-fermion behavior occurs on the lower-symmetry Ce site; and (b) that itinerant-fermion antiferromagnetism occurs. Due to the overall low site symmetries, crystal-field effects are strong; in particular, the susceptibility is highly anisotropic (by a factor of at least 20 at low temperatures) and enhanced by the presence of strong ferromagnetic correlations in the heavy-fermion state.