Pressure-induced small-moment order in heavy-fermion compounds

We report results of neutron diffraction experiments which have been carrie d out to study the magnetic response of two heavy-fermion magnets Ce(Ru0.85 Rh0.15)(2)Si-2 and CeRh2Si2 to hydrostatic pressure. In CeRh2Si2 we have ob served two characteristic features in its staggered magnetization (mu) as a function of the transition temperature (T-N): When the pressure is relativ ely small, mu is proportional to T-N, while mu decreases more rapidly than T-N does when the pressure is close to the critical magnitude to destroy th e antiferromagnetism. A similar behavior of mu and T-N was observed also in Ce(Ru0.85Rh0.15)(2)Si-2. These observations indicate that there are two re gimes in the long range order of heavy-fermion magnets, that is, the RKKY- regime and the quasi-particle regime. We discuss these results on the basis of a hypothesis that the magnetism of these systems in the critical pressu re region can be assigned to the same category as that of the small-moment order which is widely observed in the metallic Kondo-lattice compounds.