Neutron scattering from low-carrier-density strongly correlated electron systems

The results of neutron-scattering experiments on Ce- and Yb-monopnictides with very low carrier density are discussed. The experiments on a single crystal of CeP revealed that the complex phase diagram under magnetic field comes from the interplay between the long-period ferromagnetic lattice of the Ce ions with Γ₈ character and the antiferromagnetic ordering in the normal Γ₇ Ce lattice. The inelastic-scattering experiments on a polycrystalline sample of YbP show the existence of strong short-range spin correlation at temperatures far above T_N. The result indicates that the Kondo-like properties in Yb-monopnictides seen at low temperatures originate from anomalous spin correlations. The experimental results from CeP and YbP are discussed in relation with the magnetic polaron model.