NEUTRON-SCATTERING AND HEAVY-FERMION COMPOUNDS

In heavy fermion (HF) compounds the proximity of the 4f (5f) level to the Fermi energy allows a strong hybridisation between the 4f (5f) ele ctrons and the band and valence electrons. This leads to a magnetic in stability: HF either do not exhibit long range magnetic ordering or sh ow antiferromagnetism with very small ordered magnetic moment. Large m agnetic fluctuations are present even in the ordered state. The neutro n scattering techniques is an excellent tool for the study of the heav y fermion systems. The low temperature ordering can be studied in deta il by neutron diffraction while inelastic scattering give access to sp ace and time dependence of the fluctuation spectrum. The more signific ant heavy fermion systems already known will be briefly reviewed and s ome typical examples will illustrate the neutron studies of the HF com pounds.