MOMENT WASHOUT AND THE ONSET TO THE HEAVY FERMION STATE

Heavy fermion antiferromagnets are characterized by greatly reduced ordered moments and Neel temperatures (T(N)) relative to those in isostructural or other related materials showing well-ordered magnetic behavior. We have developed theory and ab initio computational technique allowing us to use the prediction of reduced ordered moment (and reduced T(N)) behavior as a diagnostic tool defining the approach to (or departure from) the correlated-electron heavy-fermion state with changing chemical environment in an isostructural series of compounds. Hybridization drives the system toward the heavy fermion state by merging the f-spectral density into the d-p band spectral density in the presence of interconfigurational correlation effects, thereby causing moment washout. Coulomb exchange counteracts this moment reduction; and the nonlinearity of the ordered moment response to the change in the hybridization/exchange balance with incremental f delocalization (associated with changing chemical environment) may provide an explanation for the circumstance that reduced magnetic ordering in the heavy fermion state seems to exhibit itself even more strongly in the ordered moment than in T(N).