Lattice disorder in strongly correlated lanthanide and actinide intermetallics

Lanthanide and actinide intermetallic compounds display a wide range of correlated-electron behavior, including ferromagnetism, antiferromagnetism, nonmagnetic (Kondo) ground states, and so-called `non-Fermi liquid' (NFL) behavior. The interaction between f electrons and the conduction band is a dominant factor in determining the ground state of a given system. However, lattice disorder can create a distribution of interactions, generating unusual physical properties. These properties may include NFL behavior in many materials. In addition, lattice disorder can cause deviations from standard Kondo behavior that is less severe than NFL behavior. A review of the lattice disorder mechanism within a tight-binding model is presented, along with measurements of the YbBCu₄ and UPd_xCu_5-x systems, demonstrating the applicability of the model. These measurements indicate that while the YbBCu₄ system appears to be well ordered, both site interchange and continuous bond-length disorder occur in the UPd_xCu_5-x series. Nevertheless, the measured bond-length disorder in UPdCu₄ does not appear to be enough to explain the NFL properties simply with the Kondo disorder model.