Lattice disorder in strongly correlated lanthanide and actinide intermetallics

C. H. Booth , E. D. Bauer, M. B. Maple, J. M. Lawrence, G. H. Kwei, and J. L. Sarrao

(invited talk for XAFS XI), J. Synchrotron Rad., 8, 191 (2000).

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. We will review the lattice disorder mechanism within a tight-binding model and present measurementsof the Yb$B$Cu$_4$ and UPd$_x$Cu$_{5-x}$ systems demonstrating the applicabilityof the model. These measurements indicate that while the Yb$B$Cu$_4$ system appears to be well ordered, both site interchange and continuous bond-length disorder occur in the UPd$_x$Cu$_{5-x}$ series. Nevertheless, the measured bond-length disorder in UPdCu$_{4}$ does not appear to be enough to explain the NFL properties simply with this Kondo disorder model.

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