Lattice disorder in strongly correlated lanthanide and actinide intermetallics

Abstract

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(x)Cu(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(x)Cu(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.

Ferromagnetic quantum critical point in UCo1−xFexGe

“…We note, however, that similar studies of compounds with comparable RRRs (and thus a comparable amount of disorder) such as UCoGe 1−x Si x (RRR ≈ 4) 19 and URh 1−x Ru x Ge (RRR ≈ 2) 35 have usually concluded that the QPT is of second-order. More detailed studies that go beyond the scope of this work that can access the amount of disorder by determining discrepancies between the local structure and average crystal structure, such as EXAFS 39 and PDF 40 may ultimately allow this issue to be clarified.…”

Alloying and pressure effect on the mixed-valence state of Yb in YbInCu4

“…According to the Anderson single-impurity model, the deviation of the valence from 3+ is expected in the high-temperature phase by the Kondo effect (T K = 25 K), which reduces the effective 4f hole occupation [4]. Measurements of x-ray absorption at the Yb L III edge show that the valence of Yb in the high-temperature phase of YbInCu 4 is slightly lower than 3:v = 2.9 [3] or 2.93-2.96 [4,21,22]. In the present study we adopt the value v = 2.94 for the valence of Yb in the high-temperature phase of YbInCu 4 .…”

Effects of lattice disorder in theUCu5−xPdxsystem

“…With increasing continuous disorder, σ static , the initial discrete P (T K ) is quickly washed out even for small amounts of disorder σ static ∼ 0.005Å, and broadens considerably with more weight shifting to lower T K . 39 Sources of Kondo disorder other than a bond length distribution in the hybridization energy such as a distribution of f − ion energies or density of states N (E F are not included in this model.…”