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Temperature-dependent x-ray diffraction study of Pd/Cu site interchange in non-Fermi liquid UCu(4)Pd

Description: A pair distribution function (PDF) analysis of temperature-dependent x-ray diffraction measurements from UCu{sub 4}Pd is presented. Fits to the displacement parameters (u{sup 2}'s) with a Debye model show better agreement with a model that includes 25% of the Pd atoms on 16$e$ (Cu) sites. In addition, significant non-thermal disorder is observed in the Cu environment, in contrast to previous measurements of local order in the U-Cu pairs.
Date: June 1, 2002
Creator: Han, S.-W.; Booth, C.H.; Bauer, E.D. & Maple, M.B.
Partner: UNT Libraries Government Documents Department

Synthesis, Structure, and Physical Properties of YbNi{sub 3}Al{sub 9.23}

Description: The physical properties of YbNi{sub 3}Al{sub 9.23}, including the crystal structure, magnetization, specific heat, valence, and electrical resistivity, are reported. Single crystal X-ray diffraction reveals that the compound crystallizes with the rhombohedral space group R32 and has unit cell parameters a=7.2443(3) Å and c=27.251(3) Å with some crystallographic disorder on an Al site. The compound orders antiferromagnetically at T{sub N}=3 K despite the presence of strong ferromagnetic correlations, accompanied by a spin flop-like transition to a moment-aligned rate above 0.1 T. X-ray absorption spectroscopy and magnetic susceptibility measurements indicate a localized Yb{sup 3+} electronic configuration, while the Sommerfeld coefficient in the magnetically ordered state was determined to be approximately 135 mJ/mol-K{sup 2}, suggesting moderately heavy fermion behavior. Therefore, these data indicate a balance between competing Ruderman-Kittel-Kasuya-Yosida (RKKY) and Kondo interactions in YbNi{sub 3}Al{sub 9.23} with a somewhat dominant RKKY interaction that leads to a relatively high ordering temperature.
Date: November 4, 2010
Creator: Tobash, P. H.; Jiang, Y.; Ronning, F.; Booth, C. H.; Thompson, J. D.; Scott, B. L. et al.
Partner: UNT Libraries Government Documents Department

Pair-distribution function analysis of the structural valence transition in Cp{sub 2}{sup *}Yb(4,4'-Me{sub 2}-bipy)

Description: The Cp{sup ∗}{sub 2} Yb(L) class of compounds, where Cp{sup ∗}=pentamethylcyclopentadienyl = C{sub 5}Me{sub 5} and L is either a 1,4-diazabutadiene or bipy = 2,2′-bipyridine related ligand, have provided excellent analogies to the Kondo state on the nanoscale. Cp{sup ∗}{sub 2} Yb(4,4′-Me{sub 2}-bipy) furthers this analogy by demonstrating a valence transition as the sample is cooled below 200 K. Here, pair-distribution function (PDF) analysis of x-ray powder diffraction data demonstrate that the Cp{sup ∗}{sub 2}Yb(4,4′-Me{sub 2}-bipy) molecule is virtually unchanged through the valence transition. However, the molecule’s stacking arrangement is altered through the valence transition.
Date: July 20, 2010
Creator: Booth, C H; Bauer, E D; Bozin, E S; Billinge, S J L & Walter, M D
Partner: UNT Libraries Government Documents Department

Pd/Cu site interchange in UCu{sub 5-x}Pd{sub x}

Description: Although Pd/Cu site interchange in the non-Fermi liquid (NFL) material UCu{sub 4}Pd has been observed, the relationship between this disorder and the NFL behavior remains unclear. In order to better compare to the UCu{sub 5-x}Pd{sub x} phase diagram, they report results from Pd K edge x-ray absorption fine structure (XAFS) experiments on this series (x = 0.3-1.5) that determine the fraction of Pd atoms on the nominally Cu (16e) sites, s. They find that for these unannealed samples, s is at least 17% for all the samples measured, even for x < 1.0, although it does climb monotonically beyond its minimum at x = 0.7. These data are compared to changes in the lattice parameter as a function of x.
Date: July 11, 2001
Creator: Booth, C.H.; Bauer, E.D.; Maple, M.B.; Chau, R. & Kwei, G.H.
Partner: UNT Libraries Government Documents Department

Effects of lattice disorder in the UCu(5-x)Pd(x) system

Description: The UCu5-x Pdx system exhibits non-Fermi liquid (NFL) behavior in thermodynamic and transport properties at low temperatures for Pd concentrations 0.9 less than or approximately x less than or approximately 1.5. The local structure around the U, Cu, and Pd atoms has been measured for
Date: February 19, 2002
Creator: Bauer, E.D.; Booth, C.H.; Kwei, G.H.; Chau, R. & Maple, M.B.
Partner: UNT Libraries Government Documents Department

Magnetic frustration effects in uranium intermetallics

Description: The effect of geometrical frustration on the development of the heavy-fermion state and quantum criticality is studied in UAuCu{sub 4}, UAuPt{sub 4}, UAu{sub 3}Ni{sub 2} samples through measurements of their magnetic susceptibility, heat capacity, and electrical resistivity. In addition, since lattice disorder can play a large role in defining magnetic properties in frustrated systems, extended X-ray absorption fine structure (EXAFS) data have also been obtained. The local structure results show a strong correlation with the magnetic properties in these samples.
Date: June 10, 2010
Creator: Jiang, Yu; Booth, C. H.; Tobash, P. H.; Gofryk, K.; Torrez, M. A.; Ronning, F. et al.
Partner: UNT Libraries Government Documents Department

Lattice disorder and size-induced Kondo behavior in CeAl2 andCePt2+x

Description: When the particle size of CeAl{sub 2} and CePt{sub 2+x} samples is reduced to the nanometer scale, antiferromagnetism is suppressed and Kondo behavior dominates. We find that the Kondo temperature T{sub K} can either decrease (CeAl{sub 2}) or increase (CePt{sub 2+x}) in the nanoparticles relative to the bulk. Extended x-ray absorption fine-structure data show that the Ce-Al and Ce-Pt environments are significantly distorted in the nanoparticles. While such distortions should strongly affect magnetic and electronic properties, we find they cannot explain the observed changes in T{sub K}. Changes in the conduction density of states or other parameters must, therefore, play a significant role.
Date: March 14, 2006
Creator: Han, S.-W.; Booth, C.H.; Bauer, E.D.; P.H., Huang; Chen, Y.Y. & Lawrence, J.M.
Partner: UNT Libraries Government Documents Department

Effects of self-irradiation on local crystal structure and 5flocalization in PuCoGa5

Description: The 18.5 K superconductor PuCoGa{sub 5} has many unusual properties, including those due to damage induced by self-irradiation. The superconducting transition temperature decreases sharply with time, suggesting a radiation-induced Frenkel defect concentration much larger than predicted by current radiation damage theories. Extended x-ray absorption fine-structure measurements demonstrate that while the local crystal structure in fresh material is well ordered, aged material is disordered much more strongly than expected from simple defects, consistent with strong disorder throughout the damage cascade region. These data highlight the potential impact of local lattice distortions relative to defects on the properties of irradiated materials and underscore the need for more atomic-resolution structural comparisons between radiation damage experiments and theory.
Date: October 20, 2006
Creator: Booth, C.H.; Daniel, M.; Wilson, R.E.; Bauer, E.D.; Mitchell,J.N.; Moreno, N.O. et al.
Partner: UNT Libraries Government Documents Department

Perturbing the superconducting planes in CeCoIn5 by Snsubstitution

Description: In contrast to substitution on the Co or Ce site, Sn substitution has a remarkably strong effect on superconductivity in CeCoIn{sub 5-x}Sn{sub x}, with T{sub c} {yields} 0 beyond only {approx}3.6% Sn. Instead of being randomly distributed on in-plane and out-of-plane In sites, extended x-ray absorption fine structure measurements show the Sn atoms preferentially substitute within the Ce-In plane. This result highlights the importance of the In(1) site to impurity scattering and clearly demonstrates the two-dimensional nature of superconductivity in CeCoIn{sub 5}.
Date: January 11, 2005
Creator: Daniel, M.; Bauer, E.D.; Han, S.-W.; Booth, C.H.; Cornelius,A.L.; Pagliuso, P.G. et al.
Partner: UNT Libraries Government Documents Department

Local structure around Sn in CeCoIn{sub 5-x}Sn{sub x}

Description: The local structure around Sn dopants in CeCoIn{sub 5-x}Sn{sub z} has been probed by extended x-ray absorption fine structure (EXAFS) technique. The fit results for both x = 0.12 and x = 0.18 clearly indicate the dopant Sn atoms predominantly occupying the planar In(1) site. These results are consistent with the quasi-two-dimensional electronic properties of CeCoIn{sub 5} and is discussed in relation to the observed bulk properties.
Date: June 16, 2004
Creator: Daniel, M.; Han, S.-W.; Booth, C.H.; Cornelius, A.L.; Bauer, E.D. & Sarrao, J.L.
Partner: UNT Libraries Government Documents Department

Investigation of Anderson lattice behavior in Yb1-xLuxAl3

Description: Measurements of magnetic susceptibility {chi}(T), specific heat C(T), Hall coefficient R{sub H}(T), and Yb valence {nu} = 2 + n{sub f} [f-occupation number n{sub f} (T) determined from Yb L{sub 3} x-ray absorption measurements] were carried out on single crystals of Yb{sub 1-x}Lu{sub x}Al{sub 3}. The low temperature anomalies observed in {chi}(T) and C(T) corresponding to an energy scale T{sub coh} {approx} 40 K in the intermediate valence, Kondo lattice compound YbAl{sub 3} are suppressed by Lu concentrations as small as 5% suggesting these low-T anomalies are extremely sensitive to disorder and, therefore, are a true coherence effect. By comparing the temperature dependence of various physical quantities to the predictions of the Anderson Impurity Model, the slow crossover behavior observed in YbAl{sub 3}, in which the data evolve from a low-temperature coherent, Fermi-liquid regime to a high temperature local moment regime more gradually than predicted by the Anderson Impurity Model, appears to evolve to fast crossover behavior at x {approx} 0.7 where the evolution is more rapid than predicted. These two phenomena found in Yb{sub 1-x}Lu{sub x}Al{sub 3}, i.e., the low-T anomalies and the slow/fast crossover behavior are discussed in relation to recent theories of the Anderson lattice.
Date: October 6, 2003
Creator: Bauer, E.D.; Booth, C.H.; Lawrence, J.M.; Hundley, M.F.; Sarrao, J.L.; Thompson, J.D. et al.
Partner: UNT Libraries Government Documents Department

Crystal fields, disorder, and antiferromagnetic short-range order in (Yb{sub 0.24}Sn{sub 0.76})Ru

Description: We report extensive measurements on a new compound (Yb{sub 0.24}Sn{sub 0.76})Ru that crystallizes in the cubic CsCl structure. Valence band photoemission and L{sub 3} x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb{sup 3+} is split by the crystalline electric field (CEF) into a Γ{sub 7} doublet ground state and a Γ{sub 8} quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a Γ{sub 6} excited state resides at 32 meV; however, the Γ{sub 8}/Γ{sub 6} transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K, there is a peak in specific heat that is too broad to represent a magnetic phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand, this peak also is too narrow to represent the Kondo effect in the Γ{sub 7} ground state doublet. On the basis of the field-dependence of the specific heat, we argue that antiferromagnetic shortrange order (possibly co-existing with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.
Date: July 18, 2011
Creator: Klimczuk, T.; Wang, C. H.; Lawrence, J. M.; Xu, Q.; Durakiewicz, T.; Ronning, F. et al.
Partner: UNT Libraries Government Documents Department

Anisotropic intermediate valence in Yb2M3Ga9 (M = Rh, Ir)

Description: The intermediate valence compounds Yb{sub 2}M{sub 3}Ga{sub 9} (M = Rh, Ir) exhibit an anisotropic magnetic susceptibility. We report measurements of the temperature dependence of the 4f occupation number, n{sub f}(T), for Yb{sub 2}M{sub 3}Ga{sub 9} as well as the magnetic inelastic neutron scattering spectrum S{sub mag}({Delta}E) at 12 and 300 K for Yb{sub 2}Rh{sub 3}Ga{sub 9}. Both n{sub f}(T) and S{sub mag}({Delta}E) were calculated for the Anderson impurity model with crystal field terms within an approach based on the non-crossing approximation. These results corroborate the importance of crystal field effects in these materials; they also suggest that Anderson lattice effects are important to the physics of Yb{sub 2}M{sub 3}Ga{sub 9}.
Date: April 26, 2005
Creator: Christianson, A.D.; Lawrence, J.M.; Lobos, A.M.; Aligia, A.A.; Bauer, E.D.; Moreno, N.O. et al.
Partner: UNT Libraries Government Documents Department