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Coherence in CePd/sub 3/

Description: This paper presents results of resistivity and susceptibility measurements on CePd/sub 3/ and its alloys which support the existence of a third significant temperature, T* = 40K. Anomalous pressure dependence of rho(T) occurs and nonmagnetic impurities cause large increases in rho(T) on this scale, which is distinct from and smaller than the scale T/sub max/ over which coherence first appears. Evidence is given that the magnetic form factor anomaly known to exist in CePd/sub 3/ arises on the same scale T* suggesting that the 5d spin susceptibility which is responsible for the form factor anomaly is connected with the low temperature transport anomalies. The discussion is limited to the relationship of these results to other experimental measurements in CePd/sub 3/. In particular, we stress the relationship of these results to those of recent optical conductivity measurements which show that the quasi-particle effective mass is strongly renormalized at low temperatures. This occurs over a temperature scale proposed for T*.
Date: January 1, 1987
Creator: Lawrence, J.M.; Chen, Y.Y. & Thompson, J.D.
Partner: UNT Libraries Government Documents Department

Pressure dependence of the resistivity of Ce/sub 3/Al

Description: Ce/sub 3/Al was prepared from very high purity cerium. The resistivity at various pressures show a structural transition near 100/sup 0/K at zero pressure. This antiferromagnetic heavy fermion behavior evolves smoothly towards nonmagnetic large T/sub K/ (slightly overweight fermion) behavior as the pressure is raised. 3 figs. (DLC)
Date: January 1, 1987
Creator: Lawrence, J.M.; Chen, Y.Y.; Thompson, J.D. & Borges, H.A.
Partner: UNT Libraries Government Documents Department

Scaling in heavy-fermion systems

Description: Ambient pressure characteristics of heavy-fermion compounds, such as the ratio of the low temperature magnetic susceptibility to the electronic specific heat coefficient {gamma} and a simple relationship between the T{sup 2}-coefficient of resistivity and {gamma}{sup 2}, suggest that a single-energy scale T{sub o} dictates the physics of these materials. Such is the case for Kondo-impurity systems to which heavy-fermions are related. We consider the consequences of assuming that the electronic free energy is given by a universal function of T/T{sub o} (V) where V is the molar volume. We show that volume-dependent magnetic susceptibility, specific heat and electrical resistivity of some heavy-fermion compounds scale as T/T{sub o} (V), at least over a range in pressures and temperatures. A further consequence of the principle assumption is that Gruneisen parameters defined as - {partial_derivative}{ell}nX/{partial_derivative}nV, where X is some physical property, should be identical for all properties and equal to that determined from electronic contributions to the volume- thermal expansion coefficient and specific heat. In several materials, this equality holds, at least approximately. Although evidence is found for single-energy scaling in heavy-fermion materials, we cannot conclude unambiguously that the basic assumption is correct in detail.
Date: December 31, 1993
Creator: Thompson, J. D.; Fisk, Z. & Lawrence, J. M.
Partner: UNT Libraries Government Documents Department

Development of high magnetic fields for energy research

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The primary purpose of work has been to develop the scientific basis for DOE support of a program that would build a novel, nondestructive 100-tesla magnet that would be available as a user facility for cutting-edge, energy-related research and technology at very high magnetic fields.
Date: November 1, 1998
Creator: Thompson, J.D.; Campbell, L.J.; Modler, R.; Movshovich, R.; Lawrence, J.M. & Awschalom, D.D.
Partner: UNT Libraries Government Documents Department

Disorder and size effects on Kondo interactions and magneticcorrelations in CePt2 nanoscrystals

Description: The evolution of the Kondo effect and magnetic correlations with size reduction in CePt{sub 2} nanoparticles (3.1-26 nm) is studied by analysis of the temperature-dependent specific heat and magnetic susceptibility. The antiferromagnetic correlations diminish with size reduction. The Kondo effect predominates at small particle size with trivalent, small Kondo temperature (T{sub K}) magnetic regions coexisting with strongly mixed valent, large T{sub K} nonmagnetic regions. We discuss the role of structural disorder, background density of states and the electronic quantum size effect on the results.
Date: December 12, 2006
Creator: Chen, Y.Y.; Huang, P.H.; Ou, M.N.; Wang, C.R.; Yao, Y.D.; Lee,T.K. et al.
Partner: UNT Libraries Government Documents Department

Ytterbium divalency and lattice disorder in near-zero thermalexpansion YbGaGe

Description: While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.
Date: May 8, 2006
Creator: Booth, C.H.; Christianson, A.D.; Lawrence, J.M.; Pham, L.; Lashley, J. & Drymiotis, F.R.
Partner: UNT Libraries Government Documents Department

4f bands in Ce heavy fermions and mixed valent compounds at T {much_gt} T{sub K}

Description: We report evidence of 4f band character in Ce 4f states at {Tau}{much_gt}{Tau}{sub K} using the technique of high-resolution angle-resolved resonant photoemission. The Ce intermetallic compound CePt{sub +x} was grown and studied in situ by the method of MBE and was characterized by LEED, XPS and XAS. These new findings would suggest a need for a reexamination of 4f photoemission in Ce compounds.
Date: August 1, 1994
Creator: Andrews, A. B.; Joyce, J. J.; Arko, A. J.; Thompson, J. D.; Tang, J.; Fisk, Z. et al.
Partner: UNT Libraries Government Documents Department

Evidence for a coherence gap in Ce sub 3 Bi sub 4 Pt sub 3

Description: In this paper we examine the physical properties of the f-electron system Ce{sub 3}Bi{sub 4}Pt{sub 3}. In the majority of cases f-moment compounds are metallic, and, depending upon the relative strength of competing magnetic interactions, have a superconducting, paramagnetic, or antiferromagnetic ground state. In rare instances f-electron compounds have a narrow-gapped insulating ground state instead. This gap is thought to result from hybridization between conduction and f electrons. We have measured the magnetic susceptibility, low-temperature specific heat, resistivity, Hall effect, and thermoelectric power of Ce{sub 3}Bi{sub 4}Pt{sub 3} and find that this material is non-metallic at all temperatures. Isostructural lanthanum substitution for cerium suppresses the gap and produces transport and thermodynamic behavior that is characteristic of a relatively heavy Kondo impurity system. Further, the energy scale at which coherence develops is roughly equal to the energy gap in this compound. This suggests that the gap in Ce{sub 3}Bi{sub 4}Pt{sub 3} appears to stem from the same requirements of lattice periodicity necessary for coherence to manifest itself in metallic systems. Hence, there is strong evidence that the insulating behavior displayed by Ce{sub 3}Bi{sub 4}Pt{sub 3} results form the presence of a Kondo coherence-induced gap. 15 refs., 4 figs.
Date: January 1, 1990
Creator: Hundley, M.F.; Canfield, P.C.; Thompson, J.D. Fisk, Z. (Los Alamos National Lab., NM (USA)) & Lawrence, J.M. (California Univ., Irvine, CA (USA))
Partner: UNT Libraries Government Documents Department

Local and average crystal structure and displacements of La{sup 11}B{sub 6} and EuB{sub 6} as a function of temperature

Description: Measurements of both the average crystal structure from Rietveld refinement of neutron powder diffraction (NPD) data and the local structure from La L{sub III}-edge x-ray-absorption fine-structure (XAFS) are presented for a La{sup 11}B{sub 6} sample as a function of temperature ({approx}10-320 K). These data are compared to XAFS results on a EuB{sub 6} sample. The single-site La and B positional distribution widths and the La-B and La-La bond length distribution widths and their temperature dependence are compared. This comparison allows an estimate of the La and B site displacements, and we find that these sublattices are only slightly correlated with each other. Moreover, while the temperature dependence of the displacement parameters of the average sites from diffraction fit an Einstein model well, the temperature dependence of the La-B bond length distribution width requires at least two vibrational frequencies, corresponding to the La and B frequencies of the individual sites. XAFS data on EuB{sub 6} indicate that the situation is the same in the Eu compound. In addition, comparisons between data taken below and above the ferromagnetic transition temperature for EuB{sub 6} place stringent limits on the lattice involvement in the associated metal-insulator transition and the ensuing large magnetoresistance effect. This lack of lattice involvement in the magnetoresistance transition is in sharp contrast to the strong lattice involvement observed in the colossal magnetoresistance lanthanum manganese perovskites.
Date: January 30, 2001
Creator: Booth, C.H.; Sarrao, J.L.; Hundley, M.F.; Cornelius, A.L.; Kwei, G.H.; Bianchi, A. et al.
Partner: UNT Libraries Government Documents Department

Two energy scales and slow crossover in YbAl3

Description: We present results for YbAl{sub 3} which show that the susceptibility {chi}(T), 4f occupation number n{sub f}(T) and the entropy S(T) exhibit a slow crossover between the Fermi liquid and local moment regimes. In addition both {chi}(T) and the linear specific heat coefficient {gamma} = C/T exhibit low temperature peaks that imply that in addition to the Kondo scale (T{sub K} {approx} 500K) there is a second low temperature scale (T{sub coh} {approx} 50K) for the onset of coherence. We discuss these results in the context of Nozieres' exhaustion in the Anderson lattice.
Date: January 15, 2002
Creator: Lawrence, J.M.; Ebihara, T.; Riseborough, P.S.; Booth, C.H.; Pagliuso, P.G.; Sarrao, J.L. et al.
Partner: UNT Libraries Government Documents Department

Photoemission in YbCu sub 2 Si sub 2 : Problems with the Kondo impurity model

Description: We report valence band photoemission results for YbCu{sub 2}Si{sub 2}. The 4f{sup 13}(J=7/2) final state peak, centered 60meV below the Fermi level {epsilon}{sub F}, lacks the temperature dependence and is broader than predicted for a Kondo resonance. Together with the recent photoemission results for cerium compounds, these results raise serious doubts about the Kondo impurity explanation of heavy fermion photoemission. 7 refs., 3 figs.
Date: January 1, 1991
Creator: Lawrence, J.M. (California Univ., Irvine (United States)); Arko, A.J.; Joyce, J.J.; Canfield, P.C.; Fisk, Z. & Thompson, J.D. (Los Alamos National Lab., NM (United States))
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

Thermodynamics and transport in Ce{sub 3}Bi{sub 4}Pt{sub 3} and related compounds

Description: The transport and thermodynamic properties of the small-gap semiconductor Ce{sub 3}Bi{sub 4}Pt{sub 3} are reviewed and discussed in relation to other Kondo insulators and metals. The data are consistent with the small-gap semiconductors being Kondo-like metals at temperatures T {ge} E{sub g}/k{sub B}. Kondo insulators appear to be an unusually simple realization of the Anderson Lattice Hamiltonian in which the lower hybridization band is exactly filled, or in Kondo language, the Abrikosov-Suhl resonance exactly fills a Brillouin zone. 8 figs, 40 refs. (DLC)
Date: September 1, 1992
Creator: Thompson, J. D.; Canfield, P. C.; Fisk, Z.; Hundley, M. F.; Kwei, G. H.; Lacerda, A. et al.
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

Antiferromagnetism in Pr3In: Singlet/triplet physics withfrustration

Description: We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu{sub 3}Au structure) compound Pr{sub 3}In. This compound is believed to have a singlet ({Lambda}{sub 1}) groundstate and a low-lying triplet ({Lambda}{sub 4}) excited state. In addition, nearest-neighbor antiferromagnetic interactions are frustrated in this structure. Antiferromagnetic order occurs below T{sub N} = 12K with propagation vector (0, 0, 0.5 {center_dot}{delta}) where {delta} {approx} 1/12. The neutron diffraction results can be approximated with the following model: ferromagnetic sheets from each of the three Pr sites alternate in sign along the propagation direction with a twelve-unit-cell square-wave modulation. The three moments of the unit cell of 1 {micro}{sub B} magnitude are aligned so as to sum to zero as expected for nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12K, there is a transition near 70K below which there is a small (0.005 {micro}{sub B}) ferromagnetic moment. There is considerable field and sample dependence to these transitions. The specific heat data show almost no anomaly at T{sub N} = 12K. This may be a consequence of the induced moment in the {Lambda}{sub 1} singlet, but may also be a sample-dependent effect.
Date: November 18, 2004
Creator: Christianson, A.D.; Lawrence, J.M.; Zarestky, J.L.; Suzuki, H.; Thompson, J.D.; Hundley, M.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

Thermodynamics and transport in Ce sub 3 Bi sub 4 Pt sub 3 and related compounds

Description: The transport and thermodynamic properties of the small-gap semiconductor Ce{sub 3}Bi{sub 4}Pt{sub 3} are reviewed and discussed in relation to other Kondo insulators and metals. The data are consistent with the small-gap semiconductors being Kondo-like metals at temperatures T {ge} E{sub g}/k{sub B}. Kondo insulators appear to be an unusually simple realization of the Anderson Lattice Hamiltonian in which the lower hybridization band is exactly filled, or in Kondo language, the Abrikosov-Suhl resonance exactly fills a Brillouin zone. 8 figs, 40 refs. (DLC)
Date: January 1, 1992
Creator: Thompson, J. D.; Canfield, P. C.; Fisk, Z.; Hundley, M. F.; Kwei, G. H.; Lacerda, A. (Los Alamos National Lab., NM (United States)) et al.
Partner: UNT Libraries Government Documents Department