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Shock-induced melting and rapid solidification

Description: Model calculations are presented to estimate that approx.50 GPa is required to completely shock melt metal powders with quenching at rates up to 10/sup 8/ K/s. Experiments are discussed for powders of a Cu-Zr alloy compacted in the usual way at 16 GPa and melted by shocking to 60 GPa. 12 refs.
Date: August 1, 1987
Creator: Nellis, W.J.; Gourdin, W.H. & Maple, M.B.
Partner: UNT Libraries Government Documents Department

The degree of 5f electron localization in URu2Si2: electron energy-loss spectroscopy and spin-orbit sum rule analysis

Description: We examine the degree of 5f electron localization in URu{sub 2}Si{sub 2} using spin-orbit sum rule analysis of the U N{sub 4,5} (4d {yields} 5f) edge. When compared to {alpha}-U metal, US, USe, and UTe, which have increasing localization of the 5f states, we find that the 5f states of URu{sub 2}Si{sub 2} are more localized, although not entirely. Spin-orbit analysis shows that intermediate coupling is the correct angular momentum coupling mechanism for URu{sub 2}Si{sub 2} when the 5f electron count is between 2.6 and 2.8. These results have direct ramifications for theoretical assessment of the hidden order state of URu{sub 2}Si{sub 2}, where the degree of localization of the 5f electrons and their contribution to the Fermi surface are critical.
Date: May 19, 2010
Creator: Jeffries, J R; Moore, K T; Butch, N P & Maple, M B
Partner: UNT Libraries Government Documents Department

Low temperature properties of CeOs/sub 2/ in the C14 and C15 crystallographic Laves phases

Description: The compound CeOs/sub 2/ has been prepared in both cubic C15 and hexagonal C14 Laves phases. Measurements of ac and dc magnetic susceptibility, electrical resistivity, and specific heat have been performed on samples of both phases. The C14 phase has been found to exhibit superconductivity with a superconducting transition temperature T/sub c/ of 1.1/sup 0/K, while the C15 phase does not display superconductivity above 70 mK. Both phases exhibit a slight exchange enhancement of the susceptibility. The curves of resistivity vs temperature for both phases exhibit strong negative curvature which are reminiscent of other valence fluctuation compounds.
Date: January 1, 1984
Creator: Torikachvili, M.S.; Yang, K.N.; Maple, M.B. & Meisner, G.P.
Partner: UNT Libraries Government Documents Department

UFe/sub 4/P/sub 12/ and CeFe/sub 4/P/sub 12/: non-metallic isotypes of superconducting LaFe/sub 4/P/sub 12/

Description: The new compound UFe/sub 4/P/sub 12/, which was found to be isostructural to superconducting LaFe/sub 4/P/sub 12/ and with a lattive constant of 7.7729 A, is a semiconductor and shows ferromagnetic order below 3.15 K. CeFe/sub 4/P/sub 12/ is also a semiconductor and its magnetic susceptibility is unusually small in comparison to LaFe/sub 4/P/sub 12/. The semiconducting behaviors of both UFe/sub 4/P/sub 12/ and CeFe/sub 4/P/sub 12/ seem anomalous and may arise from strong f-electron hybridization.
Date: January 1, 1984
Creator: Meisner, G.P.; Torikachvili, M.S.; Yang, K.N.; Maple, M.B. & Guertin, R.P.
Partner: UNT Libraries Government Documents Department

Neutron scattering study of the magnetic transition in the reentrant superconductor Ho/sub 0/ /sub 6/Er/sub 0/ /sub 4/Rh/sub 4/B/sub 4/

Description: A number of different diffraction patterns were obtained with various resolutions. A high-resolution scan of the (101), (110), and (002) peaks at 1.6 and 4.2 K shows that these peaks have very small nuclear components as observed in the 4.2 K data; large magnetic (101) and (110) peaks found at 1.6 K show long-range ferromagnetic order. Analysis of the nuclear and magnetic diffraction peaks shows that the average ordered moment is about 5.0 +- 0.5 ..mu../sub B/ at 1.6 K. The temperature dependence of the intensity of the (101) powder peak is also shown. No long-range magnetic scattering is found above 3.60 K. At 3.60 K the magnetic intensity jumps suddenly to a finite value, then increases nearly linearly with temperature to about 2.5 K. Below 2.5 K the intensity rounds off and appears to saturate at about 1.6 K. There are no specific heat anomalies between 0.5 K and 1.6 K. 3 figures. (RWR)
Date: June 1, 1979
Creator: Mook, H.A.; Koehler, W.C.; Maple, M.B.; Fisk, Z. & Johnston, D.C.
Partner: UNT Libraries Government Documents Department

Observation of long-range ferromagnetic order in the heavy-fermion compuound URu/sub 1. 2/Re/sub 0. 8/Si/sub 2/ by neutron scattering

Description: We have performed a neutron scattering study of the heavy-fermion compound URu/sub 1.2/Re/sub 0.8/Si/sub 2/, in order to verify the occurrence of long-range ferromagnetic order. This study consisted of measurements of elastic, inelastic, and polarized neutron scattering, measurement of low-angle critical scattering, and the determination of the temperature dependence of the order parameter. We found a sharp peak in the critical scattering at /approx/ 30 K for the wavevector q = 0.08 /angstrom//sup /minus/1/; and an enhancement of the intensity at the position of the (101) nuclear Bragg reflection below the Curie temperature. These measurements suggest the occurrence of long-range magnetic order. The value of the ordered moment is estimated to be /approx/ 0.53 /mu//sub B/ at 10 K. 17 refs., 3 figs.
Date: January 1, 1989
Creator: Torikachvili, M.S.; Rebelsky, L.; Motoya, K.; Shapiro, S.M.; Dalichaouch, Y. & Maple, M.B.
Partner: UNT Libraries Government Documents Department

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

Anomalous surface impedance in reentrant ferromagnetic superconductors

Description: For ErRh/sub 4/B/sub 4/, owing to the critical spin fluctuations just above T/sub s/ (> T/sub c2/), the critical temperature at which surface ferromagnetism appears, the reciprocal penetration depth, lambda/sup -1/, decreases smoothly as T decreases toward T/sub s/. For Er/sub 0/ /sub 5/Ho/sub 0/ /sub 5/Rh/sub 4/B/sub 4/, the decrease in lambda/sup -1/ for T > T/sub c2/ is very small, and lambda/sup -1/ decreases abruptly at T/sub c2/.
Date: May 1, 1984
Creator: Huang, C.Y.; Kozlowski, G.; Mancini, F.; Maple, M.B.; Matsumoto, H.; Olson, C.E. et al.
Partner: UNT Libraries Government Documents Department

Interpretation of specific-heat and spontaneous-magnetization anomalies at the reentrant superconducting - ferromagnetic transition in (Ho/sub 0/. /sub 6/Er/sub 0/. /sub 4/)Rh/sub 4/B/sub 4/

Description: Analysis of neutron-diffraction data on the compound (Ho/sub 0/./sub 6/Er/sub 0/./sub 4/)Rh/sub 4/B/sub 4/ indicates that the Curie temperature is depressed by about 0.2 K due to the occurrence of superconductivity, in agreement with theoretical predictions. The temperature dependence of the specific heat in the vicinity of the first-order reentrant superconducting - ferromagnetic transition was computed by means of a simple model from the temperature dependence of the spontaneous magnetization of the Ho ions and was found to be in good agreement with the experimental data.
Date: September 1, 1981
Creator: Woolf, L.D.; Johnston, D.C.; Mook, H.A.; Koehler, W.C.; Maple, M.B. & Fisk, Z.
Partner: UNT Libraries Government Documents Department

Pressure induced Superconductivity in the Charge Density Wave Compound Tritelluride

Description: A series of high-pressure electrical resistivity measurements on single crystals of TbTe{sub 3} reveal a complex phase diagram involving the interplay of superconducting, antiferromagnetic and charge density wave order. The onset of superconductivity reaches a maximum of almost 4 K (onset) near {approx} 12.4 GPa.
Date: February 15, 2010
Creator: Hamlin, J.J.; Zocco, D.A.; Sayles, T.A.; Maple, M.B.; /UC, Davis; Chu, J.-H. et al.
Partner: UNT Libraries Government Documents Department

Experiments on heavy electron and high T/sub c/ oxide superconductors. [Gd-doped (U,Th)Be/sub 13/; RBa/sub 2/Cu/sub 3/O/sub 7/]

Description: In the first part of this paper, we briefly describe some of our efforts to determine the type of pairing and pairing mechanisms that are associated with the superconductivity of heavy electron materials by means of H/sub c2/(T) measurements in Gd-doped (U/sub 1-x/Th/sub x/)Be/sub 13/ alloys. An account of some of our recent work on the new high T/sub c/ copper oxide superconductors is given in the second part of the paper. 30 refs., 12 figs.
Date: January 1, 1987
Creator: Maple, M.B.; Dalichaouch, Y.; Ferreira, J.M.; Hake, R.R.; Lambert, S.E.; Lee, B.W. et al.
Partner: UNT Libraries Government Documents Department

Electronic structure of the quenched superconductivity materials Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-delta/

Description: The superconductivity of the Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-delta/ system is quenched as x increases. It has been speculated that Pr has valence 4+, resulting in extra charge in the Cu-O planes, and causing T/sub c/-quenching. To study the Pr electronic state, we have measured valence band resonant photoemission of the Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7- delta/ system for x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0. We find that the Pr valence is close to 3+ for all x and that the extracted Pr 4f spectral weight has a complex lineshape, implying extensive Pr 4f/O 2p hybridization which probably causes the T/sub c/-quenching by disrupting the electronic or magnetic structure of the x = 0 material, perhaps via a Pr-Cu superexchange interaction. 36 refs., 4 figs.
Date: January 1, 1988
Creator: Kang, J.S.; Allen, J.W.; Shen, Z.X.; Ellis, W.P.; Yeh, J.J.; Lee, B.W. et al.
Partner: UNT Libraries Government Documents Department

Electron spectroscopy studies of high temperature superconductors: Y/sub 1/minus/x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7/minus/delta/

Description: We itemize our previous work on high T/sub c/ superconductors, and describe more fully the results of an electron spectroscopy study and impurity Anderson Hamiltonian analysis of the Pr 4f spectrum of Y/sub 1/minus/x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7/minus/delta/, a system in which superconductivity is quenched as x increases. It has been speculated that Pr has valence 4+, resulting in extra charge in the Cu-O planes, and causing T/sub c/-suppression. We find that the Pr valence is close to 3+ for all x but that there is extensive Pr 4f hybridization with other valence band states. The Cu valence is essentially unchanged with x. From these findings, we speculate that Pr 4f hybridization with other valence band states has enabled Pr spin fluctuations to cause the T/sub c/-suppression. 41 refs., 4 figs.
Date: January 1, 1989
Creator: Kang, J.S.; Allen, J.W.; Lee, B.W.; Maple, M.B.; Shen, Z.X.; Yeh, J.J. et al.
Partner: UNT Libraries Government Documents Department

Muon spin relaxation in ErRh/sub 4/B/sub 4/

Description: We have found that the erbium magnetic moment is so large that in ErRh/sub 4/B/sub 4/ it can relax muon polarization in times shorter than can be resolved by a typical ..mu..SR apparatus. The complete relaxation signal is resolved at temperatures above 50K only because of rapid fluctuation of the erbium moment, which partially decouples it from the muon's moment. Not much signal is resolved at temperatures less than or equal to 10K, but no dramatic effect is seen in crossing the superconducting transition temperature. The higher temperature local field fluctuation rates observed appear consistent with the exchange and spin-lattice fluctuation rates to be expected of erbium in this material. Perhaps more information on moment dynamics below 10K can be obtained by alloying erbium with a nonmagnetic rare earth such as yttrium within the RERh/sub 4/B/sub 4/ structure (as has been attempted for holmium), to reduce the rms local field at the muon.
Date: January 1, 1984
Creator: Noakes, D.R.; Ansaldo, E.J.; Brewer, J.H.; Harshman, D.R.; Huang, C.Y.; Torikachili, M.S. et al.
Partner: UNT Libraries Government Documents Department

Multiple ordered phases in the filled skutterudite compound PrOs4As12

Description: Magnetization, specific heat, and electrical resistivity measurements were made on single crystals of the filled skutterudite compound PrOs{sub 4}As{sub 12}. Specific heat measurements indicate an electronic specific heat coefficient {gamma} {approx} 50-200 mJ/mol K{sup 2} at temperatures 10 K {le} T {le} 18 K, and {approx} 1 J/mol K{sup 2} for t {le} 1.6 K. Magnetization, specific heat, and electrical resistivity measurements reveal the presence of two, or possibly three, ordered phases at temperatures below {approx} 2.3 K and in fields below {approx} 3 T. The low temperature phase displays antiferromagnetic characteristics, while the nature of the ordering in the other phase(s) has yet to be determined.
Date: March 20, 2006
Creator: Yuhasz, W M; Butch, N P; Sayles, T A; Ho, P; Jeffries, J R; Yanagisawa, T et al.
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

Shock compaction of high- Tc superconductors

Description: We present the results of shock compaction experiments on high-{Tc} superconductors and describe the way in which shock consolidation addresses critical problems concerning the fabrication of high J{sub c} bulk superconductors. In particular, shock compaction experiments on YBa{sub 2}Cu{sub 3}O{sub 7} show that shock-induced defects can greatly increase intragranular critical current densities. The fabrication of crystallographically aligned Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} samples by shock-compaction is also described. These experiments demonstrate the potential of the shock consolidation method as a means for fabricating bulk high-{Tc} superconductors having high critical current densities.
Date: September 1, 1990
Creator: Weir, S.T.; Nellis, W.J.; McCandless, P.C.; Brocious, W.F. (Lawrence Livermore National Lab., CA (USA)); Seaman, C.L.; Early, E.A. et al.
Partner: UNT Libraries Government Documents Department