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Magnetism in single-crystalline CePtSn.

Description: CePtSn exhibits two antiferromagnetic transitions at low temperatures. We report on magnetoresistance and in magnetization studies of single-crystalline CePtSn in magnetic fields up to 18 T. The data were taken to establish the magnetic phase diagrams for CePtSn in fields applied along the principal directions.
Date: August 4, 1999
Creator: Bordallo, H. N.; Chang, S.; Lacerda, A. H.; Nakotte, H.; Takabatake, T. & Torikachvili, M. S.
Partner: UNT Libraries Government Documents Department


Description: Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase hard/soft composite magnets. CoPt films, with a thickness of 25 nm, were sputter-deposited from a nearly equiatomic alloy target onto oxidized Si wafers. The films were subsequently annealed at 700 C and fully transformed from the FCC phase to the magnetically hard, ordered L1{sub 0} phase. The coercivity of the films increased rapidly with annealing time until it reached a plateau at approximately 9.5 kOe. Fully-ordered CoPt films were then used as substrates for deposition of Co layers, with thicknesses in the range of 2.8--225 nm, in order to produce the hard/soft composite bilayers. As predicted by theory, the magnetic coherency between the soft Co phase and the hard, ordered CoPt phase decreased as the thickness of the soft phase increased. This decrease in coupling was clearly seen in the magnetic hysteresis loops of the bilayers. At small thicknesses of Co (a few nanometers), the shape of the loop was one of a uniform material showing no indication of the presence of two phases with extremely different coercivities. At larger Co thicknesses, constricted loops, i.e., ones showing the presence of a mixture of two ferromagnetic phases of different hardnesses, were obtained. The magnetic exchange present in the bilayer samples was qualitatively analyzed using magnetic recoil curves and the dependence of exchange coupling on the soft phase dimension in the bilayer hard/soft composite magnet films is discussed.
Date: April 5, 1999
Partner: UNT Libraries Government Documents Department

High-field magnetization studies of U{sub 2}T{sub 2}Sn (T=Co, Ir, Pt) compounds

Description: High-field magnetization measurements at 4.2 K on U{sub 2}T{sub 2}Sn (T = Co, Ir and Pt) compounds have been performed on free and fixed powders up to 57 T. An antiferromagnetic ground state of U{sub 2}Pt{sub 2}Sn is corroborated by a metamagnetic transition at 22 T with very small hysteresis going up and down with field. U{sub 2}Co{sub 2}Sn and U{sub 2}Ir{sub 2}Sn show no metamagnetic transition up to 57 T which is in agreement with the non-magnetic ground state of these compounds. In all cases, the maximum applied field is not sufficient to achieve saturation. The short-pulse measurements presented here are compared with previous results obtained in quasi-static fields up to 35 T.
Date: July 1, 1995
Creator: Prokes, K.; Nakotte, H. & de Boer, F.R.
Partner: UNT Libraries Government Documents Department

Magnetic Compton scattering studies of the Invar alloy Fe{sub 3}Pt

Description: The magnetic Compton profiles (MCP) for both ordered and disordered Fe{sub 3}Pt samples have been measured above and below their Curie temperature. These measurements show that the average moment per atom at room temperature is 2.8{sub {mu}{sub B}} {plus_minus} 0.1{sub {mu}{sub B}} for disordered Fe{sub 3}Pt and 1.8{sub {mu}{sub B}} {plus_minus} 0.1{sub {mu}{sub B}} for ordered Fe{sub 3}Pt., At temperatures above {Tc}, we measured a substantial reduction in the moment (0.6{sub {mu}{sub B}} {plus_minus} 0.1{sub {mu}{sub B}} for disordered Fe{sub 3}Pt and 0.6{sub {mu}{sub B}} {plus_minus} 0.1{sub {mu}{sub B}} for ordered Fe{sub 3}Pt) and a change in the shape of the MCP. These results indicate a decrease of the d-like moment on the Fe atoms in the disordered phase. The MCP for the ordered phase shows a change in the total moment, yet the momentum distribution is substantially different and cannot be described by this analysis.
Date: February 1, 1995
Creator: Yahnke, C.J.; Srajer, G.; Haeffner, D.R.; Mills, D.M. & Assoufid, L.
Partner: UNT Libraries Government Documents Department

Theory of exotic superconductivity and normal states of heavy electron and high temperature superconductivity materials. Progress report, February 15, 1994--February 14, 1995

Description: This is a progress report for the DOE project covering the period 2/15/94 to 2/14/95. The PI had a fruitful sabbatical during this period, and had some important new results, particularly in the area of new phenomenology for heavy fermion superconductivity. Significant new research accomplishments are in the area of odd-in-time-reversal pairing states/staggered superconductivity, the two-channel Kondo lattice, and a general model for Ce impurities which admits one-, two-, and three-channel Kondo effects. Papers submitted touch on these areas: staggered superconductivity - a new phenomenology for UPt{sub 3}; theory of the two-channel Kondo lattice in infinite dimensions; general model of a Ce{sup 3+} impurity. Other work was done in the areas: Knight shift in heavy fermion alloys and compounds; symmetry analysis of singular pairing correlations for the two-channel Kondo impurity model.
Date: February 1, 1995
Creator: Cox, D. L.
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

Rhombohedral AlPt films formed by self-propagating, high temperature synthesis.

Description: High-purity AlPt thin films prepared by self-propagating, high temperature combustion synthesis show evidence for a new rhombohedral phase. Sputter deposited Al/Pt multilayers of various designs are reacted at different rates in air and in vacuum, and each form a new trigonal/hexagonal aluminide phase with unit cell parameters a = 15.571(8) {angstrom}, c = 5.304(1) {angstrom}, space group R-3 (148), and Z, the number of formula units within a unit cell, = 39. The lattice is isostructural to that of the AlPd R-3 lattice as reported by Matkovic and Schubert (Matkovic, 1977). Reacted films have a random in-plane crystallographic texture, a modest out-of-plane (001) texture, and equiaxed grains with dimensions on the order of film thickness.
Date: November 1, 2005
Creator: Adams, David Price; Rodriguez, Mark Andrew & Kotula, Paul Gabriel
Partner: UNT Libraries Government Documents Department

Small, Inexpensive Combined NOx and O2 Sensor

Description: It has been successfully demonstrated in this program that a zirconia multilayer structure with rhodium-based porous electrodes performs well as an amperometric NO{sub x} sensor. The sensitivity of the sensor bodies operating at 650 to 700 C is large, with demonstrated current outputs of 14 mA at 500 ppm NO{sub x} from sensors with 30 layers. The sensor bodies are small (4.5 x 4.2 x 3.1 mm), rugged, and inexpensive. It is projected the sensor bodies will cost $5-$10 in production. This program has built on another successful development program for an oxygen sensor based on the same principles and sponsored by DOE. This oxygen sensor is not sensitive to NO{sub x}. A significant technical hurdle has been identified and solved. It was found that the 100% Rh electrodes oxidize rapidly at the preferred operating temperatures of 650-700 C, and this oxidation is accompanied by a volume change which delaminates the sensors. The problem was solved by using alloys of Rh and Pt. It was found that a 10%/90% Rh/Pt alloy dropped the oxidation rate of the electrodes by orders of magnitude without degrading the NO{sub x} sensitivity of the sensors, allowing long-term stable operation at the preferred operating temperatures. Degradation in the sensor output caused by temperature cycling was identified as a change in resistance at the junction between the sensor body and the external leads attached to the sensor body. The degradation was eliminated by providing strong mechanical anchors for the wire and processing the junctions to obtain good electrical bonds. The NO{sub x} sensors also detect oxygen and therefore the fully-packaged sensor needs to be enclosed with an oxygen sensor in a small, heated zirconia chamber exposed to test gas through a diffusion plug which limits the flow of gas from the outside. Oxygen is pumped from ...
Date: September 1, 2008
Creator: Lawless, W. & Clark, C.
Partner: UNT Libraries Government Documents Department

Magnetic order of Co{sub 0.1}Pt{sub 0.9} in proximity in CoPt{sub 3}

Description: A polarized neutron reflectometry study of the magnetization density depth profile of a Co{sub 0.1}Pt{sub 0.9}-CoPt{sub 3} bilayer film found evidence for an induced moment in the Co{sub 0.1}Pt{sup 0.9} overlayer in close proximity to the CoPt{sub 3} underlayer. If the moment of Co in these films is that of the bulk, then the {mu}{sub Pt} = 0.09(1){mu}{sub B} in the overlayer, and {mu}{sub Pt} = 0.04(1){mu}{sub B} in the underlayer. In addition, ferromagnetic order of the Co{sub 0.1}Pt{sub 0.9} overlayer was observed 8K above {Tc} for the material in the bulk.
Date: December 1, 1998
Creator: Shapiro, A.L.; Hellman, F. & Fitzsimmons, M.R.
Partner: UNT Libraries Government Documents Department


Description: We report new theoretical results and analysis for the transport properties of superconducting UPt{sub 3}based on the leading models for the pairing symmetry. We use Fermi surface data and the measured inelastic scattering rate to show that the low-temperature thermal conductivity and transverse sound attenuation in the A and B phase of UPt3 are in excellent agreement with pairing states belonging to the two-dimensional orbital E{sub 2u} representation.
Date: April 1, 1999
Creator: GRAF, M. & AL, ET
Partner: UNT Libraries Government Documents Department

Investigation of the electrocatalysis for oxygen reduction reaction by Pt and binary Pt alloys: an XRD, XAS and electrochemical study

Description: Electrocatalysis for the oxygen reduction reaction (ORR) on five binary Pt alloy electrocatalysts (PtCr/C, PtMn/C, PtFe/C, PtCo/C and PtNi/C) supported on carbon have been investigated. The electrochemical characteristics for ORR in a proton conducting fuel cell environment has been correlated with the electronic and structural parameters determined under in situ conditions using XANES and EXAFS technique respectively. Results indicate that all the alloys possess higher Pt 5d band vacancies as compared to Pt/C. There is also evidence of lattice contraction in the alloys (supported by XRD results). Further, the Pt/C shows increase in Pt 5 d band vacancies during potential transitions from 0.54 to 0.84 V vs. RHE, which has been ration@ on the basis of OH type adsorption. In contrast to this, the alloys do not exhibit such an enhancement. Detailed EXAFS analysis supports the presence of OH species on Pt/C and its relative absence in the alloys. Correlation of the electrochemical results with bond distances and d-band vacancies show a volcano type behavior with the PtCr/C on top of the curve.
Date: December 31, 1995
Creator: Mukerjee, S.; McBreen, J. & Srinivasan, S.
Partner: UNT Libraries Government Documents Department

The origins of ordering in CuPt

Description: The alloy CuPt is one of the few that order into a L1{sub 1} crystal structure, i.e. planes of copper and planes of planes of planes of platinum perpendicular to the < 111 > direction. For disordered CuPt, the calculated Warren-Cowley short-range order parameter indicates an instability to concentration fluctuations with a wave-vector of ({1/2}, {1/2}, {1/2}), consistent with L1{sub 1} ordering. We show that this rare tendency is due to this ordering vector arising from the large joint density of states associated with L point and X point van-Hove singularities which lie near the Fermi energy.
Date: August 4, 1993
Creator: Clark, J. F.; Pinski, F. J.; Sterne, P. A.; Johnson, D. D.; Staunton, J. B. & Ginatempo, B.
Partner: UNT Libraries Government Documents Department

Substitutional effects on the electronic transport of the Kondo insulator Ce{sub 3}Bi{sub 4}Pt{sub 3}

Description: The resistivity {rho} and thermoelectric power S of the doped Kondo insulator (Ce{sub 1-x}La{sub x}){sub 3}Bi{sub 4}Pt{sub 3} are examined to determine the effects of doping on the narrow gap exhibited by this compound. With increasing La concentration the energy gap progressively disappears in both {rho} and S and band-like transport develops below 25 K. The T-0 transport energy gap as determined from either {rho} or S scales with the single-impurity Kondo energy scale T{sub K} as determined from magnetic susceptibility measurements, independently of x for x {le} 0.25. This result strongly suggests that the gap arises from band hybridization that is driven by Kondo-like many-body correlations rather than from single-electronic interactions.
Date: April 1, 1994
Creator: Hundley, M. F.; Canfield, P. C.; Thompson, J. D. & Fisk, Z.
Partner: UNT Libraries Government Documents Department

An analysis of the pull strength behaviors of fine-pitch, flip chip solder interconnections using a Au-Pt-Pd thick film conductor on Low-Temperature, Co-fired Ceramic (LTCC) substrates.

Description: The assembly of the BDYE detector requires the attachment of sixteen silicon (Si) processor dice (eight on the top side; eight on the bottom side) onto a low-temperature, co-fired ceramic (LTCC) substrate using 63Sn-37Pb (wt.%, Sn-Pb) in a double-reflow soldering process (nitrogen). There are 132 solder joints per die. The bond pads were gold-platinum-palladium (71Au-26Pt-3Pd, wt.%) thick film layers fired onto the LTCC in a post-process sequence. The pull strength and failure modes provided the quality metrics for the Sn-Pb solder joints. Pull strengths were measured in both the as-fabricated condition and after exposure to thermal cycling (-55/125 C; 15 min hold times; 20 cycles). Extremely low pull strengths--referred to as the low pull strength phenomenon--were observed intermittently throughout the product build, resulting in added program costs, schedule delays, and a long-term reliability concern for the detector. There was no statistically significant correlation between the low pull strength phenomenon and (1) the LTCC 'sub-floor' lot; (2) grit blasting the LTCC surfaces prior to the post-process steps; (3) the post-process parameters; (4) the conductor pad height (thickness); (5) the dice soldering assembly sequence; or (5) the dice pull test sequence. Formation of an intermetallic compound (IMC)/LTCC interface caused by thick film consumption during either the soldering process or by solid-state IMC formation was not directly responsible for the low-strength phenomenon. Metallographic cross sections of solder joints from dice that exhibited the low pull strength behavior, revealed the presence of a reaction layer resulting from an interaction between Sn from the molten Sn-Pb and the glassy phase at the TKN/LTCC interface. The thick film porosity did not contribute, explicitly, to the occurrence of reaction layer. Rather, the process of printing the very thin conductor pads was too sensitive to minor thixotropic changes to ink, which resulted in inconsistent proportions of metal and ...
Date: September 1, 2008
Creator: Uribe, Fernando R.; Kilgo, Alice C.; Grazier, John Mark; Vianco, Paul Thomas; Zender, Gary L.; Hlava, Paul Frank et al.
Partner: UNT Libraries Government Documents Department


Description: Platinum and platinum/nickel alloy electrocatalysts supported on graphitized (gCNT) or nitrogen doped carbon nanotubes (nCNT) are prepared and characterized. Pt deposition onto carbon nanotubes results in Pt 'needle' formations that are 3.5 nm in diameter and {approx}100 nm in length. Subsequent Ni deposition and heat treatment results in PtNi 'needles' with an increased diameter. All Pt and Pt/Ni materials were tested as electrocatalysts for the oxygen reduction reaction (ORR). The Pt and Pt/Ni catalysts showed excellent performance for the ORR, with the heat treated PtNi/gCNT (1.06 mA/cm{sup 2}) and PtNi/nCNT (0.664 mA/cm{sup 2}) showing the highest activity.
Date: November 10, 2011
Creator: Colon-Mercado, H.
Partner: UNT Libraries Government Documents Department

LDRD final report on synthesis of shape-and size-controlled platinum and platinum alloy nanostructures on carbon with improved durability.

Description: This project is aimed to gain added durability by supporting ripening-resistant dendritic platinum and/or platinum-based alloy nanostructures on carbon. We have developed a new synthetic approach suitable for directly supporting dendritic nanostructures on VXC-72 carbon black (CB), single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs). The key of the synthesis is to creating a unique supporting/confining reaction environment by incorporating carbon within lipid bilayer relying on a hydrophobic-hydrophobic interaction. In order to realize size uniformity control over the supported dendritic nanostructures, a fast photocatalytic seeding method based on tin(IV) porphyrins (SnP) developed at Sandia was applied to the synthesis by using SnP-containing liposomes under tungsten light irradiation. For concept approval, one created dendritic platinum nanostructure supported on CB was fabricated into membrane electrode assemblies (MEAs) for durability examination via potential cycling. It appears that carbon supporting is essentially beneficial to an enhanced durability according to our preliminary results.
Date: October 1, 2008
Creator: Shelnutt, John Allen; Garcia, Robert M.; Song, Yujiang; Moreno, Andres M. & Stanis, Ronald J.
Partner: UNT Libraries Government Documents Department

Report for General Research April 1 to August 7, 1950 (Polonium Volume)

Description: Research on polonium chemistry and physics is being continued on a reduced scale. Those problems which have direct bearing on the preparation of the metal and those which will lead to a better understanding of any phenomenon encountered are being continued. Data from the calorimetric measurements of polonium on Calorimeters 39 and 46 were treated by the method of least squares to give a grand mean half life of polonium equal to 138.3993 {+-} 0.0093 days (1-13). New apparatus has been constructed for the measurement of the vapor pressure of polonium and its compounds in the low and the high temperature ranges. Technical difficulties have delayed the actual collection of data (1-22). The constant current magnet to be used for the measurement of the Hall effect of polonium has been tested and found satisfactory. A device utilizing nuclear magnetic resonance absorption for determining field strength has been constructed on a preliminary basis (1-24). A total of 208 lines in the ultraviolet region between 3200 A and 1900 A have been measured with an error of less than {+-}0.02 A (1-28). Studies on the X-ray and spark spectra of polonium and its compounds have been conducted. A preliminary study by X-ray analysis has shown an equilibrium state of polonium between 65{sup o} and 100{sup o}. No sharp change of alpha polonium to the beta form has been noted below 100{sup o} (1-49). Previous evidence of a third phase of polonium at liquid air temperatures could not be duplicated (1-53). Confirmation of previous measurements of the coefficient of expansion of polonium with a more accurate temperature control has been achieved. A study of a platinum polonide sample has been carried out (1-55). Measurements of the Hall coefficient of polonium is being delayed until the pole caps for the completed magnet are obtained ...
Date: September 11, 1950
Creator: Haring, M.M.
Partner: UNT Libraries Government Documents Department

A theoretical study of the electronic structure of Invar Fe*3Pt and related materials

Description: The Full Potential Linear Augmented Plane Wave (FPLAPW or FLAPW) method is used for a spin-polarized band calculation for ordered Fe{sub 3}Pt. As major purpose, the momentum distributions of the spin-polarized electrons are calculated and compared with results from a magnetic Compton scattering measurement. To get related information, the electronic behavior is also analyzed by examining the partial densities of states and the spatial electron distributions; the role of alloying effects is then explored by studying the electrons in some related alloys: Fe{sub 3}Ni, Fe{sub 3}Pd, Ni{sub 3}Pt and Co{sub 3}Pt.
Date: January 10, 1997
Creator: Zuo, Zhiqi
Partner: UNT Libraries Government Documents Department

Low-energy excitations, symmetry breaking and specific heat in YbBiPt

Description: The heavy fermion compound YbBiPt has a very large linear coefficient of specific heat {gamma} = 8 Jmol{sup {minus}1} K{sup {minus}2} and this is understood, to first order, in terms of the observed low-energy neutron scattering response. However, at low temperatures, symmetry forbidden splittings at 1 and 2 meV respectively are observed. These levels give good qualitative agreement with the measured specific heat, but poor quantitative agreement. Indeed, the specific heat drops more rapidly with temperature that can be accounted for assuming a temperature-independent density of states. The authors also present new low-temperature crystallographic data, which rule out any significant structural distortions.
Date: December 31, 1998
Creator: Robinson, R.A.; Christianson, A.; Nakotte, H.; Beyermann, W.P. & Canfield, P.C.
Partner: UNT Libraries Government Documents Department

Development of a remote bushing for actinide vitrification

Description: The Savannah River Site (SRS) and the Savannah River Technology Center (SRTC) are combining their existing experience in handling highly radioactive, special nuclear materials with commercial glass fiberization technology in order to assemble a small vitrification system for radioactive actinide solutions. The vitrification system or {open_quotes}brushing{close_quotes}, is fabricated from platinum-rhodium alloy and is based on early marble remelt fiberization technology. Advantages of this unique system include its relatively small size, reliable operation, geometrical safety (nuclear criticality), and high temperature capability. The bushing design should be capable of vitrifying a number of the actinide nuclear materials, including solutions of americium/curium, neptunium, and possibly plutonium. State of the art, mathematical and oil model studies are being combined with basic engineering evaluations to verify and improve the thermal and mechanical design concepts.
Date: December 31, 1996
Creator: Schumacher, R.F.; Ramsey, W.G. & Johnson, F.M.
Partner: UNT Libraries Government Documents Department

Vitrification of actinides contained in platinum alloy vessels

Description: While the use of platinum and platinum alloys for melting glass has a history dating back hundreds of years, its use for vitrification of radioactive materials has developed only within the last few years. Platinum-rhodium alloy has recently been utilized for both the containment and heating of small quantities of actinide materials during the vitrification process. Small, platinum alloy, melter systems are planned for use at the Savannah River Site (SRS) to vitrify residual actinide materials. The primary example is the SRS program to vitrify the contents of F-canyon Tank 17.1. This tank contains the majority of americium (Am) and curium (Cm) in the DOE complex. Other actinides by be verified in the future and include uranium (U) and plutonium (Pu).
Date: October 1, 1997
Creator: Schumacher, R.F.
Partner: UNT Libraries Government Documents Department

On the brass- and silver-colored forms of PTGA{sub 2}

Description: PtGa[sub 2] has previously been reported to exist as both a brass-colored, fluorite-structured phase and as a silver-colored alloy of unknown crystal structure. The crystal structure of the silver- colored form is reported here, along with a discussion of the stoichiometric factors responsible for the polymorphy of this phase. The silver- colored form belongs to the space group I4[SUB 1]/acd, with the lattice parameters a = 8.5544(4) and c = 21.574(17) Angstroms, and Z = 32. The structure consists of layers of Pt and Ga stacked along the c axis, in which two crystallographically different Pt and Ga atoms have similar environments involving eight and nine nearest neighbors, respectively. This structural arrangement may be the prototype for a family of ternary platinum metal-Group B-based phases. The present investigation also necessitates changes in the currently accepted Ga- Pt phase diagram. Stoichiometric PtGa[sub 2] undergoes a structural transformation upon cooling from a brass-colored fluorite structure to this silver-colored, tetragonal structure. However, the transformation is inhibited if the composition of the fluorite- structured phase is Ga-poor.
Date: November 1, 1996
Creator: Morosin, B. & Swenson, D.
Partner: UNT Libraries Government Documents Department

Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films

Description: OAK B204 Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films. The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and hTi-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials.
Date: October 3, 1998
Creator: Hellman, Frances
Partner: UNT Libraries Government Documents Department