Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 55, Number 9
Friday–Saturday, October 15–16, 2010; Ogden, Utah
Session D3: Condensed Matter |
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Chair: Heinrich Nakotte, New Mexico State University Room: 404B |
Friday, October 15, 2010 3:30PM - 3:42PM |
D3.00001: Negative thermal expansion in the Prussian Blue analog, Fe$_{3}$[Co(CN)$_{6}$]$_{2}$.xH$_{2}$O Sourav Adak, Luke Daemen, Heinz Nakotte, Darrick Williams The thermal expansion of the cubic Prussian Blue analog Fe$_{3}$[Co(CN)$_{6}$]$_{2}$.xH$_{2}$O has been studied below room temperature using x-ray and neutron powder diffraction. The water of hydration was found to have a large effect on the thermal expansion behavior of the material, which switches between positive and negative expansion with varying water content while the average cubic structure remains unchanged. Possible connections between local disorder and thermal expansion behavior are discussed. [Preview Abstract] |
Friday, October 15, 2010 3:42PM - 3:54PM |
D3.00002: Crystal and Magnetic Structure of UNi$_{0.52}$ Karunakar Kothapalli, Milton Torikachvili, Farzana Nasreen, Heinrich Nakotte We report the single crystal neutron diffraction studies done to resolve the room-temperature structure and the magnetic structure at 25 K of Uranium antimonide, UNi0.5Sb2. The time-of-flight single-crystal neutron diffraction experiments at room temperature and 25 K were done on the Single Crystal Diffractometer, SCD, at Los Alamos Neutron Science Center. Previous X-ray single crystal and neutron powder diffraction studies could not unambiguously resolve the structure because of the presence of hkl/2 type reflections. The studies were done on a 2 x 1 x 0.5 mm3 crystal and half-indexed reflections were observed corroborating the observations in previous studies. The room temperature structure that accounts for all the observed reflections is determined to be tetragonal P42/n m c with lattice parameters a = 4.333(2) {\AA} and c = 17.868(6) {\AA} respectively. The compound is found to order antiferromagnetically at 162 K and has a simple antiferromagnetic structure at 25 K with propagation vector q = (0, 0, 0) and with a moment of 1.82$\mu $B/U atom. [Preview Abstract] |
Friday, October 15, 2010 3:54PM - 4:06PM |
D3.00003: Non- Fermi liquid behavior and quantum criticality in UCu$_{4+x}$Al$_{8-x }$ compound Farzana Nasreen, Karunakar Kothapalli, Milton Torikachvilli, Heinrich Nakotte We report on experimental studies of electrical and magneto-transport on some of the compounds of UCu$_{4+x}$Al$_{8-x}$ family as a function of temperature, hydrostatic pressure, and/or magnetic field. It has been reported that UCu$_{4+x}$Al$_{8-x}$ can be tuned through a quantum critical point (QCP) using chemical pressure. UCu$_{4}$Al$_{8}$, the x=0 compound, shows antiferromagnetic transition at T$_{N} \sim $ 32 K. It has also been reported that T$_{N}$ goes to zero at x = 1.15 and because of the presence of this QCP, further increase in the chemical pressure yields heavy fermion behavior with the highest value of $\gamma $ = 800mJ/K$^{2}$-mol for x =1.75. Our studies show that for the magnetically-ordered compounds, hydrostatic pressure is found to increase the N\'{e}el temperature, whereas for the heavy fermion compounds T$_{\rho , max}$ is increased with pressure. We also report on the heat capacity measurements in temperature down to 300 mK. The heat capacity results are discussed in terms of physics of non-Fermi liquid scaling and its relation to QCP. [Preview Abstract] |
Friday, October 15, 2010 4:06PM - 4:18PM |
D3.00004: Long-time Behavior of Nuclear Spin Decays on Various Lattices Eric Sorte, Brian Saam The transverse nuclear magnetic resonance (NMR) decays of $^{129}$Xe in polycrystalline xenon were recently shown to have a universal property: in the long-time regime (after a few times T$_{2})$, these decays all converge to the same sinusoidally modulated exponential function irrespective of the initial transverse spin configuration (prepared by a sequence of one or more rf pulses). The present work constitutes a comprehensive experimental exploration of this phenomenon. It examines transverse decays for several different isotopic concentrations of $^{129}$Xe, employs additional pulse sequences, and performs similar measurements in a different material: $^{19}$F in single-crystal and polycrystalline CaF$_{2}$. With the possible exception of polycrystalline CaF$_{2}$ where the observation of the long-time behavior is limited by the experimental resolution, these systems all display the long-time universal behavior, characterized by particular values of the exponential decay coefficient and beat frequency that were unique for each lattice. This behavior has been theoretically predicted based on the notion that microscopic chaotic mixing plays a role in these decays. [Preview Abstract] |
Friday, October 15, 2010 4:18PM - 4:30PM |
D3.00005: Electric Field Effects on Diffuse Scattering of PZN-PT Benjamin Frandsen, Branton Campbell Relaxor ferroelectrics like Pb(Zn1/3Nb2/3)O3 in solid solution with PbTiO3 are of pressing applied interest due to their remarkable piezoelectric properties. X-ray single-crystal diffuse-scattering techniques have been shown to provide insight into the origin of PZN-PT's extreme piezoelectric response. We will present results of a synchrotron experiment in which we have mapped out large high-resolution volumes of reciprocal space to examine the effects of a strong electric field on the diffuse scattering of the material. By reconstructing regions of diffuse scattering in three dimensions, we can quantitatively determine the effect of the electric field. We will discuss a novel theoretical model that accurately reproduces the diffuse scattering both with and without an applied electric field and provides a framework for interpreting the field-induced changes in the context of the physical properties of PZN-PT. [Preview Abstract] |
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