Bulletin of the American Physical Society
2006 Four Corners Section of the APS Fall Meeting
Friday–Saturday, October 6–7, 2006; Logan, Utah
Session B3: Condensed Matter Structure and Spin |
Hide Abstracts |
Chair: Dieter Hochheimer, Colorado State University Room: Eccles Conference Center Room 201/203 |
Friday, October 6, 2006 10:30AM - 10:42AM |
B3.00001: Domain Growth Law Violations in a Compressible 2D Ising Model Matthew Wright We carry out Monte Carlo studies of a compressible two-dimensional spin-exchange Ising model, varying the Hamiltonian to imitate the ``unmixing'' of different phase-separating binary alloys. The Ising model is frequently used to model the dynamics of binary alloys or magnetic materials by simulating annealing. Normally, the domain growth law is of the form R(t) = A + B t$^{n}$. It has been found that the expected value of n = 1/3 does not hold for models where elements with differing atomic sizes are mixed together. We discuss the implications of these results on real alloys. [Preview Abstract] |
Friday, October 6, 2006 10:42AM - 10:54AM |
B3.00002: Magnetic Transitions In UCuSn Karunakar Kothapalli, Sami El-Khatib, Farzana Nasreen, Ian Swainsson, Anna Llobet, Heinz Nakotte We report on the dependence of the magnetic moment of UCuSn with temperature as determined from neutron-diffraction data that were obtained at Chalk River laboratory. In this compound, the magnetic moment is solely due to uranium. Using the Rietveld method, we were able to determine the magnitude and direction of the magnetic moments for various temperatures in the range 15 K to 70 K. Magnetic intensities are observed for temperatures below 62 K, and their temperature dependence shows that the magnetic moment increases with decreasing temperature. At around 31 K, there is a second anomaly in the temperature dependence of the moment, and this suggests that UCuSn exhibits two magnetic phase transitions at about 30 and 65 K. [Preview Abstract] |
Friday, October 6, 2006 10:54AM - 11:06AM |
B3.00003: Muon spin resonance study on UCu$_{1.5}$Sn$_{2}$ Sami El-Khatib, G. Michael Kalvius, D.R. Noakes, E.J. Ansaldo, C.E. Stronach, E. Br\"uck, A. Llobet, H. Nakotte We report on muon spin relaxation measurements results on UCu$_{1.5}$Sn$_{2}$, which crystallizes in the CaBe$_{2}$Ge$_{2}$-type structure. Our analysis is consistent with collinear antiferromagnetic order with the transition temperature at 108$\pm $1K, which is in agreement with previous reports. The Brillouin-like behavior of the temperature dependence of magnetic order indicates localized 5$f$ moments in this compound. Noticeable distortion in the magnetic structure occurring in the long-range order regime. The transition from paramagnetic region to the long-range ordered region has been explained by a model, which adopts the fast and slow relaxation rates. [Preview Abstract] |
Friday, October 6, 2006 11:06AM - 11:18AM |
B3.00004: High-pressure Raman studies of both hcp phases of Ba. Helmut Olijnyk, Satoshi Nakano, Kenichi Takemura Both hcp high-pressure phases of Ba were sudied by Raman spectroscopy. Combining the Raman data with existing equation of state data, the pressure dependence of the elastic shear modulus $C_{44} $ has been derived. The pressure shift of the E$_{2g}$ phonon frequency is discussed in terms of elastic parameters. Though the pressure response of the observed phonon mode shows normal behaviour in both phases, more subtle differences can be traced back to differences in the interatomic interactions in both phases. [Preview Abstract] |
Friday, October 6, 2006 11:18AM - 11:30AM |
B3.00005: Phase diagram of Ti metal at high pressure Yahya Al Khatatbeh, Kanani Lee, Boris Kiefer Using density-functional theory based ab-initio computations, we have investigated the hexagonal close-packed (hcp) and the hexagonal ($\omega )$ structures titanium (Ti), and find good agreement with experiment. The hcp phase yields an equation of state of a zero pressure volume V$_{0}$ = 17.37 ( 0.02) {\AA}$^{3}$, an isothermal bulk modulus K$_{0}$= 111.9 ( 0.2) GPa, and its pressure derivative K$_{0}$' = 3.60 ( 0.02). Furthermore, the $c/a$ ratio for both phases increases with increasing pressure. Additionally, the calculated transition pressure from hcp to $\omega $ phase compares well with the experimental results with the $\omega $ phase more stable than the hcp phase at pressures greater than $\sim $ 5 GPa. [Preview Abstract] |
Friday, October 6, 2006 11:30AM - 11:42AM |
B3.00006: Temperature dependence of absorption and emission spectra of Ba in solid Ar Brian Mong Detection of a single Ba daughter from extremely rare Xe-136 $\beta \beta $ decay is an essential part of the EXO (Enriched Xenon Observatory) project. At CSU we have been working on detection methods in both solid and liquid Xenon. This talk will cover the recent progress we have made on detection of Ba in solid Argon and Xenon. The absorption and fluorescence verses temperature in solid Ar and has been measured. Two Ba sites have been observed in solid Ar; site B recovers from annealing above 20K while site A does not, it converts to Site B. Recent progress with the spectroscopy of Ba and Ba+ in solid Xe will also be discussed. [Preview Abstract] |
Friday, October 6, 2006 11:42AM - 11:54AM |
B3.00007: Experimental evidence for the existence of eigenvalues of the time evolution operator governing the behavior of nuclear spins in solids Steven Morgan, Brian Saam The decay of nuclear magnetic resonance (NMR) signals in solids is an extremely difficult many-body problem with no complete solution. Utilizing frozen xenon polarized by spin-exchange optical pumping, we have observed the long-time behavior of the NMR signal decay for both free-induction decay and spin (solid) echoes. The enhanced signal has allowed us to view the behavior of the decay for up to $\sim $10 decay constants. This has given us the opportunity to test a theory about this behavior which says that at after a few time constants, the signal should decay either with a simple exponential or a simple exponential modulated by a sinusoid. The reasoning for this is that the evolution of the density matrix follows from the action of its complete time evolution operator, and that its eigenvalues determine the evolution of the spin system. Evidence for this type of behavior has been seen in classical chaotic systems, but ours is the first experimental evidence for this behavior in a quantum system. This work has the potential to help elucidate the role of chaos in quantum systems. [Preview Abstract] |
Friday, October 6, 2006 11:54AM - 12:06PM |
B3.00008: Propagator Methods in Spintronics applied to the Rashba Hamiltonian Bailey Hsu, Jean-Francois Van Huele In spintronics, the spin of the electrons is manipulated to create spin currents. New propagators are introduced in order to determine the evolution of the spin systems. Rashba potentials are considered in connection with the spin-orbit couplings in condensed matter systems. We calculate the propagator for the Rashba Hamiltonian $H=\frac{P^2}{2m}+\frac{\alpha}{\hbar}(\sigma_{x}P_y-\sigma_{y} P_x)$ and comment on how to deal with noncommuting operators. [Preview Abstract] |
Friday, October 6, 2006 12:06PM - 12:18PM |
B3.00009: Obtaining an EELS Fingerprint for the Phases of Aluminum Oxide Michael Tanner, David Cullen, Richard Vanfleet The crystal structure of $Al_2O_3$ is found naturally in a number of different atomic arrangements or phases (more than seven have been confirmed). By heating $Al(OH)_3$ (gibbsite) to different temperature levels in the lab, we obtained the alpha, gamma, and kappa phases which we confirmed by diffraction analysis. We then investigated these samples using electron energy-loss spectroscopy (EELS) in order to obtain an EELS fingerprint for each phase. A unique EELS fingerprint would allow phase identification in nanometer scale regions that cannot be measured by other means. Initial results are promising that the different phases can be differentiated by EELS. Further work will expand these measurements to include all of the phases of $Al_2O_3$. [Preview Abstract] |
Friday, October 6, 2006 12:18PM - 12:30PM |
B3.00010: Microstructural Constitutive Theory: Statistical Particulate Mechanics Michael Webb |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700