Bulletin of the American Physical Society
Joint Fall 2010 Meeting of the Texas Sections of the APS, AAPT, Zone 13 of SPS and the National Society of Hispanic Physicists
Volume 55, Number 11
Thursday–Saturday, October 21–23, 2010; San Antonio, Texas
Session FA5: Condensed Matter and Nanoscience II |
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Chair: Marcelo Marucho, University of Texas at San Antonio Room: University Center III Ballroom I, 1st floor |
Friday, October 22, 2010 3:00PM - 3:12PM |
FA5.00001: Microstructural and transport properties of highly epitaxial (LaBa)Co$_{2}$O$_{5+\delta }$ thin films on (001) SrTiO3 Chunrui Ma, Ming Liu, Jian Liu, Greg Collins, Chonglin Chen, Jie He, Jiechao Jiang, Efstathios Meletis, Allan Jacobson The (LaBa)Co$_{2}$O$_{5+\delta }$ thin films were epitaxially deposited on (001) SrTiO$_{3}$ single crystal substrates by pulsed laser deposition. Microstructure investigations from x-ray diffraction and transmission electron microscopy reveal that the films are $a$-axis oriention with a sharp atomic interface. Transport property and isothermal magnetoresistance measurements have been used to understand the physical properties of the films with anomalous magnetic phenomena and the largest reported MR value, for LBCO, of 19{\%} at 40 K. [Preview Abstract] |
Friday, October 22, 2010 3:12PM - 3:24PM |
FA5.00002: From carbon nanotubes to carbon atomic chains Gilberto Casillas Garc\'Ia, Weijia Zhang, Miguel Jos\'e-Yacam\'an Carbyne is a linear allotrope of carbon. It is formed by a linear arrangement of carbon atoms with sp-hybridization. We present a reliable and reproducible experiment to obtain these carbon atomic chains using few-layer-graphene (FLG) sheets and a HRTEM. First the FLG sheets were synthesized from worm-like exfoliated graphite and then drop-casted on a lacey-carbon copper grid. Once in the TEM, two holes are opened near each other in a FLG sheet by focusing the electron beam into a small spot. Due to the radiation, the carbon atoms rearrange themselves between the two holes and form carbon fibers. The beam is concentrated on the carbon fibers in order excite the atoms and induce a tension until multi wall carbon nanotube (MWCNT) is formed. As the radiation continues the MWCNT breaks down until there is only a single wall carbon nanotube (SWCNT). Then, when the SWCNT breaks, an atomic carbon chain is formed, lasts for several seconds under the radiation and finally breaks. This demonstrates the stability of this carbon structure. [Preview Abstract] |
Friday, October 22, 2010 3:24PM - 3:36PM |
FA5.00003: Study of texturing in Bi-2212 powder for wire development Feng Lu, Kyle Damborsky, Nathaniel Pogue, Peter McIntyre High angle grain boundaries (HAGBs) result in weak links in the current flow in high temperature superconductors. Commercially available Bi-2212 round wires do not have a macroscopical texture due to formation of HAGBs during the Partial-melt processing. In this study, we developed two methods by which to align the particles of Bi-2212 powder in thin layers. The first utilizes magnetic fields and the second is uniaxial compression. Both methods generate highly textured Bi-2212 powder layers having a-b plane in the flat dimension, which is preferable to the following wire fabrication that can preserve the texture. The influence of the different applied fields and compression on the texture and microstructure is reported. [Preview Abstract] |
Friday, October 22, 2010 3:36PM - 3:48PM |
FA5.00004: Surface Defect States in Nanopowder ZnO Yuri M. Strzhemechny, Raul M. Peters, Jacob Shafer, James Schulman, J. Antonio Paramo In our work we employed surface photovoltage (SPV) spectroscopy on a number of commercially available ZnO nanopowders to probe surface defect energies within the band gap, conduction vs. valence band nature of the defect-related transitions, as well as the surface photoresponse dynamics. SPV characterization was performed in ultra-high vacuum in situ with remote oxygen plasma treatments. Our experiments revealed a number of common spectral features related to surface states in the as-received and plasma-processed samples. Furthermore, we observed significant plasma-induced changes in the surface defect properties. Complementary ex situ photoluminescence measurements performed on the studied samples were correlated with the SPV results and demonstrated that our approach is efficient in detecting specific surface states in nanoscale ZnO specimens and in elucidating their nature. [Preview Abstract] |
Friday, October 22, 2010 3:48PM - 4:00PM |
FA5.00005: Development of a new Process for Fabricating Bi-2212/Ag Round Wire Kyle Damborsky, Feng Lu, Peter McIntyre, Nathaniel Pogue, Elizabeth Sooby Magnet technology required for the development of greater than 1 GHz NMR magnets, future hadron colliders, a proposed muon collider, and other applications above 25 T require a new generation of very high field superconducting wires. Presently, the only candidate material for manufacturing round wire in this operating range is Bi-2212/Ag composite conductor. Commercially available Bi-2212/Ag round wires are fabricated via a powder-in-tube (PIT) process which appears fundamentally limited by poor connectivity and a large degree of porosity after more than a decade of development. A modified jellyroll (MJR) conductor, designed to increase connectivity while decreasing porosity, is proposed for a new type of Bi-2212/Ag conductors. The method utilizes an oriented powder fabrication technique that allows the conductor to be constructed in a planar geometry, which is then wound to form a round wire for subsequent drawing and processing. The details of the fabrication process and preliminary results will be presented. [Preview Abstract] |
Friday, October 22, 2010 4:00PM - 4:12PM |
FA5.00006: Spin spiral order and magnetization dynamics in magnetic nanowires Oleg Tretiakov, Artem Abanov I will talk about current-induced magnetization dynamics in a thin ferromagnetic wires with spin spiral order. This order is known to be caused by Dzyaloshinskii-Moriya interaction (DMI). We analytically find a spiral domain wall configuration of the magnetization and the domain wall width. Our findings show that above a certain value of DMI a domain wall configuration cannot exist in the wire. Below this value we determine the domain wall dynamics for small currents, and calculate the drift velocity of the domain wall along the wire. We show that the DMI suppresses the minimum value of current required to move the domain wall. It also may lead to increase of the domain wall drift velocity. [Preview Abstract] |
Friday, October 22, 2010 4:12PM - 4:24PM |
FA5.00007: Modeling and simulation of charged particle beam transport in the UTA 2 meter Time of Flight Positron Annihilation Induced Auger Spectrometer Prasad Joglekar, Lawrence Lim, Sushant Kalaskar, Karthik Shastry, Suman Satyal, Alexander Weiss Time of Flight Positron Annihilation Induced Auger Electron Spectroscopy (TOF PAES) is a surface analytical technique with high surface selectivity. Almost 95{\%} of the PAES signal originates from the sample's topmost layer due to the trapping of positrons just above the surface in an image-potential well before annihilation. This talk presents a description of the TOF technique as the results of modeling of the charged particle transport used in the design of the 2 meter TOF-PAES system currently under construction at UTA. [Preview Abstract] |
Friday, October 22, 2010 4:24PM - 4:36PM |
FA5.00008: The Development of a Two-Powder Process for Bi-2212 Precursor Powders Elizabeth Sooby, Terry Holesinger Bi$_{2}$Sr$_{2}$Ca$_{1}$Cu$_{2}$O$_{y}$ (Bi-2212) is a prime candidate for high-field ($>$20 T) superconducting magnet applications, as it can be formed into a round wire conductor, a unique characteristic among all the high-temperature supercondutors (HTS) discovered to date. Round wires are manufactured by conventional oxide powder-in-tube processes (OPIT). A critical part of this process is the quality of the starting oxide powder precursor, affecting the drawing processes to form wire, the development of the superconducting phase in-situ during heat treatments and the connectivity along the wire length. To better manipulate the partial-melt behavior while better controlling the formation of 2212 by reducing the number of phases present, as 2-powder process was developed. A set of anneals has been completed on the resulting precursor powder. Initial characterization indicates the process can produce Bi-2212, though further development is necessary. [Preview Abstract] |
Friday, October 22, 2010 4:36PM - 4:48PM |
FA5.00009: Photoluminescence of etched SiC nanowires Polite D. Stewart, Jr., Ryan Rich, T.W. Zerda SiC nanowires were produced from carbon nanotubes and nanosize silicon powder in a tube furnace at temperatures between 1100$^{\circ}$C and 1350$^{\circ}$C. SiC nanowires had average diameter of 30 nm and very narrow size distribution. The compound possesses a high melting point, high thermal conductivity, and excellent wear resistance. The surface of the SiC nanowires after formation is covered by an amorphous layer. The composition of that layer is not fully understood, but it is believed that in addition to amorphous SiC it contains various carbon and silicon compounds, and SiO2. The objective of the research was to modify the surface structure of these SiC nanowires. Modification of the surface was done using the wet etching method. The etched nanowires were then analyzed using Fourier Transform Infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and photoluminescence (PL). FTIR and TEM analysis provided valid proof that the SiC nanowires were successfully etched. Also, the PL results showed that the SiC nanowire core did possess a fluorescent signal. [Preview Abstract] |
Friday, October 22, 2010 4:48PM - 5:00PM |
FA5.00010: Uncompensated Magnetization in FeF$_{2}$ Karie Badgley, Igor V. Roshchin, Mikhail Zhernenkov, Michael R. Fitzsimmons, M. Erekhinsky, Ivan K. Schuller, Hugo Ponce, Aldo H. Romero, Casey W. Miller Exchange bias (EB) between a ferromagnet (FM) and an antiferromanget (AF) manifests itself as a horizontal shift of the hysteresis loop below the critical temperature of the AF. While uncompensated magnetization has been shown to play an important role in EB, its origin is still unknown. To investigate the properties and origin of this uncompensated magnetization, AF-only samples were prepared: 36nm thick FeF$_{2}$ on MgF$_{2}$, coated with 3nm of Al to prevent oxidation. Using polarized neutron reflectometry and SQUID magnetometry, we measured the uncompensated magnetization in the samples and its depth profile. The magnitude of this magnetization is larger than what is expected from piezomagnetism or from ab-initio calculations of effects of FeF$_{2}$ surface relaxation on the uncompensated magnetization. Field and temperature dependence of this magnetization will also be presented. Funded by Texas A{\&}M University, Texas A{\&}M University--CONACyT Collaborative Research Grant Program, DOE, and NSF-9976899. [Preview Abstract] |
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