Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session Y31: Metals and Metal Physics III |
Hide Abstracts |
Sponsoring Units: DMP Room: LACC 407 |
Friday, March 9, 2018 11:15AM - 11:27AM |
Y31.00001: Many-body Wave packet Description Of Spin-transfer And Spin-orbit Torque Induced Magnetization dynamics And Conduction-electron--Magnetization Entanglement Priyanka Mondal, Petr Plechac, Branislav Nikolic
|
Friday, March 9, 2018 11:27AM - 11:39AM |
Y31.00002: Work function of Pt thin films with disorder Ezra Bussmann, David Scrymgeour, Michael Brumbach, Taisuke Ohta, Sean Smith, Harold Hjalmarson, Peter Schultz, Paul Clem, Mathew Hopkins, Christopher Moore Vacuum arcs are operation and failure mechanisms in numerous technologies for which predictive arc simulations could improve performance and lower cost. A challenge is that arc initiation is not well understood. Toward a better understanding of arc initiation, we investigate how nanoscale surface disorder on metal films influences electron emission. As a prototypical metal surface, we characterize polycrystalline Pt thin films that include grain boundaries, dislocations, crystal tilts, roughness, adsorbed gas, and thin dielectric layers. Using a toolset including scanning tunneling microscopy (STM), photoelectron emission microscopy (PEEM), and ultraviolet photoemission spectroscopy (UPS), we measure local work functions, from micrometer to Angstrom size scales. Work functions of clean Pt(111) approach 6 eV. Defects and coatings diminish the work function toward 5 eV. We connect our findings with values in a variety of prior works. |
Friday, March 9, 2018 11:39AM - 11:51AM |
Y31.00003: Magnetic Exchange Interactions of Elemental Europium at Extreme Pressures Shu-Ting Pi, Warren Pickett Elemental lanthanides are known to show strong variations in their magnetic ordering temperatures under pressure. Eu is unique that ordering disappears in the 75-80 GPa range, giving way to superconductivity at 3-4K. To clarify how the magnetism interplays with pressure, we use density functional theory in combination with linear response and the magnetic force theorem to compute the exchange constants between 4f local moments. We confirm that Eu retains divalency with strong 4f 7 (J = 7 2) local moments despite structural, Hubbard U, or pressure variations. The crystal structures are found to be crucial to the AFM-PM phase transition. High symmetry structures such as bcc and hcp tend to enhance AFM ordering, while in Pnma phase the exchange constants decrease to zero rapidly with increasing pressure. Increasing U is observed to enhance AFM exchange constants in all structures, making AFM order more robust. By choosing U about 4∼5 eV at high |
Friday, March 9, 2018 11:51AM - 12:03PM |
Y31.00004: Evidence for the Existence of Magnon-Mediated Attraction in the Parent Cuprates Mirko Moeller, Clemens Adolphs, George Sawatzky, Mona Berciu Magnon-mediated interactions are the effective interactions between two doped holes, arising from the exchange of a magnon. In the context of cuprates, this magnon-mediated interaction has long been believed to be attractive and, therefore, a main component of the "glue" leading to superconductivity. We develop a method to study these magnon-mediated interactions between two-holes injected into the otherwise undoped CuO2-layer, using a three-band model. The main challenge is to be able to distinguish processes where a magnon is exchanged between holes from those where the magnon is emitted and reabsorbed by the same hole. Our method allows us to isolate the effect of magnon-mediated interactions and to prove that they are indeed attractive in the parent cuprates. |
Friday, March 9, 2018 12:03PM - 12:15PM |
Y31.00005: Material designs of Fe-based superconductors and thermoelectric materials Chang-Jong Kang, Gabriel Kotliar Modern theoretical methods of structure prediction have been very successful in finding new interesting materials experimentally. They give a useful guideline to experiments for material synthesis and design. Notable recent successes are the prediction of superconductivity of hydrogen sulfide that has the highest critical temperature under high pressure [1, 2]. Other successes of theory-guided material searches are the prediction and synthesis of unreported missing half-Heusler compounds [3-5]. Using the ab initio evolutionary algorithm and electronic structure calculations we investigate the properties of two interesting materials: one is a new 112 family of Fe-based superconductor and the other is a new thermoelectric material, which is a material analog of the enigmatic thermoelectric FeSb2. We also investigate the phase stabilities of both materials based on the accurate total energy calculations. Finally, we discuss the existence probabilities of both materials based on our recently proposed probabilistic model. |
Friday, March 9, 2018 12:15PM - 12:27PM |
Y31.00006: Pressure and temperature dependence of hyperfine field parameters of iron and its compounds by Synchrotron Mössbauer Spectroscopy Esen Alp, Wenli Bi, Jiyong Zhao, Thomas Toellner, Michael Hu The pressure and temperature dependence of the hyperfine interaction parameters like internal hyperfine magnetic field, isomer shift, and quadrupole splitting have been measured with high precision using a pulsed synchrotron radiation source. The pressure range varied between ambient to 30 GPa, and the temperature range between 10 to 600 K. Taking advantge of a special "hybrid" filling mode of the Advanced Photon Source, we observed the nuclear decay of pure iron and several compounds over 6 lifetimes, reaching an accuracy of better than 0.1%. Relative isomer shift between bcc-iron and hcp iron is also measured with high precision, provining a direct measure of s-electron density at the iron nucleus due to phase change. |
Friday, March 9, 2018 12:27PM - 12:39PM |
Y31.00007: Hysteresis of the α – β Phase Transition in Palladium Hydride Nicholas Weadock, Aadith Moorthy, Brent Fultz In-situ x-ray diffraction analyses of the hydriding process of metal hydrides can provide insights into the connection between lattice strain and pressure hysteresis. We have examined the hydriding transition of the palladium-hydrogen system, a model case due to the fact that the isostructural transition occurs at modest temperatures and hydrogen partial pressures. By measuring the lattice parameter changes for the α and β phases during both hydriding and dehydriding, we have determined the extent of coherency of the phase transition as a function of hydride fraction, temperature, and cycle number. Precise in-situ XRD measurements have revealed a hysteresis in the lattice parameters during hydriding and dehydriding. At the same time, the formation of dislocations or defects has been qualitatively identified through refinement of microstrain parameters. The experimental results will be presented in the context of theories of the origin of hysteresis in metal hydrides; either due to coherency strains or dislocation creation/annihilation. |
(Author Not Attending)
|
Y31.00008: Atomistic details of metal additive manufacturing in powder beds Mark Wilson, Michael Chandross Selective laser sintering (SLS) has been successfully used to fabricate metal parts, but variability in mechanical performance due to microstructural defects (e.g. voids, cracks) has inhibited its widespread use. The ability to characterize and identify the origins of these defects in situ is highly desirable, with most efforts typically being restricted to destructive postmortem analysis. Atomistic simulations offer a method to explore defect nucleation during SLS. We employ non-equilibrium molecular dynamics to simulate a single pass of an energetic laser source in nanoscale powder beds. In metals, heat transport is dominated by electron mediated processes. As such, a multi-scale modeling approach is used, coupling an implicit representation of electronic processes to the atomic lattice phonon system. This talk will report on a series of simulations using this computational model to study the dynamics of melting and solidification of metal powders at the nanoscale. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. |
Friday, March 9, 2018 12:51PM - 1:03PM |
Y31.00009: Understanding the deformation mechanism of the Individual phases of Al0.7CoCrFeNi High-Entropy Alloy (HEA) at cryogenic temperatures Adenike Giwa, Peter Liaw, Julia Greer HEAs are solid solution alloys containing five or more principal elements in equal or near equal atomic percent. The uniaxial compression of nanopillars fabricated from the single crystals of the Face-Centered Cubic and Body-Centered Cubic phases present in Al0.7CoCrFeNi HEA were studied at room temperature, 143 K and 40 K. Higher yield stresses were observed at lower temperatures with the smallest pillar size for both phases. The “smaller is stronger” effect was observed at the temperatures investigated. An isothermal size dependence was observed at the temperatures investigated which is calculated as a poswer law exponent: - 0.28 for BCC which is low compared to commonly studied BCC system and - 0.66 which is typical for FCC systems due to the ease of glide dislocation motion. The deformation mechanisms of both phases differed at low temperatures. Deformation in the FCC phase can be explained by collective dislocation glide and nucleation-governed plasticity while that of the BCC phase is due to dislocation cross-slip.This is further investigated by TEM analysis to show the twinning elements. We discuss these results in the framework of nanoscale plasticity and the intrinsic lattice resistance through the interplay of the microstructural and dimensional size effects. |
Friday, March 9, 2018 1:03PM - 1:15PM |
Y31.00010: Impurities and pressure effects on the entropy change of rare earth based compounds Nilson Antunes de Oliveira, Pedro von Ranke In this work, we theoretically discuss the effects of impurities and external pressure on the entropy change and on the temperature change of metallic compounds, whose magnetism comes mainly from rare earth ions. To this end we use a Hamiltonian of 4f localized interacting magnetic moments including extra terms to take into account the magnetoelastic interaction and anisotropy [1]. We apply the model to describe the entropy change in R5Si2Ge2 (R=Gd, Tb) and Er(Co1-xSix)2. Our results show that applied pressure reduces the critical temperature of R5Si2Ge2 but keeps the peak of the entropy change almost constant. On the contrary, applied pressure increases both the critical temperature of Tb5Si2Ge2 and the entropy change around it. This finding is in good agreement with the available experimental data [2]. Similar results obtained for Er(Co1-xSix)2 are also in agreement with available experimental data |
Friday, March 9, 2018 1:15PM - 1:27PM |
Y31.00011: Point defects diffusion in pure Ni and binary nickel-based alloys: a kinetic Activation-Relaxation Technique (k-ART) study Sami Mahmoud, Mickaël Trochet, Normand Mousseau Even for simple defects, such as point defects, details of the kinetic diffusion remains incompletely understood. Using the kinetic Activation-Relaxation Technique (k-ART), an unbiased off-lattice kinetic Monte Carlo method with on-the-fly catalogue building, we study point defects diffusion in pure nickel and binary nickel-based alloys known for their resistance to corrosion and good mechanical proprieties. K-ART allows us to construct an extensive description of the energy landscape surrounding various defects and obtain detailed information regarding the various activated mechanisms and diffusion pathways. In this talk, we present the most probable diffusion pathways for systems containing one to five vacancies and one to five self-interstitial atoms in pure nickel. For these systems we find diffusion rate is not monotonic with the number of defects, we also show that, for interstitial clusters, diffusion takes place from excited states. We then analyze the effect of alloying on these pathways, focusing in nickel alloys with copper, iron and aluminum. |
Friday, March 9, 2018 1:27PM - 1:39PM |
Y31.00012: Defects and Impurities Induced Structural and Electronic Changes in Pyrite CoS2: First Principles Studies Shengwen Li, Yanning Zhang Pyrite-type transition-metal (TM) dichalcogenides are attracting considerable attention in wide application fields, in particular cobalt pyrite (CoS2) which has been widely used in many electrochemical areas such as batteries, supercapacitors, catalysts and so on. In this work, systematic first-principles calculations were performed to investigate the effects of various neutral defects and ion dopings on the structural, energetic, electronic and magnetic properties of bulk cobalt pyrite (CoS2). It was found that the single-S vacancy has more effect on electronic properties of CoS2 than Co vacancies due to the destroy of the Oh symmetry. OS centers are electronic dopants and do not induce any impurity state. The Group IV and V impurities (C, Si, N, P, and As) have effects on both majority- and minority-spin channels, resulting in the spin moment change of ~1.0 µB per impurity atom. But the Group VII elements (F, Cl, and Br) only influences the minority-spin. Our extensive calculations provide instructive information for the design and optimization of CoS2-related energy materials. |
Friday, March 9, 2018 1:39PM - 1:51PM |
Y31.00013: Electrodeposition of Aluminum Nanowire Arrays for Ultraviolet Surface Plasmonics Rodolfo Lopez Jr, Jay Sharping, Erik Menke Well-developed nanoscale fabrication techniques for metals such as silver and gold have produced continuous, high-aspect ratio, short-pitch nanowire arrays and other nanostructures with high precision, capable of sustaining localized and propagating plasmonic resonances tunable from infrared to visible wavelengths. However, the interband transition properties of noble metals limit their implementation into the ultraviolet regime, promulgating alternative metals like aluminum, which has a Drude-like response in the UV. We implement a lithographically patterned nanowire electrodeposition technique to produce Al nanowire arrays with high aspect ratio and controlled, sub-200 nm cross sections. The cross sections are directly tunable by the electrodeposition bias and time, and resulting arrays demonstrate promising plasmonic resonances in the UV for future plasmonic waveguide, biological sensor, and photovoltaic applications. |
Friday, March 9, 2018 1:51PM - 2:03PM |
Y31.00014: Role of Zr in Strengthening MoSi2 Grain Boundaries from Density Functional Theory (DFT) Calculations Hui Zheng, Richard Tran, Balachandran Radhakrishnan, Xiangguo Li, Shyue Ping Ong MoSi2 is a promising intermetallic compound for ultrahigh-temperature applications due to its high melting point and excellent oxidation resistance at high temperatures (> 1000 °C) [1]. However, its application is limited due to oxygen embrittlement at the grain boundaries (GBs) under low temperatures (400-600 °C), an effect also known as “pesting” [2]. In this work, we comprehensively investigate the role of Zr in mitigating pesting in MoSi2 using DFT calculations. We show that Zr dopants reduce the embrittling effect of interstitial oxygen at MoSi2 GBs by donating electrons to oxygen. A more significant effect is observed when Zr is present as a secondary getter nanoparticle phase. Interstitial oxygen has a strong thermodynamic driving force to migrate from MoSi2 to the Zr sub-surface region, and the work of separation of the Zr/MoSi2 interface, with or without oxygen interstitials, are much higher than that of MoSi2 GBs. Finally, we will also present an efficient screening approach to identify other potential getter elements using simple thermodynamic descriptors which can be extended to other alloy systems of interest. [1] Suzuki, Y. et al, J. Am. Ceram. Soc. 81, 3141 (1998). [2] T.C. Chou and T.G. Nieh, JOM 45, 15 (1993). |
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