Crossover In The Magnetic Response Of Single-Crystalline Ba1−Xkxfe2as2 And Lifshitz Critical Point Evidenced By Hall Effect Measurements, Yong Liu, Thomas A. Lograsso
Thomas A. Lograsso
We report on the doping evolution of magnetic susceptibility χ(T) and Hall coefficient RH in high-quality Ba1−xKxFe2As2 (0.13≤x≤1) single crystals. It is found that the normal-state magnetic susceptibility of Ba1−xKxFe2As2 compounds undergoes a crossover from linear-T dependence in the undoped and underdoped samples into KFe2As2-type magnetic response in the overdoped samples with increasing K content. Although magnetic susceptibility χ(T) of optimally doped samples (0.34≤x≤0.47) still follows a monotonic increase with increasing temperature, a big hump around 300 K emerges. As x exceeds 0.53, a broad peak forms in ...
Magnetic And Structural Transitions In La0.4na0.6fe2as2 Single Crystals, 2017 Oak Ridge National Laboratory
Magnetic And Structural Transitions In La0.4na0.6fe2as2 Single Crystals, J.-Q. Yan, S. Nandi, B. Saparov, P. Čermák, Y. Xiao, Y. Su, W. T. Jin, A. Schneidewind, Th. Brückel, R. W. Mccallum, T. A. Lograsso, B. C. Sales, D. G. Mandrus
Thomas A. Lograsso
La0.4Na0.6Fe2As2 single crystals have been grown out of an NaAs flux in an alumina crucible and characterized by measuring magnetic susceptibility, electrical resistivity, specific heat, as well as single-crystal x-ray and neutron diffraction. La0.4Na0.6Fe2As2 single crystals show a structural phase transition from a high-temperature tetragonal phase to a low-temperature orthorhombic phase at Ts=125 K. This structural transition is accompanied by an anomaly in the temperature dependence of electrical resistivity, anisotropic magnetic susceptibility, and specific heat. Concomitant with the structural phase transition, the Fe moments order along the a direction with an ordered moment of 0 ...
Upper Critical Field Of Kfe2as2 Under Pressure: A Test For The Change In The Superconducting Gap Structure, 2017 Iowa State University
Upper Critical Field Of Kfe2as2 Under Pressure: A Test For The Change In The Superconducting Gap Structure, Valentin Taufour, Neda Foroozani, Makariy A. Tanatar, Jinhyuk Lim, Udhara S. Kaluarachchi, Stella K. Kim, Yong Liu, Thomas A. Lograsso, Vladimir G. Kogan, Ruslan Prozorov, Sergey L. Bud'ko, James S. Schilling, Paul C. Canfield
Thomas A. Lograsso
We report measurements of electrical resistivity under pressure to 5.8 GPa, magnetization to 6.7 GPa, and ac susceptibility to 7.1 GPa in KFe2As2. The previously reported change of slope in the pressure dependence of the superconducting transition temperature Tc(p) at a pressure p∗∼1.8 GPa is confirmed, and Tc(p) is found to be nearly constant above p∗ up to 7.1 GPa. The T−p phase diagram is very sensitive to the pressure conditions as a consequence of the anisotropic uniaxial pressure dependence of Tc. Across p∗, a ...
Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, 2017 Iowa State University
Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield
Thomas A. Lograsso
We report in-plane thermoelectric power measurements on single crystals of (Ba1−xKx)Fe2As2(0.44≤x≤1). We observe a minimum in the S|T=const versus x at x∼0.55 that can be associated with the change in the topology of the Fermi surface, a Lifshitz transition, related to the electron pockets at the center of M point crossing the Fermi level. This feature is clearly observable below ∼75 K. Thermoelectric power also shows a change in the x∼0.8–0.9 range, where the maximum in the thermoelectric power collapses into a plateau. This Lifshitz transition ...
Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, 2017 Iowa State University
Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin
Thomas A. Lograsso
We report on the different roles of two orbital-active Fe2+ at the A site and V3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV2O4. FeV2O4 exhibits three structural transitions and successive paramagnetic (PM)–collinear ferrimagnetic (CFI)–noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM–orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbit-coupling-induced anisotropy at the Fe2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V3+ at the orthorhombic/CFI–tetragonal ...
Formation Mechanism Of Superconducting Phase And Its Three-Dimensional Architecture In Pseudo-Single-Crystal Kxfe2−Yse2, Yong Liu, Qingfeng Xing, Warren E. Straszheim, Jeff Marshman, Pai Pedersen, Richard Mclaughlin, Thomas A. Lograsso
Thomas A. Lograsso
We report how the superconducting phase forms in pseudo-single-crystal KxFe2−ySe2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase, whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition. It should be ...
Imprinting Bulk Amorphous Alloy At Room Temperature, 2017 Korea Institute of Industrial Technology
Imprinting Bulk Amorphous Alloy At Room Temperature, Song-Yi Kim, Eun-Soo Park, Ryan T. Ott, T. A. Lograsso, Moo-Young Huh, Do-Hyang Kim, Jürgen Eckert, Min-Ha Lee
Thomas A. Lograsso
We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability ...
Wave Propagation Inside Random Media, 2017 The Graduate Center, City University of New York
Wave Propagation Inside Random Media, Xiaojun Cheng
All Graduate Works by Year: Dissertations, Theses, and Capstone Projects
This thesis presents results of studies of wave scattering within and transmission through random and periodic systems. The main focus is on energy profiles inside quasi-1D and 1D random media.
The connection between transport and the states of the medium is manifested in the equivalence of the dimensionless conductance, g, and the Thouless number which is the ratio of the average linewidth and spacing of energy levels. This equivalence and theories regarding the energy profiles inside random media are based on the assumption that LDOS is uniform throughout the samples. We have conducted microwave measurements of the longitudinal energy profiles ...
Ferroelectric-Domain-Patterning-Controlled Schottky Junction State In Monolayer Mos2, 2017 University of Nebraska-Lincoln
Ferroelectric-Domain-Patterning-Controlled Schottky Junction State In Monolayer Mos2, Zhiyong Xiao, Jingfeng Song, David K. Ferry, Stephen Ducharme, Xia Hong
Stephen Ducharme Publications
We exploit scanning-probe-controlled domain patterning in a ferroelectric top layer to induce nonvolatile modulation of the conduction characteristic of monolayer MoS2 between a transistor and a junction state. In the presence of a domain wall, MoS2 exhibits rectified I-V characteristics that are well described by the thermionic emission model. The induced Schottky barrier height ΦeffB varies from 0.38 to 0.57 eV and is tunable by a SiO2 global back gate, while the tuning range of ΦeffB depends sensitively on the conduction-band-tail trapping states. Our work points to a new route to ...
Electronic And Magnetic Properties Of Carbon-Based And Boron-Based Nano Materials, 2017 Clark Atlanta University
Electronic And Magnetic Properties Of Carbon-Based And Boron-Based Nano Materials, Rosi Gunasinghe
Electronic Theses & Dissertations Collection for Atlanta University & Clark Atlanta University
The structural and electronic properties of covalently and non-covalently functionalized graphene are investigated by means of first-principles density-functional-theory. The electronic characteristics of non-covalently functionalized graphene by a planar covalent organic framework (COF) are investigated. The aromatic central molecule of the COF acts as an electron donor while the linker of the COF acts as an electron acceptor. The concerted interaction of donor acceptor promotes the formation of planar COF networks on graphene. The distinctive electronic properties of covalently functionalized fluorinated epitaxial graphene are attributed to the polar covalent C–F bond. The partial ionic character of the C–F bond ...
Surface Geometry And Heat Flux Effect On Thin Wire Nucleate Pool Boiling Of Subcooled Water In Microgravity, 2017 Utah State University
Surface Geometry And Heat Flux Effect On Thin Wire Nucleate Pool Boiling Of Subcooled Water In Microgravity, Troy Munro, Andrew Fassman, Heng Ban, Jr Dennision
In the summer of 2010, undergraduates from the USU Get Away Special team flew a nucleate pool boiling experiment on NASA’s Weightless Wonder to study nucleate boiling heat transfer in microgravity. The motivation of this research was to understand the effects of surface geometry and heat flux applied to a thin wire heater for the design and development of efficient thermal management systems for space applications. The specific objectives were to observe and characterize behaviors of boiling onset, steady state heat transfer, and bubble dynamics with respect to nucleate boiling of subcooled water.. Using three thin platinum wire geometries ...
Supercooled: An Equilibrium, Melting-Based, Energy Distribution Approach For Describing The Phenomenology Of Metastable Liquids, 2017 Washington University in St. Louis
Supercooled: An Equilibrium, Melting-Based, Energy Distribution Approach For Describing The Phenomenology Of Metastable Liquids, Nicholas Bryan Weingartner
Arts & Sciences Electronic Theses and Dissertations
The glass transition remains one of the great open problems of modern physics. This dissertation aims to increase understanding of this topic by studying the rich phenomenology of supercooled liquids, the metastable precursors to the glassy state. Principally, we aim to discover what underlying physics leads to the dramatic, non-Arrhenius increase of the viscosity and relaxation time of supercooled liquids, and what thermodynamic properties govern this physics. We propose a novel framework and associated viscosity function applicable to all supercooled liquids/glassy systems, and rigorously assess both the performance and implications of this model. We demonstrate that the theoretical framework ...
Magneto-Optical Properties Of Iron Oxide Nanoparticles For Use In Medical Imaging, 2017 University of Wyoming
Magneto-Optical Properties Of Iron Oxide Nanoparticles For Use In Medical Imaging, Kathleen B. Oolman
Honors Theses AY 16/17
Due to their non-toxic and magnetic nature, magnetite iron oxide (Fe3O4) nanoparticles have potential uses in biomedical applications such as for magnetic resonance (MR) contrast agents. In this work, the physical properties of rare-earth element doped (Tb and Eu) and undoped iron oxide nanoparticles are optically investigated. Absorption and photoluminescence (PL) from doped and undoped iron oxide nanoparticles in solution show a well-defined excitonic absorption and weak PL. When the nanoparticles are drop cast into thin films, the absorption spectra remains unchanged while the PL disappear, suggesting the thin film creates non-radiative relaxation pathways. Low-temperature absorption measurements ...
Intervalley Scattering Rates In Tellurium Observed Via Time-Resolved Terahertz Spectroscopy, 2017 Macalester College
Intervalley Scattering Rates In Tellurium Observed Via Time-Resolved Terahertz Spectroscopy, Joshua R. Rollag
Macalester Journal of Physics and Astronomy
We conducted time-resolved terahertz spectroscopy measurements on the elemental semiconductor tellurium. Pump-probe measurements were used to find the conductivity as a function of time in single crystalline tellurium samples. It was found that the excitation dynamics in tellurium changes for photon energies of 1.03 eV and 1.55 eV. The change in these excitation dynamics was attributed to intervalley scattering effects. A model using intervalley scattering and Auger recombination was fit to the data, giving a value of 2.28 ps for the intervalley scattering time constant in tellurium.
The Study Of Plasmonics In Nanohole Metallic Metamaterials, 2017 The University of Western Ontario
The Study Of Plasmonics In Nanohole Metallic Metamaterials, Kieffer J. Davieau
Electronic Thesis and Dissertation Repository
Plasmonics is the study of light-matter interaction. The interaction of incident light (photons) with surface plasmons present in metamaterials results in unique optical properties. Nanohole arrays are a metamaterial consisting of an array of sub-wavelength holes perforated in an optically thin metallic film which resides upon a dielectric material. The interaction of light with the surface plasmons present in the nanohole array leads to extraordinary optical transmission which produces resonance peaks with a higher intensity than the incident light. By changing the physical parameters of the nanohole array, such as hole size and periodicity, the resonance peaks can be tuned ...
Linear And Nonlinear Dynamics Of Spin Waves In Ferromagnetic Nanowires, 2017 The University of Western Ontario
Linear And Nonlinear Dynamics Of Spin Waves In Ferromagnetic Nanowires, Zahra Haghshenasfard
Electronic Thesis and Dissertation Repository
Motivated by recent experimental developments, we present a theoretical study of some linear and nonlinear properties of spin waves in ferromagnetic nanostructures under conditions of microwave pumping. A microscopic (or Hamiltonian-based) approach is followed including terms for both the short-range exchange and the long-range dipole-dipole interactions, as well as the eects of an external magnetic ﬁeld, single-ion anisotropy, biquadratic exchange and the Ruderman-KittelKasuya-Yosida interactions, as appropriate. In ultrathin ﬁlms and nanowires with thickness or lateral dimensions less than about 100 nm, the discreteness of the quantized spin waves (or magnons) and their spatial distributions become modiﬁed, making it appropriate to ...
Fabrication And Study Of The Structure And Magnetism Of Rare-Earth Free Nanoclusters, 2017 University of Nebraska-Lincoln
Fabrication And Study Of The Structure And Magnetism Of Rare-Earth Free Nanoclusters, Bhaskar Das
Theses, Dissertations, and Student Research: Department of Physics and Astronomy
No abstract provided.
Dynamic Secondary Electron Emission In Dielectric/Conductor Mixed Coatings, 2017 Instituto de Ciencia de Materiales de Madrid
Dynamic Secondary Electron Emission In Dielectric/Conductor Mixed Coatings, Leandro Olano, Isabel Montero, María E. Dávila, Jr Dennison
An unexpected behavior of the Secondary Emission Yield (SEY) on coatings composed by a mixture of conductor and dielectric microparticles was reported and modeled in . As a follow up, we measured for a fixed primary energy the dynamic evolution of the SEY in similar samples and proposed a charging-roughness coupled model to simulate the experimental results. Two different coatings were selected: 1) TMM and Al microparticles (type 1), and 2) zeolites and gold nanoparticles (type 2). Pulsed and continuous tests were used to obtain the SEY as a function of the primary energy.
In both types of samples extremely ...
Pumping Of Magnons In A Dzyaloshinskii-Moriya Ferromagnet, 2017 University of Nebraska - Lncoln
Pumping Of Magnons In A Dzyaloshinskii-Moriya Ferromagnet, Alexey Kovalev, Vladimir Zyuzin, Bo Li
Faculty Publications, Department of Physics and Astronomy
We formulate a microscopic linear response theory of magnon pumping applicable to multiple-magnonic-band uniform ferromagnets with Dzyaloshinskii-Moriya interactions. From the linear response theory, we identify the extrinsic and intrinsic contributions where the latter is expressed via the Berry curvature of magnonic bands. We observe that in the presence of a time-dependent magnetization Dzyaloshinskii-Moriya interactions can act as fictitious electric fields acting on magnons. We study various current responses to this fictitious field and analyze the role of Berry curvature. In particular, we obtain an analog of the Hall-like response in systems with nontrivial Berry curvature of magnon bands. After identifying ...