Cooperative And Noncooperative Magnetization Reversal In Alnicos,
2017
University of Nebraska - Lincoln
Cooperative And Noncooperative Magnetization Reversal In Alnicos, Raplh Skomski, Liqin Ke, Matthew J. Kramer, Iver E. Anderson, C.Z. Wang, W.Y. Zhang, Jeff E. Shield, D. J. Sellmyer
Nebraska Center for Materials and Nanoscience: Faculty Publications
It is investigated how magnetostatic interactions affect the coercivity of alnicotype magnets. Starting from exact micromagnetic relations, we analyze two limits, namely cooperative reversal processes operative on short lengths scales and noncooperative reversal processes on long length scales. In alnicos, intrawire interactions are predominantly cooperative, whereas interwire effects are typically noncooperative. However, the transition between the regimes depends on feature size and hysteresis-loop shape, and interwire cooperative effects are largest for nearly rectangular loops. Our analysis revises the common shape-anisotropy interpretation of alnicos.
Estimation Of Turbulence From Time-Lapse Imagery,
2017
Air Force Institute of Technology
Estimation Of Turbulence From Time-Lapse Imagery, Jack E. Mccrae, Santasri Bose-Pillai, Steven T. Fiorino
Faculty Publications
Atmospheric turbulence parameters are estimated for an imaging path based on time-lapse imaging results. Atmospheric turbulence causes frame-to-frame shifts of the entire image as well as parts of the image. The statistics of these shifts encode information about the turbulence strength (as characterized by Cn2, the refractive index structure function constant) along the optical path. The shift variance observed is simply proportional to the variance of the tilt of the optical field averaged over the area being tracked and averaged over the camera aperture. By presuming this turbulence follows the Kolmogorov spectrum, weighting functions, which relate the turbulence strength along …
Simulation Of Anisoplanatic Imaging Through Optical Turbulence Using Numerical Wave Propagation With New Validation Analysis,
2017
University of Dayton
Simulation Of Anisoplanatic Imaging Through Optical Turbulence Using Numerical Wave Propagation With New Validation Analysis, Russell C. Hardie, Jonathan D. Power, Daniel A. Lemaster, Douglas Droege, Szymon Gladysz, Santasri Bose-Pillai
Faculty Publications
We present a numerical wave propagation method for simulating imaging of an extended scene under anisoplanatic conditions. While isoplanatic simulation is relatively common, few tools are specifically designed for simulating the imaging of extended scenes under anisoplanatic conditions. We provide a complete description of the proposed simulation tool, including the wave propagation method used. Our approach computes an array of point spread functions (PSFs) for a two-dimensional grid on the object plane. The PSFs are then used in a spatially varying weighted sum operation, with an ideal image, to produce a simulated image with realistic optical turbulence degradation. The degradation …
Epitaxial Strain Controlled Magnetocrystalline Anisotropy In Ultrathin Ferh/Mgo Bilayers,
2017
Tongji University & California State University
Epitaxial Strain Controlled Magnetocrystalline Anisotropy In Ultrathin Ferh/Mgo Bilayers, Guohul Zheng, San-Huang Ke, Maosheng Miao, Jinwoong Kim, R, Ramesh, Nicholas Kioussis
Nebraska Center for Materials and Nanoscience: Faculty Publications
Using ab initio electronic structure calculations we have investigated the effect of epitazial strain on the magnetocrystalline anisotropy (MCA) of ultrathin FeRh/MgO heterostructures. Analysis of the energy- and k-resolved distribution of the orbital character of the band structure reveals that MCA largely arises from the spin-orbit coupling (SOC) between dx2-y2 and dxz/dyz orbitlas of Fe atoms at the FeRh/MhO interface. We demonstrate that the strain has significant effects on the MCA: It not only affects the value of the MCA but also induces a switching of the magnetic easy axis from perpendicular on in-plane direction. The …
Multi-Stage Axial Compressor With Counter-Rotation,
2017
Embry-Riddle Aeronautical University
Multi-Stage Axial Compressor With Counter-Rotation, Vinod Gehlot, Magdy S. Attia, Divyam Garg
Publications
A multi-stage axial compressor incorporating a counter-rotational movement is provided with a series of rotors mounted along and driven by a driveshaft, and a geared counter-rotating outer casing. A planetary gear system is assembled along a static casing, which can be assembled as a forward or aft casing for the compressor. The bearings of the planetary gear system typically will be aligned concentrically with a center rotor drum assembly mounted along the single driveshaft. The counter-rotating drum assembly will be assembled over the rotor drum assembly and will be engaged by the forward and aft casings so as to provide …
First-Principle Investigation Of Structural, Electronic And Magnetic Properties Of Co2vin And Covin Heusler Compounds,
2017
University of Nairobi
First-Principle Investigation Of Structural, Electronic And Magnetic Properties Of Co2vin And Covin Heusler Compounds, Zipporah Muthui, Rohit Pathak, Robinson Musembi, Julius Mwabora, Ralph Skomski, Arti Kashyap
Nebraska Center for Materials and Nanoscience: Faculty Publications
Investigation of the structural, electronic and magnetic properties of full-Heusler Co2VIn as well as half-Heusler CoVIn Cobalt based Heusler compounds using density functional theory (DFT) leads to the general conclusion that Co2VIn and CoVIn are half-metallic materials with a gap at the Fermi level in the minority states and majority states respectively. A Hubbard-like Coulomb correlation term U has been included in the DFT (DFT+U) for the computation of the electronic and magnetic properties of the compounds. The structural properties have been calculated for the paramagnetic and ferromagnetic phases, and both Co2VIn …
Controlling The Microstructure And Associated Magnetic Properties Of Ni0.2mn3.2ga0.6 Melt-Spun Ribbons By
Annealing,
2017
Miami University - Oxford
Controlling The Microstructure And Associated Magnetic Properties Of Ni0.2mn3.2ga0.6 Melt-Spun Ribbons By Annealing, Mahmud Khan, Ohud Alshammari, Balamurugan Balamurugan, Bhaskar Das, David J. Sellmyer, Ahmad Us Saleheen, Shane Stadler
Nebraska Center for Materials and Nanoscience: Faculty Publications
Here we report on the structural and magnetic properties of Ni0.2Mn3.2Ga0.6 melt- spun ribbons. The as-spun ribbons were found to exhibit mixed cubic phases that transform to non-cubic structure upon annealing. Additionally, an amorphous phase was found to co-exist in all ribbons. The SEM images show that minor grain forma- tion occurs on the as-spun ribbons. However, the formation of extensive nano-grains was observed on the surfaces of the annealed ribbons. While the as-spun ribbons exhibit predominantly paramagnetic behavior, the ribbons annealed under various thermal conditions were found to be ferromagnetic with a Curie temperature …
Effect Of Fe Substitution On The Structural, Magnetic And Electron-Transport Properties Of Half-Metallic Co2tisi,
2017
University of Nebraska - Lincoln
Effect Of Fe Substitution On The Structural, Magnetic And Electron-Transport Properties Of Half-Metallic Co2tisi, Y. Jin, J. Waybright, P. Kharel, I. Tutic, J. Herran, P. Lukashev, S. Valloppilly, D. J. Sellmyer
Nebraska Center for Materials and Nanoscience: Faculty Publications
The structural, magnetic and electron-transport properties of Co2Ti1-xFexSi (x = 0, 0.25, 0.5) ribbons prepared by arc-melting and melt-spinning were investi- gated. The rapidly quenched Co2Ti0.5Fe0.5Si crystallized in the cubic L21 structure whereas Co2Ti0.75Fe0.25Si and Co2TiFe0Si showed various degrees of B2-type disorder. At room temperature, all the samples are ferromagnetic, and the Curie tem- perature increased from 360 K for Co2TiSi to about 800 K for Co2Ti0.5Fe0.5Si. The measured …
Theoretical Approach To Electroresistance In Ferroelectric Tunnel Junctions,
2017
Georgia Institute of Technology
Theoretical Approach To Electroresistance In Ferroelectric Tunnel Junctions, Sou-Chi Chang, Azad Naeemi, Dmitri E. Nikonov, Alexei Gruverman
Alexei Gruverman Publications
In this paper, a theoretical approach comprising the nonequilibrium Green’s function method for electronic transport and the Landau-Khalatnikov equation for electric polarization dynamics is presented to describe polarization-dependent tunneling electroresistance (TER) in ferroelectric tunnel junctions. Using appropriate contact, interface, and ferroelectric parameters, the measured current-voltage characteristic curves in both inorganic (Co/BaTiO3/La0.67Sr0.33MnO3) and organic (Au/PVDF/W) ferroelectric tunnel junctions can be well described by the proposed approach. Furthermore, under this theoretical framework, the controversy of opposite TER signs observed experimentally by different groups in Co/BaTiO3/La0.67Sr0.33MnO3 systems is …
Ferroelectricity And The Phase Transition In Large Area Evaporated Vinylidene Fluoride Oligomer Thin Films,
2017
University of Nebraska-Lincoln
Ferroelectricity And The Phase Transition In Large Area Evaporated Vinylidene Fluoride Oligomer Thin Films, Keith Foreman, Shashi Poddar, Stephen Ducharme, Shireen Adenwalla
Shireen Adenwalla Papers
Organic ferroelectric materials, including the well-known poly(vinylidene fluoride) and its copolymers, have been extensively studied and used for a variety of applications. In contrast, the VDF oligomer has not been thoroughly investigated and is not widely used, if used at all. One key advantage the oligomer has over the polymer is that it can be thermally evaporated in vacuum, allowing for the growth of complex heterostructures while maintaining interfacial cleanliness. Here, we report on the ferroelectric properties of high-quality VDF oligomer thin films over relatively large areas on the order of mm2. The operating temperature is identified via …
Effect Of Disorder On The Magnetic And Electronic Structure Of A Prospective Spin-Gapless Semiconductor Mncrval,
2017
South Dakota State University
Effect Of Disorder On The Magnetic And Electronic Structure Of A Prospective Spin-Gapless Semiconductor Mncrval, P. Kharel, J. Herran, P. Lukashev, Y. Jin, J. Waybright, S. Gilbert, B. Staten, P. Gray, S. Valloppilly, Y. Huh, D. J. Sellmyer
Nebraska Center for Materials and Nanoscience: Faculty Publications
Recent discovery of a new class of materials, spin-gapless semiconductors (SGS), has attracted considerable attention in the last few years, primarily due to potential applications in the emerging field of spin-based electronics (spintronics). Here, we investigate structural, electronic, and magnetic properties of one potential SGS compound, MnCr-VAl, using various experimental and theoretical techniques. Our calculations show that this material exhibits ≈ 0.5 eV band gap for the majority-spin states, while for the minority-spin it is nearly gapless. The calculated magnetic moment for the com- pletely ordered structure is 2.9 μB/f.u., which is different from our experimentally measured value …
Tunneling Magnetoresistance Sensors With Different
Coupled Free Layers,
2017
University of Nebraska - Lincoln
Tunneling Magnetoresistance Sensors With Different Coupled Free Layers, Yen-Fu Liu, Xiaolu Yin, Yi Yang, Dan Ewing, Paul J. De Rego, Sy-Hwang Liou
Nebraska Center for Materials and Nanoscience: Faculty Publications
Large differences of magnetic coercivity (HC), exchange coupling field (HE), and tun- neling magnetoresistance ratio (TMR) in magnetic tunnel junctions with different coupled free layers are discussed. We demonstrate that the magnetization behavior of the free layer is not only dominated by the interfacial barrier layer but also affected largely by the magnetic or non-magnetic coupled free layers. All these parameters are sensitively controlled by the magnetic nanostructure, which can be tuned also by the magnetic annealing process. The optimized sensors exhibit a large field sensitivity of up to 261%/mT in the region of the reversal synthetic ferri- magnet at …
Compact Crabbing Cavity Systems For Particle Colliders,
2017
Old Dominion University
Compact Crabbing Cavity Systems For Particle Colliders, Subashini De Silva
Physics Faculty Publications
In circular or ring-based particle colliders, crabbing cavities are used to increase the luminosity. The first superconducting crabbing cavity system was successfully implemented at KEKB electron-positron collider that have demonstrated the luminosity increase with overlapping bunches. Crabbing systems are an essential component in the future colliders with intense beams, such as the LHC high luminosity upgrade and proposed electron-ion colliders. Novel compact superconducting cavity designs with improved rf properties, at low operating frequencies have been prototyped successfully that can deliver high operating voltages. We present single cavity and multi-cell crabbing cavities proposed for future particle colliders and addresses the challenges …
Optimization Of The Rf Cavity Heat Load And Trip Rates For Cebaf At 12 Gev,
2017
Jefferson Lab
Optimization Of The Rf Cavity Heat Load And Trip Rates For Cebaf At 12 Gev, H. Zhang, Y. Roblin, A. Freyberger, G. Krafft, B. Terzić
Physics Faculty Publications
The Continuous Electron Beam Accelerator Facility at JLab has 200 RF cavities in the north linac and the south linac respectively after the 12 GeV upgrade. The purpose of this work is to simultaneously optimize the heat load and the trip rate for the cavities and to reconstruct the pareto-optimal front in a timely manner when some of the cavities are turned down. By choosing an efficient optimizer and strategically creating the initial gradients, the pareto-optimal front for no more than 15 cavities down can be re-established within 20 seconds.
High Average Brilliance Compact Inverse Compton Light Source,
2017
Old Dominion University
High Average Brilliance Compact Inverse Compton Light Source, K. Deitrick, J. R. Delayen, G. A. Krafft
Physics Faculty Publications
There exists an increasing demand for compact Inverse Compton Light Sources (ICLS) capable of producing substantial fluxes of narrow-band X-rays. While multiple design proposals have been made, compared to typical bremsstrahlung sources, most of these have comparable fluxes and improve on the brilliance within a 0.1% bandwidth by only a few orders of magnitude. By applying cw superconducting rf beam acceleration and rf focusing to produce a beam of small emittance and magnetic focusing to produce a small spot size on the order of a few microns at collision, the source presented here provides a 12 keV X-ray beam which …
Rf Superconductivity,
2017
Old Dominion University
Rf Superconductivity, Jean R. Delayen
Physics Faculty Publications
Tutorial, based on the "RF Superconductivity" course taught by J. Delayen at the US PAS.
Unification Of Gravity And Quantum Theory,
2017
Old Dominion University
Unification Of Gravity And Quantum Theory, Adam Daniels
Faculty-Sponsored Student Research & Capstones
An overview of the four fundamental forces of physics as described by the Standard Model (SM) and prevalent unifying theories beyond it is provided. Background knowledge of the particles governing the fundamental forces is provided, as it will be useful in understanding the way in which the unification efforts of particle physics has evolved, either from the SM, or apart from it. It is shown that efforts to provide a quantum theory of gravity have allowed supersymmetry (SUSY) and M-Theory to become two of the prevailing theories for unifying gravity with the remaining non-gravitational forces.
Comment On “Electronic Structure Of Mo(1−X)Rex Alloys
Studied Through Resonant Photoemission Spectroscopy”,
2017
University of Nebraska–Lincoln
Comment On “Electronic Structure Of Mo(1−X)Rex Alloys Studied Through Resonant Photoemission Spectroscopy”, Prescott Evans, Peter A. Dowben
Peter Dowben Publications
Further analysis of the resonant photoemission data, found within Sundar et al (2016 J. Phys.: Condens. Matter 28 315502), show the intensities do not follow the elemental composition in the Mo1−xRex alloy. Similar trends are observed in the published data for Gd1−xNix alloy films. The analysis of the resonant photoemission intensities suggests that Mo in the Mo1−xRex alloy and Gd in the Gd1−xNix alloy have nearest neighbor bonds to Re and Ni respectively. This means the A–B bond is favored over the average of …
A Transfer Matrix Approach To Aid In The Design And Optimization Of Hybrid Advanced Passive Structures For Enhancing Photovoltaic Efficiency,
2017
Technological University Dublin
A Transfer Matrix Approach To Aid In The Design And Optimization Of Hybrid Advanced Passive Structures For Enhancing Photovoltaic Efficiency, James Walshe, Sarah Mccormack, Hind Ahmed, John Doran
Conference Papers
The addition of a luminescent down-shifting (LDS) layer directly onto a photovoltaic (PV) cell introduces additional loss mechanisms within the system. The combination of non-ideal photo-luminescent materials encapsulated within a limited range of viable host materials, with the increased reflection losses arising from the newly created interface represent losses which must be overcome for LDS to offer an enhancement to the underlying cells efficiency. Exploiting the interaction between the highly enhanced electric fields established close to a metal nanoparticles (MNP’s) surface is one route aimed at mitigating the poor optical properties of the luminophore-host combinations available. Alternative approaches, aimed at …
Thermal Conductivities Of Organic Semiconductors,
2017
University of Kentucky
Thermal Conductivities Of Organic Semiconductors, Yulong Yao
Theses and Dissertations--Physics and Astronomy
Organic semiconductors have gained a lot of interest due to their ease of processing, low-cost and inherent mechanical flexibility. Although most of the research has been on their electronic and optical properties, knowledge of the thermal properties is important in the design of electronic devices as well. Our group has used ac-calorimetric techniques to measure both in-plane and transverse thermal conductivities of a variety of organic semiconductors including small-molecule crystals and polymer blends. For layered crystals composed of molecules with planar backbones and silylethynyl (or germylethynyl) sidegroups projecting between the layers, very high interplanar thermal conductivities have been observed, presumably …
