Novel Half-Metallic And Spin-Gapless Heusler Compounds, 2017 University of Nebraska-Lincoln
Novel Half-Metallic And Spin-Gapless Heusler Compounds, Yunlong Jin
Theses, Dissertations, and Student Research: Department of Physics and Astronomy
This thesis is devoted to experimental studies of Heusler compounds CoFeCrAl, CoFeCrX (X = Si, Ge) and Mn2PtSn. These Heusler alloys present an interesting class of ferromagnetic materials for spintronic applications since they are predicted to be spin gapless semiconductors and have half-metallic properties with 100 % spin polarization at the Fermi level. In this thesis, the structural, magnetic, spin-polarization and electron- transport properties of the fabricated alloys were studied. CoFeCrAl thin films deposited on MgO exhibit nearly perfect epitaxy and a high degree of L21 Heusler order. All considered types of chemical disorder destroy the spin-gapless semiconductivity of ...
Electrical Characterization Of Irradiated Semiconducting Amorphous Hydrogenated Boron Carbide, 2017 University of Nebraska-Lincoln
Electrical Characterization Of Irradiated Semiconducting Amorphous Hydrogenated Boron Carbide, George Glen Peterson
Mechanical (and Materials) Engineering -- Dissertations, Theses, and Student Research
Semiconducting amorphous partially dehydrogenated boron carbide has been explored as a neutron voltaic for operation in radiation harsh environments, such as on deep space satellites/probes. A neutron voltaic device could also be used as a solid state neutron radiation detector to provide immediate alerts for radiation workers/students, as opposed to the passive dosimetry badges utilized today. Understanding how the irradiation environment effects the electrical properties of semiconducting amorphous partially dehydrogenated boron carbide is important to predicting the stability of these devices in operation. p-n heterojunction diodes were formed from the synthesis of semiconducting amorphous partially dehydrogenated boron carbide ...
Elastic Properties Of Superconductors And Materials With Weakly Correlated Spins, 2017 University of Nebraska-Lincoln
Elastic Properties Of Superconductors And Materials With Weakly Correlated Spins, Christian Binek
Christian Binek Publications
It is shown that in the ergodic regime, the temperature dependence of Young’s modulus is solely determined by the magnetic properties of a material. For the large class of materials with paramagnetic or diamagnetic response, simple functional forms of the temperature derivative of Young’s modulus are derived and compared with experimental data and empirical results. Superconducting materials in the Meissner phase are ideal diamagnets. As such, they display remarkable elastic properties. Constant diamagnetic susceptibility gives rise to a temperature independent elastic modulus for ceramic and single crystalline superconductors alike. The thermodynamic approach established in this report, paves the ...
Rhombohedral Magnetostriction In Dilute Iron (Co) Alloys, 2017 Naval Surface Warfare Center
Rhombohedral Magnetostriction In Dilute Iron (Co) Alloys, Nicholas J. Jones, Gabriela Petculescu, Marilyn Wun-Fogle, James B. Restorff, Arthur E. Clark, Kristi B. Hathaway, Deborah L. Schlagel, Thomas A. Lograsso
Thomas A. Lograsso
Iron is a well-utilized material in structural and magnetic applications. This does not mean, however, that it is well understood, especially in the field of magnetostriction. In particular, the rhombohedral magnetostriction of iron, λ111 , is anomalous in two respects: it is negative in sign, in disagreement with the prediction of first principles theory, and its magnitude decreases with increasing temperature much too rapidly to be explained by a power law dependence on magnetization. These behaviors could arise from the location of the Fermi level, which leaves a small region of the majority 3d t2g states unfilled, possibly favoring small internal ...
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 ...
Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William Mccallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. Mcqueeney
Thomas A. Lograsso
Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe0.953Co0.047)2As2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at TS, sets in well above the stripe antiferromagnetic ordering at TN. We find that the temperature-dependent dynamic susceptibility displays an anomaly at TS followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. Our findings can be consistently described by a model that ...
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 ...
Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, 2017 Iowa State University
Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles
Thomas A. Lograsso
Gd5(Six Ge 1−x)4 has mixed phases in the composition range 0.32 < x < 0.41, which have not been widely studied. In this paper, we have synthesized and indexed single crystal samples of Gd5Si1.3 Ge 2.7 and Gd5Si1.4 Ge 2.6. We have investigated the first order and second orderphase transition temperatures of these samples using magnetic moment vs. temperature andmagnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the “hidden” second order phase transition temperature of the orthorhombic II phase.
Gd5(Si,Ge)4 Thin Film Displaying Large Magnetocaloric And Strain Effects Due To Magnetostructural Transition, 2017 Iowa State University
Gd5(Si,Ge)4 Thin Film Displaying Large Magnetocaloric And Strain Effects Due To Magnetostructural Transition, Ravi L. Hadimani, Joao H. B. Silva, Andre M. Pereira, Devo L. Schlagel, Thomas A. Lograsso, Yang Ren, David C. Jiles, Joao P. Araújo
Thomas A. Lograsso
Magnetic refrigeration based on the magnetocaloric effect is one of the best alternatives to compete with vapor-compression technology. Despite being already in its technology transfer stage, there is still room for optimization, namely, on the magnetic responses of the magnetocaloric material. In parallel, the demand for different magnetostrictive materials has been greatly enhanced due to the wide and innovative range of technologies that emerged in the last years (from structural evaluation to straintronics fields). In particular, the Gd5(Six Ge1−x)4 compounds are a family of well-known alloys that present both giant magnetocaloric and colossal magnetostriction effects. Despite their ...
Effects Of Zn Additions To Highly Magnetoelastic Fega Alloys, 2017 Iowa State University
Effects Of Zn Additions To Highly Magnetoelastic Fega Alloys, Thomas A. Lograsso, Nicholas J. Jones, Deborah L. Schlagel, Gabriela Petculescu, Marilyn Wun-Fogle, James B. Restorff, Arthur E. Clark, Kristi B. Hathaway
Thomas A. Lograsso
Fe1−xMx (M = Ga, Ge, Si, Al, Mo and x ∼ 0.18) alloys offer an extraordinary combination ofmagnetoelasticity and mechanical properties. They are rare-earth-free, can be processed using conventional deformation techniques, have high magnetic permeability, low hysteresis, and low magnetic saturation fields, making them attractive for device applications such as actuators and energy harvesters. Starting with Fe-Ga as a reference and using a rigid-band-filling argument, Zhang et al. predicted that lowering the Fermi level by reducing the total number of electrons could enhance magnetoelasticity. To provide a direct experimental validation for Zhang's hypothesis, elemental additions with lower-than-Ga valence are ...
Specific Heat Investigation For Line Nodes In Heavily Overdoped Ba1−Xkxfe2as2, 2017 University of Florida
Specific Heat Investigation For Line Nodes In Heavily Overdoped Ba1−Xkxfe2as2, J. S. Kim, G. R. Stewart, Yong Liu, Thomas A. Lograsso
Thomas A. Lograsso
Previous research has found that the pairing symmetry in the iron-based superconductor Ba1−xKxFe2As2 changes from nodeless s wave near optimally doped, x≈0.4−0.55 and Tc>30K, to nodal (either d wave or s wave) at the pure end point, x=1 and Tc<4K. Intense theoretical interest has been focused on this possibility of changing pairing symmetry, where in the transition region both order parameters would be present and time-reversal symmetry would be broken. Here we report specific heat measurements in zero and applied magnetic fields down to 0.4 K of three individual single crystals ...
Phenix Detector Overview, 2017 Vanderbilt University
Phenix Detector Overview, K. Adcox, Sergey Belikov, S. Bhagavatula, Paul Constantin, K. C. Cook, John C. Hill, John G. Lajoie, Alexandre Lebedev, B. Libby, Craig Ogilvie, A. N. Petridis, T. Plagge, Marzia Rosati, Harold D. Skank, S. Skutnik, G. A. Sleege, W. D. Thomas, T. Weimer, F. K. Wohn, L. Wood, Et Al.
The PHENIX detector is designed to perform a broad study of A–A, p–A, and p–p collisions to investigate nuclear matter under extreme conditions. A wide variety of probes, sensitive to all timescales, are used to study systematic variations with species and energy as well as to measure the spin structure of the nucleon. Designing for the needs of the heavy-ion and polarized-proton programs has produced a detector with unparalleled capabilities. PHENIX measures electron and muon pairs, photons, and hadrons with excellent energy and momentum resolution. The detector consists of a large number of subsystems that are discussed ...
Eddy-Current Probe Interaction With Subsurface Cracks, 2017 University of Surrey
Eddy-Current Probe Interaction With Subsurface Cracks, John R. Bowler
John R. Bowler
Electric current will flow around on open crack in a conductor and give rise to very abrupt variations in the field. If the crack has a negligible opening it acts as a surface barrier where the field is virtually discontinuous. Effectively the crack is then equivalent to a layer of current dipoles with the dipole orientation normal to the surface and pointing upstream. An integral equation for the dipole density has been derived for an idealised subsurface crack using the Green’s function method . Numerical solutions have been found by assuming a piecewise constant dipole density and satisfying boundary ...
Tracer Counterpermeation Analysis Of Diffusivity In Finite-Length Nanopores With And Without Single-File Dynamics, David Ackerman, James W. Evans
James W. Evans
We perform a tracer counterpermeation (TCP) analysis for a stochastic model of diffusive transport through a narrow linear pore where passing of species within the pore is inhibited or even excluded (single-file diffusion). TCP involves differently labeled but otherwise identical particles from two decoupled infinite reservoirs adsorbing into opposite ends of the pore, and desorbing from either end. In addition to transient behavior, we assess steady-state concentration profiles, spatial correlations, particle number fluctuations, and diffusion fluxes through the pore. From the profiles and fluxes, we determine a generalized tracer diffusion coefficient Dtr(x), at various positions x within the pore ...
Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, 2017 Iowa State University
Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho
A directional antenna made with photonic band gap structures has been presented. The directional antenna is formed with two photonic band gap structures oriented back to back and separated from each other by a distance to form a resonant cavity between the photonic band gap structures. An antenna element is placed in the resonant cavity. The resonant frequency of the cavity is tuned by adjusting the distance between the photonic band gap structures. The resonant cavity can be asymmetrical or symmetrical.
Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, 2017 Iowa State University
Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles
We investigated the effect of magnetic doping on magnetic and transport properties of Bi2Te3thin films. CrxBi2−xTe3 thin films with x = 0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi2Te3 and increases the magnetization of CrxBi2−xTe3. When x = 0.14 and 0.29,ferromagnetism appears in CrxBi2−xTe3 thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration ...
Relaxation Of Microwave Nonlinearity In A Cuprate Superconducting Resonator, 2017 Grand Valley State University
Relaxation Of Microwave Nonlinearity In A Cuprate Superconducting Resonator, Richard A. Huizen, Sean L. Hamilton, Geoffrey T. Lenters, Stephen K. Remillard
The second- and third-order nonlinear microwave response of a superconducting YBa2Cu3O7 thin-film resonator was synchronously measured using three input tones. This technique permits the local measurement, and hence mapping, of intermodulation distortion inside the resonator. Second- and third-order IMD measured with a fixed probe relaxed in remarkably different ways after the removal of a static magnetic field. The second-order IMD relaxed by two different magnetic processes, a fast process that appears related to bulk remanent magnetization and a slow process that fits the description of Bean and Livingston. The third-order IMD relaxes by only one process that is distinct from ...
A Period Examination Through Contemporary Energy Analysis Of Kevin Roche’S Fine Arts Center At University Of Massachusetts-Amherst, 2017 University of Massachusetts - Amherst
A Period Examination Through Contemporary Energy Analysis Of Kevin Roche’S Fine Arts Center At University Of Massachusetts-Amherst, L Carl Fiocchi Jr
L. Carl Fiocchi
Studies of buildings belonging to a subset of Modernist architecture, Brutalism, have included discussions pertaining to social and architectural history, critical reception, tectonic form and geometry inspirations, material property selections, period technology limitations, and migration of public perceptions. Evaluations of Brutalist buildings’ energy related performances have been restricted to anecdotal observations with particular focus on the building type’s poor thermal performance, a result of the preferred construction method, i.e. monolithic reinforced concrete used as structure, interior finish and exterior finish. A valid criticism, but one that served to dismiss discussion that the possibility of other positive design strategies ...
Time-Resolved Thz Conductivity Of An Intermediate Band Semiconductor, 2017 Macalester College
Time-Resolved Thz Conductivity Of An Intermediate Band Semiconductor, Elliot Weiss
Macalester Journal of Physics and Astronomy
Intermediate band materials have promising applications as affordable, highly efficient solar materials. However, intermediate band solar cells exhibit low efficiency to date. Carrier recombination is a critical process that limits efficiency. If electrons relax to the valence band before they can be collected, their energy is lost. To help understand the recombination dynamics and physical properties of intermediate band semiconductors, we obtain time-resolved THz conductivity measurements of the intermediate band semiconductor, GaPAsN, at various temperatures. From our results, we build a model that provides insight to the recombination dynamics of GaPAsN.
Solar Wind-Magnetosphere Coupling: A Global Perspective Of Reconnection In The Magnetotail, 2017 Embry-Riddle Aeronautical University
Solar Wind-Magnetosphere Coupling: A Global Perspective Of Reconnection In The Magnetotail, Miles Thomas Bengtson
Dissertations and Theses
We present a case study of the 25 December 2015 substorm which occurred between 08:15 and 08:45 Universal Time. During this interval, fast particle ﬂows and ﬁeld geometry consistent with magnetic reconnection were detected in the mid-tail region. An ejected plasmoid was observed by the lunar-orbiting Acceleration, Reconnection, Turbulence and Electrodynamics of Moon’s Interaction with the Sun (ARTEMIS) probes and corresponding dipolarization signature was observed by the Time History of Events and Macroscale Interactions During Substorms (THEMIS) spacecraft earthward of the reconnection site, which was determined to be approximately -33 RE. Ground signatures indicative of substorm activity ...