Tuning The Effective Anisotropy In A Voltage-Susceptible Exchange-Bias Heterosystem,
2017
University of Nebraska-Lincoln
Tuning The Effective Anisotropy In A Voltage-Susceptible Exchange-Bias Heterosystem, Will Echtenkamp, Mike Street, Ather Mahmood, Christian Binek
Christian Binek Publications
Voltage- and temperature-tuned ferromagnetic hysteresis is investigated by a superconducting quantum-interference device and Kerr magnetometry in a thin-film heterostructure of a perpendicular anisotropic Co/Pd ferromagnet exchange coupled to the magnetoelectric antiferromagnet Cr2O3. An abrupt disappearance of exchange bias with a simultaneous more than twofold increase in coercivity is observed and interpreted as a competition between the effective anisotropy of Cr2O3 and the exchange-coupling energy between boundary magnetization and the adjacent ferromagnet. The effective anisotropy energy is given by the intrinsic anisotropy energy density multiplied by the effective volume separated from the bulk through …
Model For Charge Injection With Electron Beams Into Highly Disordered Insulating Materials,
2017
Utah State Univesity
Model For Charge Injection With Electron Beams Into Highly Disordered Insulating Materials, Jr Dennison
Presentations
The Walden-Wintle model for charge injection and transport through highly disordered insulating materials has been extended to include charge injection with a charged particle beam. The original model is applicable to charge injection into a dielectric material from a pair of electrodes in a parallel-plate geometry. It provides a versatile approach to predict the time-dependent current at a rear grounded electrode and the incident surface voltage, as the injection current density evolves over time with the development of a space charge barrier near the injection electrode. The Walden-Wintle model has been applied to many standard cases including Fowler-Nordheim injection, Schottky …
A New Physical Model For Dc Partial Discharge In Polymeric Insulators,
2017
Utah State University
A New Physical Model For Dc Partial Discharge In Polymeric Insulators, Allen Andersen, Jr Dennison
Presentations
The physics of DC partial discharge (DCPD) continues to pose a challenge to researchers. We present a new physically-motivated model of DCPD in amorphous polymers based on our dual-defect model of dielectric breakdown. The dual-defect model is an extension of standard static mean field theories, such as the Crine model, that describe avalanche breakdown of charge carriers trapped on uniformly distributed defect sites. It assumes the presence of both high-energy chemical defects and low-energy thermally-recoverable physical defects. We present our measurements of breakdown and DCPD for several common polymeric materials in the context of this model. Improved understanding of DCPD …
Model For Charge Injection With Electron Beams Into Highly Disordered Insulating Materials,
2017
Utah State Univesity
Model For Charge Injection With Electron Beams Into Highly Disordered Insulating Materials, Jr Dennison
Presentations
No abstract provided.
Novel Physical Model For Dc Partial Discharge In Polymeric Insulators,
2017
Utah State Univesity
Novel Physical Model For Dc Partial Discharge In Polymeric Insulators, Allen Andersen, Jr Dennison
Presentations
No abstract provided.
Effect Of Disorder On The Resistivity Of Cofecral Films,
2017
University of Nebraska-Lincoln
Effect Of Disorder On The Resistivity Of Cofecral Films, Y. Jin, R. Skomski, P. Kharel, S.R. Valloppilly, D. J. Sellmyer
Nebraska Center for Materials and Nanoscience: Faculty Publications
Structural and electron-transport properties of thin films of the ferrimagnetic Heusler compound CoFeCrAl have been investigated to elucidate structure-property relationships. The alloy is, ideally, a spin-gapless semiconductor, but structural disorder destroys the spin-gapless character and drastically alters the transport behavior. Two types of CoFeCrAl films were grown by magnetron sputtering deposition at 973 K, namely polycrystalline films on Si substrates and epitaxial films on MgO (001) substrates. The resistivity decreases with increasing temperature, with relatively small temperature coefficients of –0.19 cm=K for the polycrystalline films and –0.12 cm=K for the epitaxial films. The residual resistivity of the polycrystalline films deposited …
Universal Slip Dynamics In Metallic Glasses And Granular Matter – Linking Frictional Weakening With Inertial Effects,
2017
Bucknell University
Universal Slip Dynamics In Metallic Glasses And Granular Matter – Linking Frictional Weakening With Inertial Effects, Dmitri V. Denisov, Kinga A. Lorincz, Wendelin J. Wright, Todd C. Hufnagel, Aya Nawano, Xiaojun Gu, Jonathan T. Uhl, Karin A. Dahmen, Peter Schall
Faculty Journal Articles
Slowly strained solids deform via intermittent slips that exhibit a material-independent critical size distribution. Here, by comparing two disparate systems - granular materials and bulk metallic glasses - we show evidence that not only the statistics of slips but also their dynamics are remarkably similar, i.e. independent of the microscopic details of the material. By resolving and comparing the full time evolution of avalanches in bulk metallic glasses and granular materials, we uncover a regime of universal deformation dynamics. We experimentally verify the predicted universal scaling functions for the dynamics of individual avalanches in both systems, and show that both …
Designing Novel Nanostructured Permanent Magnets,
2017
University of Nebraska at Omaha
Designing Novel Nanostructured Permanent Magnets, Ali Al Kadhim
UNO Student Research and Creative Activity Fair
Rare earth element based alloys have been the source of high performance magnetic alloys, and have played a paramount role in the development of various technologies, including: memory devices (such as credit cards, random-access memory), sensors, and various biomedical applications. However, there is a tremendous need to replace rare earth metals with material with powerful magnetic properties. Our group recently found CrTe-based materials that show very promising magnetic properties in nanostructured form. The magnetic modeling of such material in nanostructured form prior to their fabrication demonstrates their magnetic properties in bulk form. In this project, we investigate the behavior of …
Satellite Survivability In A Harsh Space Environment: A Materials Perspective,
2017
Utah State Univesity
Satellite Survivability In A Harsh Space Environment: A Materials Perspective, Jr Dennison
Presentations
No abstract provided.
Temperature Dependency Of Electrostatic Breakdown In Ldpe And Peek,
2017
Utah State University
Temperature Dependency Of Electrostatic Breakdown In Ldpe And Peek, Tyler Kippen, Allen Andersen, Jr Dennison
Posters
Electrostatic breakdown is a leading cause of many of the anomalies and failures attributed to spacecraft interactions with the space environment. It is therefore critical to understand how the electrostatic field strength varies due to changing environmental conditions, including temperature and radiation dose. Standard step-up to electrostatic discharge (ESD) tests were performed on two polymers, low density polyethylene (LDPE) and polyetheretherketone (PEEK). Tests were done at room temperature and at other temperatures ranging from ~130 K to ~350 K. Preliminary analysis found that samples tested at a higher temperature had lower average breakdown field strength and a narrower distribution of …
Using Quantile-Quantile Plots To Compare Experimental Apples And Oranges In Physics Labs,
2017
Utah State University
Using Quantile-Quantile Plots To Compare Experimental Apples And Oranges In Physics Labs, Allen Andersen, Jr Dennison
Presentations
No abstract provided.
Brownian Motion Of Solitons In A Bose-Einstein Condensate,
2017
University of Maryland
Brownian Motion Of Solitons In A Bose-Einstein Condensate, Lauren M. Aycock, Hilary M. Hurst, Dimitry K. Efimkin, Dina Genkina, Hsin-I Lu, Victor M. Galitski, I. B. Spielman
Faculty Research, Scholarly, and Creative Activity
We observed and controlled the Brownian motion of solitons. We launched solitonic excitations in highly elongated 87 Rb Bose-Einstein condensates (BECs) and showed that a dilute background of impurity atoms in a different internal state dramatically affects the soliton. With no impurities and in one-dimension (1D), these solitons would have an infinite lifetime, a consequence of integrability. In our experiment, the added impurities scatter off the much larger soliton, contributing to its Brownian motion and decreasing its lifetime. We describe the soliton's diffusive behavior using a quasi-1D scattering theory of impurity atoms interacting with a soliton, giving diffusion coefficients consistent …
Predicted Electronic Markers For Polytypes Of Laobis2 Examined Via Angle-Resolved Photoemission Spectroscopy,
2017
University of Colorado - Boulder
Predicted Electronic Markers For Polytypes Of Laobis2 Examined Via Angle-Resolved Photoemission Spectroscopy, Xiaoqing Zhou, Qihang Liu, J. A. Waugh, T. Nummy, Xiuwen Zhang, Xiangde Zhu, Gang Cao, Alex Zunger, D. S. Dessau
Physics and Astronomy Faculty Publications
The natural periodic stacking of symmetry-inequivalent planes in layered compounds can lead to the formation of natural superlattices; albeit close in total energy, (thus in their thermodynamic stability), such polytype superlattices can exhibit different structural symmetries, thus have markedly different electronic properties which can in turn be used as “structural markers”. We illustrate this general principle on the layered LaOBiS2 compound where density-functional theory (DFT) calculations on the (BiS2)/(LaO)/(BiS2) polytype superlattices reveal both qualitatively and quantitatively distinct electronic structure markers associated with the Rashba physics, yet the total energies are only ∼ 0.1 meV apart. …
Half-Metallic Magnetism In Ti3co5-Xfexb2,
2017
Indian Institute of Technology
Half-Metallic Magnetism In Ti3co5-Xfexb2, Rohit Pathak, Imran Ahamed, W. Y. Zhang, Shah Vallopilly, D. J. Sellmyer, Ralph Skomski, Arti Kashyap
Nebraska Center for Materials and Nanoscience: Faculty Publications
Bulk alloys and thin films of Fe-substituted Ti3Co5B2 have been investigated by first-principle density-functional calculations. The series, which is of interest in the context of alnico magnetism and spin electronics, has been experimentally realized in nanostructures but not in the bulk. Our bulk calculations predict paramagnetism for Ti3Co5B2, Ti3Co4FeB2 and Ti3CoFe4B2, whereas Ti3Fe5B2 is predicted to be ferromagnetic. The thin films are all ferromagnetic, indicating that moment formation may be facilitated at nanostructural …
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.
The Effects Of Tilted Magnetic Fields On Quantum Transport In 2d Electron Systems,
2017
CUNY Graduate Center
The Effects Of Tilted Magnetic Fields On Quantum Transport In 2d Electron Systems, William A. Mayer
Dissertations, Theses, and Capstone Projects
There exists a myriad of quantum transport phenomena in highly mobile 2D electrons placed in a perpendicular magnetic field. We study the effects of tilted magnetic field on these transport properties to understand how the energy spectrum evolves. We observe significant changes of the electron transport in quantum wells of varying widths with high electron densities at high filling factors. In narrow quantum wells the spin splitting of Landau levels due to Zeeman effect is found to be the dominant mechanism reducing Quantum Positive Magnetoresistance. In wider quantum wells with two populated subbands Magnetointersubband oscillations appear to exhibit effects from …
Structure And Physical Properties Of Srniru5O11 Single Crystals: An R-Type Ferrite Based On Ordered Kagome Nets,
2017
Universität Stuttgart, Germany
Structure And Physical Properties Of Srniru5O11 Single Crystals: An R-Type Ferrite Based On Ordered Kagome Nets, L. Shlyk, Lance E. De Long, R. Niewa
Physics and Astronomy Faculty Publications
Single crystals of the R-type ferrite SrNiRu5O11 were grown from a chloride flux. The hexagonal crystal structure contains ruthenium located on distorted kagome nets. The low-temperature dc magnetic susceptibilities (χ⊥ and χ∥, perpendicular and parallel to the c axis, respectively) diverge as T−0.3, and do not exhibit any indication of long-range magnetic order down to 4.5 K. The electrical resistivity varies as T1.6 below 40 K, which is typical of non-Fermi liquids, and may originate from a competition between residual magnetic interactions among Ni2+ (S = 1) spins …
How The Space Environment Affects Seed Germination And Growth,
2017
Utah State University
How The Space Environment Affects Seed Germination And Growth, Alexander Souvall, Gareema Dhiman, Andre Nguyen, Michelle Jung, Astrid Ji, Takayuki Sakai, Takahiro Shimizu, Midori Morikawa, Shusuke Okita, Akihiro Nagata, Shaunda Wenger, Toshihiro Kameda, Jr Dennison
Posters
Understanding observed space environment effects on biological organisms such seeds are important in design of long duration space missions, such as to those planned for Mars, where appropriate storage and growth of food resources is essential. Evaluation of the effects of the real and simulated space environment on seed germination and growth in space is the purpose of this research. Preliminary tests of germination rate and growth of radish seeds in a controlled environment have identified statistically significant differences between control samples and seeds flown for 30 days in low earth orbit on the Bion M-1 launch capsule Russian research …
Microcontroller And Memory Card Survivability In Space Conditions,
2017
Utah State University
Microcontroller And Memory Card Survivability In Space Conditions, Windy Olsen
Senior Theses and Projects
No abstract provided.
Relaxation Of Charge In Monolayer Graphene: Fast Nonlinear Diffusion Versus Coulomb Effects,
2017
University of Virginia
Relaxation Of Charge In Monolayer Graphene: Fast Nonlinear Diffusion Versus Coulomb Effects, Eugene B. Kolomeisky, Joseph P. Straley
Physics and Astronomy Faculty Publications
Pristine monolayer graphene exhibits very poor screening because the density of states vanishes at the Dirac point. As a result, charge relaxation is controlled by the effects of zero-point motion (rather than by the Coulomb interaction) over a wide range of parameters. Combined with the fact that graphene possesses finite intrinsic conductivity, this leads to a regime of relaxation described by a nonlinear diffusion equation with a diffusion coefficient that diverges at zero charge density. Some consequences of this fast diffusion are self-similar superdiffusive regimes of relaxation, the development of a charge depleted region at the interface between electron- and …
