Physical Sciences and Mathematics Commons^™

Electronic Structure And Magneto-Optical Properties Of Mnbi And Mnbial, Sitaram Jaswal, J. X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

MnBiAl films are of considerable current interest for possible magneto-optical applications because of their perpendicular anisotropy, large polar Kerr rotation, reduced grain size, and structural stability. We report here experimental and theoretical studies of the effect of Al alloying on the electronic structure and magneto-optical properties of MnBi. Our measured spectral dependencies of the polar Kerr rotation in the two systems are similar. We carried out relativistic self-consistent spin-polarized electronic structure calculations on MnBi and MnBiAl, and the calculated densities of states are in good agreement with available x-ray photoemission spectroscopy data for both materials. The spin magnetic moment of …

Magnetization Reversal In Nanoscale Magnetic Films With Perpendicular Anistropy, Roger D. Kirby, J.X. Shen, Robert J. Hardy, David J. Sellmyer

Department of Physics and Astronomy: Faculty Publications

We present experimental results on magnetization reversal for a class of nanoscale magnetic films with perpendicular magnetic anistropy and develop a model that describes a variety of related experiments. In this model the sample is divided into identical single domain cells that interact through dipolar fields and a nearest-neighbor domain-wall interaction. Monte Carlo simulations give insights into the relationship between macroscopic magnetic parameters and the reversal behavior and demonstrate the important role that thermal activation plays in the reversal process.

Possible Extension Of The Chiral Perturbation Theory Program, Joseph Schechter

Physics - All Scholarship

After a brief discussion of how chiral dynamics has evolved from the ``universal V-A theory of weak interactions'', we present some evidence that symmetry breaking for the vector meson multiplet is not simpler than but rather analogous to that for the pseudoscalar multiplet. This provides a motivation for speculating on how to extend in a systematic way the chiral perturbation theory program to include vectors.

Heterojunction Fabrication By Selective Area Chemical Vapor Deposition Induced By Synchrotron Radiation, Dongjin Byun, Seong-Don Hwang, Peter A. Dowben, F. Keith Perkins, F. Filips, N.J. Ianno

Peter Dowben Publications

We have fabricated a B₅C, boron-carbide/Si(111) heterojunction diode by the synchrotron radiation-induced decomposition of orthocarborane. This diode can be compared with similar boron-carbide/Si(111) heterojunction diodes fabricated by plasma enhanced chemical vapor deposition. The synchrotron radiation induced chemical vapor deposition is postulated to occur via the decomposition of weakly chemisorbed species and the results suggest that “real-time'' projection lithography (selective area deposition) of boron-carbide devices is possible.

Parallels Between High Doubly Excited State Spectra In H– And Li– Photodetachment, Cheng Pan, Anthony F. Starace, Chris H. Greene

Anthony F. Starace Publications

Eigenchannel R-matrix calculations for photodetachment of H^– up to the H(n = 6) threshold provide complete theoretical confirmation of observed high-lying, doubly excited state spectra. Long-range multipole interactions beyond the reaction volume are found to play an important role. Similar calculations for Li^– photodetachment up to the Li(n = 6) threshold predict analogous resonance structures. These results indicate that recent advances in understanding two-electron correlations in H^– and He have application to many electron systems.

Teaching And Learning Physics With Interactive Video, Dean Zollman, Robert Fuller

Robert G. Fuller Publications

Using computer-controlled digital video, students can view and analyze the physics of events as common as the snapping of a towel, as graceful as the motion of a dancer or as extraordinary as the collapse of the Tacoma Narrows Bridge.

Spin-Resolved (E,2e) Coincidences For Heavy Rare-Gas Targets, Stephenie J. Jones, Don H. Madison, G. Friedrich Hanne

Physics Faculty Research & Creative Works

It has been well established that the Coulomb force alone can produce spin-dependent effects for electron-impact excitation of heavy rare-gas atoms if the incident electrons are spin polarized and the final J state of the atom is resolved. This effect has become known as the fine-structure effect. Here we demonstrate that the same type of effect may be expected for electron-impact ionization.

X-Rays From Microstructured Targets Heated By Femtosecond Lasers, S. P. Gordon, Thomas D. Donnelly, A. Sullivan, H. Hamster, R. W. Falcone

All HMC Faculty Publications and Research

We have demonstrated efficient conversion of ultrashort-pulse laser energy to x rays with energies above 1 keV, using laser-produced plasmas generated on a variety of microstructured surfaces. Lithographically produced grating targets generated 0.1 mJ of kilo-electron-volt x rays, and porous gold and aluminum targets emitted 1 mJ. This represents an improvement of a factor of 100 over flat targets. The K-shell emission spectrum of porous aluminum was composed primarily of heliumlike spectral lines.

Observation Of Free And Bound Excitons Associated With The 2-Dimensional Electron-Gas In Modulation-Doped Heterostructures, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz

Physics Faculty Publications

Overlapping bulk and two-dimensional excitons have been observed in modulation-doped heterostructures. Their differing behavior in a magnetic field allows them to be studied separately. Both free and bound excitons, associated with the two-dimensional electron gas, have been observed in the photoluminescence spectra of these structures. These excitons show a reduced binding energy due to screening and are found in a region of the structure where band-gap renormalization occurs due to many-body interactions. The two-dimensional excitons are identified from measurements conducted in applied magnetic fields.

Phase Diagram Of The Ising Model On Percolation Clusters, Miron Kaufman, T. Berger, P. D. Gujrati, D. Bowman

Physics Faculty Publications

The annealed Ising magnet on percolation clusters is studied by means of a mapping into a Potts-Ising model and with the Migdal-Kadanoff renormalization-group method. The phase diagram is determined in the three-dimensional parameter space of the Ising coupling K, the bond-occupation probability p, and the fugacity q, which controls the number of clusters. Three phases are identified: percolating ferromagnetic, percolating paramagnetic, and nonpercolating paramagnetic. For large q the phase diagram includes a multicritical point at the intersection of the Ising critical line and the percolation critical line. In the case of random bond percolation (q = 1) the Ising critical …

Flow Simulations About Steady-Complex And Unsteady Moving Configurations Using Structured-Overlapped And Unstructured Grids, James Charles Newman Iii

Mechanical & Aerospace Engineering Theses & Dissertations

The limiting factor in simulating flows past realistic configurations of interest has been the discretization of the physical domain on which the governing equations of fluid flow may be solved. In an attempt to circumvent this problem, many Computational Fluid Dynamic (CFD) methodologies that are based on different grid generation and domain decomposition techniques have been developed. However, due to the costs involved and expertise required, very few comparative studies between these methods have been performed. In the present work, the two CFD methodologies which show the most promise for treating complex three-dimensional configurations as well as unsteady moving boundary …

Unsteady Flow Simulations About Moving Boundary Configurations Using Dynamic Domain Decomposition Techniques, Guan-Wei Yen

Mechanical & Aerospace Engineering Theses & Dissertations

A computational method is developed to solve the coupled governing equations of an unsteady flowfield and those of rigid-body dynamics in six degrees-of-freedom (6-DOF). This method is capable of simulating the unsteady flowfields around multiple component configurations with at least one of the components in relative motion with respect to the others. Two of the important phenomena that such analyses can help us to understand are the unsteady aerodynamic interference and the boundary-induced component of such a flowfield. By hybridizing two dynamic domain decomposition techniques, the grid generation task is simplified, the computer memory requirement is reduced, and the governing …

Derivative Absorption Spectroscopy With Tunable Laser Diodes, Andrew D. Jackson

Electrical & Computer Engineering Theses & Dissertations

Derivative Absorption Spectroscopy using tunable diode lasers provides a non­ intrusive, sensitive, and convenient method for monitoring gaseous characteristics such as concentration, temperature, and flow velocity. In addition, the specie type can be identified, and if the equation of state is known, pressure may be deduced.

This technique was used on molecular oxygen, in which the rovibronic transitions of the A-band ( b ¹ ∑_g ⁺ ← X ³ ∑g ^- ; v^II = O, v^I = O) were probed. Phase sensitive detection with a lock-in amplifier provides the flexibility to examine lineshape derivatives; several such derivative …

High Energy Coupled Nucleon Tranpsort In One Dimension, Stanley L. Lamkin

Physics Theses & Dissertations

The problem of energetic nucleon transport through extended bulk matter is considered in the context of the 'straight ahead' approximation. The applicable form of the Boltzmann transport equation is derived and solved in one dimension. The production term for secondary generation nucleons due to nuclear fragmentation includes 'coupling' of the flux to other types of nucleon projectiles. A physically motivated perturbation series approach is developed to enhance solution convergence. The Boltzmann operator is inverted and the flux is computed using a numerical marching scheme. The secondary production integrals are optimized for second order accuracy using a set of analytical benchmarks. …

Slowing Of 85Rb Atoms With Isotropic Light, Herman Batelaan, S. Padua, D. H. Yang, C. Xie, R. Gupta, Harold Metcalf

Department of Physics and Astronomy: Faculty Publications

We have demonstrated the slowing of a rubidium atomic beam by isotropic monochromatic light. The results agree with a model calculation, thus allowing its use for designing a practical isotropic light slower. The large hyperfine splittings of rubidium lead to natural multifrequency slowing, which is also included in our model.

Absence Of Size Dependence Of The Kondo Resistivity, V. Chandrasekhar, P. Santhanam, N. A. Penebre, Richard A. Webb, H. Vloeberghs, C. Van Haesendonck, Y. Bruynseraede

Faculty Publications

We have measured the low temperature resistivity of AuFe wires in the dilute magnetic impurity limit as a function of wire width, temperature, and magnetic field. When the width dependence of the electron-electron interaction contribution to the resistivity is taken into account, the temperature dependence of the remaining Kondo contribution to the resistivity of all samples with the same impurity concentration is identical. Similar behavior is observed for the magnetic field dependent resistivity. Thus, the Kondo contribution to the resistivity is independent of width down to 38 nm, much smaller than the Kondo length ξ_K=ħv_F/k_{B …}

Solar Spectroscopy Using 50 Meters Of Fiber Optic Cable And Ccd Camera, Christopher P. Smith

Opportunities for Undergraduate Research Experience Program (OURE)

Measurements of the variation of the Can K line profile using very modest equipment is discussed. The equipment used included a Spex 0.75 meter spectrometer, a Santa Barbara Instrument Group 16 bit ST-6 Charge Coupled Device (CCD) camera, fiber optic cable, and a 10-inch Cassegrain telescope. Observations were made in both regions of little or no solar activity as well as in regions of high solar activity (sunspots). A roughly 8% increase in Ca II K emission was observed over a sunspot. The combination of the unique observing apparatus and the intensity resolution of the CCD camera was essential for …

Feasibility Of Using Ultrasonic Cavitation To Produce Silica Sol, Gary L. Vines

Honors Capstone Projects and Theses

No abstract provided.

On The Absence Of An Exponential Bound In Four Dimensional Simplicial Gravity, Simon Catterall, John B. Kogut, R. Renken

Physics - All Scholarship

We have studied a model which has been proposed as a regularisation for four dimensional quantum gravity. The partition function is constructed by performing a weighted sum over all triangulations of the four sphere. Using numerical simulation we find that the number of such triangulations containing V simplices grows faster than exponentially with V. This property ensures that the model has no thermodynamic limit.

Unoccupied Surface Electronic Structure Of Gd(0001), Dongqi Li, Peter A. Dowben, J.E. Ortega, F.J. Himpsel

Peter Dowben Publications

The unoccupied surface electronic structure of Gd(0001) was investigated with high-resolution inverse-photoemission spectroscopy. An empty surface state near E_F is observed at Γ¯. Two other surface-sensitive features are also revealed at 1.2 and 3.1 eV above the Fermi level. Hydrogen adsorption on Gd surfaces was used to distinguish the surface-sensitive features from the bulk features. The unoccupied bulk-band critical points are determined to be Γ_3^- at 1.9 eV and A₁ at 0.8 eV.

Surface Core-Level Shifts Of Ta(110) And W(110) Vs. Alkali-Atom Coverage: Implications For Thealkali-Substrate Interaction, A. B. Andrews, D. Mark Riffe, G. K. Wertheim

All Physics Faculty Publications

The change in the average surface-atom core-level shift (SCS) produced by submonolayer coverages of alkali adsorbates is quite small for both Ta(110) and W(110), less than 45 meV in magnitude. The small change of the measured SCS’s as a function of coverage decisively supports the covalent-bonding picture of alkali adsorption proposed by Ishida and Terakura.

Coherence Parameters For Electron Capture In H⁺ + He Collisions, C. J. Lundy, Ronald E. Olson, D. R. Schultzi, J. P. Pascale

Physics Faculty Research & Creative Works

The classical trajectory Monte Carlo method is used to calculate coherence parameters for electron capture to H(n = 2, 3 and 4) in 30 to 250 keV H+ + He collisions. The parameters evaluated are the x- and z-components of the dipole moment (D) and the z-component of the perihelion velocity of the captured electron (L x A). The calculated integral values are found to be in reasonable agreement with available experimental results. Components of the dipole moment and (L x A) were also evaluated as a function of projectile scattering angle. Here, rapid variations of the parameters are observed …

Scaling Of Voltage-Current Characteristics Of Thin-Film Y-Ba-Cu-0 At Low Magnetic Fields, Brandon R. Brown

Physics and Astronomy

We have measured voltage-current characteristics for YBa2Cu3O7 thin films in magnetic fields from 5 T to ambient, including some in the millitesla range. In all cases, the resistivity-current density isotherms can be separated into two classes: those which exhibit upward curbature, and have constant resistivity at low currents, and those which exhibit downward curvature at all currents. These two classes of isotherms are separated by a field-dependent temperture Tg. For each field, the isotherms scale in a manner consistent with a three dimensional vortex-liquid to vortex-glass phase transition. The region that can be scaled is several kelving at 5 T …

Magnetoresistance In Nanostructured Co-Ag Prepared By Mechanical- Alloying, J.M.D. Coey, A.J. Fagan, Ralph Skomski, J. Gregg, K. Ounadjela, S.M. Thompson

Ralph Skomski Publications

Fine cobalt and silver powders have been ball-milled to yield a granular solid of composition Co₃₀Ag₇₀ in the form of coarse powder. The material is an intimate mixture of grains of fcc CO in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10 % at 4.2 K.

Magnetoresistance In Nanostructured Co-Ag Prepared By Mechanical- Alloying, J.M.D. Coey, A.J. Fagan, Ralph Skomski, J. Gregg, K. Ounadjela, S.M. Thompson

Ralph Skomski Publications

Fine cobalt and silver powders have been ball-milled to yield a granular solid of composition Co₃₀Ag₇₀ in the form of coarse powder. The material is an intimate mixture of grains of fcc CO in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10 95 at 4.2 K.

Exchange Coupling And Energy Product In Random Two- Phase Aligned Magnets, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Size effects in two-phase Boolean magnets composed of an aligned hard phase and a soft phase with high magnetization are investigated. In 'over-critical' magnets, where the size of the soft regions is larger than the Blochwall width δ_h of the hard phase, the energy product is reduced compared to the corresponding 'undercritical' magnets with small soft regions, where theoretical energy products as high as 1 M J / m³ have been predicted. Nevertheless, the theoretical energy product only gradually drops with increasing size of the soft regions, and it may still exceed the theoretical energy product 516 kJ/m …

Non-Equilibrium Gas-Phase Nitrogenation, S. Brennan, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Non-equilibrium nitrogenation of transition-metal rich rare-earth intermetallics can be used to increase the nitrogen content beyond its equilibrium concentration. For example, nitrogenation of Sm₂Fe₁₇ using ammonia yields volume expansions up to 8.3 vol %, which correspond to a composition Sm₂Fe₁₇N_x with x = 4. This effect is related to catalytic action at the metal surface where ammonia is decomposed into nitrogen and hydrogen, with nitrogen absorption on a site where it is weakly bound, as an intermediate step. For overloaded Sm₂Fe₁₇N_x with x>3 the net reaction …

A Measurement Of B(D+S → Φl+Ν) B(D+S → Φπ+), Cleo Collaboration, F. Butler, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

Using the CLEO II detector at CESR, we have measured the ratio of branching fractions B(D → φlν) B(D → φπ) = 0.54 ± 0.05 ± 0.04. We use this measurement to obtain a model dependent estimate of B(D → φπ). © 1994.

A Mössbauer Effect Study Of The Microscopic Magnetic Properties Of Th₂Fe₁₇ And Its Nitride, Th₂Fe₁₇N₂.₆, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, T. H. Jacobs, K. H. Buschow

Chemistry Faculty Research & Creative Works

The Mössbauer spectra of Th₂Fe₁₇ and Th₂Fe₁₇N_2.6 have been measured at various temperatures between 85 and 295 K and analyzed with a model that is based on the Wigner-Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron-diffraction measurements or band-structure calculations. Upon nitrogenation of Th₂Fe₁₇, the 85 K weighted average isomer shift increases from 0.037 to 0.156 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed …

Correlated Two-Electron Wave Functions Of Any Symmetry, Christopher Bottcher, David R. Schultz, Don H. Madison

Physics Faculty Research & Creative Works

Using a procedure originally due to Hylleraas, a convenient expansion in coupled spherical harmonics which terminates in a very small number of terms is applied to the treatment of fully correlated two-electron wave functions of any symmetry (total angular momentum, parity, and spin). Coupled equations satisfied by these wave functions are derived which are well adapted to computation and which we discretize on a numerical lattice utilizing the basis-spline collocation method. Use of this method which relies on very flexible basis functions is intended to facilitate subsequently the consideration of time-dependent rearrangments such as autoionization, photoionization, and electron-impact excitation and …