Digital Commons Network^™

Temperature Dependence Of Magnetic Hysteresis Of RcoX:Co Nanocomposites (R=Pr And Sm), J. Ping Liu, Ralph Skomski, Yi Liu, David J. Sellmyer

David Sellmyer Publications

The temperature dependence of magnetic hysteresis of RCo_x:Co (R=Pr and Sm) nanocomposite films is reported. These films are prepared by dc and rf sputtering and subsequent thermal processing. It is found that the squareness of the hysteresis loops deteriorates with decreasing temperature. This is attributed to the enhanced magnetic anisotropy of the hard phases at low temperatures. The analysis of the magnetic reversal process shows that the anisotropy enhancement leads to a transition from cooperated to independent behavior. This analysis agrees well with the experimental results.

Hysteresis-Loop Overskewing In The Light Of A Novel Nucleation Mode, Ralph Skomski, J. Ping Liu, David J. Sellmyer

David Sellmyer Publications

It is demonstrated that the magnetostatic demagnetizing factor is not the only sample-shape dependent contribution to the hysteresis loop. There are also exchange contributions, which lead to interesting effects, particularly in nanostructures. An example is the recently discovered bulging mode in two-phase nanomagnets. The bulging mode exhibits the angular symmetry of the coherent mode, but it is incoherent due to its radial variation and gives rise to negative demagnetizing factors.

Structure And Magnetic Properties Of Smco7-XTiX With Tbcu7-Type Structure, Jian Zhou, I.A. Al-Omari, J. Ping Liu, David J. Sellmyer

David Sellmyer Publications

The SmCo_7-xTi_x, x = 0–0.56 bulk samples are prepared by arc melting. X-ray diffraction indicates that samples with 0.2<x7-type structure phase and other minor phases appear for other values of x, which indicates that Ti helps stabilize the 1-7 phase. The lattice parameters ratio (c/a) increases with increasing Ti concentration. Room temperature saturation magnetization and Curie temperature decrease with increasing x. X-ray diffraction and magnetization measurements on aligned samples show that all samples studied have uniaxial anisotropy. The anisotropy field is found to increase with increasing x reaching …

Magnetic Properties Of Cluster-Beam-Synthesized Cobalt: Noble-Metal Films, J.M. Meldrim, Y. Qiang, Yi Liu, H. Haberland, David J. Sellmyer

David Sellmyer Publications

A cluster-beam deposition technique has been used to produce magnetic clusters embedded in a nonmagnetic matrix. We report here on films with cobalt clusters of average diameter of 5.5 nm embedded both in Cu and Ag. Volumetric concentrations of Co ranged from 10% to 50%. Magnetization and low temperature hysteresis loops, both field cooled (FC) and zero-field cooled (ZFC), have been measured between 4.2 and 300 K. The FC and ZFC magnetization bifurcate at or above room temperature with the clusters having a nonzero remanence at room temperature. Low temperature hysteresis loops exhibit a two-phase nature with one phase displaying …

Magnetic Spectroscopy And Characterization Of La0.65Pb0.35Mno3, M. I. Chipara, Shireen Adenwalla, Peter A. Dowben, Qin Lan Xu, Sy_Hwang Liou, R. Shoemaker

Peter Dowben Publications

Crystalline films of La_0.65Pb_0.35MnO₃ grown on Si (100) substrates by rf sputtering have been investigated by ferromagnetic resonance and MOKE. The dependence of the ferromagnetic resonance line parameters on the sample orientation and temperature is investigated. An expression for the angular dependence of the resonance field on the orientation of the sample is proposed, based on the assumption that close to the Curie temperature the Zeeman and demagnetizing terms are dominant. MOKE data support this hypothesis. The temperature dependence of the magnetization at saturation, in relative units, estimated from ferromagnetic resonance agrees with SQUID data. …

The Surface Terminal Layer And Composition Of The Colossal Magnetoresistance Perovskite: La0.65Pb0.35Mno3, C.N. Borca, Delia Ristoiu, Q.L. Xu, Sy_Hwang Liou, Shireen Adenwalla, Peter A. Dowben

Peter Dowben Publications

The composition in the surface region of the colossal magnetoresistance perovskite manganite materials, La_0.65Pb_0.35MnO₃ has been studied using angle resolved x-ray photoemission spectroscopy. The results are consistent with a Mn–O terminal layer and Pb segregation to the near-surface region. This is similar to the behavior exhibited by La_0.65Pb_0.35MnO₃ and La_0.65Pb_0.35MnO₃. The O–Mn–O terminal layer appears to be close to the Mn³+ valence state. ©2000 American Institute of Physics.

Measurement Of The Differential Dijet Mass Cross Section In Pp̅ Collisions At √S =1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present a measurement of the cross section for production of two or more jets as a function of dijet mass, based on an integrated luminosity of 86 pb^-1 collected with the Collider Detector at Fermilab. Our dijet mass spectrum is described within errors by next-to-leading order QCD predictions using CTEQ4HJ parton distributions, and is in good agreement with a similar measurement from the DØ experiment.

The Influence Of Both Coordination Number And Lattice Constant On The Nonmetal To Metal Transition, I.N. Yakovkin, Peter A. Dowben

Peter Dowben Publications

We show that both coordination and lattice constant can have an important influence on the nonmetal to metal transition and the two parameters are not easily separated. Using example theoretical calculations for barium, we provide a compelling case that atomic coordination is a critical factor in determining the critical lattice constant for the nonmetal to metal transition. A comparison between the nonmetal to metal transition three-dimensional and two-dimensional systems is not possible on the basis of the atomic coordination alone. This is discussed in the context of a comparison of the available experimental data for both elemental expanded fluids (three-dimensional) …

Selective Area Chemical Vapor Deposition Of Chromium Oxides, Ruihua Cheng, C.N. Borca, Peter A. Dowben

Peter Dowben Publications

We demonstrate that two-phase CrO₂ and Cr₂O₃ thin films can be grown by using selective organometallic chemical vapor deposition through the oxidation of Cr(CO) ₆ in an oxygen environment. While the magnetization measurements show that both chromium oxides are present, the relative weight of each phase depends on the oxygen partial pressure. Changes of the Curie temperature, T_c, and the saturation magnetization field may be possible by controlling the stoichiometry.

Esr Investigations On Ca Perovskite, M. Chipara, Sy-Hwang Liou, C.N. Borca, R. Shoemaker, Shireen Adenwalla, Peter A. Dowben

Peter Dowben Publications

Electron spin resonance studies on fine powders of La_0.65Ca_0.35MnO₃, performed in the X band, are reported. The coexistence of paramagnetic and ferromagnetic phases, in a narrow temperature range close to the Curie temperature, is observed. The electron spin resonance measurements do not support the presence of bipolarons above the Curie temperature. Temperature dependence of the ESR linewidth is governed by the hopping of polarons and the corresponding activation energy is about 150 meV above T_c.

Comparative Thermal-Expansion Study Of Β″-(Et)2sf5ch2cf2so3 And Κ-(Et)2cu(Ncs)2: Uniaxial Pressure Coefficients Of Tc And Upper Critical Fields, J. Müller, M. Lang, F. Steglich, J. A. Schlueter, A. M. Kini, U. Geiser, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard, T. Sasaki, N. Toyota

Chemistry Faculty Publications and Presentations

We report high-resolution measurements of the coefficient of thermal expansion, α=l⁻¹ x (δl/δΤ), on single crystals of the organic superconductors β″-(ET)₂SF₅CH₂CF₂SO₃ and κ-(ET)₂Cu(NCS)₂. For both salts we find large and highly anisotropic phase-transition anomalies at Tc. Combining these data with literature results on the specific heat via the Ehrenfest relation, the uniaxial pressure coefficients of Tc can be determined. Most remarkably, a strikingly similar in-plane vs out-of-plane anisotropy is found for both compounds: the strong suppression of Tc observed in hydrostatic-pressure experiments is dominated by a huge negative uniaxial stress effect perpendicular to the conducting planes. Therefore we expect that …

Theoretical Studies Of Penetration Of Magnetospheric Electric Fields To The Ionosphere, Stanislav Sazykin

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Ionospheric disturbance electric fields of magnetospheric origin play an important role in determining the global morphology and dynamics of the ionosphere of the Earth. In this work, we present a number of numerical simulations of the transient electric fields in the middle and inner magnetosphere and the ionosphere equatorward of the auroral zone caused by idealized changes in the magnetospheric driving parameters. For these studies, we use the Rice Convection Model (RCM), a large computer code of the magnetosphere-ionosphere coupling which consistently computes the electric fields, currents, and plasma densities in the magnetosphere and the electric field and currents in …

Imaging The Phase Of An Evolving Bose-Einstein Condensate Wave Function, J. E. Simsarian, J. Denschlag, Mark Edwards, Charles W. Clark, L. Deng, E. W. Hagley, K. Helmerson, S. L. Rolston, W. D. Phillips

Physics & Astronomy: Faculty Publications

We demonstrate a spatially resolved autocorrelation measurement with a Bose-Einstein condensate and measure the evolution of the spatial profile of its quantum mechanical phase. Upon release of the condensate from the magnetic trap, its phase develops a form that we measure to be quadratic in the spatial coordinate. Our experiments also reveal the effects of the repulsive interaction between two overlapping condensate wave packets and we measure the small momentum they impart to each other.

Manganese Surface Segregation In Nimnsb, Delia Ristoiu, J. P. Nozie`Res, C.N. Borca, B. Borca, Peter A. Dowben

Peter Dowben Publications

A quantitative analysis of the surface composition of the Heusler alloy NiMnSb has been undertaken using angle-resolved x-ray photoemission spectroscopy and the surface composition characterized. With sufficient annealing cycles, the stoichiometric surface evolves to a surface that is manganese rich. This indicates that the surface enthalpy is different from the bulk for the Heusler alloy NiMnSb. ©2000 American Institute of Physics.

The Q2 Dependence Of Dijet Cross Sections In Γp Interactions At Hera, J. Breitweg, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Stanek, R. Yoshida, Margarita C. K. Mattingly, G. Abbiendi, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, N. Coppola, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Laurenti

Faculty Publications

The dependence of the photon structure on the photon virtuality, Q2, is studied by measuring the reaction e+p → e+ + jet + jet + X at photon-proton centre-of-mass energies 134 < W < 223 GeV. Events have been selected in the Q2 ranges ≃ 0 GeV2, 0.1-0.55 GeV2, and 1.5-4.5 GeV2, having two jets with transverse energy E(T)/(jet) > 5.5 GeV in the final state. The dijet cross section has been measured as a function of the fractional momentum of the photon participating in the hard process, x(γ)/(OBS). The ratio of the dijet cross section with x(γ)/(OBS) < 0.75 to that with x(γ)/(OBS) > 0.75 decreases as Q2 increases. The data are compared with the predictions of NLO pQCD and leading-order Monte Carlo programs using various parton distribution functions of the photon. The measurements can …

A Dynamical Solution To The Problem Of A Small Cosmological Constant And Late-Time Cosmic Acceleration, Christian Armendariz-Picon, V. Mukhanov, Paul J. Steinhardt

Physics - All Scholarship

Increasing evidence suggests that most of the energy density of the universe consists of a dark energy component with negative pressure, a ``cosmological constant" that causes the cosmic expansion to accelerate. In this paper, we address the puzzle of why this component comes to dominate the universe only recently rather than at some much earlier epoch. We present a class of theories based on an evolving scalar field where the explanation is based entirely on internal dynamical properties of the solutions. In the theories we consider, the dynamics causes the scalar field to lock automatically into a negative pressure state …

Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, Alan Middleton, M. Cristina Marchetti, Thomas Prellberg

Physics - All Scholarship

We have investigated the mean field dynamics of an overdamped viscoelastic medium driven through quenched disorder. The model introduced incorporates coexistence of pinned and sliding degrees of freedom and can exhibit continuous elastic depinning or first order hysteretic depinning. Numerical simulations indicate mean field instabilities that correspond to macroscopic stick-slip events and lead to premature switching. The model is relevant for the dynamics of driven vortex arrays in superconductors and other extended disordered systems.

Dissociative Electron Attachment To Vibrationally And Rotationally Excited H2 And Hf Molecules, Yinfan Xu, Gordon A. Gallup, Ilya I. Fabrikant

Gordon Gallup Publications

The vibrational and rotational state dependence of dissociative attachment (DA) in low-energy e-H₂ and e-HF collisions is studied within the framework of nonlocal resonance theory. The dynamics of nuclear motion in the nonlocal complex potential is treated by the quasiclassical approach. The resonance energy, width function, and level-shift function are taken from our previous calculations based on the projection operator formalism. Results for all vibrational states up to the dissociative attachment thresholds and selected rotational states are presented. Our cross sections for H₂ exhibit a plateau structure in the energy range above the dissociation threshold, and …

Reducing The Complexity Of Linear Optics Quantum Circuits, John C. Howell, John A. Yeazell

Mathematics, Physics, and Computer Science Faculty Articles and Research

Integrated optical elements can simplify the linear optics used to simulate quantum circuits. These linear optical simulations of quantum circuits have been developed primarily in terms of the free space optics associated with single-photon interferometry. For an L-bit simulation the number of required free-space optical elements is ∝2^L if 50/50 beam splitters are used. The implementation (construction and alignment) of these circuits with these free-space elements is nontrivial. On the other hand, for the cases presented in this paper in which linear integrated optics (e.g., 2^L×2^L fiber couplers) are used, the number of optical devices does …

On The Spatial Distribution Of Cloud Particles, Alexander Kostinski, A. R. Jameson

Department of Physics Publications

Recent studies have led to the statistical characterization of the spatial (temporal) distributions of cloud (precipitation) particles as a doubly stochastic Poisson process. This paper arrives at a similar conclusion (larger-than-Poissonian variance) via the more fundamental route of statistical physics and significantly extends previous findings in several ways. The focus is on the stochastic structure in the spatial distribution of cloud particles.

A new approach for exploring the stochastic structure of clouds is proposed using a direct relation between number density variance and the pair correlation function. In addition, novel counting diagrams, particularly useful for analyzing counts at low data …

Probability Distribution Of Distance In A Uniform Ellipsoid: Theory And Applications To Physics, Michelle Parry, Ephraim Fischbach

Chemistry & Physics Faculty Publications

A number of authors have previously found the probability P_n(r) that two points uniformly distributed in an n-dimensional sphere are separated by a distance r. This result greatly facilitates the calculation of self-energies of spherically symmetric matter distributions interacting by means of an arbitrary radially symmetric two-body potential. We present here the analogous results for P₂(r;ϵ) and P₃(r;ϵ) which respectively describe an ellipse and an ellipsoid whose major and minor axes are 2a and 2b. It is shown that …

Blending History With Physics: Acoustic Refraction, Charles D. Ross

Chemistry & Physics Faculty Publications

A brief overview of atmospheric acoustics is followed by a description of how acoustic refraction can provide an interesting way of blending history with a traditional physics topic.

Dense And Relativistic Plasmas Produced By Compact High-Intensity Lasers, Donald Umstadter, Shouyuan Chen, G. Ma, Anatoly Maksimchuk, G. Mourou, M. Nantel, S. Pikuz, G. Sarkisov, R. Wagner

Donald Umstadter Publications

High-intensity lasers interacting with plasmas are used to study processes in the laboratory that would otherwise only occur in astrophysics. These include relativistic plasmas, electron acceleration in ultrahigh Ðeld-gradient wake Ðelds, pressure ionization and continuum lowering in strongly coupled plasmas, and X-ray line emission via Raman scattering.

Reply To ‘‘Comment On ‘Dynamically Maintained Steady-State Pressure Gradients’ ’’, D. P. Sheehan

Physics and Biophysics: Faculty Scholarship

A reply is made to Duncan’s Comment [T. L. Duncan, Phys. Rev. E 61, 4661 (2000)] on my earlier paper [D. P. Sheehan, Phys. Rev. E 57, 6660 (1998)] in which he raises an apparent second-law paradox arising from dynamically maintained, steady-state pressure gradients. Resolutions to this paradox are considered in light of current theoretical and experimental understanding.

On The Main Irradiation-Induced Defect In Gan, L. Polenta, Z-Q. Fang, David C. Look

Physics Faculty Publications

We show that the usual Arrhenius analysis of the main electron-irradiation-induced defect trap in n-type GaN, observed by deep-level transient spectroscopy (DLTS), is not sufficiently accurate. Instead, an exact fitting of the DLTS spectrum for this trap reveals two components, each of which has a thermal energy near 60 meV, not the apparent 140–200 meV, as given in other DLTS studies. This result resolves the discrepancy between Hall-effect and DLTS determinations of the thermal energy of this defect center.

Magnetite Biomineralization And Ancient Life On Mars, Richard B. Frankel, Peter R. Buseck

Physics

Certain chemical and mineral features of the Martian meteorite ALH84001 were reported in 1996 to be probable evidence of ancient life on Mars. In spite of new observations and interpretations, the question of ancient life on Mars remains unresolved. Putative biogenic, nanometer magnetite has now become a leading focus in the debate.

Precision Measurement Of The Spin Structure Of The Proton And The Deuteron, Frank R. Wesselmann

Physics Theses & Dissertations

Experiment E155 at the Stanford Linear Accelerator Center measured the spin structure functions g1 and g2 of the proton and deuteron using deep inelastic scattering of 50 GeV polarized electrons from dynamically polarized, solid ¹⁵NH₃ and ⁶LiD targets. Three independent spectrometers, covering a large kinematic region, 0.014 < x_Bjorken < 0.9 and 1 < Q² < 40 (GeV /c)^2, detected 200 million events. A fully self-consistent and statistically sound approach to calculating radiative corrections was developed, providing well-defined statistical errors for the E155 data set. Also, a comprehensive fit to the global data set was created which simultaneously …

Divalent Metal Binding Properties Of The Methionyl Aminopeptidase From Escherichia Coli, Ventris M. D'Souza, Brian Bennett, Alicja J. Copik, Richard C. Holz

Physics Faculty Research and Publications

The metal-binding properties of the methionyl aminopeptidase from Escherichia coli (MetAP) were investigated. Measurements of catalytic activity as a function of added Co(II) and Fe(II) revealed that maximal enzymatic activity is observed after the addition of only 1 equiv of divalent metal ion. Based on these studies, metal binding constants for the first metal binding event were found to be 0.3 ± 0.2 μM and 0.2 ± 0.2 μM for Co(II)- and Fe(II)-substituted MetAP, respectively. Binding of excess metal ions (>50 equiv) resulted in the loss of ∼50% of the catalytic activity. Electronic absorption spectral titration of a 1 …

Wavelength Modulation Spectroscopy Of Water Vapor And Line Center Stabilization At 1.462 Μm For Lidar Applications, Colleen Marie Fitzgerald

Electrical & Computer Engineering Theses & Dissertations

Wavelength modulation spectroscopy was employed to investigate water vapor absorption lines in the 1.462 µm wavelength region using an external-cavity diode laser. These measurements were necessary in the development of a lidar (light detection and ranging) instrument for differential absorption measurement of the concentration and movement of water vapor in the Earth's atmosphere. Differential absorption measurements require that the laser frequency remain stable throughout the duration of the measurement. To ensure this stability, the laser output wavelength is monitored and a feedback control loop set up to minimize laser line drift. Three lines were investigated in the 1.462 µm region. …

The Interplay Between The Surface Band Structure And Possible Surface Reconstructions Of Mo(112), T. Mcavoy, Jun Zhang, C. Waldfried, D.N. Mcilroy, Peter A. Dowben, O. Zeybek, T. Bertrams, S.D. Barrett

Peter Dowben Publications

The experimental band structure of Mo(112) and the effects by temperature and adsorbate are presented. A surface resonance, identified as crossing the Fermi level at about 1/3 from Γ̅ to Χ̅ of surface Brillouin zone, was observed to be very sensitive to both contamination and temperature. We find evidence of adsorbate and temperature induced reconstruction of the Mo(112) surface. Examination of low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) data provides evidence for an adsorbate induced reconstruction of the Mo(112) surface with periodicities consistent with the Fermi level crossingThe experimental band structure of Mo(112) and the effects by temperature …