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Physics Faculty Research & Creative Works

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Articles 1231 - 1260 of 1959

Full-Text Articles in Physical Sciences and Mathematics

Neutron Diffraction, Structural And Magnetic Properties Of (La1-Ypry)0.9na0.1mno3, S. Megdiche, Mohamed Ellouze, A. Cheikh-Rouhou, Q. Cai, William B. Yelon Jan 2003

Neutron Diffraction, Structural And Magnetic Properties Of (La1-Ypry)0.9na0.1mno3, S. Megdiche, Mohamed Ellouze, A. Cheikh-Rouhou, Q. Cai, William B. Yelon

Physics Faculty Research & Creative Works

A systematic study of the structural and magnetic properties of the diluted perovskite manganite oxides (La1-yPry)0.9Na0.1MnO3 (0.2≤y≤0.8) had been carried on. in this study, the average ionic radius 〈rA〉 of a cation site was systematically varied while keeping fixed the carrier concentration (Mn3+/Mn4+ ratio). X-Ray diffraction investigations showed a structural transition from the rhombohedral to the orthorhombic system for 0.33≤y≤0.5. the unit cell volume decreases with increasing Pr3+ content. Magnetic measurements showed that our synthesized samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. Neutron diffraction …

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How To Establish Successful Cooperative Student Learning Centers For Stem Courses, Ronald James Bieniek, Douglas R. Carroll, Cesar Mendoza, Oran Allan Pringle, Ekkehard Sinn, Kai-Tak Wan, Donald C. Wunsch Jan 2003

How To Establish Successful Cooperative Student Learning Centers For Stem Courses, Ronald James Bieniek, Douglas R. Carroll, Cesar Mendoza, Oran Allan Pringle, Ekkehard Sinn, Kai-Tak Wan, Donald C. Wunsch

Physics Faculty Research & Creative Works

Students learn more if they are actively involved in the learning process, particularly in a cooperative manner. Several UMR faculty have operated course-based learning centers (LCs) as part of the campus-wide Learning Enhancement Across Disciplines (LEAD) Program of student learning assistance and enhancement. LCs are designed to assist large numbers of students in a cost- and time-efficient manner that promotes student engagement without requiring undue amounts of faculty time. Course instructors spend time in the open learning environment of the LC, in lieu of office hours, guiding students to master course material and skills in their evolution from novice to …

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Doubly Differential Measurements For Multiple Ionization Of Argon By Electron Impact: Comparison With Positron Impact And Photoionization, Antonio C. Santos, Ahmad Hasan, T. Yates, Robert D. Dubois Jan 2003

Doubly Differential Measurements For Multiple Ionization Of Argon By Electron Impact: Comparison With Positron Impact And Photoionization, Antonio C. Santos, Ahmad Hasan, T. Yates, Robert D. Dubois

Physics Faculty Research & Creative Works

Doubly differential cross sections for single and multiple ionization of Ar have been measured for 500, 750, and 1000 eV electron impact. the cross sections were measured as a function of projectile energy loss and scattering angle. the energy loss range was 0–85 % of the initial projectile energy and scattering angles were between [Formula Presented] the data were put on an absolute scale by normalizing to total ionization cross sections available in the literature and found to be in good agreement with the absolute electron impact cross sections from DuBois and Rudd. for 750 eV impact, a comparison was …

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High Precision Wavelength Measurements Of Qed-Sensitive Forbidden Transitions In Highly Charged Argon Ions, I. Draganić, J. R. Crespo López-Urrutia, Robert D. Dubois, S. Fritzsche, V. M. Shabaev, R. Soria Orts, I. I. Tupitsyn, Y. Zou, J. Ullrich Jan 2003

High Precision Wavelength Measurements Of Qed-Sensitive Forbidden Transitions In Highly Charged Argon Ions, I. Draganić, J. R. Crespo López-Urrutia, Robert D. Dubois, S. Fritzsche, V. M. Shabaev, R. Soria Orts, I. I. Tupitsyn, Y. Zou, J. Ullrich

Physics Faculty Research & Creative Works

We present the results of an experimental study of magnetic dipole ([Formula presented]) transitions in highly charged argon ions (ArX, ArXI, ArXIV, ArXV) in the visible spectral range using an electron beam ion trap. their wavelengths were determined with, for highly charged ions, unprecedented accuracy up to the sub-ppm level and compared with theoretical calculations. the QED contributions, calculated in this Letter, are found to be 4 orders of magnitude larger than the experimental error and are absolutely indispensable to bring theory and experiment to a good agreement. This method shows great potential for the study of QED effects in …

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Brane Factories, Eun-Joo Ahn, Marco Cavaglia, Angela V. Olinto Jan 2003

Brane Factories, Eun-Joo Ahn, Marco Cavaglia, Angela V. Olinto

Physics Faculty Research & Creative Works

We propose that higher-dimensional extended objects (p-branes) are created by super-Planckian scattering processes in theories with TeV scale gravity. As an example, we compute the cross section for p-brane creation in a (n + 4)-dimensional spacetime with asymmetric compactification. We find that the cross section for the formation of a brane which is wounded on a compact submanifold of size of the fundamental gravitational scale is larger than the cross section for the creation of a spherically symmetric black hole. Therefore, we predict that branes are more likely to be created than black holes in super-Planckian …

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Perturbative And Nonperturbative Calculations Of Electron-Hydrogen Ionization, Stephenie J. Jones, Don H. Madison, Mark D. Baertschy Jan 2003

Perturbative And Nonperturbative Calculations Of Electron-Hydrogen Ionization, Stephenie J. Jones, Don H. Madison, Mark D. Baertschy

Physics Faculty Research & Creative Works

We compare calculations of the fully differential cross section for ionization of atomic hydrogen by electron impact using two different theories-the perturbative CDW-EIS (continuum distorted wave with eikonal initial state) approximation and the nonperturbative ECS (exterior complex scaling) method. For this comparison, we chose an impact energy of 54.4 eV, since this is near the lowest energy that our perturbative approach would be applicable and near the highest energy that can be tackled by the ECS method with our present computational resources. For the case of equal-energy outgoing electrons investigated here, the two theories predict nearly identical results except that …

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Dynamic Nonlinear Effect On Lasing In Random Media, B. Liu, Alexey Yamilov, Y. Ling, J. Y. Xu, Hui Cao Jan 2003

Dynamic Nonlinear Effect On Lasing In Random Media, B. Liu, Alexey Yamilov, Y. Ling, J. Y. Xu, Hui Cao

Physics Faculty Research & Creative Works

We investigate the dynamic effect of nonlinearity on lasing in disordered medium. The third-order nonlinearity not only changes frequency and size of lasing mode, but also modifies laser emission intensity and laser pulse width.

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Collision Cross Sections And The Size Of A Coin, Antonio C. Santos, A. Fröhlich Jan 2003

Collision Cross Sections And The Size Of A Coin, Antonio C. Santos, A. Fröhlich

Physics Faculty Research & Creative Works

An important question in education nowadays is how to convey some concepts of Modern Physics to students in high school, secondary education or the sixth form. This article presents an approach to atomic collisions suitable for intermediate level students. We describe an alternative way of measuring the area of a coin using a macroscopic analogy of the scattering of radiation by an atom or molecule—the collision cross section. We hope this article will help educators to illustrate such an important procedure and related concepts of Modern Physics. © 2003 IOP Publishing Ltd.

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Electron Loss From 0.74- And 1.4-Mev/U Low-Charge-State Argon And Xenon Ions Colliding With Neon, Nitrogen, And Argon, Robert D. Dubois, Antonio C. Santos, Ronald E. Olson, Th Stöhlker, F. Bosch, A. Bräuning-Demian, A. Gumberidze, S. Hagmann, C. Kozhuharov, R. Mann, A. Oršić Muthig, U. Spillmann, S. Tachenov, W. Barth, L. Dahl Jan 2003

Electron Loss From 0.74- And 1.4-Mev/U Low-Charge-State Argon And Xenon Ions Colliding With Neon, Nitrogen, And Argon, Robert D. Dubois, Antonio C. Santos, Ronald E. Olson, Th Stöhlker, F. Bosch, A. Bräuning-Demian, A. Gumberidze, S. Hagmann, C. Kozhuharov, R. Mann, A. Oršić Muthig, U. Spillmann, S. Tachenov, W. Barth, L. Dahl

Physics Faculty Research & Creative Works

Absolute total-, single-, and multiple-electron-loss cross sections are measured for (Ar+-, Ar2+-, Xe3+)-~Ne, N2 Ar) collisions at 0.74 and 1.4 MeV/u. in addition, a many-body classical trajectory Monte Carlo model was used to calculate total- and multiple-electron-loss cross sections for Ar+ impact. for N2 and Ar targets, excellent agreement between the measured and calculated cross sections is found; for the Ne target the experimental data are approximately 40% smaller than the theoretical predictions. the experimental data are also used to examine cross-section scaling characteristics for electron loss from fast, low-charge-state, heavy …

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Postcollisional Decay In Ne Multiple Ionization By H2+ Ions In Breakup Collisions, M. M. Sant'anna, H. Luna, Antonio C. Santos, C. Mcgrath, M. B. Shah, E. G. Cavalcanti, G. M. Sigaud, E. C. Montenegro Jan 2003

Postcollisional Decay In Ne Multiple Ionization By H2+ Ions In Breakup Collisions, M. M. Sant'anna, H. Luna, Antonio C. Santos, C. Mcgrath, M. B. Shah, E. G. Cavalcanti, G. M. Sigaud, E. C. Montenegro

Physics Faculty Research & Creative Works

We measured the Neq+ charge-state yield distribution for Ne atoms multiply ionized by 1-MeV/amu H2+ in coincidence with the final state of the projectile, for both breakup and Non breakup channels. Measurements with 1-MeV H+ projectiles were also performed. While the H2+ Non breakup channel produces results similar to equal-velocity proton or electron projectiles, the breakup channels lead to a charge-state yield distribution very close to the known Ne 2s-1 post collisional decay distribution, measured through photoionization [T. A. Carlson, W. E. Hunt, and M. O. Krause, Phys. Rev. 151, 41 (1966)]. This …

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Target Z Dependence And Additivity Of Cross Sections For Electron Loss By 6-Mev/Amu [Formula Presented] Projectiles, R. L. Watson, Yong Peng, V. Horvat, G. J. Kim, Ronald E. Olson Jan 2003

Target Z Dependence And Additivity Of Cross Sections For Electron Loss By 6-Mev/Amu [Formula Presented] Projectiles, R. L. Watson, Yong Peng, V. Horvat, G. J. Kim, Ronald E. Olson

Physics Faculty Research & Creative Works

The dependence of electron loss by 6-MeV/amu Xe18+ on target atomic number was investigated by measuring single-collision cross sections for loss of one to eight electrons in targets of the noble gases He, Ne, Ar, Kr, and Xe. the total-electron-loss cross sections were found to increase linearly with target atomic number, but an abrupt slope change was observed to occur between Ne and Kr. Calculated total-loss cross sections obtained using the n-body classical trajectory Monte Carlo method were in good agreement with the measurements. the dependence of the individual cross sections on the number of electrons lost was reasonably …

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Magnetic Properties Of Er2mn3si5, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, A. V. Morozkin, Z. Chu, William B. Yelon, S. K. Malik, Y. Yamamoto, H. Hori Dec 2002

Magnetic Properties Of Er2mn3si5, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, A. V. Morozkin, Z. Chu, William B. Yelon, S. K. Malik, Y. Yamamoto, H. Hori

Physics Faculty Research & Creative Works

Magnetization measurements have been carried out on the Er2Mn3Si5 compound (tetragonal Sc2Fe3Si5-type, space group P4/mnc) in the temperature range 1.8-300 K. There is a crossover from a room temperature paramagnetic phase to a ferromagnetic phase at 75 K (TC1). A second magnetic transition is observed at 11.5 K (TC2). The magnetic susceptibility in the paramagnetic region, above 100 K, follows simple Curie-Weiss type behavior. The magnetization does not saturate at 2 K even in applied fields of 7 T. Neutron diffraction data collected at 300 …

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Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison Dec 2002

Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison

Physics Faculty Research & Creative Works

It is usually assumed that the first-Born approximation for electron-atom ionization becomes valid for the fully differential cross section at sufficiently high impact energies, at least for asymmetric collisions where the projectile suffers only a small energy loss and is scattered by a small angle. Here we investigate this assumption quantitatively for ionization of hydrogen atoms. We find that convergence of the Born approximation to the correct nonrelativistic result is generally achieved only at energies where relativistic effects start to become important. Consequently, the assumption that the Born approximation becomes valid for high energy is inaccurate, since by the time …

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Intersubband Spin-Density Excitations In Quantum Wells With Rashba Spin Splitting, Carsten A. Ullrich, M. E. Flatté Nov 2002

Intersubband Spin-Density Excitations In Quantum Wells With Rashba Spin Splitting, Carsten A. Ullrich, M. E. Flatté

Physics Faculty Research & Creative Works

In inversion-asymmetric semiconductors, spin-orbit coupling induces a κ-dependent spin splitting of valence and conduction bands, which is a well-known cause for spin decoherence in bulk and heterostructures. Manipulating nonequilibrium spin coherence in device applications thus requires understanding how valence and conduction band spin splitting affects carrier spin dynamics. This paper studies the relevance of this decoherence mechanism for collective intersubband spin-density excitations (SDE's) in quantum wells. A density-functional formalism for the linear spin-density matrix response is presented that describes SDE's in the conduction band of quantum wells with subbands that may be nonparabolic and spin split due to bulk or …

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Degeneracy In Density Functional Theory: Topology In The V And N Spaces, Carsten A. Ullrich, W. Kohn Oct 2002

Degeneracy In Density Functional Theory: Topology In The V And N Spaces, Carsten A. Ullrich, W. Kohn

Physics Faculty Research & Creative Works

The problem of v-representability had cast a shadow of uncertainty over density functional theory (DFT). Building on CCR, the topology of the v(r)-n(r) mapping is clarified. The Be series and a lattice model are used for rl, to a continuous variable, r, does not appear to offer difficulties.

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Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi Sep 2002

Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi

Physics Faculty Research & Creative Works

We investigate de Sitter/conformal field theory (dS/CFT) correspondence in two dimensions. We define the conserved mass of de Sitter spacetime and formulate the correspondence along the lines of the anti–de Sitter/conformal field theory duality. The asymptotic symmetry group, mass, and central charge of de Sitter spacetime are equal to those of anti–de Sitter spacetime. The entropy of two-dimensional de Sitter spacetime is evaluated by applying the Cardy formula. We calculate the boundary correlators induced by the propagation of the dilaton in two-dimensional de Sitter space. Although the dilaton is a tachyonic perturbation in the bulk, boundary conformal correlators have a …

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Double-Logarithmic Two-Loop Self-Energy Corrections To The Lamb Shift, Ulrich D. Jentschura, I. Nandori Aug 2002

Double-Logarithmic Two-Loop Self-Energy Corrections To The Lamb Shift, Ulrich D. Jentschura, I. Nandori

Physics Faculty Research & Creative Works

Self-energy corrections involving logarithms of the parameter Z α can often be derived within a simplified approach, avoiding calculational difficulties typical of the problematic nonlogarithmic corrections (as customary in bound-state quantum electrodynamics, we denote by Z the nuclear charge number, and by α the fine-structure constant). For some logarithmic corrections, it is sufficient to consider internal properties of the electron characterized by form factors. We provide a detailed derivation of related self-energy “potentials” that give rise to the logarithmic corrections; these potentials are local in coordinate space. We focus on the double-logarithmic two-loop coefficient B62 for P states and …

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Nolan-Pollak Type Cn Counters In The Vienna Aerosol Workshop, J. L. Gras, Josef Podzimek, T. C. O'Connor, K. H. Enderle Jul 2002

Nolan-Pollak Type Cn Counters In The Vienna Aerosol Workshop, J. L. Gras, Josef Podzimek, T. C. O'Connor, K. H. Enderle

Physics Faculty Research & Creative Works

Three "standard" Nolan-Pollak (N-P) and modified N-P design condensation nucleus (CN) counters were included in the Vienna Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle counters. These counters came from diverse backgrounds, namely programs in USA, Europe and Australia. In this work, principles of the operation and previous history of calibration of the N-P expansion counter are briefly reviewed and comparisons between the particular counters used in the workshop are presented and discussed. Counting agreement was found to be very good between the N-P counters, typically better than ± 12% for a range of aerosol sizes and compositions from …

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Coincident Fragment Detection In Strong Field Photoionization And Dissociation Of H₂, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Alexander Dorn, Claus Dieter Schroter, Daniel Fischer, Jose R. Crespo Lopez-Urrutia, Paul B. Neumayer, J. Deipenwisch, C. Hohr, Bernold Feuerstein, Joachim Hermann Ullrich Jul 2002

Coincident Fragment Detection In Strong Field Photoionization And Dissociation Of H₂, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Alexander Dorn, Claus Dieter Schroter, Daniel Fischer, Jose R. Crespo Lopez-Urrutia, Paul B. Neumayer, J. Deipenwisch, C. Hohr, Bernold Feuerstein, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

An investigation of the correlated electronic and nuclear motion in fragmentation of H2 in 4 x 1014 W/cm2, fs laser pulses at 795 nm was presented using the electron-ion momentum spectroscopy. The channel selective electron energy distribution indicated assumption of a new H2 ionization mechanism to interpret the differences found in the fragmentation channels. The results showed that the momentum distribution of H+ ions in the dissociation channels H(1s) + H+ + e- and 2H+ + 2e- was independent of the kinetic energy of photoelectrons.

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A Problematic Set Of Two-Loop Self-Energy Corrections, Ulrich D. Jentschura, Jorg Evers, Christoph H. Keitel, Krzysztof Pachucki Jul 2002

A Problematic Set Of Two-Loop Self-Energy Corrections, Ulrich D. Jentschura, Jorg Evers, Christoph H. Keitel, Krzysztof Pachucki

Physics Faculty Research & Creative Works

We investigate a specific set of two-loop self-energy corrections involving squared decay rates and point out that their interpretation is highly problematic. The corrections cannot be interpreted as radiative energy shifts in the usual sense. Some of the problematic corrections find a natural interpretation as radiative nonresonant corrections to the natural line shape. They cannot uniquely be associated with one and only one atomic level. While the problematic corrections are rather tiny when expressed in units of frequency (a few hertz for hydrogenic P levels) and do not affect the reliability of quantum electrodynamics at the current level of experimental …

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Electron Correlation In Double Ionization Of Excited Helium By Fast Ion Impact, L. G. Gerchikov, S. A. Sheinerman, Michael Schulz, R. Moshammer, J. Ullrich Jun 2002

Electron Correlation In Double Ionization Of Excited Helium By Fast Ion Impact, L. G. Gerchikov, S. A. Sheinerman, Michael Schulz, R. Moshammer, J. Ullrich

Physics Faculty Research & Creative Works

The correlation function between two emitted electrons has been calculated as a function of their momentum difference for double ionization of 1s2s excited He atoms by fast ion impact. A simple quantum mechanical approach is developed to take into account the dynamics of two-electron ejection as well as the effects of electron exchange and correlated electron motion in the final state. A clear difference between the correlation functions of the excited and ground state targets is reported.

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Mechanism For Carrier Velocity Saturation In Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris Jun 2002

Mechanism For Carrier Velocity Saturation In Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

We present a possible mechanism for the saturation of the velocity of photoinjected charge carriers in pure organic crystals, the analysis having been motivated by observations in pentacene. The mechanism is based on the strong wave vector dependence of the damping coefficient appearing in the appropriate effective mass equation. Our primary goal is to explore this mechanism in general terms rather than to apply it to a specific system such as pentacene. Our analysis is based on a Fokker-Planck equation treatment. We indicate how the damping coeffcient is related to relaxation times in usual Boltzmann equations and how it can …

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Differential Cross Sections And Cross-Section Ratios For The Electron-Impact Excitation Of The Neon 2p⁵3s Configuration, Murtadha A. Khakoo, James M. Wrkich, Mary Lu Larsen, G. Kleiban, Isik Kanik, Sandor Trajmar, Michael J. Brunger, P. J O Teubner, Albert Crowe, Christopher J. Fontes, Robert E H Clark, Vlado Zeman, Klaus Bartschat, Don H. Madison, Rajesh C. Srivastava, Allan Daniel Stauffer Jun 2002

Differential Cross Sections And Cross-Section Ratios For The Electron-Impact Excitation Of The Neon 2p⁵3s Configuration, Murtadha A. Khakoo, James M. Wrkich, Mary Lu Larsen, G. Kleiban, Isik Kanik, Sandor Trajmar, Michael J. Brunger, P. J O Teubner, Albert Crowe, Christopher J. Fontes, Robert E H Clark, Vlado Zeman, Klaus Bartschat, Don H. Madison, Rajesh C. Srivastava, Allan Daniel Stauffer

Physics Faculty Research & Creative Works

Electron-impact differential cross-section measurements for the excitation of the 2p53s configuration of Ne are reported. The Ne cross sections are obtained using experimental differential cross sections for the electron-impact excitation of the n = 2 levels of atomic hydrogen [Khakoo et al., Phys. Rev. A 61, 012701-1 (1999)], and existing experimental helium differential cross-section measurements, as calibration standards. These calibration measurements were made using the method of gas mixtures (Ne and H followed by Ne and He), in which the gas beam profiles of the mixed gases are found to be the same within our experimental errors. We …

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Possible Ordering Of Ru And Cu In The Charge-Reservoir Of Magneto-Superconductor Rusr₂Gdcu₂O₈ (Ru-1212): Magnetic, Transport, And Tem Microstructural Studies, V. P. S. Awana, S. Ichihara, J. Nakamura, M. Karppinen, H. Yamauchi, Jinbo Yang, William B. Yelon, William Joseph James, Satish K. Malik May 2002

Possible Ordering Of Ru And Cu In The Charge-Reservoir Of Magneto-Superconductor Rusr₂Gdcu₂O₈ (Ru-1212): Magnetic, Transport, And Tem Microstructural Studies, V. P. S. Awana, S. Ichihara, J. Nakamura, M. Karppinen, H. Yamauchi, Jinbo Yang, William B. Yelon, William Joseph James, Satish K. Malik

Physics Faculty Research & Creative Works

Magnetization vs temperature behavior of RuSr2GdCu2O8-δ (Ru-1212) measured in an field of 5 Oe, shows a clear branching of zero-field-cooled (ZFC) and field-cooled (FC) curves around 140 K, a cusp at 135 K, and a diamagnetic transition around 20 K (in the ZFC branch). The cusp at 135 K is due to the antiferromagnetic ordering of the Ru moments. The magnetization-field isotherms, below 50 K, show a nonlinear contribution from a ferromagnetic component. The resistance vs temperature behavior of the compound, in applied fields of 0, 3, and 7 T, confirms that the sample is …

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Observation Of Novel Disordered Rhombohedral R₂Fe₁₇ (R=Rare Earth) Based Compounds, William B. Yelon, William Joseph James, Jinbo Yang, Kishore Kamaraju, Qingsheng Cai, Zili Chu, Satish K. Malik May 2002

Observation Of Novel Disordered Rhombohedral R₂Fe₁₇ (R=Rare Earth) Based Compounds, William B. Yelon, William Joseph James, Jinbo Yang, Kishore Kamaraju, Qingsheng Cai, Zili Chu, Satish K. Malik

Physics Faculty Research & Creative Works

A recent study of (SmGd)Fe 14Si3 showed an anomalous x-ray diffraction pattern [P. C. Ezekwenna, G. K. Marasinghe, J.-H. Nam, W. J. James, W. B. Yelon, M. Ellouze, and Ph. I'Héritier, J. Appl. Phys. 87, 6716 (2000)]. Although all observed peaks could be indexed to the rhombohedral 2:17 phase (R-3m) many lines were strongly reduced in intensity. Subsequently, the same phenomenon was seen in neutron diffraction patterns from Nd2-xDysFe17-ySiy alloys and conventional refinement using the rhombohedral phase left significant residuals. Fourier mapping revealed additional density along the c-axis chains of Fe dumbbells …

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Structure And Magnetic Properties Of The Mnbi Low Temperature Phase, Jinbo Yang, William B. Yelon, William Joseph James, Qingsheng Cai, Samit Roy, Naushad Ali May 2002

Structure And Magnetic Properties Of The Mnbi Low Temperature Phase, Jinbo Yang, William B. Yelon, William Joseph James, Qingsheng Cai, Samit Roy, Naushad Ali

Physics Faculty Research & Creative Works

High purity MnBi low temperature phase has been prepared and analyzed using magnetic measurements and neutron diffraction. The low-temperature phase of the MnBi alloy has a coercivity μ0iHc of 2.0 T at 400 K, and exhibits a positive temperature coefficient from 0 to at least 400 K. The neutron data refinement indicated that the Mn atom changes its spin direction from c axis above room temperature to nearly perpendicular to the c axis at 50 K. A canted magnetic structure has been observed below 200 K. The anisotropy field increases with increasing temperature which gives rise to …

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Magnetic And Mössbauer Studies On Oxygen Deficient Perovskite, La₀.₆Sr₀.₄Feo3-Δ, Jinbo Yang, William B. Yelon, William Joseph James, X.-D. Zhou, Yixiang Xie, Harlan U. Anderson, Zili Chu May 2002

Magnetic And Mössbauer Studies On Oxygen Deficient Perovskite, La₀.₆Sr₀.₄Feo3-Δ, Jinbo Yang, William B. Yelon, William Joseph James, X.-D. Zhou, Yixiang Xie, Harlan U. Anderson, Zili Chu

Physics Faculty Research & Creative Works

Samples of La0.6Sr0.4Fe3-δ with varying oxygen vacancy contents were prepared by heating them in different gas flows. Magnetization measurement showed that samples with low oxygen vacancies have a magnetic ordering temperature in the range of 300-325 K while those with 9%-12% oxygen vacancies have a magnetic ordering temperature of 800 K and higher. Mössbauer spectra at 300 K exhibit paramagnetic or weak magnetic characteristics for the N2, O2, and air-quenched samples, whereas an average hyperfine field of 52 T is found for the CO/CO2 reduced samples. The heat treatment in …

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Magnetic Properties Of Iron-Rich Mixed Rare-Earth Sm₂-ₓtbₓfe17-YSiY Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, William Joseph James, Ph. I'Héritier May 2002

Magnetic Properties Of Iron-Rich Mixed Rare-Earth Sm₂-ₓtbₓfe17-YSiY Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, William Joseph James, Ph. I'Héritier

Physics Faculty Research & Creative Works

A series of Sm2-xTbxFe17-ySiy solid solutions with x = 0, 1, and 1.5 and y = 1, 2, and 3 were prepared by induction melting stoichiometric amounts of high purity elements. The x-ray diffraction data confirm that the postannealed samples are 2:17 intermetallics of the R3 space group. The lattice parameters and the unit cell volumes were calculated using a modified Rietveld program. The fitted intensities showed behavior related to a disordered rhombohedral structure as inferred from neutron data. It was observed that for a particular y, the unit cell volume decreased almost …

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Magnetic And Neutron Diffraction Studies On Prmnsb₂, Satish K. Malik, Zili Chu, Amish G. Joshi, Jinbo Yang, William B. Yelon, Qingsheng Cai, William Joseph James, Kishore Kamaraju May 2002

Magnetic And Neutron Diffraction Studies On Prmnsb₂, Satish K. Malik, Zili Chu, Amish G. Joshi, Jinbo Yang, William B. Yelon, Qingsheng Cai, William Joseph James, Kishore Kamaraju

Physics Faculty Research & Creative Works

Magnetic and neutron diffraction studies have been carried out on PrMnSb2. Magnetization data in the temperature range of 5-400 K show two magnetic transitions: one at ∼175 K attributed to the antiferromagnetic ordering of the Mn moments, and the other at ∼35 K possibly due to the antiferromagnetic ordering of the Pr moments. The magnetization-field isotherms at various temperatures are consistent with the above. Neutron diffraction data obtained at various temperatures can be fitted with a nearly antiferromagnetically coupled Mn moment of ∼3μB at 70 K. At 10 K, moments both on Mn (∼3.5μB) and …

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Structure And Superconductivity Of Dy (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤ 0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon May 2002

Structure And Superconductivity Of Dy (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤ 0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon

Physics Faculty Research & Creative Works

Structural and superconducting properties of single-phase La-substituted compounds of the formula Dy(Ba 2-yLay)Cu3Oz (0.0≤y≤0.5) have been investigated by neutron diffraction, electrical resistivity, and magnetization measurements. The compound DyBa 2Cu3O7-δ (orthorhombic, space group Pmmm) exhibits superconductivity with transition temperature, T c, of about 90 K. Rietveld analysis of the neutron diffraction data on La containing compounds reveals that the orthorhombicity decreases with increasing La concentration and the compounds become tetragonal for higher La content. The overall oxygen content increases as divalent Ba is replaced by trivalent La and approximately compensates for …

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