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Possible Origins Of High-Tc, Superconductivity, John R. Hardy, John W. Flocken May 1988

Possible Origins Of High-Tc, Superconductivity, John R. Hardy, John W. Flocken

Physics Faculty Publications

A new mechanism is proposed to explain high-T, superconductivity in copper-oxide-based, open perovskitelike systems. It is shown that, should the oxygen ions be moving in a double-well potential, an order-of-magnitude enhancement of the electron-lattice coupling follows automatically from a consistent treatment of this motion. Both theoretical and experimental evidence for the presence of such double wells is cited.

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Possible Origins Of High-TC, Superconductivity, John R. Hardy, J. W. Flocken May 1988

Possible Origins Of High-TC, Superconductivity, John R. Hardy, J. W. Flocken

John R. Hardy Papers

A new mechanism is proposed to explain high-Tc superconductivity in copper-oxide-based, open perovskitelike systems. It is shown that, should the oxygen ions be moving in a double-well potential, an order-of-magnitude enhancement of the electron-lattice coupling follows automatically from a consistent treatment of this motion. Both theoretical and experimental evidence for the presence of such double wells is cited.

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Y-Ba-Cu-O Films By Rf Magnetron Sputtering Using Single Composite Targets: Superconducting And Structural Properties, Sy_Hwang Liou, M. Hong, J. Kwo, B.A. Davidson, H.S. Chen, S. Nakahara, T. Boone, R.J. Felder May 1988

Y-Ba-Cu-O Films By Rf Magnetron Sputtering Using Single Composite Targets: Superconducting And Structural Properties, Sy_Hwang Liou, M. Hong, J. Kwo, B.A. Davidson, H.S. Chen, S. Nakahara, T. Boone, R.J. Felder

Sy-Hwang Liou Publications

High Tc superconducting Y-Ba-Cu-O films have been produced by rf magnetron sputtering using single unreacted composite targets of Y2O3, BaF2, and CuO powders. Transport measurements of the films showed a sharp resistive Tc (R=0) at 89 K and a metallic behavior of resistivity versus temperature. The films show preferred orientations when deposited on single-crystal SrTiO3 substrates (100) or (110) and followed by a post O2 annealing at 825 °C.

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Experimental Study Of Nonlinear Conductance In Small Metallic Samples, Richard A. Webb, S. Washburn, C. P. Umbach May 1988

Experimental Study Of Nonlinear Conductance In Small Metallic Samples, Richard A. Webb, S. Washburn, C. P. Umbach

Faculty Publications

We have directly observed current-dependent, nonlinear contributions to the conductance fluctuations of phase-coherent metallic wires and loops. The fluctuations in the current-voltage curves are reproducible, asymmetric about I=0, and in qualitative agreement with theoretical predictions. In ac measurements, the nonlinear terms also generate large harmonic signals of the conductance fluctuations whose dependence on the drive current can be understood qualitatively. The spectra of harmonics from loops and wires have different dependences on the voltage across the sample.

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Modulated Phases In Thin Ferroelectric Liquid-Crystal Films, George A. Hinshaw Jr., Rolfe G. Petschek May 1988

Modulated Phases In Thin Ferroelectric Liquid-Crystal Films, George A. Hinshaw Jr., Rolfe G. Petschek

Faculty Scholarship

We discuss modulated phases that can occur in thin liquid-crystal films composed of tilted, chiral molecules. While the phase diagram depends on all orders of a Landau expansion we find that either a striped phase of parallel defect walls or a lattice of hexagonal unit cells containing disclinations and bounded by intersecting walls can occur. The striped phase can occur with either a positive or negative bend elastic constant depending on the underlying microscopic parameters. The transition into the modulated phase is, in general, continuous with infinite defect separation at the transition.

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Projectile-Charge Dependence Of Ejected-Electron Spectra, V. D. Irby, Timothy J. Gay, J. Wm. Edwards, E. B. Hale, M. L. Mckenzie, R. E. Olson May 1988

Projectile-Charge Dependence Of Ejected-Electron Spectra, V. D. Irby, Timothy J. Gay, J. Wm. Edwards, E. B. Hale, M. L. Mckenzie, R. E. Olson

Timothy J. Gay Publications

We have studied H++He and 3He+++He ionizing collisions at intermediate energies (60 to 120 keV/amu) and have observed a significant shift in the velocity position of the maxima in forward-ejected electron spectra when changing projectiles from protons to α particles. In ionizing collisions, a large portion of the ejected electrons are stranded near the transitory equiforce, or saddle point, position between the target ion and receding projectile. The shift in the electron spectra maxima to smaller velocities, due to changing projectiles from protons to α particles, is consistent with the shift in the saddle-point velocity …

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Hylleraas Variational Perturbation Theory: Application To Correlation Problems In Molecular Systems, Robert J. Cave, Ernest R. Davidson May 1988

Hylleraas Variational Perturbation Theory: Application To Correlation Problems In Molecular Systems, Robert J. Cave, Ernest R. Davidson

All HMC Faculty Publications and Research

Hylleraas variational perturbation theory is applied through second order in energy to estimate the correlation energy in several molecular systems. The specific choices for H0 and V which are made lead to equations nearly identical to the multireference linearized coupled‐cluster method of Laidig and Bartlett. The results obtained are in virtually exact agreement where comparisons have been made. Results from test calculations are presented for BeH2, CH2, and C2H4. In addition, the utility of perturbation theory for selecting correlating configurations is examined. This procedure is found to be quite accurate while …

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Cayley-Tree Ising Model With Antiferromagnetic Nearest-Neighbor And Ferromagnetic Equivalent-Neighbor Interactions, Miron Kaufman, M. Kahana May 1988

Cayley-Tree Ising Model With Antiferromagnetic Nearest-Neighbor And Ferromagnetic Equivalent-Neighbor Interactions, Miron Kaufman, M. Kahana

Physics Faculty Publications

The phase diagram of the Ising model with antiferromagnetic nearest-neighbor interactions and ferromagnetic equivalent-neighbor interactions on the Cayley tree is determined exactly. A nonuniversal critical line separates the disordered and the ordered phases. A line of first-order transitions separating ferromagnetic order from antiferromagnetic order ends in the midst of the ordered phase at a classical ordered critical point. For a small range of values of the ratio of the two couplings, two transitions occur as the temperature is varied. In this case the uniform magnetization is not a monotonic function of the temperature.

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General Analysis And Optimization Of The Four-Detector Photopolarimeter, R. M.A. Azzam, I. M. Elminyawi, A. M. El-Saba May 1988

General Analysis And Optimization Of The Four-Detector Photopolarimeter, R. M.A. Azzam, I. M. Elminyawi, A. M. El-Saba

Electrical Engineering Faculty Publications

The four-detector photopolarimeter (FDP) is analyzed for an arbitrary spatial configuration and any reflection characteristics (ri, ψi, Δi) of the first three detectors. The instrument matrix A, which relates the output signal vector I to the input Stokes vector S by I = AS, and its determinant are derived explicitly. The essential condition that A be nonsingular (det A ≠ 0) is satisfied in general with uncoated absorbing detector surfaces, assuming that the plane of incidence (POI) is rotated between successive reflections by other than 90°. Therefore no special coatings on …

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Oxygen Defect In Yba2Cu3OX: An X-Ray Photoemission Approach, W.K. Ford, C.T. Chen, J. Anderson, J. Kwo, Sy_Hwang Liou, M. Hong, G.V. Rubenacker, J.E. Drumheller May 1988

Oxygen Defect In Yba2Cu3OX: An X-Ray Photoemission Approach, W.K. Ford, C.T. Chen, J. Anderson, J. Kwo, Sy_Hwang Liou, M. Hong, G.V. Rubenacker, J.E. Drumheller

Sy-Hwang Liou Publications

A combined x-ray photoemission and diamagnetic-susceptibility study of YBa2Cu3Ox with x≃6 and 7 has been performed, with emphasis on the oxygen defect and the effect of heating in vacuum. By comparing spectra taken at these two oxygen contents, the core levels observed in the O 1s and Ba 4d spectral range are identified. Peak-intensity analysis indicates (1) that the oxygen released during the in situ heating is derived from or near the Cu-O-Cu-O chains of YBa2Cu3O7 and (2) that there is a random distribution of oxygen defects in …

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Summary Abstract: Formation Of Cr2N Overlayers On A Fe/Cr{110} Crystal, H. Ruppender, M. Grunze, Peter A. Dowben May 1988

Summary Abstract: Formation Of Cr2N Overlayers On A Fe/Cr{110} Crystal, H. Ruppender, M. Grunze, Peter A. Dowben

Peter Dowben Publications

In this communication we summarize our experiments related to the formation of chromium surface nitride layers on a Fe72Cr28{110} surface. These surface nitrides were produced by (i) exposure to molecular nitrogen, (ii) exposure to ammonia, and (iii) segregation of nitrogen to the crystal surface. It was found in all cases that the nitrogen concentration in the selvedge scales linearly with the chromium concentration and that chromium segregation is the rate determining step for the formation of a surface nitride.

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Modal Interference Techniques For Strain Detection In Few-Mode Optical Fibers, Bradley D. Duncan Apr 1988

Modal Interference Techniques For Strain Detection In Few-Mode Optical Fibers, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

Interference between the modes of an optical fiber results in specific intensity patterns which can be modulated as a function of disturbances in the optical fiber system. These modulation effects are a direct result of the difference in propagation constants of the constituent modes. In this presentation it is shown how the modulated intensity patterns created by the interference of specific mode groups in few-mode optical fibers (V < 5.0) can be used to detect strain. A detailed discussion of the modal phenomena responsible for the observed strain induced pattern modulation is given and it is shown that strain detection sensitivities on the order of 10-9 can be expected. Data taken during the evaluation of an actual experimental strain detection system based on the developed theory is also presented.

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Magnetic Properties Of Rare-Earth Transition-Metal Borides, S.H. Aly, E. Singleton, George C. Hadjipanayis, David J. Sellmyer, Z.R. Zhao Apr 1988

Magnetic Properties Of Rare-Earth Transition-Metal Borides, S.H. Aly, E. Singleton, George C. Hadjipanayis, David J. Sellmyer, Z.R. Zhao

David Sellmyer Publications

The magnetic and structural properties of quaternary RCo4-xFexB alloys with R=Nd, Sm, Er have been examined with magnetometry and x-ray diffraction. The CeCo4B-type phase is found for all x in Er, for x≤3 in Sm, and for x=0, 1, and 2 in Nd. Maximum coercivities have been obtained in a crystallized SmFe2Co2B sample with Hc>17 kOe at room temperature.

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Coherent Population Trapping In N-Level Quantum Systems, Foek T. Hioe, C. E. Carroll Apr 1988

Coherent Population Trapping In N-Level Quantum Systems, Foek T. Hioe, C. E. Carroll

Physics Faculty/Staff Publications

A multilevel quantum system interacting with an intense laser Seld is shown to exhibit many invariants, or constants of evolution, under various conditions. Our results also apply to other similar physical problems.

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Ellipsometric And Magneto-Optic Properties Of Sputtered Dysprosium-Iron Multilayers, Thomas E. Tiwald, John A. Woollam, David J. Sellmyer Apr 1988

Ellipsometric And Magneto-Optic Properties Of Sputtered Dysprosium-Iron Multilayers, Thomas E. Tiwald, John A. Woollam, David J. Sellmyer

David Sellmyer Publications

Ellipsometric and magneto-optical properties of Dy (3.5 Å thick) and Fe (2.5–12.5 Å thick) multilayers were investigated over the spectral range from 3000 to 8000 Å in magnetic fields to 0.21 T. In this range of layer thickness the magnetic anisotropy is vertical. Kerr rotations, were found to be weakly spectrally dependent, and as large as 0.06°. The magnetically driven change of ellipticity of reflected light was as large as 0.13, depending on sample and wavelength. Ellipsometric analysis of layer thickness was performed assuming a multilayer geometry. In addition, the optical constants were determined assuming the multilayer was a homogeneous …

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Particle Size Dependence Of The Magnetic Properties Of Ultrafine Granular Films, Sy_Hwang Liou, C.L. Chien Apr 1988

Particle Size Dependence Of The Magnetic Properties Of Ultrafine Granular Films, Sy_Hwang Liou, C.L. Chien

Sy-Hwang Liou Publications

Magnetic granular solids consist of ultrafine metal granules of nanometer sizes embedded in an insulating medium. The magnetic properties are dictated by the microstructure such as particle size, metal volume fraction, which are process controlled. We report the results of a series of granular Fe60(SiO2)40 films in which the particle size has been systematically varied. The magnetic coercivity, ranging from 500 to 2200 Oe, increases with particle size. The ferromagnetic-superparamagnetic transition had been studied by SQUID magnetometry and Mössbauer spectroscopy. The value of the magnetic anisotropy energy is found to be much larger than that …

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Magnetic Transitions And Phases In Random-Anisotropy Magnets, David J. Sellmyer, S. Nafis, Michael J. O'Shea Apr 1988

Magnetic Transitions And Phases In Random-Anisotropy Magnets, David J. Sellmyer, S. Nafis, Michael J. O'Shea

David Sellmyer Publications

The generality and universality of the Ising spin-glass-like phase transitions observed in several rare-earth, random-anisotropy magnets are discussed. Some uncertainties and practical problems in determining critical exponents are considered, and a comparison is made to insulating spin glasses and crystalline spin glasses where an apparent anisotropy-induced crossover from Heisenberg to Ising-like behavior is seen. The observation of a reentrant transition in a weak anisotropy system and its correlation with the theory of Chudnovsky, Saslow, and Serota [Phys. Rev. B 33, 251 (1986)] for the correlated spin glass is discussed. Journal of Applied Physics is copyrighted by The American Institute of …

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Magnetic Properties, Anisotropy, And Microstructure Of Sputtered Rare-Earth Iron Multilayers, Z.S. Shan, S. Nafis, K.D. Aylesworth, David J. Sellmyer Apr 1988

Magnetic Properties, Anisotropy, And Microstructure Of Sputtered Rare-Earth Iron Multilayers, Z.S. Shan, S. Nafis, K.D. Aylesworth, David J. Sellmyer

David Sellmyer Publications

A study of compositionally modulated magnetic films of the form Fe/RE, particularly for RE=Nd and Dy, has been performed by vibrating sample magnetometry, ac susceptibility and x-ray diffraction. The relationship between the magnetic properties and the layer thickness was studied systematically for X-Å Fe/Y-Å Dy, as the layer thicknesses X and Y were varied from 1.8 to 20 Å. The ranges of layer thicknesses required for perpendicular anisotropy were determined. The interface and volume anisotropy energies were estimated for X-Å Fe/Y-Å Nd and the differences in the magnetic properties between X-Å Fe/7-Å Dy and X-Å Fe/7-Å …

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Magnetic Properties Of Rapidly Quenched And Annealed Fe10Rti And Related Alloys, Z.R. Zhao, Y.G. Ren, K.D. Aylesworth, David J. Sellmyer, E. Singleton, J. Strzeszewski, George C. Hadjipanayis Apr 1988

Magnetic Properties Of Rapidly Quenched And Annealed Fe10Rti And Related Alloys, Z.R. Zhao, Y.G. Ren, K.D. Aylesworth, David J. Sellmyer, E. Singleton, J. Strzeszewski, George C. Hadjipanayis

David Sellmyer Publications

Magnetic measurements are reported for iron-rich ternary alloys with the following compositions: Fe10NdxDy1-xTi (0≤x≤1), Fe10SmM (M=Ti, V, and Mo), and Fe10RV (R=Y, Gd, and Dy). The samples were prepared by splat cooling or melt spinning and selected samples were heat treated. The results of x-ray diffraction, electron microscopy, and thermomagnetic measurements on the Fe10NdxDy1-xTi series are presented and indicate that the rapidly quenched alloys are nearly single phase and become multiphase upon heating. Magnetic measurements on the other two series show that the substitution …

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Nonisothermal Relaxation In A Nonlocal Medium, Alexander Umantsev, A L. Roitburd Apr 1988

Nonisothermal Relaxation In A Nonlocal Medium, Alexander Umantsev, A L. Roitburd

Chemistry and Physics Faculty Working Papers

A study is made of the thermodynamics of a non-local medium whose evolution is governed not only by the temperature and pressure, but also by the field of a relaxation parameter. For solid-state materials which undergo a phase transition, such a relaxation parameter is the order parameter. Heat transport equations are derived together with a thermodynamic inequality which must be satisfied during relaxation. The motion of an interphase boundary during a first-order phase transition is investigated. It is shown that, if the width of the boundary exceeds a critical value, there are steady-state conditions under which the new phase formed …

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Ionization Of K-Shell Electrons By Highly Relativistic Protons, M. L. Rustgi, P.T. Leung, S. A. Long Apr 1988

Ionization Of K-Shell Electrons By Highly Relativistic Protons, M. L. Rustgi, P.T. Leung, S. A. Long

Physics Faculty Publications and Presentations

A comparative study of three decent theoretical formalisms by Anholt, Scofield, Becker, and coworkers (1978-85) for K-shell ionization by highly relativistic protons has been carried out. The importance of the spin-flip mechanism is emphasized. It is concluded that in the analysis of such inner-shell ionization processes, an accurate description of the projectile-target interaction is of much more significance than the accuracy of the wave functions of the atomic electrons.

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A Study Of An Integral Equations For Computing Radial Distribution Functions, Noraini Ismail Apr 1988

A Study Of An Integral Equations For Computing Radial Distribution Functions, Noraini Ismail

Masters Theses

A two parameter integral equation, equation T is studied to compute radial distribution functions for a classical fluid whose single component particles interact pairwise according to a square-well potential function. A computer program originally written for a DEC 10 was modified to run on a DEC VAX. At the same time, modifications were made to take advantage of the faster VAX and to reduce the time an operator must spend to get a solution to the integral equation. Solutions were obtained for several densities, temperatures, and parameter values. Temperatures ranged from a high temperature gas to near critical temperatures. Accurate …

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N-Level Quantum Systems With Gell-Mann Dynamic Symmetry, Foek T. Hioe Apr 1988

N-Level Quantum Systems With Gell-Mann Dynamic Symmetry, Foek T. Hioe

Physics Faculty/Staff Publications

A set of conditions is presented for an N-level quantum system to possess the Gell-Mann-type dynamic symmetry, which was introduced in an earlier paper. The characteristic set of constants of motion that the system has when it possesses the symmetry and also the equivalent two-level system, which the system can be reduced to, are also presented.

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Some Issues Of Thermodynamic Consistency In Binary Nucleation Theory, Gerald Wilemski Apr 1988

Some Issues Of Thermodynamic Consistency In Binary Nucleation Theory, Gerald Wilemski

Physics Faculty Research & Creative Works

The "generalized" Kelvin equations used to determine the critical nucleus composition in some binary nucleation theories are shown to be thermodynamically inconsistent. Also, the surface tension calculated by the method of Flageollet-Daniel, Gamier, and Mirabel [J. Chem. Phys. 78, 2600 (1983)] is shown to be thermodynamically consistent with respect to the dynamic surface tension, contrary to the recent assertion of Spiegel, Zahoransky, and Wittig.

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Self Consistent Model Of The Glow Discharge, Hao Chen Apr 1988

Self Consistent Model Of The Glow Discharge, Hao Chen

Electrical & Computer Engineering Theses & Dissertations

The strong spatial variation of the electric field intensity in the vicinity of the cathode of a gas discharge requires the use of microscopic methods to describe the nonequilibrium behavior of the electron dynamics in this region. A one-dimensional Monte Carlo code was developed. It allows one to obtain the distribution of the electron drift velocity and rate coefficients for a given electric field intensity in the cathode fall. The results of this calculation are used to find the density distribution of charged particles in this region and consequently, by means of Poisson's equation, a corrected electric field intensity. In …

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Hyperspherical Description Of Two-Electron Systems, Anthony F. Starace Mar 1988

Hyperspherical Description Of Two-Electron Systems, Anthony F. Starace

Anthony F. Starace Publications

While the use of hyperspherical coordinates to describe two-electron systems is quite old, it was Macek's introduction of a quasi-separable approximation in hyperspherical coordinates which made possible a host of theoretical studies elucidating the symmetries of doubly-excited states and the dynamics of processes involving two-electron atoms and ions. This work, up to about mid-1982, has been reviewed by Fano. However, much additional progress has been made since 1982, particularly on the symmetries of doubly excited electronic states, on the correspondences with molecular descriptions of two-electron systems, on the limitations of the quasi-separable approximation at small and at large distances, and …

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The Calculation Of Photoionization Cross Sections, Anthony F. Starace Mar 1988

The Calculation Of Photoionization Cross Sections, Anthony F. Starace

Anthony F. Starace Publications

Photoionization is a sensitive probe of many-body and spin-dependent interactions. One can test our understanding of these interactions and the role they play in atomic dynamics by comparing the results of theoretical calculations with corresponding experimental measurements. One finds from such comparisons that our understanding of the photoionization process in atoms is excellent in many cases, imperfect in many others, and inadequate in still others. One finds in general also that the kinds of many-body and spin-dependent interactions included in a calculation is, in many cases, a more important consideration than the particular calculational method employed. In this brief report …

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Spectral Momentum Density From Graphite From Spectroscopy: Comparison With First Principles Calculations, Chao Gao, A. L. Ritter, John R. Dennison, N. A. Holzwarth Mar 1988

Spectral Momentum Density From Graphite From Spectroscopy: Comparison With First Principles Calculations, Chao Gao, A. L. Ritter, John R. Dennison, N. A. Holzwarth

All Physics Faculty Publications

We have measured the spectral momentum density ρ(E,q) of graphite by (e,2e) spectroscopy for momentum parallel and perpendicular to the crystal c axis. In the independent-electron approximation, ρ(E,q)=ΣG‖Uk(G)‖2 δ(q-k-G)δ(E-E(k)) where the one-electron wave function is Ψk(r)=eik⋅rΣGUk(G)eiG⋅r) and G is a reciprocal-lattice vector. The measurements covered a range of momentum parallel to the c axis equal to 0≤‖q‖≤1.84 Å-1 and a range of momentum perpendicular to the c axis equal to 0≤‖q‖≤2.35 Å-1. The energy range spanned the valence band of graphite from …

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Limitation Of The Semirelativistic Approach In Sum Rules And Related Calculations In Atomic Physics, M. L. Rustgi, P.T. Leung, S. A. Long Mar 1988

Limitation Of The Semirelativistic Approach In Sum Rules And Related Calculations In Atomic Physics, M. L. Rustgi, P.T. Leung, S. A. Long

Physics Faculty Publications and Presentations

It is shown that the semirelativistic approach, when applied consistently to atomic calculations involving the Thomas-Reiche-Kuhn sum rule or its applications, may lead to very inaccurate results.

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Static Magnetic Susceptibility Of Zn1-XMnXSe, J. K. Furdyna, N. Samarth, Richard B. Frankel, J. Spalek Mar 1988

Static Magnetic Susceptibility Of Zn1-XMnXSe, J. K. Furdyna, N. Samarth, Richard B. Frankel, J. Spalek

Physics

We present results of an investigation of the static magnetic susceptibility of Zn1-xMnxSe for x=0.05, 0.15, 0.30, and 0.45. From the Curie-Weiss behavior of the susceptibility at high temperatures, we determine the effective Mn-Mn exchange constant J1 to be -13.5±0.95 K. By using the results of our study in conjunction with direct measurements of the nearest-neighbor exchange integral JNN from inelastic neutron scattering by nearest-neighbor pairs, we obtain an estimate of the next-nearest-neighbor exchange constant J2=-2.4 K.

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