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Final Report Fermionic Symmetries and Self consistent Shell Model

Description: In this final report in the field of theoretical nuclear physics we note important accomplishments.We were confronted with "anomoulous" magnetic moments by the experimetalists and were able to expain them. We found unexpected partial dynamical symmetries--completely unknown before, and were able to a large extent to expain them.The importance of a self consistent shell model was emphasized.
Date: November 7, 2008
Creator: Zamick, Larry
Partner: UNT Libraries Government Documents Department

Immiscibility in the Fe3O4-FeCr2O4 Spinel Binary

Description: A recent thermodynamic model of mixing in spinel binaries, based on changes in cation disordering (x) between tetrahedral and octahedral sites, is investigated for applicability to the Fe{sub 3}O{sub 4}-FeCr{sub 2}O{sub 4} system under conditions where incomplete mixing occurs. Poor agreement with measured consolute solution temperature and solvus is attributed to neglect of: (1) ordering of magnetic moments of cations in the tetrahedral sublattice antiparallel to the moments of those in the octahedral sublattice and (2) pair-wise electron hopping between octahedral site Fe{sup 3+} and Fe{sup 2+} ions. Disordering free energies ({Delta}G{sub D}), from which free energies of mixing are calculated, are modeled by {Delta}G{sub D} = {alpha}{chi} + {beta}{chi}{sup 2} - T(S{sub c} + {chi}{sigma}{sub el} + {gamma}{chi}{sigma}{sup mag}) where the previously-neglected effects are accommodated by: (1) adding a non-configurational entropy term to provide coupling between cation disordering and magnetic ordering and (2) revising the configurational entropy (S{sub c}) analysis. Applying the constraint {alpha} = -(2/3){beta} and regressing the existing database for Fe{sup 2+} ion disorder in Fe{sub 3}O{sub 4} gives: {beta} = -31,020 {+-} 1050 J mol{sup -1}, {sigma}{sub el}/R = -0.730 {+-} 0.081 and {gamma}, the coupling parameter between cation disordering and magnetic ordering, = -0.664 {+-} 0.075. The revised mixing model predicts a consolute solution temperature (T{sub cs}) = 600 C and a solvus at 500 C of n = 0.05 and 0.70 for the Fe(Fe{sub 1-n}Cr{sub n}){sub 2}O{sub 4} spinel binary.
Date: March 20, 2003
Creator: Ziemniak, S.E. & Castelli, R.A.
Partner: UNT Libraries Government Documents Department

The nuclear spins, hyperfine structure separations, and magnetic moments of Cs¹²⁷, Cs¹²⁹, Cs¹³⁰, and Cs¹³²

Description: From abstract: "The nuclear spins, hyperfine structure separations, and magnetic moments of four cesium isotopes have been measured, using an atomic beam magnetic resonance apparatus designed to utilize the low background flop-in method."
Date: 1957
Creator: Shugart, Howard Alan, 1931-2016
Partner: UNT Libraries Government Documents Department

Density-functional calculations of a, b, g, d, dp, and e plutonium

Description: Total energies for the six known polymorphs of plutonium metal have been calculated within spin and orbital polarized density-functional theory as a function of lattice constant. Theoretical equilibrium volumes and bulk moduli correspond well with experimental data and the calculated total energies are consistent with the known phase diagram of Pu. It is shown that a preference for formation of magnetic moments, increasing through the {alpha} {yields} {beta} {yields} {gamma} phases, explain their position in the ambient pressure phase diagram and their anomalous variation of atomic density. A simple model is presented that establishes a relationship between atomic density, crystal symmetry, and magnetic moments which is universally valid for all Pu phases.
Date: October 22, 2003
Creator: Soderlind, P & Sadigh, B
Partner: UNT Libraries Government Documents Department

Reconstruction of FXR Beam Conditions

Description: Beam-envelope radius, envelope angle, and beam emittance can be derived from measurements of beam radius for at least three different transport conditions. We have used this technique to reconstruct exit parameters from the FXR injector and accelerator. We use a diamagnetic loop (DML) to measure the magnetic moment of the high current beam. With no assumptions about radial profile, we can derive the beam mean squire radius from the moment under certain easily met conditions. Since it is this parameter which is required for the reconstruction, it is evident that the DML is the ideal diagnostic for this technique. The simplest application of this technique requires at least three shots for a reconstruction but in reality requires averaging over many more shots because of shot to shot variation. Since DML measurements do not interfere with the beam, single shot time resolved measurements of the beam parameters appear feasible if one uses an array of at least three DMLs separated by known transport conditions.
Date: May 31, 2001
Creator: Nexen, W E; Scarpetti, R D & Zentler, J
Partner: UNT Libraries Government Documents Department

Effect of permanent-magnet irregularities in levitation force measurements.

Description: In the measurement of the levitation force between a vertically magnetized permanent magnet (PM) and a bulk high-temperature superconductor (HTS), PM domains with horizontal components of magnetization are shown to produce a nonnegligible contribution to the levitation force in most systems. Such domains are typically found in all PMs, even in those that exhibit zero net horizontal magnetic moment. Extension of this analysis leads to an HTS analog of Earnshaw's theorem, in which at the field-cooling position the vertical stiffness is equal to the sum of the horizontal stiffnesses, independent of angular distribution of magnetic moments within the PM.
Date: October 14, 1999
Creator: Hull, J. R.
Partner: UNT Libraries Government Documents Department

The Brookhaven muon g-2 experiment

Description: A new experiment is being mounted at BNL to measure the anomalous magnet moment of the muon to 3 parts in 10{sup 7}. In this talk I will describe the physics issues that this precision allows us to explore, the experimental method, and an interesting new device which we will use to inject muons into our muon storage ring. The device is a 1.45T non-ferrous superconducting magnet, where all fringe field is contained by a superconducting sheet.
Date: March 1, 1995
Creator: Bunce, G.
Partner: UNT Libraries Government Documents Department

Constraints on anomalous top quark couplings at the LHC

Description: Measurements of distributions associated with the pair production of top quarks at the LHC can be used to constrain (or observe) the anomalous chromomagnetic dipole moment(k) of the top. For example, using either the tt(bar) invariant mass or the Pt distribution of top we find that sensitivities to ; k; of order 0.05 are obtainable with 100 /fb of integrated luminosity. This is similar in magnitude to what can be obtained at a 500 GeV NLC with an integrated luminosity of 50 /fb through an examination of the e(+)e(-) right arrow tt(bar)g process.
Date: September 1, 1996
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Use of thin films in high-temperature superconducting bearings.

Description: In a PM/HTS bearing, locating a thin-film HTS above a bulk HTS was expected to maintain the large levitation force provided by the bulk with a lower rotational drag provided by the very high current density of the film. For low drag to be achieved, the thin film must shield the bulk from inhomogeneous magnetic fields. Measurement of rotational drag of a PM/HTS bearing that used a combination of bulk and film HTS showed that the thin film is not effective in reducing the rotational drag. Subsequent experiments, in which an AC coil was placed above the thin-film HTS and the magnetic field on the other side of the film was measured, showed that the thin film provides good shielding when the coil axis is perpendicular to the film surface but poor shielding when the coil axis is parallel to the surface. This is consistent with the lack of reduction in rotational drag being due to a horizontal magnetic moment of the permanent magnet. The poor shielding with the coil axis parallel to the film surface is attributed to the aspect ratio of the film and the three-dimensional nature of the current flow in the film for this coil orientation.
Date: September 30, 1999
Creator: Hull, J. R. & Cansiz, A.
Partner: UNT Libraries Government Documents Department

Hyperon static properties

Description: The static properties of the hyperons include masses, lifetimes, magnetic moments and CPT test from the asymmetries of these quantities for hyperon and anti-hyperon. The author reviews the present status of these measurements with an eye toward identifying places where new or improved measurements can have a significant physics impact. Most of these measurements are from the PDG where there have been only two new measurements quoted since 1995. He also reports two new measurements not yet published.
Date: March 24, 2000
Creator: Cooper, P.S.
Partner: UNT Libraries Government Documents Department

Fermion masses and anomalous dipole moments

Description: Fermion mass generation via quantum loops is briefly described. The potential for large anomalous dipole moments, {delta}a{sub f} {approx_equal} m{sub f}{sup 2}/M{sup 2}, in such schemes is demonstrated. Implications for the muon`s anomalous magnetic moment as well as the top quark`s chromo and electroweak moments are discussed.
Date: August 1, 1995
Creator: Marciano, W.J.
Partner: UNT Libraries Government Documents Department

Hyperons at Fermilab

Description: Magnetic moment measurement of the baryon octet and decouplet have recently been measurements illustrated the success as well as the limitations of the simpple qazrk model. Measurements of hyperon production polarizations have shown this to be a rich and complex process. It has forced us to reconsider our basic understanding of hyperon polarization processes.
Date: November 1, 1995
Creator: Lach, J.
Partner: UNT Libraries Government Documents Department

Phenomenological aspects of heterotic orbifold models at one loop

Description: We provide a detailed study of the phenomenology of orbifold compactifications of the heterotic string within the context of supergravity effective theories. Our investigation focuses on those models where the soft Lagrangian is dominated by loop contributions to the various soft supersymmetry breaking parameters. Such models typically predict non-universal soft masses and are thus significantly different from minimal supergravity and other universal models. We consider the pattern of masses that are governed by these soft terms and investigate the implications of certain indirect constraints on supersymmetric models, such as flavor-changing neutral currents, the anomalous magnetic moment of the muon and the density of thermal relic neutralinos. These string-motivated models show novel behavior that interpolates between the phenomenology of unified supergravity models and models dominated by the superconformal anomaly.
Date: August 5, 2003
Creator: Birkedal-Hansen, A.; Binetruy, P.; Mambrini, Y. & Nelson, B.
Partner: UNT Libraries Government Documents Department

Multi-teraflops spin dynamics studies of the magnetic structure of FeMn/Co interfaces

Description: The authors have used the power of massively parallel computers to perform first principles spin dynamics (SD) simulations of the magnetic structure of Iron-Manganese/Cobalt (FeMn/Co) interfaces. These large scale quantum mechanical simulations, involving 2016-atom super-cell models, reveal details of the orientational configuration of the magnetic moments at the interface that are unobtainable by any other means. Exchange bias, which involves the use of an antiferromagnetic (AFM) layer such as FeMn to pin the orientation of the magnetic moment of a proximate ferromagnetic (FM) layer such as Co, is of fundamental importance in magnetic multilayer storage and read head devices. Here the equation of motion of first principles SD is used to perform relaxations of model magnetic structures to the true ground (equilibrium) state. Our code is intrinsically parallel and has achieved a maximum execution rate of 2.46 Teraflops on the IBM SP at the National Energy Research Scientific Computing Center (NERSC).
Date: November 30, 2002
Creator: Canning, Andrew; Ujfalussy, B.; Schulthess, T.C.; Zhang, X.-G.; Shelton, W.A.; Nicholson, D.M.C. et al.
Partner: UNT Libraries Government Documents Department


Description: Insight into the anisotropy behavior of Nd{sub 2}Fe{sub 14}B may be obtained by measurements of the spin reorientation temperature T{sub S} where the overall magnetocrystalline anisotropy changes to allow the magnetic moment to relax from an easy axis to an easy cone configuration. DC magnetization measurements made at various applied fields on sintered and nanocrystalline forms of Nd{sub 2}Fe{sub 14}B indicate a T{sub S} that remains constant for the sintered sample but is strongly field-dependent for the nanocrystalline forms of the material. Specifically, T{sub S} decreases with decreasing applied fields of strengths 5 T, 1 T and 0.01 T. A simple model that minimizes the total energy of the system leads to the conclusion that the spin reorientation temperature is insensitive to applied field. Therefore it is concluded that the apparent decrease in the system's spin reorientation temperatures with decrease in measuring field can be attributed to the nanoscale structure of the system and a difference in the anisotropy constants compared to their bulk values.
Date: August 18, 2002
Creator: LEWIS,L.H. & HARLAND,C.L.
Partner: UNT Libraries Government Documents Department

Mechanisms of Stochastic Diffusion of Energetic Ions in Spherical Tori

Description: Stochastic diffusion of the energetic ions in spherical tori is considered. The following issues are addressed: (I) Goldston-White-Boozer diffusion in a rippled field; (ii) cyclotron-resonance-induced diffusion caused by the ripple; (iii) effects of non-conservation of the magnetic moment in an axisymmetric field. It is found that the stochastic diffusion in spherical tori with a weak magnetic field has a number of peculiarities in comparison with conventional tokamaks; in particular, it is characterized by an increased role of mechanisms associated with non-conservation of the particle magnetic moment. It is concluded that in current experiments on National Spherical Torus eXperiment (NSTX) the stochastic diffusion does not have a considerable influence on the confinement of energetic ions.
Date: January 18, 2001
Creator: Kolesnichenko, Ya.I.; White, R.B. & Yakovenko, Yu.V.
Partner: UNT Libraries Government Documents Department

Surface-Sensitive, Element-Specific Magnetometry with X-Ray Linear Dichroism

Description: Here it is shown that the magnetic linear dichroism in x-ray photoemission (XMLD) signal can be used to measure the element specific magnetic moments in ultra thin alloy films. Comparison with recent SQUID data provides a quantitative check that demonstrates that the total magnetization derived from summing the constituent elemental moments is correct.
Date: October 6, 1999
Creator: Schumann, F.O.; Willis, R.F. & Tobin, J.G.
Partner: UNT Libraries Government Documents Department

Experience with measuring magnetic moments of permanent magnet blocks at Lawrence Berkeley Laboratory

Description: Since May 1985, The Magnetic Measurements Engineering Group at LBL has measured and sorted a total of 3834 permanent magnet blocks. These magnetic blocks have been used in the construction of various successful beam-line elements including dipoles, quadrupoles, and wigglers. We report on observed variations in magnetic moments among blocks supplied by five manufacturers, describe the operational capabilities (accuracy, precision, and resolution) of the LBL Magnetic-moment Measurement and Sorting System (MMSS), cite the results of comparative calibrations by permanent-magnet manufacturers and other National Laboratories, and suggest criteria for automating the MMSS for measuring the large number of permanent-magnet blocks required for the insertion devices for the projected LBL 1-2 GeV Synchrotron Radiation Source. 14 refs., 2 figs., 2 tabs.
Date: September 1, 1987
Creator: Nelson, D.H.; Barale, P.J.; Green, M.I. & Van Dyke, D.A.
Partner: UNT Libraries Government Documents Department

Stochastic nature of domain nucleation process in magnetization reversal

Description: Whether domain configurations that occur during magnetization reversal processes on a nanoscale are deterministic or nondeterministic is both fundamentally of great interest and technologically of utmost relevance[1]. However, due to the limited spatial resolution of the microscopic measurement techniques employed so far, no direct observation on the stochastic behavior of local domain nucleation during magnetization reversal in real space at the nanometer scale has yet been reported. In this work, we have investigated a stochastic nature of domain nucleation process during magnetization reversal by utilizing magnetic soft X-ray transmission microscopy with high spatial resolution of 15 nm [2]. The sample used in our study is CoCrPt alloy film,which is the promising candidate for high-density perpendicular magnetic recording media. Typical domain configurations of (Co{sub 83}Cr{sub 17}){sub 87}Pt{sub 13} taken at an applied magnetic field of 383 Oe during three successive hysteretic cycles are illustrated in Fig. 1. Interestingly enough, one clearly notes that the domain nucleation process of CoCrPt alloy film is not deterministic, but stochastic for repeated hysteretic cycles. The stochastic nature was quantitatively confirmed by correlation coefficient, where the correlation coefficients increase as magnetization reversal was progressed. Nanomagnetic simulations considering thermal fluctuations of the magnetic moments of the grains explains the stochastic nature of the domain nucleation behavior observed in CoCrPt alloy film.
Date: June 1, 2007
Creator: Im, Mi-Young; Lee, S.-H.; Kim, D.-H.; Fischer, Peter & Shin, S.-C.
Partner: UNT Libraries Government Documents Department

Zinc surface complexes on birnessite: A density functional theory study

Description: Biogeochemical cycling of zinc is strongly influenced by sorption on birnessite minerals (layer-type MnO2), which are found in diverse terrestrial and aquatic environments. Zinc has been observed to form both tetrahedral (Zn{sup IV}) and octahedral (Zn{sup VI}) triple-corner-sharing surface complexes (TCS) at Mn(IV) vacancy sites in hexagonal birnessite. The octahedral complex is expected to be similar to that of Zn in the Mn oxide mineral, chalcophanite (ZnMn{sub 3}O{sub 7} {center_dot} 3H{sub 2}O), but the reason for the occurrence of the four-coordinate Zn surface species remains unclear. We address this issue computationally using spin-polarized Density Functional Theory (DFT) to examine the Zn{sub IV}-TCS and Zn{sup VI}-TCS species. Structural parameters obtained by DFT geometry optimization were in excellent agreement with available experimental data on Zn-birnessites. Total energy, magnetic moments, and electron-overlap populations obtained by DFT for isolated Zn{sup IV}-TCS revealed that this species is stable in birnessite without a need for Mn(III) substitution in the octahedral sheet and that it is more effective in reducing undersaturation of surface O at a Mn vacancy than is Zn{sub VI}-TCS. Comparison between geometry-optimized ZnMn{sub 3}O{sub 7} {center_dot} 3H{sub 2}O (chalcophanite) and the hypothetical monohydrate mineral, ZnMn{sub 3}O{sub 7} {center_dot} H{sub 2}O, which contains only tetrahedral Zn, showed that the hydration state of Zn significantly affects birnessite structural stability. Finally, our study also revealed that, relative to their positions in an ideal vacancy-free MnO{sub 2}, Mn nearest to Zn in a TCS surface complex move toward the vacancy by 0.08-0.11 {angstrom}, while surface O bordering the vacancy move away from it by 0.16-0.21 {angstrom}, in agreement with recent X-ray absorption spectroscopic analyses.
Date: January 5, 2009
Creator: Kwon, Kideok D.; Refson, Keith & Sposito, Garrison
Partner: UNT Libraries Government Documents Department

Fundamental Curie temperature limit in ferromagnetic Ga1-xMnxAs

Description: We provide unambiguous experimental evidence that the upper limit of {approx}110 K commonly observed for the Curie temperature TC of Ga{sub 1-x}Mn{sub x}As is caused by the Fermi-level-induced hole saturation. This conclusion is based on parallel studies of the location of Mn in the lattice, the effectiveness of acceptor center, and ferromagnetism on a series of Ga{sub 1-x-y}Mn{sub x}Be{sub y}As layers, in which the concentration of magnetic moments and of free holes can be independently controlled by the Mn and Be contents. Ion channeling and magnetization measurements show a dramatic increase of the concentration of Mn interstitials accompanied by a reduction of T{sub C} with increasing Be concentration. At the same time the free hole concentration remains relatively constant at {approx}5 x 10{sup 20}cm{sup -3}. These results indicate that the concentrations of free holes as well as of ferromagnetically active Mn spins are governed by the position of the Fermi level, which controls the formation energy of compensating interstitial Mn donors. Based on these results, we propose to use heavy n-type counter-doping of Ga{sub 1-x}Mn{sub x}As (by, e.g., Te) to suppress the formation of Mn interstitials at high x, and thus improve the T{sub C} of the alloy system.
Date: September 24, 2002
Creator: Yu, K. M.; Walukiewicz, W.; Wojtowicz, T.; Lim, W. L.; Liu, X.; Bindley, U. et al.
Partner: UNT Libraries Government Documents Department

First-order Isostructural Mott transition in highly-compressed MnO

Description: We present evidence for an isostructural, first-order Mott transition in MnO at 105 {+-} 5 GPa, based on high-resolution x-ray emission spectroscopy and angle-resolved x-ray diffraction data. The pressure-induced structural/spectral changes provide a coherent picture of MnO phase transitions from paramagnetic B1 to antiferromagnetic distorted B1 at 30 GPa, to paramagnetic B8 at 90 GPa, and to diamagnetic B8 at 105 {+-} 5 GPa. The last is the Mott transition, accompanied by a complete loss of magnetic moment, an {approx}6.6% volume collapse and a visual appearance change to metallic luster consistent with recent resistivity measurements.
Date: June 18, 2004
Creator: Yoo, C
Partner: UNT Libraries Government Documents Department