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X-ray resonant scattering studies of charge and orbital ordering in Pr{sub 1{minus}z}, Ca{sub x}, MnO{sub 3}

Description: We present the results of x-ray scattering studies of the charge and orbital ordering in the manganite series Pr{sub 1{minus}z}, Ca{sub x}, MnO{sub 3} with x = 0.25, 0.4 and 0.5. The polarization and azimuthal dependence of the charge and orbital ordering in these compounds is characterized both in the resonant and nonresonant limits, and compared with the predictions of current theories. The results are qualitatively consistent with both cluster and LDA+U calculations of the electronic structure.
Date: August 14, 2000
Partner: UNT Libraries Government Documents Department

Exchange-Coupling in Magnetic Nanoparticles to Enhance Magnetostrictive Properties

Description: Spark erosion is a versatile and economical method for producing particles of virtually any type of material that has a nominal conductivity: particles can be prepared in sizes ranging from a few nm to tens of {micro}m. The purpose of this feasibility study was to demonstrate the capability of making spherical particles of specific magnetic materials. We chose (Tb Dy)Fe{sub 2} (Terfenol-D) due to its potential use as the magnetostrictive component in magneto-elastomer composites. We also chose to work with pure Ni as a model system. Improvements in the properties of magneto-elastomer composites have broad applications in the areas of sensor development, enhanced actuators and damping systems.
Date: January 31, 2002
Creator: Radousky, H; McElfresh, M; Berkowitz, A & Carman, G P
Partner: UNT Libraries Government Documents Department

Comparison of equations for the EDTD solution in anisotropic and dispersive media

Description: The recursive-convolution solution for anisotropic and dispersive media was seen to yield accurate results for reflection from ferrite slabs up to a frequency limit set by the sampling interval. Depending on the application, the results shown might be considered usable up to about 300 GHz, which corresponds to about 13 cells per wavelength. Results at still higher frequencies might be usable when a time delay or frequency shift due to dispersion can be tolerated. Several different forms of the update equations were considered which can result from different approximations in reducing the continuous equations to discrete form.
Date: January 1, 1997
Creator: Burke, G.J. & Steich, D.J.
Partner: UNT Libraries Government Documents Department

Evaluation of Industrial Magnetic Heat Pump/Refrigerator Concepts that Utilize Superconducting Magnets

Description: This report provides a preliminary assessment of some magnetic heat pump (MHP)/refrigeration concepts for cryogen liquefaction and other industrial applications. The study was performed by Astronautics Corporation of America for Argonne National Laboratory under the sponsorship of the U.S. Department of Energy.
Date: June 1989
Creator: Waynert, J. A.; DeGregoria, A. J.; Foster, R. W. & Barclay, J. A.
Partner: UNT Libraries Government Documents Department

Magnetic Separation of Ores

Description: Report issued by the Bureau of Mines over studies conducted on the removal of magnetic materials from iron ores. As stated in the introduction, "this report discusses briefly operations and trends in magnetic separation, explains magnetic separation, describes and classifies the machines used, and outlines their development" (p. 1). This report includes tables, and illustrations.
Date: 1941
Creator: Dean, Reginald S. & Davis, Charles Wesley
Partner: UNT Libraries Government Documents Department

UA/ORNL Collaboration: Neutron Scattering Studies of Antiferromagnetic Films, Final Report

Description: The work reported here was a collaborative project between the research groups of Dr. J.L. Robertson at Oak Ridge National Laboratory and Dr. G.J. Mankey at the University of Alabama. The main thrust is developing neutron optical devices and materials for the study of magnetic thin films and interfaces. The project is particularly timely, since facility upgrades are currently underway at the High Flux Isotope Reactor. A new neutron optical device, a multicrystal analyzer, was designed and built to take maximum advantage of the increased flux that the upgraded beamlines at HFIR will provide. This will make possible detailed studies of the magnetic structure of thin films, multilayers, and interfaces that are not feasible at present. We performed studies of the antiferromagnetic order in thin films and crystals using neutron scattering, determined magnetic structures at interfaces with neutron reflectometry and measured order in magnetic dispersions using small angle neutron scattering. The collaboration has proved fruitful: generating eleven publications, contributing to the training of a postdoc who is now on staff at the High Flux Isotope Reactor and providing the primary support for two recent Ph.D. recipients. The collaboration is still vibrant, with anticipated implementation of the multicrystal analyzer on one of the new cold source beamlines at the High Flux Isotope Reactor.
Date: July 26, 2006
Creator: Mankey, Gary J.
Partner: UNT Libraries Government Documents Department

Recovery Act: Integrated DC-DC Conversion for Energy-Efficient Multicore Processors

Description: In this project, we have developed the use of thin-film magnetic materials to improve in energy efficiency of digital computing applications by enabling integrated dc-dc power conversion and management with on-chip power inductors. Integrated voltage regulators also enables fine-grained power management, by providing dynamic scaling of the supply voltage in concert with the clock frequency of synchronous logic to throttle power consumption at periods of low computational demand. The voltage converter generates lower output voltages during periods of low computational performance requirements and higher output voltages during periods of high computational performance requirements. Implementation of integrated power conversion requires high-capacity energy storage devices, which are generally not available in traditional semiconductor processes. We achieve this with integration of thin-film magnetic materials into a conventional complementary metal-oxide-semiconductor (CMOS) process for high-quality on-chip power inductors. This project includes a body of work conducted to develop integrated switch-mode voltage regulators with thin-film magnetic power inductors. Soft-magnetic materials and inductor topologies are selected and optimized, with intent to maximize efficiency and current density of the integrated regulators. A custom integrated circuit (IC) is designed and fabricated in 45-nm CMOS silicon-on-insulator (SOI) to provide the control system and power-train necessary to drive the power inductors, in addition to providing a digital load for the converter. A silicon interposer is designed and fabricated in collaboration with IBM Research to integrate custom power inductors by chip stacking with the 45-nm CMOS integrated circuit, enabling power conversion with current density greater than 10A/mm2. The concepts and designs developed from this work enable significant improvements in performance-per-watt of future microprocessors in servers, desktops, and mobile devices. These new approaches to scaled voltage regulation for computing devices also promise significant impact on electricity consumption in the United States and abroad by improving the efficiency of all computational platforms. In 2006, ...
Date: March 31, 2013
Creator: Shepard, Kenneth L
Partner: UNT Libraries Government Documents Department

Orbital Moment Determination in (MnxFe1-x)3O4 Nanoparticles

Description: Nanoparticles of (Mn{sub x}Fe{sub 1-x}){sub 3}O{sub 4} with a concentration ranging from x = 0 to 1 and a crystallite size of 14-15 nm were measured using X-ray absorption spectroscopy and X-ray magnetic circular dichroism to determine the ratio of the orbital moment to the spin moment for Mn and Fe. At low Mn concentrations, the Mn substitutes into the host Fe{sub 3}O{sub 4} spinel structure as Mn{sup 2+} in the tetrahedral A-site. The net Fe moment, as identified by the X-ray dichroism intensity, is found to increase at the lowest Mn concentrations then rapidly decrease until no dichroism is observed at 20% Mn. The average Fe orbit/spin moment ratio is determined to initially be negative and small for pure Fe{sub 3}O{sub 4} nanoparticles and quickly go to 0 by 5%-10% Mn addition. The average Mn moment is anti-aligned to the Fe moment with an orbit/spin moment ratio of 0.12 which gradually decreases with Mn concentration.
Date: October 22, 2010
Creator: Pool, V. L.; Jolley, C.; Douglas, T.; Arenholz, E. & Idzerda, Y. U.
Partner: UNT Libraries Government Documents Department


Description: The techniques of design and fabrication of red magnets for the Bulk Shielding Reactor II are presented. An experimental model, designed to eliminate the can and its associated air gap, is described. Data on magnet performance are included. (C.J.G.)
Date: July 1, 1960
Creator: Tallackson, J R & Santoro, R T
Partner: UNT Libraries Government Documents Department

Imaging at high spatial resolution: Soft x-ray microscopy to 15nm

Description: Soft x-ray microscopy has now achieved 15 nm spatial resolution with new zone plates and bending magnet radiation. Combined with elemental sensitivity and flexible sample environment (applied magnetic or electric fields, wet samples, windows, overcoatings) this emerges as a valuable tool for nanoscience and nanotechnology, complimenting common electron and scanning tip microscopies. In this presentation we describe recent advances in spatial resolution, expectations for the near future, and applications to magnetic materials, bio-tomography, etc.
Date: April 5, 2006
Creator: Attwood, D.; Chao, W.; Anderson, E.; Liddle, J.A.; Harteneck, B.; Fischer, P. et al.
Partner: UNT Libraries Government Documents Department

Fundamental Scientific Problems in Magnetic Recording

Description: Magnetic data storage technology is presently leading the high tech industry in advancing device integration--doubling the storage density every 12 months. To continue these advancements and to achieve terra bit per inch squared recording densities, new approaches to store and access data will be needed in about 3-5 years. In this project, collaboration between Oak Ridge National Laboratory (ORNL), Center for Materials for Information Technology (MINT) at University of Alabama (UA), Imago Scientific Instruments, and Seagate Technologies, was undertaken to address the fundamental scientific problems confronted by the industry in meeting the upcoming challenges. The areas that were the focus of this study were to: (1) develop atom probe tomography for atomic scale imaging of magnetic heterostructures used in magnetic data storage technology; (2) develop a first principles based tools for the study of exchange bias aimed at finding new anti-ferromagnetic materials to reduce the thickness of the pinning layer in the read head; (3) develop high moment magnetic materials and tools to study magnetic switching in nanostructures aimed at developing improved writers of high anisotropy magnetic storage media.
Date: June 27, 2007
Creator: Schulthess, T.C. & Miller, M.K.
Partner: UNT Libraries Government Documents Department

The Spin- and Angel-Resolved Photelectron Spectrometer

Description: A spin- and angle-resolved x-ray photoelectron spectrometer for the study of magnetic materials will be discussed. It consists of a turntable with electron lenses connected to a large hemispherical analyzer. A mini-Mott spin detector is fitted to the output of the hemispherical analyzer. This system, when coupled to a synchrotron radiation source will allow determination of a complete set of quantum numbers of a photoelectron. This instrument will be used to study ferromagnetic, antiferromagnetic and nonmagnetic materials. Some prototypical materials systems to be studied with this instrument system will be proposed.
Date: May 8, 2007
Creator: Mankey, G J; Morton, S A; Tobin, J G; Yu, S W & Waddill, G D
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

Spontaneous Generation of Voltage in Single-Crystal Gd5Si2Ge2 During Magnetostructural Phase Transformations

Description: The spontaneous generation of voltage (SGV) in single-crystal and polycrystalline Gd{sub 5}Si{sub 2}Ge{sub 2} during the coupled magnetostructural transformation has been examined. Our experiments show reversible, measurable, and repeatable SGV responses of the materials to the temperature and magnetic field. The parameters of the response and the magnitude of the signal are anisotropic and rate dependent. The magnitude of the SGV signal and the critical temperatures and critical magnetic fields at which the SGV occurs vary with the rate of temperature and magnetic-field changes.
Date: April 19, 2006
Creator: Zou, M.; Tang, H.; Schlagel, D.L.; Lograsso, T.A.; K.A. Gschneidner,jr. & Pecharsky, V.K.
Partner: UNT Libraries Government Documents Department

Magnetic flocculation and filtration

Description: A model is available in predicting flocculation frequencies between particles of various properties under the influence of a magnetic field. This model provides a basic understanding of fundamental phenomena, such as particle-particle and particle-collector interactions, occurring in HGMF (high gradient magnetic field), and will be extended to describe experimental data of particle flocculation and filtration and predict the performance of high- gradient magnetic filters. It is also expected that this model will eventually lead to a tool for design and optimization of magnetic filters for environmental, metallurgical, biochemical, and other applications.
Date: October 1, 1996
Creator: Yiacoumi, Sotira; Chin, Ching-Ju; Yin, Tung-Yu; Tsouris, C., DePaoli, D.W.; Chattin, M.R. & Spurrier, M.
Partner: UNT Libraries Government Documents Department

Magnetic anisotropy, coupling and transport in epitaxial Co/Cr superlattices on MgO (100) and (110) substrates

Description: Superlattices of Co/Cr have been epitaxially sputtered onto MgO (100) and (110) substrates coated with Cr(100) and (211) buffer layers. The Co thickness is fixed at 20{angstrom} and the Cr thickness varied from 7 to 22{Angstrom}. On the MgO(110)/Cr(211) substrates, coherent hcp-Co(1{bar 1}00)/bcc-Cr(211) superlattice structures are formed. On MgO(100)/Cr(100), XRD suggest strained hcp-Co(11{bar 2})/bcc-Cr(100) superlattices. Magnetization measurements show fourfold magnetic in- plane anisotropy for the MgO(100) orientation and twofold for the MgO(110). By utilizing a simple model based on perpendicular uniaxial anisotropies, we have concluded that the fourfold anisotropy has its origin in the second-order uniaxial Co anisotropy energy. The antiferromagnetic interlayer coupling strength exhibits a maximum value of 0.15 erg/cm{sup 2} at a Cr thickness of 13{angstrom} in the MgO(110) orientation. The MgO(100) orientation exhibits its strongest coupling of 0.55 erg/cm{sup 3} at 10{angstrom} Cr thickness. Modest GMR values no larger than 3% are observed and we find no evidence of enhanced AMR effects recently reported for Co(1{bar 1}00)/Cr(211) superlattices.
Date: November 1996
Creator: Picconatto, J. J.; Pechan, M. J. & Fullerton, E. E.
Partner: UNT Libraries Government Documents Department

CMR of Co/Cu multilayers with reduced hysteresis and low-field response

Description: We present the results of a systematic study on optimization of the giant magnetoresistance (GMR) response in Co/Cu multilayers (MLs) for copper layer thickness near the second oscillatory peak. Co/Cu MLs with alternating thick (t(1)Co) and thin (t(2)Co) layers have been prepared in the from of [Cot(1)CoA/Cu20A/Cot(2)CoA/Cu20A]15. We have found that the magnetoresistive hysteresis of these MLs is reduced with decreasing t(2)Co and has disappeared when t(2)Co<4.5A. We have obtained an optimal GMR response with a field sensitivity of 0. 013%/Oe over a field region of -60 Oe centered at -50 Oe. This architecture may enable the use of Cu/Co MLs in low-field magnetic sensor applications.
Date: February 1, 1997
Creator: Mao, M.; Gibbons, M.; Law, B.; Grabner, F.; Veron, S. & Cerjan, C.
Partner: UNT Libraries Government Documents Department

High-resolution magnetic imaging and investigations of thin-film magnetism with spin-polarized electron, ion and atom probes. Progress report, November 1, 1994--October 31, 1995

Description: This is a progress report for the period 1 November, 1994 to 31 October, 1995. Research during this grant year includes: (1) Completion of the Spin-Polarized Electron Energy Loss Spectroscopy (SPEELS) research program. (2) Design of an improved and much more intense metastable atom source that can also be converted to a Rydberg atom beam, for continuing studies utilizing Spin-Polarized Metastable (Atom) Deexcitation Spectroscopy (SPMDS), and to initiate new investigations of interactions of Rydberg atoms with surfaces. (3) Development of a spin-polarized He{sup +} ion source for studies of ion-surface interaction dynamics and epitaxially grown magnetic films utilizing Spin-Polarized Ion Neutralization Spectroscopy (SPINS).
Date: April 1, 1995
Creator: Walters, G.K. & Dunning, F.B.
Partner: UNT Libraries Government Documents Department

Spin spring behavior in exchange coupled soft and high-coercivity hard ferromagnets.

Description: The magnetization reversal processes in an epitaxial Fe/Sm{sub 2}Co{sub 7} structure were investigated using the magneto-optical indicator film technique. The dependence of the magnitude and the orientation of the structure average magnetization have been studied on both cycling and rotating the external magnetic field. It was discovered that the magnetization reversal of the soft ferromagnet can proceed by formation of not only one-dimensional, but also two-dimensional, exchange spin springs. Experimental data is compared with a theoretical estimation of the rotational hysteresis loop for a spin system containing a one-dimensional exchange spring.
Date: November 1, 2000
Creator: Shull, R. D.; Shapiro, A. J.; Gornakov, V. S.; Nikitenko, V. I.; Jiang, J. S.; Kaper, H. et al.
Partner: UNT Libraries Government Documents Department