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The Uranium-Cobalt System

Description: Abstract: "A phase diagram for the uranium-cobalt system has been constructed, based on thermal, microscopic, X-ray and chemical data. The results indicate the existence of three compounds and two eutectics, one of which shows a lowering of the melting point of uranium by approximately 400 C."
Date: March 1, 1946
Creator: Noyce, William Knight & Daane, A. H.
Partner: UNT Libraries Government Documents Department

Effect of heat treatment upon the microstructure and hardness of a wrought cobalt-base alloy stellite 21 (AMS 5385)

Description: Report presenting an investigation of the response of wrought Stellite 21, a typical cobalt-base alloy, to heat treatment. The alloy was solution-treated and transformed by aging and isothermal transformation at temperatures of 1200 to 1950 degrees Fahrenheit for periods of 5 minutes to 72 hours. Results regarding the solution-treated structure, precipitation by isothermal transformation, precipitation by aging, grain boundary behavior, and hardness are provided.
Date: March 1954
Creator: Clauss, F. J. & Weeton, J. W.
Partner: UNT Libraries Government Documents Department

Synthesis of Samarium Cobalt Nanoblades

Description: As new portable particle acceleration technologies become feasible the need for small high performance permanent magnets becomes critical. With particle accelerating cavities of a few microns, the photonic crystal fiber (PCF) candidate demands magnets of comparable size. To address this need, samarium cobalt (SmCo) nanoblades were attempted to be synthesized using the polyol process. Since it is preferable to have blades of 1-2 {micro}m in length, key parameters affecting size and morphology including method of stirring, reaction temperature, reaction time and addition of hydroxide were examined. Nanoparticles consisting of 70-200 nm spherical clusters with a 3-5 nm polyvinylpyrrolidone (PVP) coating were synthesized at 285 C and found to be ferromagnetic. Nanoblades of 25nm in length were observed at the surface of the nanoclusters and appeared to suggest agglomeration was occurring even with PVP employed. Morphology and size were characterized using a transmission electron microscope (TEM). Powder X-Ray Diffraction (XRD) analysis was conducted to determine composition but no supportive evidence for any particular SmCo phase has yet been observed.
Date: August 25, 2010
Creator: Steele, Darren M.
Partner: UNT Libraries Government Documents Department

Evaporation of Iron-, Nickel-, and Cobalt-Base Alloys at 760 to 980°C in High Vacuums

Description: Report issued by the Oak Ridge National Laboratory discussing the evaporation of alloys in high vacuums. As stated in the introduction, "the investigation encompasses measurements of the evaporation rates, identification of the evaporating elements, and correlation of these measurements to the alloy composition for specimens in both the polished and oxidized conditions" (p. 2). This report includes tables, illustrations, and photographs.
Date: November 1964
Creator: Bourgette, D. T.
Partner: UNT Libraries Government Documents Department

Reaction synthesis of intermetallics

Description: Exothermicity associated with the synthesis of aluminides was utilized to obtain nickel, iron, and cobalt aluminides. Combustion synthesis, extrusion, and hot pressing were utilized to obtain intermetallics and their composites. Extrusion conditions, reduction ratios, and hot-pressing conditions of the intermetallics and their composites are discussed.
Date: December 1994
Creator: Deevi, S. C. & Sikka, V. K.
Partner: UNT Libraries Government Documents Department

Crystal structure and phase stability in Fe{sub 1{minus}x}Co{sub x} from AB initio theory

Description: For alloys between Fe and Co, their magnetic properties determine their structure. From the occupation of d states, a phase diagram is expected which depend largely on the spin polarization. A method more elaborate than canonical band models is used to calculate the spin moment and crystal structure energies. This method was the multisublattice generalization of the coherent potential approximation in conjunction with the Linear-Muffin-Tin-Orbital method in the atomic sphere approximation. To treat itinerant magnetism, the Vosko-Wilk-Nusair parameterization was used for the local spin density approximation. The fcc, bcc, and hcp phases were studied as completely random alloys, while the {alpha}{prime} phase for off-stoichiometries were considered as partially ordered. Results are compared with experiment and canonical band model.
Date: June 1, 1996
Creator: Soederlind, P.; Abrikosov, I.A.; James, P.; Johansson, B. & Eriksson, O.
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

Comparative Coarsening Kinetics of Gamma Prime Precipitates in Nickel and Cobalt Base Superalloys

Description: The increasing technological need to push service conditions of structural materials to higher temperatures has motivated the development of several alloy systems. Among them, superalloys are an excellent candidate for high temperature applications because of their ability to form coherent ordered precipitates, which enable the retention of high strength close to their melting temperature. The accelerated kinetics of solute diffusion, with or without an added component of mechanical stress, leads to coarsening of the precipitates, and results in microstructural degradation, limiting the durability of the materials. Hence, the coarsening of precipitates has been a classical research problem for these alloys in service. The prolonged hunt for an alternative of nickel base superalloys with superior traits has gained hope after the recent discovery of Co-Al-W based alloys, which readily form high temperature g precipitates, similar to Ni base superalloys. In the present study, coarsening behavior of g precipitates in Co-10Al-10W (at. %) has been carried out at 800°C and 900°C. This study has, for the first time, obtained critical coarsening parameters in cobalt-base alloys. Apart from this, it has incorporated atomic scale compositional information across the g/g interfaces into classical Cahn-Hilliard model for a better model of coarsening kinetics. The coarsening study of g precipitates in Ni-14Al-7 Cr (at. %) has shown the importance of temporal evolution of the compositional width of the g/g interfaces to the coarsening kinetics of g precipitates. This study has introduced a novel, reproducible characterization method of crystallographic study of ordered phase by coupling of orientation microscopy with atom probe tomography (APT). Along with the detailed analysis of field evaporation behaviors of Ni and Co superalloys in APT, the present study determines the site occupancy of various solutes within ordered g precipitates in both Ni and Co superalloys. This study has explained the role of structural ...
Date: August 2014
Creator: Meher, Subhashish
Partner: UNT Libraries

Enhanced spin-valve giant magneto-resistance in non-exchange biased sandwich films

Description: A large giant magnetoresistance (GMR) value of 7.5% has been measured in simple NiFeCo(1)/Cu/NiFeCo(2) sandwich films grown on a 30 {angstrom} Cr seed layer. This spin-valve GMR effect is consistent with the differential switching of the two NiFeCo layers due to an enhanced coercivity of the NiFeCo(1) layer grown on the Cr seed layer. A change in growth texture of the NiFeCo(1) layer from fcc (111) to bcc (110) crystallographic orientation leads to an increase in magnetic anisotropy and an enhancement in coercivity. The GMR value increases to 8.7% when a thin CoFe interfacial enhancing layer is incorporated. Further enhancement in GMR values up to 14% is seen in the sandwich films by nano-oxide layer formation. The specular reflection at oxide/magnetic layer interface further extends the mean free path of spin-polarized electrons.
Date: February 17, 2000
Creator: Mao, M; Cerjan, C; Law, B; Grabner, F; Miloslavsky, L & Chien, C
Partner: UNT Libraries Government Documents Department

Magnetic dichroism effect of binary alloys using circularly-polarized x-ray

Description: We have studies the magnetic propertied of CoNi binary alloy films with various atomic compositions using soft x-ray magnetic circular dichroism (XMCD) technique. The alloy films were deposited on single Cu(100) crystals in situ using our well-established epitaxial growth technique to achieve a layer-by-layer growth and a metastable fcc structure, with all films exhibiting an in-plane magnetic anistrophy. Utilizing the element-specific ability and nanostructure magnetization sensitivity of this technique, we have been able to perform the absorption measurements at L2 and L3 edge of Co and Ni atoms and observed large dichroism signals. The extraction of spin moment and orbital moment for varying elemental stoichiometry using magneto- optical sum rules is discussed.
Date: May 1, 1997
Creator: Wu, S. Z.; Schumann, F.O.; Willis, R.F.; Goodman, K.W.; Tobin, J.G. & Carr, R.
Partner: UNT Libraries Government Documents Department


Description: Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase hard/soft composite magnets. CoPt films, with a thickness of 25 nm, were sputter-deposited from a nearly equiatomic alloy target onto oxidized Si wafers. The films were subsequently annealed at 700 C and fully transformed from the FCC phase to the magnetically hard, ordered L1{sub 0} phase. The coercivity of the films increased rapidly with annealing time until it reached a plateau at approximately 9.5 kOe. Fully-ordered CoPt films were then used as substrates for deposition of Co layers, with thicknesses in the range of 2.8--225 nm, in order to produce the hard/soft composite bilayers. As predicted by theory, the magnetic coherency between the soft Co phase and the hard, ordered CoPt phase decreased as the thickness of the soft phase increased. This decrease in coupling was clearly seen in the magnetic hysteresis loops of the bilayers. At small thicknesses of Co (a few nanometers), the shape of the loop was one of a uniform material showing no indication of the presence of two phases with extremely different coercivities. At larger Co thicknesses, constricted loops, i.e., ones showing the presence of a mixture of two ferromagnetic phases of different hardnesses, were obtained. The magnetic exchange present in the bilayer samples was qualitatively analyzed using magnetic recoil curves and the dependence of exchange coupling on the soft phase dimension in the bilayer hard/soft composite magnet films is discussed.
Date: April 5, 1999
Partner: UNT Libraries Government Documents Department

High-field magnetization studies of U{sub 2}T{sub 2}Sn (T=Co, Ir, Pt) compounds

Description: High-field magnetization measurements at 4.2 K on U{sub 2}T{sub 2}Sn (T = Co, Ir and Pt) compounds have been performed on free and fixed powders up to 57 T. An antiferromagnetic ground state of U{sub 2}Pt{sub 2}Sn is corroborated by a metamagnetic transition at 22 T with very small hysteresis going up and down with field. U{sub 2}Co{sub 2}Sn and U{sub 2}Ir{sub 2}Sn show no metamagnetic transition up to 57 T which is in agreement with the non-magnetic ground state of these compounds. In all cases, the maximum applied field is not sufficient to achieve saturation. The short-pulse measurements presented here are compared with previous results obtained in quasi-static fields up to 35 T.
Date: July 1, 1995
Creator: Prokes, K.; Nakotte, H. & de Boer, F.R.
Partner: UNT Libraries Government Documents Department

The effect of stoichiometry in C15 HfCo[sub 2]

Description: In binary Laves phases (AB{sub 2}) that exhibit a homogeneity range, the ability to accommodate nonstoichiometry is related to the atomic size requirements for the topologically close-packed structure. Based upon a hard sphere model, Laves phases with a metallic atom size ratio R{sub A}/R{sub B} close to the ideal value of {approx}1.225 exhibit homogeneity ranges. The C15 phase, HfCo{sub 2}, has a radius ratio of R{sub H}/R{sub Co} = 1.26 and a reported range of solubility of 9 at.%. The solubility limits and constitutional defects have been investigated, and with this information, the elastic and mechanical properties as a function composition were experimentally investigated. The results indicate that anti-site substitution is the governing defect mechanism on both sides of stoichiometry, The elastic and mechanical properties show a maximum at stoichiometry (unlike most intermetallics), with the brittle behavior decreasing with increasing Co content. The properties are described in terms of geometric models of space filling.
Date: January 1, 2001
Creator: Thoma, D. J. (Dan J.); Chen, K. C. (Katherine C.); Baskes, M. I. (Michael I.) & Peterson, E. J. (Eric J.)
Partner: UNT Libraries Government Documents Department

Improving exchange-spring magnets with interfacial modification.

Description: Using magnetic thin film multilayers as model exchange-spring systems proves to be the promising intellectual path that helps generate the mechanistic and materials insights needed to create high-performance permanent magnet materials. We demonstrate a new route to improve exchange-spring magnets whereby the hard/soft interface in epitaxial Sm-Co/Fe and Sm-Co/Co bilayer thin film structures is modified via thermal processing. The effect of thermal processing is modeled with a graded interfacial region across which the material parameters vary linearly. We discuss the mechanism for improved exchange-spring behavior and the implication on magnet processing toward realizing the full potential of the exchange-spring principle.
Date: May 16, 2002
Creator: Jiang, J. S.; Pearson, J. E.; Bader, S. D. & Liu, J. P.
Partner: UNT Libraries Government Documents Department

Magnetic order of Co{sub 0.1}Pt{sub 0.9} in proximity in CoPt{sub 3}

Description: A polarized neutron reflectometry study of the magnetization density depth profile of a Co{sub 0.1}Pt{sub 0.9}-CoPt{sub 3} bilayer film found evidence for an induced moment in the Co{sub 0.1}Pt{sup 0.9} overlayer in close proximity to the CoPt{sub 3} underlayer. If the moment of Co in these films is that of the bulk, then the {mu}{sub Pt} = 0.09(1){mu}{sub B} in the overlayer, and {mu}{sub Pt} = 0.04(1){mu}{sub B} in the underlayer. In addition, ferromagnetic order of the Co{sub 0.1}Pt{sub 0.9} overlayer was observed 8K above {Tc} for the material in the bulk.
Date: December 1, 1998
Creator: Shapiro, A.L.; Hellman, F. & Fitzsimmons, M.R.
Partner: UNT Libraries Government Documents Department

Correlation of magnetic dichroism in x-ray absorption and photoelectron emission using ultrathin magnetic alloy films

Description: We have begun a program to characterize magnetic alloy overlays using both magnetic x-ray circular dichroism (MXCD) and magnetic x-ray linear dichroism (MXLD). This will allow a direct comparison of MXCD-absorption and MXLD-photoelectron emission. First results from the Advanced Light Source will be presented.
Date: April 1, 1996
Creator: Tobin, J.G.; Goodman, K.W.; Mankey, G.J.; Willis, R.F.; Denlinger, J.D.; Rotenberg, E. et al.
Partner: UNT Libraries Government Documents Department

Theory of point-defects, non-stoichiometry, and solute additions in SmCo{sub 5+x}-Sm{sub 2}Co{sub 17{minus}y} and related compounds

Description: There is considerable interest in the possibility of producing Sm-Co-based nanocomposite magnets by rapid solidification and other far-from-equilibrium processing methods. Thermodynamic and kinetic models are quite valuable in understanding and optimizing such methods. This paper describes a method of estimation, utilizing tight-binding-based bond-order interatomic interaction potentials, of the thermodynamic properties of point defects such as vacancies, interstitials, antisite defects, and solute additions in the SmCo{sub 5+x} and Sm{sub 2}Co{sub 17{minus}y} phases and related rare-earth-transition metal compounds. Illustrative calculations for point defects in SmCo{sub 5} will be presented. The results suggest a unified model of the thermodynamic properties of the SmCo{sub 5+x}-Sm{sub 2}Co{sub 17{minus}y} region of the phase diagram, based on the 1-5 structure and the replacement of Sm by interacting dumb-bell interstitials to form the 2-17 structure; the model is similar in nature to theories of the thermodynamics of metal hydrides.
Date: August 1, 1998
Creator: Welch, D.O.
Partner: UNT Libraries Government Documents Department

Neutron scattering characterization of microstructure in uranium silicides, ceramic composites and Ni-based alloys

Description: Neutron scattering has proven to be a valuable tool for studying the microstructural properties of technologically important materials. The exceptionally high penetration power of neutrons enables the investigation of bulk materials, while unusual scattering contrasts observed in many materials provide unique access to important properties. Macroscopic performance of components under extreme conditions, which ultimately determines their viability for special applications, is often closely related to microstructural properties such as particle size, residual stress and phase stability. Neutron scattering experiments performed with samples exposed to realistic environmental conditions provide direct correlation between microscopic and macroscopic properties. Neutron irradiation of uranium silicide (a prospective reactor fuel), is used here as a prototypical example of in situ residual stress generation and evolution, accompanied by direct amorphization. Neutron diffraction studies at IPNS identified structural instabilities which contributed to material failure. Highly accurate measurements of residual strains in ceramic composites are used to validate computer models for stress variation with temperature and the effects of interfacial fiber coatings on residual stress. Coarsening and lattice mismatch of {gamma}{prime}-type Ni{sub 3}(Al,Si) particles in Ni-based alloys, which strongly influence coherency strains in these materials, are also measured directly using neutron scattering.
Date: October 1, 1997
Creator: Richardson, J.W. Jr.
Partner: UNT Libraries Government Documents Department

Magnetic stability of novel exchange coupled systems

Description: The magnetic stability of two different interracial exchange coupled systems are investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 10{sup 7} times. For Fe/Cr double-superlattice exchange biased systems, small but rapid initial decay of exchange bias field H{sub E} and the remanent magnetization is observed. Also the Sin-Co/Fe bilayers grown epitaxially with uniaxial in-plane anisotropy show similar decay. However, the H{sub E} of biaxial and random in-plane bilayers, shows gradual decay without large reduction of the magnetization. These different decay behaviors explained by their different microstructure and interracial spin configurations.
Date: November 8, 1999
Creator: Inomata, A.; Jiang, J. S.; You, C.-Y.; Pearson, J. E. & Bader, S. D.
Partner: UNT Libraries Government Documents Department