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Trend of superconductivity in amorphous superconducting transition metals and their alloys

Description: A plausible interpretation for the trend of superconducting transition temperature T/sub c/ in amorphous transition metal TM alloys is presented from a chemical point of view. It is shown that the T/sub c/ behavior is not a reflection of the dependence of the atomic parameter eta on the number of electrons per atom, but rather due to two other effects. One is the changes in the density of states due to the mixing of antibonding and bonding states in the bcc amorphous metals. The other is an increase in the number of valence d electrons participating in the phonon-induced d-d coupling towards the mid series. (auth)
Date: December 1, 1975
Creator: Poon, S.J.
Partner: UNT Libraries Government Documents Department

Superconductivity in tight-binding approximation

Description: An interpretation of Barisic's relation for transition elements between the d-electron contribution to the cohesive energy and the local atomic parameter eta is presented. This relation is extended to a lattice with more than one atom per unit cell in the tight- binding approximation of rigid ions. It is conjectured that Barisic's relation is correct to first order approximation for transition metal alloys, provided the phonon induced d-d coupling is the dominant mechanism for superconductivity. (auth)
Date: October 1, 1975
Creator: Poon, S.J.
Partner: UNT Libraries Government Documents Department

Influence of magnetic ordering on the superconducting properties of amorphous (Zr/sub 1-x/Er/sub x/)/sub 3/Rh alloys

Description: The effect of Er impurities on the superconducting properties of an amorphous Zr/sub 3/Rh alloy has been studied. The Er impurities are found to exhibit magnetic behavior characteristic of a free Er/sup 3 +/ ion in a weak crystal field. Magnetic ordering of the Er moments is observed to occur at a temperature T/sub M/ which is proportional to the Er concentration. This ordering strongly influences superconductivity as evidenced by anomalous behavior in the concentration dependence of T/sub c/. For concentrations near the critical Abrikosov-Gor'kov value superconductivity appears to be induced by magnetic ordering. The superconducting critical field H/sub c2/(T) is strongly effected by magnetic ordering and can be used to deduce information concerning the nature of the ordering. The results are analyzed in terms of theoretical models.
Date: August 1, 1979
Creator: Johnson, W.L.
Partner: UNT Libraries Government Documents Department

Magnetic impurities in amorphous superconductors: T/sub KONDO/ > T/sub c/

Description: Measurements of upper critical field as a function of temperature and Fe-concentration are reported for the amorphous superconductors ((Mo /sub 6/Ru /sub 4/) /sub 80/G /sub 20/)/sub l-c/Fe/sub c/, where G is a glass-former. The linear shapes of the H/sub c2/ vs T curves near T/sub c/ agree well with predictions made by Matsura, Ichinose, and Nagaoka, for T/sub Kondo/ much greater than T/sub c/.
Date: February 1, 1979
Creator: Domb, E.R.; MacDonald, C.A. & Johnson, W.L.
Partner: UNT Libraries Government Documents Department

Effects of thermal relaxation on an amorphous superconducting Zr--Rh alloy

Description: The electronic and superconducting properties of an amorphous transition metal alloy are used to evaluate the effects of low temperature annealing. It is observed that the superconducting transition temperature and the electrical resistivity relax exponentially in time from their initial value to a final relaxed value. From this an activation energy for the relaxation process is derived and an explanation is suggested which involves internal stress.
Date: May 1, 1978
Creator: Drehman, A.J. & Johnson, W.L.
Partner: UNT Libraries Government Documents Department

Structure and properties of transition metal-metalloid glasses based on refractory metals

Description: The structure and properties of several new transition metal-metalloid (TM/sub 1-x/M/sub x/) metallic glasses based on refractory transition metals (e.g. Mo, W, Ru etc.) have been systemically investigated as a function of composition. The structure of the alloys has been investigated by x-ray diffraction methods and measurements of superconducting properties, electrical resistivity, density, hardness, and mechanical behavior were made. These data are used in developing a novel description of the structure of TM/sub 1-x/M/sub x/ glasses. The experimental evidence suggests that an ideal amorphous phase forms at a specific composition x/sub c/ and that this phase has a well defined atomic short range order. For metallic glasses having x < x/sub c/ (metalloid poor glasses) vacancy-like defects form, which are characterized by the excess volume which they contribute to the glass. Another, as yet unspecified defect appears to form in glasses with x > x/sub c/. This novel picture can explain the variation of many properties of these glasses with metalloid concentration.
Date: January 1, 1979
Creator: Johnson, W.L. & Williams, A.R.
Partner: UNT Libraries Government Documents Department

Superconductivity, magnetic susceptibility, and electronic properties of amorphous (Mo/sub 1-x/Ru/sub x/)/sub 80/P/sub 20/ alloys obtained by liquid quenching

Description: Results of x-ray diffraction, transmission electron diffraction, and crystallization studies on amorphous (Mo/sub 1-x/Ru/sub x/)/sub 80/P/sub 20/ alloys obtained by liquid quenching are presented and discussed. The alloys are all found to be superconducting with transition temperatures ranging from approximately 3/sup 0/K to approximately 9/sup 0/K. The variation of T/sub c/ with alloy composition is compared to that obtained by Collver and Hammond for vapor quenched transition metal films. Results of magnetic susceptibility measurements are used to estimate the variation of the electronic density of states at the Fermi level, N(0), from the Pauli paramagnetic contribution. The relationship between the variation of T/sub c/ and N(0) is discussed in terms of the microscope theory of superconductivity. Finally, results of measurements of the upper critical field H/sub c2/, and the normal state electronic transport properties are presented and compared with recent theoretical models for amorphous superconductors.
Date: November 1, 1977
Creator: Johnson, W.L.; Poon, S.J. & Duwez, P.
Partner: UNT Libraries Government Documents Department

Superconducting properties of rapidly quenched and heat treated Zr-V and Hf-V foils

Description: The results of rapid quenching and subsequent heat treatments on the superconducting properties of the Zr-V and Hf-V binary systems are presented. Metallic glasses can be prepared in these systems which have very attractive properties for practical application. The existence of a flexible glassy phase raises the prospect of alternative methods for the construction of superconducting devices. As-quenched, partially crystalline material is characterized by small critical currents, yet relatively large upper critical fields and transition temperatures. Heat treatments considerably enhance the current carrying capability.
Date: September 1, 1979
Creator: Tenhover, M.
Partner: UNT Libraries Government Documents Department

Metastable superconducting alloys. [Amorphous alloys]

Description: The study of metastable metals and alloys has become one of the principal activities of specialists working in the field of superconducting materials. Metastable crystalline superconductors such as the A15-type materials have been given much attention. Non-crystalline superconductors were first studied over twenty years ago by Buckel and Hilsch using the technique of thin film evaporation on a cryogenic substrate. More recently, melt-quenching, sputtering, and ion implantation techniques have been employed to produce a variety of amorphous superconductors. The present article presents a brief review of experimental results and a survey of current work on these materials. The systematics of superconductivity in non-crystalline metals and alloys are described along with an analysis of the microscopic parameters which underlie the observed trends. The unique properties of these superconductors which arise from the high degree of structural disorder in the amorphous state are emphasized.
Date: July 1, 1978
Creator: Johnson, W.L.
Partner: UNT Libraries Government Documents Department

Magnetic cluster mean-field description of spin glasses in amorphous La-Gd-Au alloys

Description: Bulk magnetic properties of splat-cooled amorphous alloys of composition La/sub 80-x/Gd/sub x/Au/sub 20/ (0 less than or equal to x less than or equal to 80) were studied. Zero-field susceptibility, high-field magnetization (up to 75 kOe) and saturated remanence were measured between 1.8 and 290/sup 0/K. Data were analyzed using a cluster mean-field approximation for the spin-glass and mictomagnetic alloys (x less than or equal to 56). Mean-field theories can account for the experimental freezing-temperatures of dilute spin-glasses in which the Ruderman-Kittel-Kasuya-Yosida interaction is dominant. For the dilute alloys, the role of amorphousness on the magnetic interactions is discussed. By extending the mean-field approximation, the concentrated spin-glasses are represented by rigid ferromagnetic clusters as individual spin-entities interacting via random forces. Scaling laws for the magnetization M and saturation remanent magnetization M/sub rs/ are obtained and presented graphically for the x less than or equal to 32 alloys in which M/x = g(H/x*, T/x), M/sub rs/(T)/x = M/sub rs/(0)/x/ exp (-..cap alpha..*T/x/sup p/) where x* is the concentration of clusters, ..cap alpha..* is a constant, and p is the freezing-temperature exponent given by T/sub M/ infinity x/sup p/. It is found that p = 1 and 1.3 for the regions 4 less than or equal to x less than or equal to 40 respectively. An attempt is also made to account for the freezing temperatures of concentrated spin glasses. The strength of the interaction among clusters is determined from high-field magnetization measurements using the Larkin-Smith method modified for clusters. It is shown that for the x < 24 alloys, the size of the clusters can be correlated to the structural short-range order in the amorphous state. More concentrated alloys are marked by the emergence of cluster percolation.
Date: March 1, 1978
Creator: Poon, S.J. & Durand, J.
Partner: UNT Libraries Government Documents Department

Structure of some refractory transition metal metalloid glasses

Description: The radial distribution function of four refractory alloys of composition (W /sub 5/Ru /sub 5/) /sub 8/M /sub 2/ where M = some metalloid are presented, along with densities, atomic volumes of metalloids and coordination numbers. The results are discussed and some comparisons made with some model calculations of dense random packings of hard spheres.
Date: December 1, 1978
Creator: Williams, A. & Johnson, W.L.
Partner: UNT Libraries Government Documents Department

Paraconductivity of three-dimensional amorphous superconductors: evidence for a short-wavelength cutoff in the fluctuation spectrum

Description: Measurements of the temperature dependence and magnetic field dependence of the paraconductivity of a three dimensional amorphous superconductor are presented. The data are analyzed in terms of several current theories and are found to give good agreement for low fields and temperatures near T/sub c/. The paraconductivity falls well below predicted theoretical values in the high temperature and high field limits. This is attributed to the reduced role of high wavevector contributions to the paraconductivity. It is shown that the introduction of a short wavelength cutoff in the theoretical fluctuation spectrum provides a phenomelogical account of the discrepancy between theory and experiment.
Date: October 1, 1977
Creator: Johnson, W.L.
Partner: UNT Libraries Government Documents Department

Effects of neutron irradiation on a superconducting metallic glass

Description: The effects of fast neutron irradiation on a superconducting metallic glass (Mo /sub 6/Ru /sub 4/)/sub 82/B/sub 18/ have been studied. Following irradiation to a total fluence of 10/sup 19/ n/cm/sup 2/, T/sub c/ increases from 6.05 K to 6.19 K, and the width of the transition decreases sharply. The density of the material decreases by 1.5%, and the x-ray scattering intensity maxima are broadened. An improvement in the ductility of the samples is observed which together with the other observations suggests the production of defects having atomic scale dimensions and characterized by excess volume.
Date: June 1, 1979
Creator: Kramer, E.A.; Johnson, W.L. & Cline, C.
Partner: UNT Libraries Government Documents Department