Superconductivity and the Very Strong Electron-Phonon Interaction in Amorphous Bi and Bi-Pb Alloys

The temperature dependence of the electrical resistance R(T) and the upper critical field H_(T) have been measured in quench-condensed amorphous Bi and Bi-Pb alloys. The value of the electron-phonon interaction parameter λ was estimated based on the nearly free electron model and the strong coupling theory of superconductivity and turned out to be very large (λ≅1-3) in the amorphous state. The fact that the estimated λ-value is in good agreement with that estimated from tunnel effect measurements by Chen et al. and Knorr and Barth, verified that the nearly free electron model is fairly applicable to the amorphous phase. After an analysis based on the nearly free electron model and the BCS theory, some other physically important parameters, such as the mean free path l, the Fermi velocity v_F, the coherence length ζ_0, the London penetration depth λ_L(0), and the GL parameter κ, were also estimated

Magnetoresistivity Behavior of some Dilute Cu-Fe, Cu-Mn, and Cu-Zn Alloys at Liquid Helium Temperatures

Resistance measurements in magnetic fields up to 100 kilo-oersteds have been made on some Cu-Fe, Cu-Mn, and Cu-Zn alloys in the liquid helium temperature range, where the Cu alloys containing paramagnetic impurities exhibit resistance anomalies. The sign of both the transverse and longitudinal magnetoresistivity in Cu-Fe alloys at 4.2°K is positive for alloys containing less than 0.04 at. % Fe and negative for alloys containing more than this concentration of iron. For all of the Cu-Fe alloys studied the magnitude of the magnetoresistance normalized to the zero-field resistivity is larger at 4.2°K than at lower temperatures. The sign of both the transverse and longitudinal magnetoresistivity in a Cu-0.007 at. % Mn alloy at 4.2°K is positive for all magnetic field values. However, at lower temperatures (1.3°K) the same alloy has a negative magnetoresistivity at low fields, which saturates and becomes positive at higher field values. The rate of change of the normalized transverse and longitudinal magnetoresistivity for Cu-Mn is also larger at 4.2°K than at lower temperatures. The magnetoresistivity of the Cu-Zn alloys decreases with decreasing field strength and increasing Zn concentration, with a modified Kohler law fitting the experimental data. The transverse magnetoresistivity is always larger than the longitudinal one, and for the most dilute Cu-Zn alloy the magnitude of both components is of the same order as that of pure Cu. It is found possible empirically to separate the Cu-Mn magnetoresistivity data into a positive and negative component ; however, for the Cu-Fe alloys studied the present analysis proves the existence of a negative component for the more concentrated alloys but does not permit a separation from the total magnetoresistivity effect

Ripple Shielding for Accurate Resistivity Measurements in Hybrid Magnets(Part II. Several Instruments and Techniques Developed in HFLSM)

After a preliminary test of ripple shielding by a coil using a prereacted pure Nb_3Sn multifilamentary superconducting wire, a few ripple shielding coils were developed employing a Ti-doped Nb-tube method processed multifilamentary Nb_3Sn superconducting wire with so far highest J_c by the so called W&R method, making it possible to measure the temperature dependence of the resistivity in Nb_Ti_ alloy within the accuracy of 10^ at very high magnetic fields above 20 T in the hybrid magnets in the High Field Laboratory for Superconducting Materials at Tohoku University

On the 16.5 T Superconducting Magnet Operation(Part II. Several Instruments and Techniques Developed in HFLSM)

A 16.5 T superconducting magnet employing a surface diffusion processed Nb_3Sn tape was installed in High Field Laboratory for Superconducting Materials at Tohoku University in 1982. The magnet generates high fields up to 16.5 T in a 57 mm diameter bore and has the maximum stored energy of 660 kJ. Since 1982, the magnet has been used for 622 days and charged up about 1070 times up to the field higher than 14 T without serious troubles. In this paper, results of 16.5 T superconducting magnet operations in the last 4 years are described

Superconducting Properties and Microstructure in Dilute Copper Alloys Containing Small Amounts of V_3Ga Particles(Metallurgy)

The superconducting properties (T_c and J_c) were investigated by the resistivity measurement, and the structure was observed by a transmission electron microscopy in the dilute copper alloys containing small amounts of V_3Ga particles prepared by quenching from the liquid state and aging. No superconductivity could be observed at 4.2 K in as-quenched and/or in overaged samples. The highest T_ (=12.5 K), T_ (=9.6 K), and J_c (=525 A/cm^2) were obtained by aging at 700℃ for 96 h and corresponded with the structure of fine V_3Ga precipitates dispersed homogeneously in the copper matrix. Therefore, it is concluded that superconductivity in these alloys results from the superconducting path due to the proximity effect of the superconducting V_3Ga particles

Design and Performance of Superconducting Magnets for Hybrid Magnets(Part I. Establishment and Tests of Hybrid Magnet System at HFLSM)

Design, construction and performance of three superconducting magnets for the hybrid magnets installed in the High Field Laboratory for Superconducting Materials are described in detail. The compact solenoid, SM-3, without fully cryostable design forms the outer part of the most compact hybrid magnet in the world, HM-3 (32 mm bore, 20 T). Fully cryostable superconducting magnet designed under the Steckly criterion, SM-2, is the outer part of HM-2 (52 mm bore, 23 T), which has been most attractive to many experimentalists. SM-1, the outer part of HM-1 (32/52 mm bore, 31/28 T), with the Williams cryostability criterion is the world largest one of the superconducting magnets which employ Ti-doped Nb_3Sn multifilamentary conductors and can generate more than 12 T

General Survey of Tohoku Hybrid Magnet System(Part I. Establishment and Tests of Hybrid Magnet System at HFLSM)

Outline of Tohoku Hybrid Magnet system is briefly described. High Field Laboratory was established in the Research Institute for Iron, Steel and Other Metals, Tohoku University, in 1981, for accelerating research and development of high field superconducting materials. Three hybrid magnets generating magnetic fields more than 20 T have been constructed as its main apparatuses. The strongest hybrid magnet, HM-1, could produce 31.1 T in November, 1986, which was the world record as this kind of hybrid magnet. Several important features of the hybrid magnet system are introduced which will be also useful to understand the following papers

Thermal Conductivity in a Pure Type II Superconductor near the Upper Critical Field

The thermal conductivity, K, of a pure Nb (RRR=1900) has been studied as a function of longitudinal and transverse magnetic field between 1.8°K and the transition temperature (9.2°K). The thermal conductivity shows a deep minimum just above H_ and increases with infinite slope in the gapless region near H_ like ΔK/K_=C(H_-H)^ in good agreement with the Maki theory for both longitudinal and transverse field configurations. The temperature dependence of the coefficient C is compared with numerically calculated one from the revised Maki theory which includes both the impurity scattering and the phonon scattering, and a fairly good agreement is found between them, when the density of states is assumed to be 1.6×10^ states/cm^3 erg

Type I to Type II Transition in Superconducting In-3.9 at.%Pb Alloy

The magnetization and the thermal conductivity of In-3.9 at.% Pb alloy are measured between 1°K and 4.2°K. It is found that this alloy sample does show type I to type II transition of the superconductivity at T_=2.2°K. Below T_, the magnetization decreases with finite slope near the upper critical field, H_, and the thermal conductivity shows deep minima both in the magnetic field dependence and in the temperature dependence. Above T_, on the other hand, the sample does not show any such effects mentioned above. The data concerning the residual resistivity ρ_n=2.46μΩcm, the transition temperature T_c=3.64°K, the mean free path l=5.69×10^cm, the G-L parameters K_1(0) =0.77 (at 0°K), k_1(1)=0.68 (at T_c) and the ratio k_1(0)/K_1(1)=1.13 are obtained. These values are all in good agreement with the results of previous investigations on In-Pb alloys

A Test of Modified Indium Seal of a Window at Liquid Helium Temperature(Physics)

A modified version of an indium seal with a very small loss area, in which pure In solder is used instead of pure In wire, has been tried for a glass window of 20 mm in diameter. It has turned out that this seal is vacuum tight against the liquid helium at 4.2K. A seal of a 10 mmφ sapphire window with STYCAST 2, 850 GT was also successfully tested at 4.2 K