Magnetoresistances of Dilute Alloys of Manganese in Copper, Manganese in Zinc and Chromium in Zinc at Liquid Helium Temperatures

Magnetoresistances of alloys of Mn in Cu (5.4 atomic per cent Mn), Mn in Zn (0.12 atomic per cent Mn) and Cr in Zn (0.10 atomic per cent Cr) are measured in the magnetic field up to about 76 KOe at liquid helium temperature. The magnetoresistance of CuMn alloy decreases with increasing field and shows a reproducible hysteresis. The ratio of the decrease of resistance for the strongest magnetic field applied here to the field-free resistance at 0°K is about 7 per cent, while the ratio of the decrease of resistance for an infinite magnetic filed at 4.24°K to the field-free value at 0°K is estimated to be 38 per cent, using our experimental results and the method proposed by K. Yosida. Magnetoresistances of ZnMn and ZnCr alloys are also measured under the same experimental conditions as that for CuMn alloy

Specific Heat of Tellurium and Selenium at Very Low Temperature

The specific heat of tellurium and selenium was measured in the range of liquid helium temperatures. The measurements were made with a calorimeter of Nernst-Eucken\u27s type. A carbon composition resistor, having a nominal room-temperature resistance of ten ohms, was used as the suitable thermometer in this temperature region. It was found that the observed values of the specific heat of these metals did not consist of the electronic specific heat but only of the lattice one which is proportional to T^3. Discussions were given of the specific heat of these metals at low temperatures from the viewpoint of the anisotropy of the chain-like crystal lattice

Electrical Resistance of Copper-Gold Alloys at Low Temperatures

Electrical resistance of the copper-gold alloys containing 5.0_6, 24.1, 25.0_7, 50.8, 74.0 and 75.0_6 at. % gold was measured in the range from liquid helium to room temperature in the annealed and quenched states. It was established that the residual resistance of the 75.0_6 per cent alloy is lower in the ordered state than in the disordered one, and that the ratios of the residual resistance to the ice point resistance are 0.699 and 0.800 for the ordered and disordered states, respectively. Also it was found for the 74.0 per cent alloy that the residual resistance of the partly ordered state is higher than that of the disordered state. The Debye temperatures of the alloys were evaluated by using the Gruneisen formula. 185°and 160°K were obtained for the 75.0_6 per cent alloy in the ordered and disordered states, respectively. A resistance minimum of the magnitude of 0.01 μΩ-cm was found in the neighborhood of 13°K for the 25.0_7 per cent alloy. Such a minimum seems to be little affected by the degree of order, and was thought to be due to the presence of small amounts of certain impurities. This view was supported by an appearance of more distinct minimum near 19°K for the 23.5_7 per cent alloy containing 0.16 per cent iron as an impurity

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

Magnetic-Field-Induced Superconductivity in Eu_<0.8>Sn_<0.2>Mo_6S_<7-y>Se_y (Transport and Fermiology)

The electrical resistance of Eu_Sn_Mo_6S_Se_y (0≤y≤0.7) was measured under the magnetic fields up to 230 kOe. The hysteresis of the resistance was observed in the field range where the superconductive-normal-superconductive transitions appear. Analysis of the hysteresis provides a direct evidence that the magnetic-field-induced superconductivity of these compounds is caused by the Jaccarino-Peter compensation mechanism

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

The Specific Heat of Copper Alloys Containing Small Amounts of Iron

The specific heat of copper alloys containing small amounts of iron (0.3 to 3.5 at. % of iron) was measured under various heat treatment conditions at liquid helium temperatures. The excess specific heat of copper-iron alloys in solid solution was observed and it would be due to a magnetic origin. It is tried to explain the specific heat by the Marshall-Klein theory based on s-d interactions and the Ising model. The specific heat of copper alloys containing γ-iron precipitates involves a temperature independent contribution from the superparamagnetic character of γ-iron precipitates

Electrical Contact Resistance between Metallic Surfaces Subjected to Various Treatments

Electrical contact resistance between two tungsten rods, which are placed crosswise and pressed together with a pressure from 10 to 100g, is measured over the temperature range from room temperature down to the boiling point of liquid nitrogen. The experiment is performed with the specimen which have been subjected to three kinds of surface treatments, namely, mechanical polishing, electrolytic polishing and etching. It is found that the contact resistance depends on the contact pressure and varies linearly with temperatures, pursuant to the kind of surface treatment. From the experimental results, the contact resistance is considered as consisting of two parts, namely, the convergence resistance and the transition resistance which is independent of temperature. By using these relations, the contact area and distance are estimated under certain assumptions. Some explanatory discussion is also attempted on the relationship between contact resistance and surface condition on the basis of the experimental results