Thermal conductivity and electrical resistivity of Nb---Ti alloys at low temperatures

Results are presented of an experimental study of the thermal conductivity, electrical resistivity, critical temperature and upper critical field of solid solutions of Nb---Ti with 22–80 at % Nb in cold-worked and recrystallized states. The temperature range of the measurements is 4.2 to 30 K. The correlation between the critical parameters and the behaviour of the thermal conductivity and electrical resistivity has been found. The residual resistivity increases and the thermal conductivity decreases with increasing the Ti concentration.     

The electrical and thermal conductivities of dilute copper-chromium alloys at low temperatures

Electrical and thermal conductivity measurements are reported on dilute copper-chromium alloys containing 32 and 50 at. ppm chromium, in their unannealed state and also after annealing at 530–550°C for 16 and 66 h in each case, under fore-vacuum. From the electrical resistivity measurements evidence of a possible cluster formation is obtained in the annealed sample. The electronic Lorenz number of the alloys increases with decrease of temperature in the temperature range 4.2–1.6 K. Lower temperature measurements might show a maximum around the Kondo temperature (～1 K) as predicted by the available theories on dilute magnetic alloys.     

Relation between the anomalous resistivity and the susceptibility for dilute magnetic alloys

It follows from scattering theory that the anomalous resistivity of dilute magnetic impurities may be written as =A–B cos 2S(/5), whereS is a temperature-dependent spin value. This relation is experimentally verified for various systems whenS undergoes an almost complete compensation fromS _max to zero. Illustrations are given with available data onAu-V,Cu-Cr,Cu-Fe,Au-Fe,Cu-Mn,Au-Co, andCu-Ni.     

Density,electrical resistivity and magnetic susceptibility of Sn-Bi alloys at high temperatures

Temperature dependencies of density (by the gamma-penetrating method), electrical resistivity (by the contact-less method in rotating magnetic field), and magnetic susceptibility (by the Faraday method) of Sn-Bi alloys with near-eutectic compositions are investigated. The alloy with eutectic composition, Sn —58% (mass) Bi, is shown to differ significantly in the electron structure from hypo- and hypereutectic ones. The melt overheating above the given temperature provides the hysteresis of the properties sensitive to electron structure.     

Magnetic behavior of dilute Cu(Mn) alloys at very low temperatures

The static magnetization of dilute Cu(Mn) alloys with Mn concentrations between 4.2 and 106 ppm has been measured between 10 mK and 0.4 K in fields between 1 and 200 Oe. Magnetic ordering is observed and attributed to impurity-impurity interactions. However, a concentration-independent Weiss constant and a decreasing moment per impurity in the low-field, low-temperature limit are evidence for the increasing importance of single-impurity effects with characteristic temperatureT _k 2 mK.This work has been supported by the U.S. Atomic Energy Commission under Contract No. AT(04-3)-34, P.A. 143.     

Magnetic impurity pairs in dilute Cu(Fe) alloys at very low temperatures

The temperature-dependent static magnetization of several dilute Cu(Fe) alloys with Fe concentrations between 102 and 478 ppm has been measured in fields between 1 and 200 Oe and at temperatures between 9 mK and 0.4 K. At higher temperatures and in small fields, the magnetization displays the following concentration, field, and temperature dependences:M c ² HT ^–2/3. At lower temperatures, magnetic ordering is observed. These results are interpreted in terms of the behavior of pairs of impurities acting as individual entities. They are quite likely correlated with the anomalous low field, low-temperature observations made in previous measurements of the resistivity and specific heat of the Cu(Fe) system.This research was supported in part by the U.S. Atomic Energy Commission under Contract No. AT(04-3)-34, P.A. 143, and by the National Science Foundation.     

Effect of chromium carbides on electrical resistivity of nickel based alloys by low temperature aging

Abstract

To clarify the physical and mechanical properties of nickel based alloys (Alloy 600 and 690), the effects of chromium carbides on the electrical resistivity and hardness were examined after low temperature aging following cold working. In Alloy 600, chromium carbide precipitates were dispersed at grain boundaries and within the grains and the electrical resistivity and hardness increased markedly after short time aging. In Alloy 690, chromium carbides precipitated mainly at grain boundaries and the increases in electrical resistivity and hardness were relatively small, even after long aging times. The most probable mechanism causing the large increases in electrical resistivity in Alloy 600 is the segregation of solute atoms, such as carbon and nitrogen atoms, to dislocation loops around chromium carbides introduced by cold working.

MST/939     

Sensitivity of the anomalous thermoelectric power to lattice defects in a dilute copper-iron alloy

The thermoelectric power (TEP) of a Cu-Fe alloy containing 115 at ppm iron in the temperature range 1.5–80 K is measured in its unannealed state as well as after annealing at 530–550 C under fore-vacuum for 16 and 66 h, respectively. The TEP curves present a giant negative peak, which increases numerically with annealing and also shifts to lower temperatures. This observed numerical increase of the peak TEP value is attributed to the removal of the lattice defects rather than the decrease of the effective isolated impurity concentration consequent upon a partial precipitation of the impurity during annealing. Such an explanation is quite consistent with our inference of a phase shift for ordinary scattering increasing with impurity concentration in dilute magnetic alloys characterized by a negatives-d exchange interaction. The shift of the TEP peak to lower temperature is caused by an increase of the phonon drag component due to the removal of lattice defects. Such a decrease of the temperature of the peak TEP,T _p, is reminiscent of a similar variation of its counterpart,T _K in electrical resistivity. However,T _p seems to be even more sensitive to the physical environment of the magnetic impurity.     

Local ordering in dilute ortho-para-hydrogen mixtures at low temperatures

We report experimental observations of the local orientational ordering of ortho-H₂ molecules in dilute solid ortho-para mixtures for low temperatures. The results indicate a smooth, continuous freezing of the rotational degrees of freedom without any evidence for a distinct discontinuity in the temperature dependence of the local order parameters for the 37–600 mK temperature range.     

Nqr experiments on Sc-Y alloys at very low temperatures

We have performed Nuclear Quadrupole Resonance (NQR) experiments on an alloy of scandium and yttrium. We find that the characteristic resonance frequencies in zero external field are 50 percent larger than in pure scandium. This increase in frequency makes the Sc-Y alloy a better candidate for absolute thermometry below 500 µK. However, the spin-lattice relaxation time of this alloy is more than an order of magnitude longer than in the pure scandium. In addition, we have observed an abrupt increase in the Korringa constant for temperatures below 5mK.     

Oxygen annealing of silver for obtaining low electrical resistivity: technique and interpretation

A single crystal Ag rod has been annealed in stages in a deliberate but low oxygen partial pressure. The change in the residual resistivity ratio (RRR) after each anneal is reported. During the course of the anneals the RRR is increased from 140 to 9500. The details of the annealing procedure are given, and the dynamics of internal oxidation of impurities in Ag are discussed. It is shown that for achieving high RRR, high annealing temperatures and low partial pressure of oxygen should be employed. In addition, the necessity of including size effects in the interpretation of electron transport phenomena in incompletely oxygen annealed samples is demonstrated.     

Ultrasonic fatigue of nickel-chromium alloys at low temperatures

The influence of low temperature ultrasonic deformation on the electrical resistivity and magnetic properties of nickel-chromium dilute solid solutions is examined. It is shown that changes in the electrical resistivity and magnetic properties of prequenched samples after ultrasonic fatigue can be explained by order-disorder processes during fatigue. It is concluded that ordering at low temperatures during the ultrasonic deformation is associated with high strain rate and high vacancy concentration produced by deformation.     

Temperature dependence of the high-frequency resistivity in dilute magnetic alloys

The temperature dependence of the microwave resistivity at 70 GHz in diluteCuCr,CuMn, andCuFe alloys was measured between 1.6 and 4.2 K by the calorimetric method. The observed resistivity decreases slightly with decreasing temperature inCuFe. These results are in qualitative agreement with the recent theory of Moriya and Inoue on the high-frequency conductivity of Kondo alloys. InCuCr the resistivity increases remarkably with decreasing temperature, whereas, according to the theory, it should decrease. This fact seems to suggest that our present knowledge of thes-d scatteringt matrix is not sufficient to describe the high-frequency resistivity of dilute magnetic alloys.     

Effect of substrate temperatures on the electrical resistivity of thermally evaporated Mn thin films

Resistivity measurements have been performed on three samples of Mn thin films from 300 to 1.4 K using the van der Pauw four probe technique. The films were grown by thermal evaporation onto glass substrates held at 523, 323 and 77 K, respectively in a bell jar held at 6 × 10⁻⁶ Torr. The resistivity-temperature results of the three specimens reveal a variety of low temperature behaviours. A behaviour typical of the bulk α-Mn is obtained with the film grown at a substrate temperature of 523 K whilst with the film grown at a substrate temperature of 323 K, the resistivity tends to a saturation at low temperatures exhibiting a behaviour reminiscent of Kondo scattering. The resistivity-temperature behaviour of the sample held at a substrate temperature of 77 K may be regarded as typical of a metallic alloy glass with a negative temperature coefficient of resistivity at high temperatures and this turns to a T² dependence of resistivity at very low temperatures.