Upper limit for magnetoresistance in silicon bronze and phosphor bronze wire

The electrical resistivity of silicon bronze and phosphor bronze was measured in magnetic fields from 0 to 14 T and at temperatures between 2 and 300 K. At any fixed temperature, the change in resistivity to 14 T was less than a few parts in 10⁵. Thus, these bronzes are excellent for use in high magnetic fields where constant resistance is required. Welding leads to the sample was found to be superior to soldering. The soldered contacts were subject to spurious resistivity changes that resulted from superconducting transitions in the solder.     

Mechanical properties of Zr-3Sn-1Mo-1Nb alloy at various temperatures

The deformation characteristics of Zr-3Sn-1Mo-1Nb alloy have been investigated by tensile testing in the temperature range 300–1000 K at a constant crosshead speed corresponding to the strain rate of 6.7×10^–5s^–1. At lower temperatures, below about 500 K, the flow stress of the sample decreased with increasing temperature, whereas an inverse temperature dependence of the yield stress was found at temperatures between 500 and 700 K. At higher temperatures, above 700 K, the normal dependence of the yield stress on temperature was again observed. The maximum stress exhibited a similar temperature dependence. At higher temperature, serrations were found on the flow stress curves at the very beginning of deformation. The main deformation mechanisms are assumed to be a locking-unlocking mechanism connected with cross-slipping.     

Spin Fluctuations and Itinerant Magnetism in PrCo2B2C Compound

Resistivity as a function of the temperature and applied magnetic field was studied in PrCo₂B₂C intermetallic compound. The resistivity as a function of temperature at different magnetic fields shows a parabolic behavior at low temperatures which persists for magnetic fields up to 7.8 T. Magnetoresistance measurements show negative values at temperatures below 15 K and low fields, and becomes positive at high fields. Specific heat measurements reveal a high value of the Sommerfeld coefficient of about 300 mJ(mol?K²)^?1. These results at low temperatures are interpreted from the point of view of the spin fluctuations theory.     

The impurity resistivity ofZnFe alloys

Measurements are presented of the electrical resistivity of several ZnFe alloys with concentrations between 0.04 and 0.05 at % Fe in the temperature interval 0.5–280 K. The low temperature resistivity behavior of even the most dilute alloys is dominated by impurity-impurity interactions leading to fortuitous characteristic temperature ?～90 K. At higher temperatures (T?15 K) the impurity resistivity is dependent mainly on single impurities with much higher ? values. The estimated characteristic temperature of isolated Fe impurities θ₁ ～ 350 K is in better agreement with recent magnetic susceptibility and thermopower measurements.     

Theory of electrical resistivity of metal-matrix composites at cryogenic and higher temperatures

This paper presents a theory describing the electrical resistivity (conductivity) in the axial direction of unidirectional fibre-reinforced metal-matrix composite (MMC) materials at cryogenic and higher temperatures. The theory is derived from the solution of Boltzmann's equation. A triple-integral expression is obtained to describe the change in the electrical conductivity in the matrix metal due to electron scattering from the fibre surfaces. It is shown that at cryogenic temperatures, the electrical resistivity can rise by a factor of 2200 over a decrease in temperature of about 6 K below about 10 K. This effect is due entirely to electron scattering from fibre surfaces. The model developed shows that the composite resistivity agrees well with known experimental data at temperatures above 80 K. At very low temperatures, _c (T) _c (T _R) (1–CT ^–4)^–1, whereT is the absolute temperature. Shortcomings and implications of the theory are discussed.     

Temperature-dependent Hall analysis of carbon-doped GaAs

The temperature dependence of the electrical properties, such as hole concentration, Hall mobility and resistivity of carbon-doped GaAs epilayers over a wide range of doping levels has been investigated. The carbon-doped GaAs epilayers have been grown by low pressure metalorganic chemical vapor deposition. The electrical properties have been obtained by Hall measurements. Experimental data on the carrier mobility, Hall effect, and resistivity over a wide temperature range have been analyzed and possible scattering mechanisms have been explained. Our experimental data show that the ionized impurity scattering tend to be dominant at temperatures below 100 K, while the lattice scattering as well as the ionized impurity scattering plays an important role at temperatures above 100 K. The dependence of the electrical on the doping levels has also been studied. In the case of heavily C-doped GaAs, the mobility curves are nearly flat at temperatures below 100 K and the mobility decreases as temperature increases above 100 K. The reason is that the degenerate conduction occurs at high doping level. The degenerate conduction begins at the hole concentration of about 2 × 10¹⁸ cm⁻³ at 77 K and at room temperature.     

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.     

Very Low Temperature Electronic Transport in Al-Pd-Re Quasicrystalline Alloys

Electrical resistivities of two icosahedral (I) Al-Pd-Re alloys have been measured between room temperature and mK temperatures. One quasicrystalline (QC) polygrain Al-Pd-Re sample exhibited insulating behavior in its resistivities, increasing by a factor of r=R(4 K)/R(300 K)=7.76; its room temperature resistivity was 9,890 μΩ cm. A “phenomenological” expression fitted the conductivity data well between 300 K to 0.5 K. Below 0.4 K a crossover to an activated variable-range hopping law was observed. Low temperature magnetoresistance ratio data and fits using the wave function shrinkage theory are presented. A second QC Al-Pd-Re sample had a small resistance temperature ratio r=2.12. The room temperature resistivity was extremely large, ρ(300 K)≈40,980 μΩ cm. Its conductivity could be described well using a simple temperature power law between 300 K to 20 K. Below 20 K there was a crossover to a new behavior. Below 1 K, the conductivity could be fitted using a very weakly insulating power law where σ(T)≈11.37T ^0.032 in (Ω cm)⁻¹, suggesting that this sample is located just below the metal-insulator transition. The magnetoconductivity data could not be fitted successfully using the 3D weak localization (WL) theory and inserting into it physical and realistic fitting magnitudes for the inelastic magnetic field B _in.      

Semiconducting properties of nonstoichiometric manganese silicides

Electrical resistivity, Hall coefficient and thermoelectric power were measured on manganese silicides of composition MnSi_2–x withx ranging from 0.25 to 0.28 in the temperature range from 80 to 1100K. At higher temperatures a forbidden energy gap estimated from the resistivity data was about 0.40 eV. It was confirmed that MnSi_2–x was a degenerated semiconductor and that the hole concentrations in the degenerated state varied from 1.8 to 2.3×10²¹ cm^–3. The ratio of electron to hole mobility was less than unity. The intrinsic resistivity and the hole mobility varied with temperature as 3.6×10^–4 exp(2320/T) and 1.2×10⁴ T ^–3/2 respectively. The value of Hall coefficient calculated by using a mobility ratio of 0.02 was in good agreement with that observed in the intrinsic region. From the relationship between hole concentration and thermoelectric power for MnSi_1.73 near room temperature, the hole effective mass was estimated to be twelve times as large as the free electron mass. The calculation of the thermoelectric power was carried out based on the assumptions that the scattering of carriers is dominated by acoustic lattice scattering and that the carriers obey Fermi-Dirac statistics. The calculated results were in reasonable agreement with the observed thermoelectric powers in the temperature range from 150 to 1100K.     

Aluminium based resistance alloys for low temperatures

The resistivity of several (AlMgMn)-alloys with a magnesium mass content of 5%, and manganese contents of 0% up to 1%, has been measured in the temperature range of 1.5 to 4.2 K. It is shown that a Mn concentration of 0.078% produces a broad resistivity minimum at about 4.2 K; this means that the resistivity only varies by about 1.3 ppm between 1.5 and 4.2 K. It is further shown that the technical aluminium alloy AlMg 5 also has a similar small temperature coefficient of resistivity (TCR), in particular, the TCR is a few parts in 10⁷/K for temperatures between 2 and 4.2 K. The fact that this alloy is commercially available and inexpensive, makes it very attractive as a low temperature resistance material for various applications.     

Electrical properties of electrochemically prepared thin polytetrahydrofuran films II: Characterization under D.C. conditions

The electrical characteristics of electrochemically prepared polytetrahydrofuran (poly-THF) films were studied under d.c. conditions. At low fields (?10⁵ V cm^?1) a phonon-assisted hopping conduction occurs in poly-THF films 2000 Å thick. The low temperature dependence of the conductivity (T< 243 K) is related to interchain hopping, whereas the high temperature dependence of the conductivity (>320 K) is ascribed to trap hopping. At high fields (E>10⁵ V cm^?1) and high temperatures (T>320 K) Schottky conduction is observed and the Schottky barrier height depends both on the electrode metal and on the field direction. At temperatures below 320 K, Poole-Frenkel conduction occurs and the current intensity is independent of the nature of the electrodes and of the field direction. At very low temperatures (T<100 K) and high fields (E>10⁶ V cm^?1), thermally assisted tunnel effect conduction (δj∞T²) is observed. These changes in conduction with the temperature and the field are ascribed to changes in the polymer structure.     

Adsorption of3He on cesium

Adsorption isotherms of³He on cesium substrates have been measured in the temperature range from 0.2 K to 1.5 K. At liquid-vapor coexistence³He wets cesium at all temperatures studied. Step-like features are found in the isotherms which are similar to the prewetting transitions of⁴He on Cs substrates, but the width of these steps is ∼20 times wider for³He than for⁴He. In the case of³He on Cs, the steps are located at a chemical potential about 0.6 K below liquid-vapor coexistence. If the low temperature behavior is interpreted to be first order prewetting, the prewetting critical point temperature is 0.6±0.1 K.     

Investigation of the heat conductivity of niobium in the temperature range 0.05–23 K

We report thermal conductivity measurements on a single-crystal niobium specimen of resistivity ratio 33,000 over the temperature range 0.05–23 K in the superconducting state and above 9.1 K in the normal state. The axis of the niobium rod was [110] oriented. The surface roughness was varied by sandblasting of the sample. The values of the thermal conductivity in the range from the lowest temperatures up to the maximal value covered a range of six orders of magnitude (=2×10^–5 W cm^–1 K^–1 at 50 mK to =22 W cm^–1 K^–1 at 9 K). Above 2 K the results for the untreated and the sandblasted sample are in accord, whereas below 2 K the influence of the sample surface is discernible. The various conduction and scattering mechanisms are discussed.     

Electrical conductivity and optical properties of ZnO films annealed in hydrogen atmosphere after chemical vapor deposition

The d.c. electrical conductivity and optical properties of polycrystalline zinc oxide films (220–450 nm thick) annealed in hydrogen after chemical vapor deposition are investigated. A minimum film resistivity after the annealing gives 0.31 cm for the film as-deposited at a substrate temperature of 823 K. From the temperature dependence of conductivity, band conduction is confirmed for the films at temperatures above 250 K. The effect of grain-boundary scattering is due to thermionic emission of electrons over grain boundary barriers. At temperatures below 250 K, variable-range hopping transport is found to be dominant. The films are transparent in the wavelength range 400 to 1000 nm and have sharp ultraviolet absorption edges at 380 nm. The absorption edge analysis reveals the optical band gap energy for the films to be 3.18–3.23 eV. The Urbach tail analysis gives the width of localized states E_e=0.06-0.14eV.     

Magneto-electrical transport in V-patterned La0.7Sr0.3MnO3 nanostructures

We investigate the electrical transport and magnetic field dependence of nano-patterned La_0.7Sr_0.3MnO₃ devices. We find that the resistivity versus temperature dependence is the same as that observed in thin films, indicating that our nano-patterning preserves the fundamental properties of the material. At temperatures below 20 K there is resistivity upturn of ~ 5 % in the smallest and thinnest device. Structures in a “V” pattern were fabricated in order to investigate domain wall resistance. We find a much smaller resistance area product as compared to previous reports observed in nanoconstrictions and also that the switching field matches that in micromagnetic simulations.     

Space-charge-limited currents and carrier trapping in plasma-polymerized malononitrile films

The dark electrical conductivity of plasma-polymerized malononitrile (PPMa) films in an Ag/PPMa/Ag sandwich structure was investigated over the temperature range 300–525 K at a reduced pressure of 10^-5 Torr. The room temperature current-voltage characteristics indicate space-charge-limited currents. The results for the conductivity as a function of inverse temperature are in accordance with the band model proposed by Barbe and Westgate, and the thermal energy gap between the top of the valence band and the bottom of the conduction band was determined to be 0.86±0.01 eV. At temperatures below about 380±5 K the conduction process is consistent with the presence of an electron trapping level situated 0.34±0.05 eV below the conduction band edge with a density of (5.02±0.05) × 10¹⁶ cm^-3. It is assumed that above about 435±5 K the conduction process is intrinsic. Experiments on the chemisorption of oxygen suggest that electrons are the majority carriers in PPMa films.     

The electrical resistivity and specific heat of americium metal

The electrical resistivity and specific heat of samples of ²⁴¹Am and ²⁴³Am are reported. The electrical resistivity at room temperature is reduced compared with the value for plutonium, while the power law exponent at low temperatures is increased. The electronic specific heat coefficient is lower than for the lighter actinides. These features lead to the conclusion that americium is the first of the actinides in which the 5 f electrons are essentially localized. Anomalies occur in the electrical resistivity and in the specific heat in the region of 60 K, the cause of which is unknown.     

Combined DSC and Pulse-Heating Measurements of Electrical Resistivity and Enthalpy of Tungsten,Niobium, and Titanium

Measurements of thermophysical properties such as enthalpy, electrical resistivity, and specific heat capacity as a function of temperature starting from the solid state into the liquid phase for W, Nb, and Ti are presented in this work. An ohmic pulse-heating technique allows measurements of enthalpy and electrical resistivity from room temperature to the end of the stable liquid phase within 60 μ s. The simultaneous optical measurement of temperature is limited by the fast pyrometers with an onset temperature of T_min = 1200–1500 K; below these temperatures, the fast pyrometers are not sensitive. A differential scanning calorimeter (DSC) is used for determination of the specific heat capacity, and also to obtain enthalpy values in the temperature range of 600–1700 K. Combining the two methods entends the range of values of electrical resistivity and enthalpy versus temperature down to 600 K. Results on the metals W, Nb, and Ti are reported and compared to literature values. This paper is a continuation of earlier work. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Size and temperature dependences of the resistivity of thin alkali metal wires at liquid nitrogen,hydrogen and helium temperatures

The temperature variation of the resistivity ?, the size effect on the resistivity and the residual resistivity were investigated for thin wires of the alkali metals Na, K, Rb and Cs (which were of high purity and had a high crystalline order) from room to liquid He temperatures.The results obtained allowed us to determine the fundamental quantity ?_∞l and also the resistivity ?(T)_∞ of the bulk metal and the mean free path l(T) of the conduction electrons.The values of ?_∞l obtained near 0 K for these thin alkali metal wires of high crystalline order were found to correspond, within experimental error, to those obtained previously using highly disordered thin films of the same alkali metals at liquid nitrogen temperatures. Both sets of ?_∞l valuescorrespond to the values expected theoretically according to the fundamental equation $\text{1}\text{?}{}_{\mathrm{\infty }}\text{l}\text{=}\text{const.}\text{× N}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ (where N is the density of effective conduction electrons), thus proving that ?∞l is independent of temperature and of degree of crystalline order as expected.The results on the temperature variation of the resistivity ?(T)_pho due only to electron-phonon scattering reveal a T⁵ law for Na in the temperature interval 15?T?20 K and for Rb and Cs in the range 1.6?T?3 K, and a T³ law for K in the range 14?T?20 K. Moreover, at temperatures below 4 K the resistivities of the thinnest wires of Cs and, to a lesser extent, of Rb deviate from Matthiessen's rule, thus revealing a temperature-dependent size effect.     

Thermal conductivity and electrical resistivity of cadmium arsenide (Cd3As2) in the temperature range 4.2–40 K

Results on electrical resistivity and thermal conductivity measured in the temperature range 4.2–40 K are presented for single-crystal and polycrystalline samples of Cd₃As₂. Hall effect has been studied at temperatures of 4.2, 77, and 300 K. The calculated value of the conduction electron concentration was in the range 1.87–1.95 10²⁴m^–3. Electrical resistivity of all investigated samples was independent of temperature up to about 10K and increased slowsly at higher temperatures. The thermal conductivity shows a maximum in the region in which the lattice component of thermal conductivity dominates. The strong anisotropy of the lattice component determines the anisotropy of the total thermal conductivity. The electronic component of thermal conductivity does not exhibit any anisotropy and shows a maximum at a temperature of about 300 K.Paper submitted to the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.