Total Resistivity Research Articles

Electron transport properties of Al-Y-Ni metallic glasses

Electronic transport properties of Al 85Y x Ni 15 − x ( x=3–12 at.%) and Al y,(Y 8/15Ni 7/15) 100 − y, ( y= 75–88 at.%) melt-spun amorphous ribbons have been studied. The room temperature resistivity exhibits a strong dependence on Al content in the second series dropping from 136 to 60 μΩ·cm as the proportion of Al is increased. In the first series with Al content fixed, the resistivity is nearly constant over the entire compositional range, varying from 65 to 71 μΩ·cm. Calculations based on the Drude model do not fully account for the measured resistivity as the Al content is decreased. A significant contribution to the total resistivity from s-d scattering at transition metal atomic sites may be responsible for this departure from the free electron calculation. The temperature coefficient of resistivity in these alloys was found to obey the Mooij correlation.

Effect of Ti additions on the electrical resistivity of copper

Electrical resistivity of Cu Ti alloys containing 1.5, 2.7, 4.5 and 5.4 wt.% Ti, has been determined from the resistance values measured using Kelvins Bridge apparatus at room temperature. The resistivity in solution-treated alloys increases with Ti content linearly up to about 4.0 wt.% Ti, beyond which it decreases with further additions of Ti. However, in peak-aged condition, the resistivity continues to increase linearly up to 5.4 wt.% Ti without showing any decrease. Nordheim's rule of resistivity is followed up to approximately 4.0 wt.% Ti in the solution-treated alloys. Further, Nordheim's rule modified with the incorporation of the law of mixtures for two-phase systems ( ρ t = ρ m ν fm + ρ p ν fp) is obeyed right up to 5.4 wt.% Ti in the peak-aged alloys. The difference in behaviour is attributed to the fine scale precipitation formed during quenching in solution-treated Cu—4.5Ti and Cu—5.4Ti alloys, as revealed by transmission electron microscopy (TEM). The contribution to the total resistivity by β′-Cu 4Ti precipitate and prior cold deformation is considerable in deformed and peak-aged Cu Ti alloys.

Interrelation between lattice vibration and magnetic state in structural and magnetic transitions of γMnNi alloy

Electrical resistivities of antiferromagnetic γMn-17.0 and 18.7 at.%Ni alloys were measured at temperatures from 300 to 520 K in magnetic fields from 0 to 0.23 Wb/m 2. Based on the measured resistivities, change in magnetic states of the alloys when the structural and the magnetic transitions took place were studied. It was observed that the magnetic states at these temperatures showed strong temperature dependence as expected for an itinerant electron antiferromagnet dominated by spin density fluctuation of itinerant 3d-electrons. However, magnetic changes as if in a localized spin magnet were observed in temperature ranges of the transitions. In order to study these complicated magnetic changes, the measured total resistivities in the temperature ranges were separated into two terms of lattice resistivity and magnetic resistivity. It was determined from the study of these two terms, that localized magnetic moment at the lattice site can be large enough to change the lattice vibration. The lattice vibration and the spin fluctuation show complementary change to each other with an increase in the field and show different amplitude of change by the field for each transition. Based on these results, the complicated magnetic changes and interrelation between the lattice vibration and the spin fluctuation in the structural and the magnetic transitions are studied.

Comparison of experimental, calculated and observed values for electrical and thermal conductivity of aluminium alloys

A model has been developed for calculating the electrical resistivity of commercial aluminium alloys from composition and heat treatments using the Matthiessen rule. The model is based on the approximation that the solubility of the alloying elements in heat treated alloys is equivalent to the equilibrium solubility at a higher temperature. These temperatures were determined from heat treatment data. The resistivity of a wide range of commercial alloys was calculated using the model, showing an agreement with most observed resistivity values of within 3 nΩm, except for alloys with special composition characteristics. According to the model, magnesium and manganese are important contributors to the resistivity for all main groups of alloys. In heat treated alloys the contribution of precipitates is 6–17% of the total resistivity. Thermal conductivity was calculated for alloys given in the literature using the Wiedeman–Franz law and the calculated resistivity. The calculated thermal conductivity agreed with the experimental values for the AlMg-alloys, but it was lower than the experimental values for pure aluminium and the AlCu-alloys in the annealed condition.

Electrical resistivity studies of Cr - Ir alloy single crystals

Electrical resistivity has been measured for four Cr - Ir alloy single crystals for concentrations between 0.07 and 0.25 at.% Ir in the temperature range 4 to 1200 K. Well defined magnetic anomalies were observed at the Néel temperature of each alloy as well as at the incommensurate - commensurate (I - C) spin-density-wave (SDW) phase transition temperature of a Ir alloy. The latter transition is hysteretic, of hysteresis width about 20 K, which is indicative of a first-order ISDW - CSDW phase transition. Analyses of the data show that the fraction of the electron and hole Fermi surface sheets that nests is roughly the same in the ISDW and CSDW phases. A magnetic contribution to the resistivity, amounting to between 20% and 25% of the total resistivity at the Néel point, is observed in the alloys. This contribution, probably due to spin-fluctuation effects, persists to temperatures well above , up to about .

A model of fullerene conductance

An attempt has been made to describe fullerene conductance on the basis of the additive conductance Dresselhaus-Dresselhaus model for graphite, taking into account the topology of a fullerene molecule in the crystal lattice. It has been shown that fullerene conductance is related to the σ c component of the conductance of graphite through the relation σ full ≈ 10 −2 σ c graph , because only 1 out of 60 atoms in a fullerene molecule is involved in creating a path of conductance between electrodes and the ratio of fullerene to graphite density is ρ full / ρ graph = 0.74. Total resistivity of fullerene is determined by resistivites of individual fullerene balls. Doping, like in graphite, causes an increase in the conductivity of intercalated Me x C 60 for low value of x.

The thickness dependence of anisotropic magnetoresistance in a Co 35Pd 65 film

Co 35Pd 65 films have been prepared by the vapor deposition method. The thickness of the films varies from t = 150 to 2500 A ̊ . We have measured the electrical resistivity ρ, anisotropic magnetoresistance Δρ/ ρ 0, and saturation magnetization M s of these films at room temperature. The crystal structure and grain size D of the films were also characterized. Our interest is in the thickness dependence of these quantities. Using the various scattering mechanisms, the surface, bulk (impurity and phonon), and grain-boundary terms of the total resistivity and anisotropic magnetoresistance could be separated and estimated quantitatively. We found that, for Co 35Pd 65 films, although grain-boundary scattering makes a significant contribution to the total electrical resistivity ρ over the whole thickness range, it has little effect on the (absolute) anisotropic magneto-resistivity Δρ, so long as t > 500 A ̊ .

Computer simulation of series resistance of an SDR silicon IMPATT diode in the X band

Spatial variation of negative resistivity has been studied through computer simulation by considering experimental bias current and the device capacitance of single drift (n+ np+) silicon IMPATT diode operating in the X band. From the total device negative resistivity and reactivity, device negative conductance, susceptance and the diode series resistance have been calculated. Computed values of series resistance nearly fit with the experimental results. The present analysis also gives an idea about the load conductance of the circuit in the small signal condition.

Giant magnetoresistance: Comparison of band-structure and interfacial-roughness contributions.

A real-space Green-function technique, in which the scattering is treated exactly, is used in a single-band tight-binding model to evaluate the Ohmic resistivities and the giant magnetoresistance in trilayer systems. The model includes (i) spin dependence of the density of states and Fermi velocity in the magnetic material, giving a qualitative representation of Co/Cu and Fe/Cr systems; (ii) spin-independent bulk disorder, representing intrinsic defects in real systems; (iii) chemically sharp interfacial roughness. It is found that for parameters that produce realistic total resistivities, the spin-polarized band structure in conjunction with the spin-independent bulk disorder gives the main contribution to the giant magnetoresistance. The chemically sharp interfacial roughness enhances the effect. Its contribution becomes significant in the limit of sufficiently dense roughness steps, sufficiently weak bulk disorder, and sufficiently thin magnetic layers.

Short-range order kinetics in α-AgZn for various states of post-deformation defect annealing after cold-rolling

Kinetics of short-range ordering (SRO) in Ag with 21, 23 and 28 at% Zn is investigated by residual resistometry during isochronal and isothermal heat treatment for different states of post-deformation defect annealing after cold-rolling to about 30 and 60% thickness reduction. Resistivity changes due to pure ordering can be separated from the as-measured total resistivity change which includes defect annealing. Although the initial state of SRO of the as-rolled material can be estimated to be comparably low, for as-rolled and partially annealed states by appropriate thermal treatment evolution of SRO is achieved which corresponds quite well to that of recrystallized samples. It is observed, however, that quenched-in surplus vacancies contribute considerably to the ordering process for the recrystallized state and that this contribution is still increased by the grain growth during the final stage of annealing. It therefore turns out that SRO-kinetics under equilibrium vacancy conditions can be better observed in a state of post-deformation annealing, for which deformation induced point defects are annealed-out, but a relatively high dislocation density is still present to act as a vacancy sink.

Microwave sintering of zirconia-yttria electrolytes and measurement of their ionic conductivity

Yttria-zirconia electrolytes of 3 and 8 mol% Y 2O 3 nominal content have been prepared by sintering in a microwave furnace under several different conditions to obtain crack-free high density specimens. The ionic conductivity of both compositions has been investigated with a four-probe DC technique as a function of temperature over the 400 °–1000 °C range and as a function of time at the normal fuel cell operating temperature of 1000 °C. Impedance spectroscopy has been used to separate the grain boundary contribution to the total resistivity. The results have been compared with conventionally sintered (radiant heat) materials.

The effects of overlayer thicknesses on the electrical resistivity of polycrystalline Cu/Cr double-layered thin films

The total electrical resistivity of the Cu/Cr double-layered thin films, the copper base layers of which have thicknesses of 13.0-26.0 nm, is studied as a function of the temperature in the interval 100-300 K and overlayer thickness. The temperature dependence of the electrical resistivity show two types of behaviour. The temperature-dependent resistivity of the Cu/Cr films, the Cr overlayers of which have thicknesses of 1.5 and 2 nm, shows a linear variation, but the variation in the resistivity of the Cu/Cr films, the Cr overlayers of which have thicknesses greater than 7.5 nm, with the temperature exhibits an oscillatory behaviour over the whole temperature range from 100 to 300 K. Our analysis has shown that the observed resistivity increase is caused by an increased surface scattering of the Cu/Cr-I double-layered film in comparison with those of the uncovered copper base films. The interface scattering cannot be the cause of the excess resistivity of both Cu/Cr-I and Cu/Cr-II double-layered films.

Analytical Solutions for the Total Field Magnetometric Resistivity (TFMMR) Technique

The analytical solutions for the TFMMR parameter of the Sub-Audio Magnetics technique are important as a tool in indirect interpretation of the field data, in assessing which subsurfact structures will produce measurable signals, and for designing optimal field survey configurations. In this paper, we investigate the theoretical TFMMR anomalies that would be observed over simple model structures such as an homogeneous isotropic and anisotropic earth, vertical contacts or faults, inclined contacts, thick dikes and outcropping hemispherical-depression models. For each model, comparisons are made with the MMR method. In general, the magnitude and shape of the TFMMR signal varies with changes in the geomagnetic field. For 2-D structures, in particular, such as faults and dikes, the TFMMR and MMR methods produce signals of similar quality. In cases where subsurface conductive bodies are striking paralel to the line joining the electrodes, our results show that the MMR method produces relatively small signals whereas the SAM signal is still quite measurable. We have also shown that the TFMMR type responses is sensitive to the geomagnetic field rather than geological strike directions as MMR is. TFMMR measurements have higher resolution, higher data acquisition rate, lower field costs and higher amplitudes for certain subsurface geometries than MMR.

Anisotropies of the electrical resistivity and Hall effect in UAsSe

We show that anisotropy of the resistivity in UAsSe proves that its total resistivity contains both an isotropic spin disorder component (controlled by RKKY exchange interaction) and an anisotropic single impurity Kondo-like (TK = 50 K) component. They are present in both paramagnetic and ordered states. This uniaxial and collinear ferromagnet (below 113 K) exhibits high magnetocrystalline anisotropy. Examination of the Hall effect in the paramagnetic phase (up to 430 K) showed that the isotropic normal Hall coefficient R0 = −8.8×10−4cm3 C−1 (0.47 e− fu−1 in the single band model) is accompanied by a highly anisotropic spontaneous Hall coefficient. This is equal to 0.78 and 3.0 cm3 C−1 for Rsac and Rsab (magnetic field along the c or b axis) respectively.

Simulation of the resistivity of heavily cold worked Cu-20 wt.%Nb wires

Fiber reinforced in-situ metal matrix composites (MMCs) consisting of Cu and 20 wt.% Nb were produced by large strain wire drawing. The microstructure of the composite wires was investigated by use of optical and scanning electron microscopy. The resistivity of the MMC wires was examined as a function of strain and temperature and compared to that of pure Cu and Nb. A strong degradation of the electrical conductivity of the MMC after heavy deformation was experimentally observed. In this strain regime the fibre diameters and spacings are comparable with the mean free path of the conduction electrons. Corresponding simulations, accounting for inelastic scattering of conduction electrons at internal phase boundaries as primary and scattering at dislocations as secondary contribution to the total resistivity of the composite, were carried out.

Magnetoresistance Effects in Spin-Valve Multilayers Including Three Ni–Fe–Co Layers

Magnetoresistance effects have been investigated in spin-valve multilayers including three Ni–Fe–Co layers. The layered structure of the spin-valve multilayers are [AF1/Ni–Fe–Co/Cu/Ni–Fe–Co/Cu/Ni–Fe–Co/AF2/Si], where AF1 and AF2 are antiferromagnetic layers. The spin-valve multilayers including three Ni–Fe–Co layers show magneto-resistance ratios Δρ/ρ of 3.7% and 5.6% at around 1.5 kA/m. These values are higher than the 2.2% of a spin-valve sandwich that includes two Ni–Fe–Co layers, [Ni–Fe–Co/Cu/Ni–Fe–Co/Fe–Mn/Cu/Hf/Si]. It is found that the total resistivity changes (Δρ) of the spin-valve multilayers including three Ni–Fe–Co layers are twice that for the spin-valve sandwich that includes two Ni–Fe–Co layers. This is due to the fact that the number of Ni–Fe–Co/Cu interfaces in the spin-valve multilayers that include three Ni–Fe–Co layers is double that in the spin-valve sandwich that includes two Ni–Fe–Co layers.

Irreversible conductivity change of Ca β[formula omitted]alumina at high temperature

Polycrystalline Caβ-̋alumina was produced in a relatively gentle way by increasing stepwise the Ca content of (Na, Ca) β-̋ alumina in suitable mixtures of molten salts (Ca(NO3)2 and CaCl2). When determining the conductivity of Ca β-̋alumina as a function of temperature by the four-probe technique, an irreversible decrease of the conductivity was observed in subsequent measurements if the temperature during the first conductivity measurement was extended beyond 600°C. Impedance measurements on such samples demonstrated that the conductivity decrease was due to an increase of the contribution of the grain boundary resistivity to the total specific resistivity.

Microstructural designs and electrical properties of Y2O3-doped ZrO2s

The changes of electrical resistivity of Y2O3-doped ZrO2s with microstructural modifications were investigated. Using ZrO2 powders containing 3 mol% Y2O3 and 8 mol% Y2O3, seven kinds of microstructures were designed by various preparing techniques; two single phase specimens and five mixed phase specimens. The contributions of structural components, i.e., bulk and boundaries, and apparent total resistivities were identified by impedance analysis method. At low temperature region, grain and/or phase boundaries play an important role in electrical resistivity.

A scanning tunnelling microscopy study of thin gold films evaporated on silicon

Gold films evaporated on silicon were studied by scanning tunnelling microscopy as a function of the thickness of deposited material (in the range 10–300 nm), evaporation rate (5, 20, 50 Å s −1) and post-deposition anneal temperature (100, 300, 500°C). A wide ranging distribution of topographical features was observed on all the films. However, from statistical extrapolation a number of observations are made regarding surface grains lateral spread and height evolution with varying deposition parameters and anneal temperature. Surface grains size were found to increase on average with increasing evaporation rates and film thickness. Annealing resulted in larger grain sizes but smaller height thus reducing the actual roughness of the surface. Electrical measurements were also performed on the films using a four-point probe instrument in order to monitor the resistivity of the films. The results are related to the surface roughness, and by implication to the defect structure of the film. The resistivity of the films were found to decrease with increasing evaporation rate and anneal temperature and the contribution of scattering at grains boundaries to the total resistivity of the films was found to decrease with increasing film thickness.

Frequency-field dependence of total electrical resistivity of magnetically-soft conductors

The frequency-field dependence of total electrical resistivity is studied for thin magnetically-soft alloy conductors with a crystalline and amorphous structures, and it is compared with the giant inagnetoresistance effect observed for superlattices.