The resistivity of fine platinum wires

We have measured the resistivity of pure platinum wires ranging in diameter from 16 mil to 0.3 mil in the temperature range 1.2 to 4.2°K, and observed size-dependent deviations from Matthiessen’s rule. The temperature dependent portion of the resistivity is dominated in this temperature range by a term of the formAT ², whereA increases from about 12×10^?12 Ω cm/°K² for the thickest wires to 18×10^?12 Ω cm/°K² for the thinnest ones. There is an additional resistivity contribution which appears to increase more rapidly thanT ⁵, and which also evidences some increase with decreasing wire diameter. The observed deviations from Matthiessen’s rule display temperature and size variations consistent with the theory ofBlatt andSatz, and the magnitude of the deviations can be accounted for by this theory taking into account only that portion of the electrical resistivity produced by electron-phonon scattering. Thus the data are consistent with arguments suggesting that interband electron-electron scattering does not lead to size-dependent deviations from Matthiessen’s rule.     

Spin-disorder resistivity in Ni2Mn(Sn1−xInx) heusler alloys

Electrical resistivity measurements have been performed on Ni₂Mn(Sn_1?xIn_x) Heusler alloys, where x = 0, 0.02, 0.05, 0.10 and 0.15, in the temperature range of 4–300 K. The experimental data clearly show the existence of two distinct kinds of resistivity behaviour, both described by an aTⁿ law, for 7 ? T ? 20 K. Between 170 and 300 K the data are well described by an AT + BT² phenomenological fit, and the results obtained are in good agreement with an interpretation based on electron-phonon and spin-disorder scattering.     

Transport properties of dilute magnetic alloys

The electrical resistivity, thermopower, and the electronic part of the thermal resistivity of dilute magnetic alloys are calculated in the framework of the Suhl-Nagoaka theory. Using Bloomfield's and Hamann's solution of the Nagaoka equations, we derive expressions for the transport quantities in the limitT? ¯ T_K andT?¯ T_K to order (In ¯T _K /T)^?4 where ¯T _K is the Kondo temperature which may depend on the spin independent scattering. We find that the thermopower and deviations from the Wiedemann-Franz law in this limit decrease as ¦In ¯T_K/T¦^?3 if one neglects a trivial temperature dependence of the thermopower due to the electron-phonon interaction.     

Electron-phonon scattering in potassium at high magnetic fields

We have measured the temperature dependence of both the zero-field resistivity and the transverse magnetoresistance of polycrystalline potassium wires (?(300 K)/?(4.2 K)=140 to 6000) in fieldsH?35 kG and at temperaturesT?4.2 K. Our principal findings are: 1) The presence of a large magnetic fieldH=35 kG does not alter the temperature dependence of ? from that observed atH=0; below 4.2 K theT-dependent part of the resistivities,_?T (H=0) and_?T (H=35 kG), fit well to the function exp (?Θ*/T) with the same Θ*=23K. 2) Deviations from Matthiessen's rule are significantly reduced in a strong field so that the magnitude of_?T (H=0) approaches that of_?T (H=35 kG) as sample purity decreases. 3) The slope of the high-field linear magnetoresistance increases slightly (?8%) from 1.5 K to 4.2 K. We attribute the exponential temperature dependence of_?T (H) to the freezing out of electron-phonon umklapp processes as has been shown for the zero-field resistivity. The reduction in deviations from Matthiessen's rule at high fields can be understood within semiclassical theory, but the latter cannot explain the failure of_?T (H) to saturate at high fields. A proposal by Young that electron-phonon umklapp scattering may contribute aT-dependent high-field linear magnetoresistance in potassium is considered.     

Electron heating in a submicron-size n GaAs wire

We have studied electron heating in a submicron-size GaAs wire from 4.2 K to 50 K. We find that the energy relaxation rate for the electrons is of the form τ_E⁻¹ = α + βT_eⁿ where α, β are constants and T_e is the electron temperature. We associate the temperature-independent term with a quasi-elastic surface scattering process in which an electron losses 1% of its energy at each collision. The temperature dependent term may be due to electron-phonon scattering. It is possible to fit the data to 2 < n < 3.     

Electrical transport in La1−x Ca x MnO3 thin films at low temperatures

We report here the low-temperature resistivity of the chemical solution deposited La_1−x Ca _x MnO₃ (x=0.2, 0.3 and 0.33) thin films on LaAlO₃ substrates. The films were post-annealed in atmosphere at 850°C. The low temperature resistivity data has been studied in order to understand the nature of low-temperature conduction processes. The data showed T ² dependence from 60 K to 120 K consistent with the single magnon scattering process. The deviation from this quadratic temperature dependence at low temperatures is attributed to the collapse of the minority spin band. The two-magnon and electron-phonon processes contribute to scattering of carriers in the temperature range above 120 K.     

The electronic properties of chromium borides

Measurements of magnetic susceptibility between 300 and 100°K and of resistivity between 300 and 4.2°K are reported for the five intermediate compounds Cr₂B, Cr₃B₃, CrB, Cr₃B₄ and CrB₂. With the exception of CrB₂ (antiferromagnetic T_N = 88°K) all the compounds were found to be weakly temperature dependent paramagnets. Large, orbital contributions to the susceptibility are proposed for Cr₂B and Cr₅B₃. It is suggested that with the formation of discrete boron networks and the associated change in band structure in the higher borides this contribution diminishes very rapidly. At low temperatures Cr₂B₁ CrB and CrB₂ were all found to have a prominent T² behaviour in ρ(T). At high temperatures the resistivities of CrB and CrB₂ were found to vary linearly with temperature, the resistivity of Cr₂B on the other hand seemed to follow a T(1 ? BT²) law.     

Kinetic effects in manganites La1 − x Ag y MnO3 (y ≤ x)

We have measured the resistivity, magnetoresistance, and thermopower of ceramic manganite samples La_{1 ? x} Ag _y MnO₃ (y ≤ x) doped with silver as functions of temperature (4.2–350 K) and magnetic field (up to 26 kOe). A metal-insulator phase transition is observed in all investigated samples at temperatures close to room temperature. The behavior of the resistivity and thermopower in the high-temperature paramagnetic region is interpreted using the concept of small radius polaron; the activation energy decreases with increasing doping level. The resistivity in the low-temperature ferromagnetic region is approximated by the expression ρ_FM(T) = ρ₀ + AT ² + BT ^4.5 presuming the existence of electron-electron and electron-magnon interactions. A resistivity minimum and a strong magnetoresistive effect are observed at low temperatures. The latter effect is associated with scattering of charge carriers at grain boundaries, which are antiferromagnetically ordered relative to one another. The temperature dependence of thermopower in the magnetically ordered phase is described in the framework of a model taking into account the drag of charge carriers by magnons.     

Magnetotransport of the low-carrier density one-dimensional S=1/2 antiferromagnet Yb4As3

The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb₄As₃ have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT ² with huge and nearly field-independent coefficient A ≈ 3 μΩ cm/K² is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m ₀ and a charge-carrier mean-free path of 215 ? are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed.     

Optical investigation of DyFeO3

Optical absorption spectra of DyFeO₃ have been investigated at 1.2≦T≦4.2 °K, andT=77 °K From the temperature dependent lineshift a Néel temperature ofT _N=(3.8±0.5) °K is deduced for the dysprosium sublattices. The groundstate splitting due to the iron-dysprosium interactions is about 1.5 cm^?1 and due to the dysprosiumdysprosium interactions (5.0±1.4) cm^?1. Zeeman studies give the magnetic moment of the dysprosium ions asμ=(9.2±1.0)μ _B.     

Relaxation effects and evidence for one dimensional ordering in KFeCl3 studied by Mössbauer spectroscopy

Mössbauer measurements of KFeCl₃ over the temperature range 4.2–293°K show a transition to a magnetically ordered phase at T_N ? 18.5°K and evidence for one-dimensional order above T_N. In the region 10–25°K striking relaxation effects appear. An approximate analysis of the quadrupole splitting data was used for the determination of the fine structure of the ⁵D levels below T_N which in turn was used for a theoretical reproduction of the relaxation spectra between 10–25°K.     

Superconducting fluctuations,weak anti-localization and interaction effects in Nb0.53Ti0.47-Ge multilayers

The effect of weak anti-localization, electron interactions and superconducting fluctuations on the transport properties of disorder Nb_0.53Ti_0.47-Ge multilayers were studied. The temperature dependence of the inelastic scattering time was found to be τ_in ∼ T^−1±0.25 and τ_in ∼ T^{−1.75±0.25} for temperatures lower and higher than ∼ 6K, repectively for a sample with thick Ge layers. The effect of the Ge thickness on the prefacter A in the expression R□ ∼ ln T may arise from an interlayer electron-phonon process.     

The impurity resistivity and resistivity minima in AlCr and AlMn alloys

The impurity resistivity of $\text{Al}$Cr between 1.5 and 50°K was determined with a characteristic temperature for the T² variation θ₁=960±40°K. The behaviour of the resistivity minimum both in $\text{Al}$Cr and $\text{Al}$Mn alloys with impurity concentration provides evidence that a T³ phonon resistivity is found also in aluminium with anomalous impurity resistivity.     

Susceptibility — Knight shift correlation and the band structure of VO2

The magnetic susceptibility and⁵¹V Knight shift have been measured in powdered VO₂ from the semiconductor-metal transition temperatureT _t=341°K to 478°K. The fact that both depend linearly on temperature enables the orbital and spin contributions to both quantities to be evaluated. The orbital and spin susceptibilities at 341°K are found to be 1.30±0.07 and 7.49±0.07μemu g^?1, respectively, and the corresponding shifts +0.61±0.04% and ?1.00±0.04%. The existence and magnitude of the orbital term are consistent with the currently accepted two band model of VO₂ aboveT _t.     

Transport properties of Ti3Ir compound at low temperature

Electrical resistivity and magnetoresistivity of Ti₃Ir compound have been measured in the temperature range 2.0 K ≤T ≤ 300 K in absence as well as in presence of magnetic field upto 7.7 T. The low temperature resistivity shows aT ² behaviour whereas the high temperature resistivity shows a linear behaviour. The magnetoresistivity is positive and cannot be explained by simple s-d scattering model. The enhancement of the coefficient A of theT ² term and the deviation from the quadratic field dependence of the resistivity may be due to the anisotropy in the compound. This work has been performed under the grant by the Department of Science and Technology, Govt. of India.     

Effect of spin fluctuations on the electrical resistivity in the pressure-induced metallic phase of 7 at.% Co-doped NiS2

The electrical resistivity measurements were made from 4.2 K to room temperature on 7 at.% Co-doped NiS₂ at pressures from 19 to 71 kbar. T²-dependence of electrical resistivity due to the spin fluctuations was found, and the pressure dependence of its coefficient was determined.     

Low temperature resistivity minimum and its correlation with magnetoresistance in La0.67Ba0.33MnO3 nanomanganites

A systematic investigation of structural, magnetic and electrical properties of nanocrystalline La_0.67Ba_0.33MnO₃ materials, prepared by citrate gel method has been undertaken. The temperature-dependant low-temperature resistivity in ferromagnetic metallic (∼50 K) phase shows upturn behavior and is suppressed with applied magnetic field. The experimental data (<75 K) can be best fitted in the frame work of Kondo-like spin-dependant scattering, electron-electron and electron-phonon interactions. It has been found that upturn behavior may be attributed to weak spin disorder scattering including both spin polarization and grain boundary tunneling effects, which are the characteristic features of extrinsic magnetoresistance behavior, generally found in nanocrystalline manganites. The variation of electrical resistivity with temperature in the high temperature ferromagnetic metallic part of electrical resistivity (75K<T<T_P) has been fitted with grain/domain boundary, electron-electron and magnon scattering mechanisms, while the insulating region (T>T_P) of resistivity data has been explained based on adiabatic small polaron hopping mechanism.     

Electrical behavior of some silver-doped lanthanum-based CMR materials

With a view to understand the structural, magnetic and electrical properties of La_1−xAg_xMnO₃ (x=0.05-0.3), a series of samples were prepared by polyvinyl alcohol (PVA) gel route. It has been found that both the metal-insulator and ferro- to paramagnetic transition temperatures after increasing up to the composition x=0.20, are found to remain constant thereafter. The electrical resistivity vs. temperature plot of the sample x=0.10 is found to exhibit an insulating behavior below 36 K, while the sample, x=0.20 exhibits two peaks, and the observed behavior is explained on the basis of the phase separation model. The low-temperature (T<T_P), electrical resistivity data were analyzed by a theoretical model, ρ=ρ₀+ρ₂T²+ρ_4.5T^4.5, indicating the importance of grain/domain boundary effects, electron-electron and two-magnon scattering processes. The low-temperature resistivity data (T<50 K) were fitted to an equation, which is based on the combined effect of weak localization, electron-electron and electron-phonon scattering.     

Optical investigation of HoFeO3

The absorption spectra of HoFeO₃ were investigated in the near infrared spectral region at temperatures of 1.2, 4.2, 20 and 77 °K respectively. At every temperatureT≦20 °K all the absorption lines show the same splitting which is attributed to the groundstate; this splitting is (7.2±0.5) cm^?1 at 20 °K and decreases to (4.9±0.8) cm^?1 extrapolated to 0 °K. From these splittings the holmium-iron and the holmiumholmium interactions can be deduced. Measurements with an external magnetic field yield a magnetic moment ofμ=(7.6±0.7)μ _B per holmium ion. The moments are directed at angles of ?28° and ?152° with respect to theb-axis.     

Possible manifestation of spin fluctuations in the temperature behavior of the resistivity of Sm<Subscript>1.85</Subscript>Ce<Subscript>0.15</Subscript>CuO<Subscript>4</Subscript> thin films

A pronounced step-like (kink) behavior in the temperature dependence of resistivity ρ(T) is observed in the optimally doped Sm_1.85Ce_0.15CuO₄ thin films around T _sf = 87 K and attributed to the manifestation of strong-spin fluctuations induced by Sm³⁺ moments with the energy ħω_sf = k _B T _sf ≃ 7 meV. The experimental data are found to be well fitted by the residual (zero-temperature) ρ_res, electron-phonon ρ_e-ph(T) = AT, and electron-electron ρ_e-e(T) = BT ² contributions in addition to the fluctuation-induced contribution ρ_sf(T) due to thermal broadening effects (of the width ω_sf). According to the best fit, the plasmon frequency, impurity scattering rate, electron-phonon coupling constant, and Fermi energy are estimated as ω_p = 2.1 meV, τ ₀ ⁻¹ = 9.5 × 10⁻¹⁴ s⁻¹, λ = 1.2, and E _F = 0.2 eV, respectively. The text was submitted by the authors in English.