Temperature dependences of electrical resistivity and magnetic susceptibility in (SN)x single crystal

Pauli-paramagnetism is observed in high quality (SN)x single crystal. Density of state at Fermi level is estimated to be 0.14 ± 0.06 states/(eV spin molecule) from the observed magnetic susceptibility. Curie Weiss like laws are observed in γ-ray irradiated and low quality (SN)x crystals which show the resistivity minimum at 30–40 K. The resistivity minimum is discussed in terms of carrier scattering by localized paramagnetic centers.     

Raman scattering in brominated (SN)x crystals

Detailed Raman scattering data on brominated (SN)_x crystals ranging in composition from (SNBr_0.27)_x to (SNBr_0.55)_x, and preliminary Raman data on [SN(ICI)_0.125]_x are discussed. The investigation involved a study under various conditions of temperature, pressure and levels of bromination, of the two primary Raman lines at 154 and 230 cm^-1 in brominated (SN)_x, which are polarized along the polymer axis direction. The analysis of the data is consistent with a model in which bromine enters the interfibrillar regions as Br^-₃ and the (SN)_x lattice as Br₂. Infrared data is also presented showing an appreciable decrease in intensity of the SN modes at 995 and 670 cm^-1 on bromination.     

Electrical resistance of epitaxial crystalline films of (SN)x

The electrical resistance of oriented (SN)_x-films has been measured from 300 to 0.07 K. The results indicate a finite intrinsic conductivity in the direction perpendicular to the chains, supporting that (SN)_x is a strong anisotropic conductor rather than a quasi-one-dimensional system.     

Anisotropy of interchain interaction in polymeric (SN)x crystals

The technique of polarized reflection microspectroscopy was used to study anisotropy of polymeric sulfur nitride (SN)_x in plasma edge region. The spectra taken from different faces of single crystals indicate the presence of strong anisotropy of interchain interaction due to orientation of the π-electron orbitals and suggest two-dimensional metallic behavior of the π-electron system in (SN)_x.     

Electric and magnetic properties of the system between Cr3S4 and VCr2S4

The electrical resistivity and magnetization of V_xCr_3?xS₄ (x = 0.0 - 1.0) have been measured. Weak ferromagnetic moments are observed at low temperatures for x ≠ 0.0. Curie temperatures are determined from magnetization curves and resistivity anomalies.     

Nuclear relaxation of the water protons included in (SN)x crystals

The temperature and frequency dependences of the proton spin-lattice relaxation time in H₂O included in (SN)_x crystals have been measured and discussed. It is suggested that a significant amount of water is adsorbed on the surface of the (SN)_x fibers.     

Electrical resistivity of GdInxSn3-x below TN

Electrical resistivity measurements are used to determine that GdIn_xSn_3-x samples are antiferromagnetic with T_N varying linearly from 20 K for GdSn₃ (x = 0) to 46 K for GdIn₃ (x = 3). Pure GdSn₃ and GdIn₃ samples show Fisher-Langer-like resistivity behavior while intermediate concentration samples evolve to Suezaki-Mori type behavior. It is shown that this behavior can be qualitatively understood in terms of varying the relative strenght of the spin fluctuation and superzone energy gap contributions to the resistivity which appear in the Suezaki-Mori theory of the resistivity of an antiferromagnetic metal.     

Electrical properties and spin fluctuations studies of Y(Co1−xNix)2 compounds

Synthesis by arc melting, the structural and the electric properties of Y(Co_1−xNi_x)₂ alloys were studied by X-ray diffraction (XRD) and four probe dc electrical measurements. XRD analysis (300 K) shows that all samples crystallize in a cubic MgCu₂-type structure. The lattice parameters linearly decrease with Ni content. Electrical resistivity for the Y(Co_1−xNi_x)₂ intermetallic series was measured in a temperature range of 15-1100 K. The parameters involved in the dependence of resistivity on temperature were determined. Residual, phonon and spin fluctuations resistivity were separated from electrical resistivity using both the Matthiesen formula and the Bloch-Gruneisen formula. The spin fluctuations resistivity of the Y(Co_1−xNi_x)₂ series are compared to the mean square amplitudes of spin fluctuations previously calculated by the Linear Muffin Tin Orbital-Tight Binding Approach method for these series in the literature. The contribution of spin fluctuations to total resistivity ρ_sf is proportional to T² at low temperatures. The proportionality parameter strongly reduces across the Y(Co_1−xNi_x)₂ series.     

Electrical resistivity of microinhomogeneous PdMnxFe1−x alloys

The electronic band-structure calculations of the PdFe ferromagnet and the PdMn antiferromagnet performed in this work permit one to conclude that the specific features of the electrical resistivity observed in the ternary PdMn_xFe_1−x alloy system [the deviation from the Nordheim-Kurnakov rule ρ₀(x)∼x(1−x), which is accompanied by a high maximum of residual resistivity (not typical of metals) ρ ₀ ^m ∼220 μΩ cm at x _C∼0.8 and a negative temperature resistivity coefficient in the interval 0.5≤x≤1] are due to the microinhomogeneous (multiphase) state of the alloys and a variation in the band-gap parameter d spectrum caused by antiferromagnetic ordering of a PdMn-type phase. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 2, 2002, pp. 193–197. Original Russian Text Copyright ? 2002 by Kourov, Korotin, Volkova.     

Electrical properties of (SN)x films

The temperature dependence of the thermopower S and the conductivity σ of (SN)_x films has been investigated as a function of the substrate temperature during film deposition T_s. In contrast to the transport properties of SN_x films previously reported, films made with high T_s have metallic-like transport properties approaching those of (SN)_x crystals. For low substrate temperatures σ and S are found to increase strongly with rising temperature and thermopower values up to 0.9 mV/K are observed. This conduction behavior is explained by a heterogeneous model with areas having different electronic gaps. Annealing as well as decomposition effects suggest that the gap width is correlated to the (SN)_x chain length. No evidence was seen for superconductivity in these films.     

High-temperature electronic transport properties of La1−xCaxMnO3+δ (0.0?x?1.0)

La_1−xCa_xMnO_3+δ (0.0?x?1.0) samples were prepared and their resistivity and Seebeck coefficients were measured in the high-temperature range. Ca doping changes the ratio of Mn³⁺/Mn⁴⁺ and influences the electronic transport behavior markedly. With the increase of Ca concentration, the samples change from a p-type semiconductor to an n-type one and Seebeck coefficient becomes increasingly negative. Low doping (x=0.2) and high doping (x=0.8) induces the drop of the resistivity compared with undoped LaMnO_3+δ and CaMnO_3+δ samples due to the rise of carrier concentration. However, the resistivity of moderate-doped samples (x=0.4, 0.6) is larger than low- and high-doped samples because dopant scattering decreases carrier mobility.     

Theory of plasmon excitations in (SN)x

The anomalous anisotropy and dispersion of plasmons in polymeric sulfur nitride (SN)_x are explained within a model of an electron gas with an anisotropic effective mass ratio. Calculations in the random phase approximation yield very good agreement with the electron loss data. Exchange corrections for the model are shown to be small for systems of the (SN)_x type which exhibit reduced dimensionality.     

Electrical resistivity of alkali metal doped manganites LaxAyMnwO3 (A = Na,K, Rb): Role of electron–phonon,electron–electron and electron–magnon interactions

The electrical resistivity behaviour of alkali metal (Na, K, Rb) substitutions at La site in La_xA_yMn_wO₃ (A = Na, K, Rb) manganites is studied caused by electron–phonon, electron–electron and electron–magnon scattering. Substitutions affect average mass and ionic radii of A-site and hence resulting lattice and optical phonon softening. Estimated resistivity compared with reported metallic resistivity, accordingly ρ_diff. = [ρ_exp ? {ρ₀ + ρ_e–ph (=ρ_ac + ρ_op)}], infers electron–electron and electron–magnon dependence over most of the temperature range. Electron–phonon contribution indicates that alkali metal K doping provoked larger lattice distortion, while electron–electron interaction is more dominating process for Na and Rb doped compound favouring motion of excess charge carrier. Semiconducting nature is discussed with variable range hopping and small polaron conduction model. The change in activation energies and the density of states at the Fermi-level is consistently explained by cationic disorder and Mn valence.     

Searching for key parameter for determining Tc in Fe-based superconductors: Study of P/As substitution in RFe(P,As)(O,F) [R=La and Nd]

We have investigated the relation between the temperature-dependence of resistivity and superconducting transition temperature T_c in RFeP_1−xAs_xO_0.90F_0.10 (x=0-1.0) (R=La and Nd). In contrast to the linear change of the crystal structure with increasing x, the temperature dependence of resistivity and T_c show non-monotonous x-dependence. When the As concentration x is increased, the temperature-dependence of resistivity changes from T² to T-linear, and T_c distinctly increases in all the La compounds and the Nd ones with x<0.60. The results indicate that the substitution of As for P induces the spin fluctuation and resultantly enhances T_c. On the other hand, we could not find any relation between the temperature-dependence of resistivity and T_c in the Nd samples with x>0.60. This may suggest the existence of other parameters for determining T_c besides the antiferromagnetic correlation in this system.     

Magnetic susceptibility and electrical resistivity of CexY1−xAl2

The magnetic susceptibility and the electrical resistivity have been measured for Ce_xY_1−xAl₂ (x = 0, 0.05, 0.15, 0.25) between 4.2°K and 300°K. _x3kT vanishes at low temperature. We find a minimum in resistivity at 60°K (x = 5) and 68°K (x = 0.25).     

The interplay of superconductivity and localization in Nd2−xCexCuO4+δ single crystal films

The influence of nonstoichiometric disorder on the in-plane resistivity and SC-transition has been investigated for Nd_2−xCe_xCuO_4+δ single crystal films (x=0.15 and 0.18). It is shown that with increasing of δ the in-plane normal state resistivity increases (the mean free path diminishes) and SC-transition temperature decreases with essential broadening of the transition region. The observed evolution from homogeneous metallic (and superconducting) Nd_2−xCe_xCuO_4+δ system to inhomogeneous dielectric one is described as Anderson-type disorder-induced transition in a two-dimensional electron system.     

Effect of Si/Ge ratio on resistivity and thermopower in Gd5SixGe4−x magnetocaloric compounds

The effect of Si/Ge ratio on resistivity and thermopower behavior has been investigated in the magnetocaloric ferromagnetic Gd₅Si_xGe_4−x compounds with x=1.7-2.3. Microstructural studies reveal the presence of Gd₅(Si,Ge)₄-matrix phase (5:4-type) along with traces of secondary phases (5:5 or 5:3-type). The x=1.7 and 2.0 samples display the presence of a first order structural transition from orthorhombic to monoclinic phase followed by a magnetic transition of the monoclinic phase. The alloys with x=2.2 and 2.3 display only magnetic transitions of the orthorhombic phase. A low temperature feature apparent in the AC susceptibility and resistivity data below 100 K reflects an antiferromagnetic transition of secondary phase(s) present in these compounds. The resistivity behavior study correlates with microstructural studies. A large change in thermopower of −8 μV/K was obtained at the magneto-structural transition for the x=2 compound.     

Hall effect in Al-W thin films

The Hall coefficient, R_H, electrical resistivity, ρ, and temperature coefficient of resistivity, α, of Al_xW_100−x (61≤x≤88) thin films and amorphous-like tungsten films are reported. The Al_xW_100−x films have been prepared by magnetron co-deposition of pure metals onto glass substrate. Films are X-ray amorphous for 63≤x≤86. Amorphous-like tungsten films (x=0) were obtained at sputtering conditions different from those applied for the preparation of Al-W alloys. The R_H value is strongly dependent upon the alloy composition: it changes sign from positive to negative at x≈78, and exhibits a maximum for x≈68 at.%. With the decrease of Al content, ρ steeply increases and exhibits a maximum at x≈80 at.%. The temperature coefficient of the resistivity exhibits large negative values, with a well-defined minimum at x≈80. The Hall coefficient of films with 67≤x≤80 has also been determined at liquid nitrogen temperature, and the values obtained were the same as the room temperature values. Since the value of electrical resistivity of the examined alloys in the temperature interval from 77 to 300 K noticeably changes (10%), a significant anomalous contribution to the Hall effect is thus excluded.     

Hall effect and magnetoresistance of (SN)x films

Hall effect and electrical conductivity have been investigated between 77 K and 300 K and the magnetoresistance at 4.2 K for a number of (SN)_x films deposited at substrate temperatures between — 10 and 50°C. The small magnitude of the Hall mobility (? 1 cm² Vsec^?1 at 300 K) and its activated temperature dependence are interpreted in terms of a heterogenous model for (SN)_x films with thin depletion layers separating highly conductive islands. The hole concentration in these islands (p ≈ 10²¹ cm^?3, the microscopic mobility (μ ≈ 500 cm² Vsec^?1 at 4.2 K) and the temperatures dependence of μ are found to be close to values for (SN)_x crystals.     

Phase separation region in the phase diagram of polycrystalline Pr0.65Ca0.35−xSrxMnO3

We have performed measurements of thermoelectric power, electrical resistivity and DC magnetization in polycrystalline samples of Pr_0.65Ca_0.35−xSr_xMnO₃ with x=0, 0.02, 0.05, 0.10 and 0.20. The system presents an evolution from a charge-ordered manganite at x=0, with an insulating-like resistivity and low magnetization values, towards a ferromagnetic (FM) metallic state for x=0.20. We show that in the intermediate region a strong competition between the FM double-exchange and the localized charge-ordering occurs, inducing the phase segregation of the two competing states in a wide temperature range. We estimate the temperature (T) evolution of the FM phase fraction of the x=0.10 sample and construct a complete T−x phase diagram.