Anomalous Resistivity Behavior Research Articles

Anomalous behavior of the electrical resistivity in the giant magnetocaloric compoundGd5(Si0.1Ge0.9)4

High-resolution electrical resistance R and $dR/dT$ measurements have been done in the (giant magnetocaloric) orthorhombic ${\mathrm{Gd}}_{5}({\mathrm{Si}}_{0.1}{\mathrm{Ge}}_{0.9}{)}_{4}$ compound to study their evolution through more than 50 thermal cycles between 300 K and 10 K. A detailed characterization of R and $dR/dT$ behavior was made near the first-order magnetostructural transition at ${T}_{S}\ensuremath{\sim}80\mathrm{K}$ and the second-order magnetic transition at ${T}_{N}\ensuremath{\sim}128\mathrm{K}.$ Important precursor effects of the magnetostructural transition exist for $0.85<~{T/T}_{S}<~1,$ causing an oscillatory regime in $dR/dT$ below ${T}_{S}.$ The resistance of a ${\mathrm{Gd}}_{5}({\mathrm{Si}}_{0.1}{\mathrm{Ge}}_{0.9}{)}_{4}$ sample initially exhibits a sharp peak at ${T}_{S}$ followed by an abrupt decrease towards a minimum slightly above ${T}_{S},$ but after a certain number of thermal cycles, a new $R(T)$ regime sets in with no peak at ${T}_{S}.$ However, no significant changes occur in $R(T)$ near ${T}_{N}.$ Thermal hysteresis associated with the first-order transition at ${T}_{S}$ shows a slow decrease upon thermal cycling, approaching virtual extinction after $\ensuremath{\sim}50$ thermal cycles. The change of the residual resistance with the number of thermal cycles was also studied and similarly displayed a saturation regime. A simple phenomenological approach is adopted in relation with the $R(T)$ behavior in different thermal cycles, since a rigorous microscopic description is very problematic at the stage due to the complexity of the problems at hand.

Saturation of dephasing and magnetoresistance features in heavily doped polyacetylene

We studied the anomalous behavior of resistivity and magnetoresistance (MR) of polyacetylene (PA) heavily doped with ClO 4 -, FeCl 4 - and iodine at magnetic fields H=0-30 T in the temperature range 500 mK - 300 K. We attributed these anomalies to the low temperature saturation of electron dephasing by two-level systems of a special type (at low H). We demonstrate that the linear negative MR observed at high H indicates that a network of point interfibrillar contacts controls the current transport even in heavily doped PA.

Electrical Characterization of p-Type Pb1−xEuxTe

The transport properties of p-type Pb 1-x Eu x Te epitaxial layers were studied as a function of Eu content, temperature, and magnetic field. The low-temperature hole mobility is drastically reduced when the Eu concentration is increased from 0 to 6%, while the hole concentration remains almost constant. A metal-insulator transition was observed for x ≃ 0.04, which is probably induced by the disorder caused by the introduction of Eu. For temperatures down to 10K, only positive magnetoresistance has been observed at low magnetic fields. An anomalous behavior of the resistivity as a function of temperature has been detected for a Eu content about 5%, which is attributed to the resonance between the localized Eu 4f level and the valence band maximum.

The Effect of Zn-Substitution on the Anomalous Resistance Behavior of La1−xCaxMn1−yZnyO3 Compounds

We have studied the effect of Zn substitution on the temperature dependence of the resistivity and the Curie temperature T p of La1−xCa x Mn1−yZn y O3 system (with x=0, y=0, and x=0.33, 0.00≤y≤0.15) during their pass to the paramagnetic conducting phase. All the specimens show a clear metal-insulator transition passing through the Curie temperature T p . With increasing Zn concentration, T p decreases for La/Ca substitution and also for Zn/Mn substitution with fixed 33 at.% of Ca. T p is found to be slightly decreases for low concentrations of Zn (up to y=0.075) followed by a sharp decrease up to y=0.15. A possible explanation is given. Moreover, the activation energy Ea is calculated in the three different temperature regions characterized in the (ρ-T) curve. Decreasing the temperature below T p can increase the parallel alignment of the Mn spins and, thus decreases the resistivity of the samples. Ea increases with Zn content (up to y=0.075) followed by a sharp decrease. A strong correlation in the behavior of the normal state and residual resistivity as well as T p and Ea with Zn content is reported.

Anomalous behavior of electrical resistivity in glass transition region of a bulk Pd 40Ni 40P 20 metallic glass

The electrical resistivity of a bulk Pd 40Ni 40P 20 metallic glass was measured as a function of temperature. This glass showed a positive slope, dρ/ dT=(1.28±0.03)×10 −4 μΩ m/K, with a residual resistivity ρ 300 of 1.29±0.03 μΩ m at room temperature. Also, the change in the resistivity due to the glass transition was carefully investigated, but, no variation in the neighborhood of glass transition temperature was observed. Bulk glasses Pd 40Cu 3Ni 37P 20 and Pd 43Ni 37P 20 with slightly different composition were also prepared for a comparison. In case of these glasses, the slope, d ρ/d T, varied at the glass transition, i.e. the resistivity decreased after the glass transition for the former and increased for the latter. The slope of the resistivity curve measured for the Pd 40Ni 40P 20 melt was larger than that of the glass. Thus, the extrapolated resistivity to higher temperature did not connect smoothly with the resistivity of the liquid phase.

Electric properties on iodine doped pentacene

Electric conductivity and NMR properties on iodine doped pentacene have been studied below room temperature. It was found that the electric conductivity parallel to the pentacene molecular layer becomes 10 7 times larger than that perpendicular to the molecular layer at room temperature. Moreover, NMR results show that the frequency f dependence of spin-lattice relaxation time T 1 at room temperature obeys the relation (l/T 1 = In f) indicating two-dimensional nature. It was also found that the anomalous behaviour of the electric resistivity is observed at 46 K with a thermal hysteresis of about 5 K. This anomaly was also observed in the spin-lattice relaxation time.

A comparative study of transport properties of composites HTSC + MgTiO 3 and HTSC + NiTiO 3. The effect of paramagnetic NiTiO 3

Bulk composites Y 3/4Lu 1/4Ba 2Cu 3O 7+NiTiO 3 and Y 3/4Lu 1/4Ba 2Cu 3O 7+MgTiO 3 with insulator volume content 7.5% and 15% modelling a network of Superconductor-Insulator-Superconductor (S-I-S) junctions have been prepared. The ρ(T) dependences of composites HTSC+MgTiO 3 are described well by the mechanism of Thermally Activated Phase Slippage (TAPS). The anomalous behavior of resistivity ρ(T) of HTSC+NiTiO 3 composites manifesting as a kink on ρ(T) curves at some temperature T m have been observed. In the temperature range T m<T<T c the dissipation is Ohmic while below T m the CVCs are strongly non-linear. This peculiariy is interpreted as arisen owing to Abrikosov vortices flow.

Electromagnetic and mechanical AC loss of an ITER TF model coil conductor (DP4) under transverse cyclic loading

Energising a coil results in a transverse force on the strands pushing the cable towards one side of the jacket. This load causes a transverse compressive strain in strands and in particular in strand crossover points. Besides this, contact surfaces interfere by micro-sliding resulting in friction and anomalous contact resistance behaviour versus force. Two Central Solenoid Model Coil conductors have been tested previously in a cryogenic press and now the experimental results are presented for the Toroidal Field Model Coil (TFMC) conductor (DP4). The press can transmit a variable (cyclic) force of at least 650 kN/m directly to a cable section of 400 mm at 4.2 K. The magnetisation of the conductor and the interstrand resistance (R/sub c/) between various strands inside the cable can be measured by varying pressure. The force on the cable and the displacement are monitored simultaneously in order to determine the effective cable Young's modulus and the mechanical heat generation due to friction and deformation. The mechanical heat generation, the coupling loss time constant n/spl tau/ and the R/sub c/ of the full-size ITER TFMC conductor have been studied under load up to 40 full loading cycles. The evolution of R/sub c/ is comparable to the behaviour found for the CS Model Coil type of conductors. A significant decrease of the cable coupling current time constant, n/spl tau/ and mechanical heat generation after cyclic loading is found.

Physical properties of Tm monochalcogenides under pressure

The resistivity of TmSe has been measured under pressure up to 8 GPa, below room temperature. At low temperatures below about 10 K, the pressure dependence of the resistivity shows two maxima; one occurring at about 1 GPa where the magnetic phase transition takes place, and the other at about 7 GPa. The resistivity at 7 GPa shows a remarkable temperature dependence, which increases with decreasing temperature rapidly below 8 K. The anomalous behavior in pressure and temperature dependent resistivity in Tm monochalcogenide may be caused by the change in Tm valence under high pressure.

Anomalous transport behavior of La0.825Sr0.175MnO3−δ polycrystalline samples below Curie temperature

The temperature (T) dependencies of resistivity (ρ0) and magnetoresistance (MR) in the range of 100–300 K have been investigated in La0.825Sr0.175MnO3−δ polycrystalline samples with different sintering temperatures TS (1300 °C and 1360 °C). Two peaks on the ρ0(T) curve were found in the sample with the lower value of TS. Inhomogeneity of the spin configuration and multiply-connectedness of ferromagnetic phase is believed to give rise to anomalous behavior of resistivity below the Curie temperature.

Metal-insulator transition below the Curie temperature in layered manganites

In contrast to the traditional viewpoint that a metal-insulator transition (MIT) occurs just at the resistivity peak temperature ${T}_{p},$ we propose that in perovskite manganites with temperature-dependent disorder, ${T}_{\mathrm{MI}}$ at which the MIT occurs may be well below the Curie temperature ${T}_{C}(\ensuremath{\simeq}{T}_{p}).$ At temperatures between ${T}_{\mathrm{MI}}$ and ${T}_{C},$ due to a decrease in localization length upon heating, the resistivity of the localized electrons behaves with metallic temperature dependence. Only above ${T}_{C}$ does the resistivity exhibit semiconductorlike temperature behavior. Such an idea that the MIT occurs below ${T}_{C}$ can account for the anomalous resistivity behavior in the layered manganite crystal ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ with $x=0.3.$

Characterizing and modeling the apparent anomalous behavior of resistivity in Cr–Si–O thin films

The Cr–Si–O material system is of interest for use in thin film resistors. The films are sputter deposited onto conducting substrates from metal-oxide compacts using various reactive gas mixtures. The cermet film compositions range from 50 to 100 vol.% SiO2 as determined from elemental measurements of the Cr, Si and O content. In a wide range of resistivities from 10 to 1014 Ω -cm measured through the film thickness, an apparent anomalous behavior is found as a function of the Cr, Si and O composition. The anomaly can be attributed to a discontinuous variation of resistivity with film composition near 80 vol.% SiO2. The film microstructure is characterized as a distribution of conducting metal–silicide particles within an insulating matrix. The ‘effective medium’ theory is used to predict the variation of conductivity and successfully models the anomalous resistivity behavior.

Anomalous resistance behavior observed across the interface of superconducting YBa 2Cu 3O 7 and ferromagnetic La 0.7Ca 0.3MnO 3

Temperature dependencies of the resistance across the interface of superconducting YBa 2Cu 3O 7 and ferromagnetic La 0.7Ca 0.3MnO 3 were investigated in La 0.7Ca 0.3MnO 3/YBa 2Cu 3O 7 double-layer and cross-strip samples. Anomalous resistance behavior, a relatively large resistance value with a superconducting-like transition, was observed in both samples. In the cross-strip sample the voltage signal changed to extremely large negative values in the temperature region of 170–90 K, which was corresponding to the resistance peak in the LCMO strip. A possible explanation is discussed.

Microstructural and anomalous resistivity behavior of modified ferroelectric Ba6Ti2Nb8O30

The present communication describes the preparation and characterisation of Ba6-3x R2 xTi2Nb8O30 (where x = 0.0 and 0.05, R = La, Pr, Nd, Sm and Gd) Ceramics. Tetragonal symmetry has been noticed from XRD studies. Microstructural studies using SEM revealed, substitution of rare-earth ion in BTN inhibits the grain growth of BTN. DC resistivity measurements in these compositions indicated PTCR anomalous behaviour. This type of behaviour is explained on the basis of Heywang's model. Curie temperature of rare-earth substituted BTN found to decrease from the value of BTN.

Magnetic susceptibility and inelastic electrical resistivity of GdZnxCu1−x alloys

The deviation from the Nordheim-Kurnakov rule and the anomalous behavior of spin-disordered electrical resistivity in quasi-binary GdZn (T C =268 K)-GdCu (T N =142 K) solid solutions is explained in effective medium approximation within percolation theory for the case of three phases, viz., ferro-, antiferro-, and paramagnetic. The strong increase of ρ at zinc concentrations x∼0.45 is attributed to the closeness of the system to the percolation threshold. The phase volumes calculated for the random-distribution case fit well to the concentration dependence of magnetic susceptibility.

STUDY ON THE HIGH-TEMPERATURE RESISTIVITY OF Bi1.6Pb0.4Sr2Ca2Cu3Ox

The effects of heat treatments on the resistivity of BPSCCO-2223 superconductor were studied. The anomalous behavior in high-temperature resistivity was observed. It was shown that upon annealing in N2 at high temperatures, the oxygen escaped not only from Bi-O layer but also from Cu-O layer accompanied with the movement of metal ions. The change in oxygen content and the redistri-bution of oxygen and metal atoms diversified the microstructure of BPSCCO-2223 phase.

Effect of pressure on transport properties of Ni(S 1− xSe x) 2

Resistivity and Hall effect measurements were made on single crystals of NiS 2 and Ni(S 0.9Se 0.1) 2 under high pressure in a temperature range between 4.2 and 300 K. NiS 2 and Ni(S 0.9Se 0.1) 2 show insulator-metal transitions. Anomalous behavior of resistivity corresponding to a para-antiferromagnetic transition was found in the metallic phase. The Hall coefficient and the Hall mobility decrease with increasing pressure. It is suggested that the electronic structure of Ni(S 1− x Se x ) 2 in the insulating phase is modified toward the phase boundary of the insulator-metal transition.

Small-angle neutron scattering of the system Fe 80− xNi xB 12Si 8 in the amorphous state with 0 ⩽ x ⩽ 80: comparison with the evolution of crystallization studied by the controlled Joule effect analysis

The evolution of crystallization of amorphous ribbons has previously been studied by the controlled Joule effect analysis (CJEA) in the system Fe 80− x Ni x B 12Si 8. The sign and magnitude of resistivity changes due to the relaxation depend strongly on the Ni/Fe ratio. The anomalous behavior observed during crystallization was explained by large fluctuations of local environments of Ni and Fe atoms which have a high mobility in these glasses. Depending on x, small amorphous local units with different atomic compositions would be present in the glassy matrix. To confirm these results, the small-angle neutron scattering (SANS) of: these amorphous alloys has been measured at room temperature. A significant contribution to the SANS intensity is observed for all the alloys. The radii of gyration of the scattering particles depend on x and vary between 230 and 300 Å. Except for 50 < x < 65, an interference peak present in the intensity curves confirms the presence of numerous other aggregates for which the radii of gyration are distributed between 65 and 90 Å and their mean distances between 300 and 400 Å. Sizes and distances have been determined with an accuracy equal to ±10% using more than one approximation method. Their rough volume has been evaluated from the normalized intensities assuming spherical form and particular compositions defined from the X-ray patterns. The presence of aggregates in the glasses partially explains the anomalous behavior of resistivity but it is not possible to confirm the real composition of these aggregates for all x-values.

Size dependence of electrical resistivity in 1D-layered nanostructures

The Landauer electrical resistivity R of one-dimensional (1D) layered nanostructures is calculated. The analysis of the logarithm of the resistance as a function of grain size reveals that there is a minimum value of resistivity R min when the grain size takes a value of d c, where d c depends on the barrier height and excess volume of interface. R increases in the region of d cl > d > d c, where d is the grain size, and d cl is another critical value of grain size. The mechanism of the anomalous resistivity behavior is discussed briefly.

Anomalous Behaviour of Resistivity in Aluminium

Anomalous Behaviour of Resistivity in Aluminium