Anomalous Increase In Resistivity Research Articles

Interplay between the Coulomb Interaction and Hybridization in Ca and Anomalous Pressure Dependence of the Resistivity

Increasing external pressure gives rise to s–d electron transfer in calcium that results in the localization of the charge density in the interstices of the crystal structure, i.e., the formation of an electride. The corresponding electronic states are partially filled and localized and, hence, electronic correlations could arise. We have carried out theoretical calculations for the high-pressure phases of Ca taking into account the Coulomb interactions between the electronic states centered on the interstitial site. The results of our calculations and proposed microscopic model showed that the structural phase transition under high pressure is due to an interplay of hybridization and correlation effects. Furthermore, it was found that the Coulomb repulsion can explain the experimentally observed anomalous increase in resistivity of the simple cubic phase of calcium under pressure.

Strong Anisotropic Spin-Orbit Interaction Induced in Graphene by Monolayer WS_{2}.

We demonstrate strong anisotropic spin-orbit interaction (SOI) in graphene induced by monolayer WS_{2}. Direct comparison between graphene-monolayer WS_{2} and graphene-bulk WS_{2} systems in magnetotransport measurements reveals that monolayer transition metal dichalcogenide can induce much stronger SOI than bulk. Detailed theoretical analysis of the weak antilocalization curves gives an estimated spin-orbit energy (E_{so}) higher than 10meV. The symmetry of the induced SOI is also discussed, and the dominant z→-z symmetric SOI can only explain the experimental results. Spin relaxation by the Elliot-Yafet mechanism and anomalous resistance increase with temperature close to the Dirac point indicates Kane-Mele SOI induced in graphene.

Fermi Surface with Dirac Fermions in CaFeAsF Determined via Quantum Oscillation Measurements

Despite the fact that 1111-type iron arsenides hold the record transition temperature of iron-based superconductors, their electronic structures have not been studied much because of the lack of high-quality single crystals. In this study, we completely determine the Fermi surface in the antiferromagnetic state of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum oscillation measurements and band-structure calculations. The determined Fermi surface consists of a symmetry-related pair of Dirac electron cylinders and a normal hole cylinder. From analyses of quantum-oscillation phases, we demonstrate that the electron cylinders carry a nontrivial Berry phase $\pi$. The carrier density is of the order of 10$^{-3}$ per Fe. This unusual metallic state with the extremely small carrier density is a consequence of the previously discussed topological feature of the band structure which prevents the antiferromagnetic gap from being a full gap. We also report a nearly linear-in-$B$ magnetoresistance and an anomalous resistivity increase above about 30 T for $B \parallel c$, the latter of which is likely related to the quantum limit of the electron orbit. Intriguingly, the electrical resistivity exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal phase ($T >$ 118 K), which may suggest an incoherent state. Our study provides a detailed knowledge of the Fermi surface in the antiferromagnetic state of 1111 parent compounds and moreover opens up a new possibility to explore Dirac-fermion physics in those compounds.

The structure, magnetism and electronic transport properties of Mn3Sn1-xZnxC(x=0, 0.1, 0.2, 0.3, 0.4, 0.5)

The structure, magnetic and electronic transport properties of the compounds Mn3Sn1-xZnxC (0 ≤ x ≤ 0.5) are investigated. The studies have shown that Zn-doping in the anti-perovskite structure Mn3SnC reduces the cell parameter, but the compounds Mn3Sn1-xZnxC remain cubic anti-perovskite structure. When the temperature is reduced, the magnetization curve changes from PM-FM for Mn3SnC and Mn3Sn0.9Zn0.1C into PM-FM-AFM for Mn3Sn1-xZnxC(x ≥ 0.2). With the increase of doping amount x, both the Tc and the TT reduce, but when x = 0.5, they are raised. In addition, the magnetization of Mn3Sn1-xZnxC is reduced as the doping amount increases. For Mn3Sn1-xZnxC(x = 0, 0.1, 0.2,0.3, 0.4, 0.5) compounds, there exists an anomalous increase in resistivity at a certain temperature that is in agreement with their magnetic transition temperature, and doping Zn in Mn3SnC reduces the resistivity of Mn3SnC.

An approach to estimate gas hydrate saturation from 3-D heterogeneous resistivity model: A study from Krishna-Godavari basin, Eastern Indian offshore

A method is proposed to estimate gas hydrate saturation from three dimensional (3-D) heterogeneous model of resistivity simulated using resistivity log. Pure gas hydrates are highly resistive compared to the host sediments, and their presence in the pore space of sediments increase the resistivity of the formation. The anomalous increase of resistivity is used as a proxy for the delineation of gas hydrates using the resistivity log. A 3-D heterogeneous resistivity model has been constructed from one dimensional resistivity log in Krishna Godavari (KG) basin, eastern Indian offshore. The simulated model contains all small scale variation in resistivity of the reservoir and maintains all properties associated with covariance, like root mean square fluctuation, characteristic scales and fractal dimension of the observed log. We have estimated volumetric hydrate saturation using the three dimensional simulated model. The porosity used for estimating hydrate saturation is calculated from the simulated density field generated using the observed density log. Estimated average gas hydrate saturation is about 9.84% of the pore volume over a 1000 m × 1000 m x 131 m cubic meters area.

Effect of pressure and high magnetic field on phase transitions and magnetic properties of Ni1.92Mn1.56Sn0.52 and Ni2MnSn Heusler compounds

Complex study of magnetic, magnetocaloric and structural properties of the Ni2MnSn and Ni1.92Mn1.56Sn0.52 compounds was performed. The stoichiometric single-crystal of Ni2MnSn was prepared by Czochralski method. The remarkable pressure effect on the martensitic magnetization and the martensite-austenite transition temperature TM–A was observed in the Ni1.92Mn1.56Sn0.52 compound. The coefficient dTM–A/dp reached value of 18 K/GPa. The already low value of martensite magnetization of Ni1.92Mn1.56Sn0.52 was further substantially decreased by external pressure, in contrast with pressure almost insensitive magnetization of the stoichiometric Ni2MnSn single-crystal. The pulse magnetic field of 58 T invoked the structural transition at temperature 180 K that is of about 100 K below TM–A of Ni1.92Mn1.56Sn0.52 at zero field. An anomalous increase of resistivity of the compound has been observed at temperature range below TM–A, however, it does not copy the sharp change of magnetization at TM–A. The obtained results indicate the important role of interatomic distances on the magnetic ordering and electronic structure of the studied Heusler alloys and are in agreement with the Jahn-Teller mechanism of the martensitic transition in these compounds.

The magnetism and electronic transport properties of Mn3Sn1−xSixC

The lattice, magnetic and electronic transport properties of the compounds Mn3Sn1−xSixC (0≤x≤0.4) are investigated. The results have shown that Si-doping in the antiperovskite Mn3SnC induces the decrease of the nearest neighbouring Mn–Mn bond distance of Mn3Sn1−xSixC, and the magnetic structure transforms from ferrimagnetic to antiferromagnetic when x≥0.2. With the increase of Si, the Neel temperature TN rises. The TN of Mn3Sn1−xSixC(x=0.2, 0.3, 0.4) are 217K, 257K and 290K, respectively. However, the magnetovolume effect is quenched. In Mn3SnC and Mn3Sn1−xSixC (x=0.2, 0.3, 0.4) compounds, there exists an anomalous increase in resistivity at a certain temperature that coincides well with their Curie temperature TC or Neel temperature TN. The temperature dependence of the resistivity of Mn3Sn1−xSixC (x=0, 0.2, 0.3, 0.4) exhibits semiconducting-like behavior at low temperature and metallic-like behavior at high temperature.

Surface Morphology and Electrical Properties of ZnO:Ga Films Formed by Magnetron Sputtering

In a previous study, it was found that the resistivity of ZnO:Ga films sputtered-deposited at 250 °C initially decreased with increasing film thickness up to 200 nm, but then began to increase. In the present study, the cause of this anomalous increase in resistivity was investigated, and was found to be related to an increase in the porosity of thicker films. For the film deposited at a nominal substrate temperature of 250 °C, this was the result of surface agglomeration due to unintentional substrate heating to about 290 °C caused by plasma irradiation during the deposition process. On the other hand, no such agglomeration was observed for undoped ZnO films, even when heated to 410 °C, indicating that the Ga doping plays a crucial role in the agglomeration process.

Possible high-pressure orbital quantum criticality and an emergent resistive phase in PbRuO3

The orbital ordering transition in the metallic perovskite PbRuO${}_{3}$ is suppressed from 90 K at ambient pressure towards zero temperature at 50 kbar, where non-Fermi liquid resistivity with a temperature exponent $n$ $=$ 1.6 is observed. This evidences a possible quantum critical point brought about by orbital fluctuations, rather than spin fluctuations as observed in Sr${}_{3}$Ru${}_{2}$O${}_{7}$ and heavy fermion conductors. An anomalous increase of resistivity is observed at pressures above \ensuremath{\sim}100 kbar, and a transition to a more resistive, possibly semiconducting, phase is observed at 300 kbar and ambient temperature.

(Ba1+xTiO3)–(Bi0.5Na0.5TiO3) Lead‐Free, Positive Temperature Coefficient of Resistivity Ceramics: PTC Behavior and Atomic Level Microstructures

Positive temperature coefficient of resistivity (PTCR) ceramics of 0.912(Ba1+xTiO3)–0.088(Bi0.5Na0.5TiO3) (BT–BNT) (x = −0.03 to 0.03) were prepared using the mixed oxide route and sintered at 1340°C for 4 h. Products were predominantly single phase with a tetragonal structure and grains in 2–6 μm size containing 90° ferroelectric domains. Samples with Ti/Ba > 1 contained second‐phase Ba6Ti17O40. HRTEM and aberration‐corrected Z‐contrast high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) suggested that the dopants, Bi and Na, occupy the Ba site of the perovskite lattice, and revealed the presence of dissociated dislocations in x = −0.03 and x = 0.00 materials. The interval between two partial dislocations was 1.9–3.4 nm, yielding stacking fault energies of 363–649 mJ/m2. The PTCR behavior of the ceramics increased with Ti/Ba content, reaching a maximum of six decades change in resistivity for x = −0.03. The anomalous increase in resistivity depends critically on stoichiometry, increasing with the Ti/Ba ratio; this in turn is directly correlated with an increase in the amount of second‐phase Ba6Ti17O40, an increase in the stacking fault energy, and an increase in the tilt angle of the grain boundaries.

Temperature and time dependence of electrical resistivity in an anisotropically conductive polymer composite with in situ conductive microfibrils

AbstractAn anisotropically conductive polymer composite (ACPC) based on conductive carbon black (CB) and binary polymer blend of polyethylene (PE) and polyethylene terephthalate (PET) was successfully fabricated under shear and elongational flow fields. The PET phase formed in situ the aligned conductive microfibrils whose surfaces were coated by CB particles. This ACPC material exhibited a strong electrical anisotropy within a broad temperature range. When the ACPC samples were subjected to isothermal treatment (IT), they showed anomalous variations of the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects. The PTC intensity was attenuated gradually with the increase of the IT time, and the NTC intensity was nearly eliminated after IT of 8 or 16 h. Beyond 16 h, the resistivity in the NTC region rose anomalously with the temperature after the elimination of NTC effect, which was the result of much transformation from the potential pathways to the intrinsic pathways due to the disordering of oriented conductive microfibrils. When the amount of potential pathways was very small, the effect of the intrinsic pathway separation surmounts that of the potential pathways, leading to the anomalous resistivity increase in the NTC region. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Anomalous Increase in the Resistivity of n‐Doped BaTiO3‐Based Ceramics with Pressure Observed at Room Temperature

In this article, the observation of a large anomalous increase in room temperature resistivity with pressure following the pressure‐induced ferroelectric‐paraelectric phase transition in n‐doped BaTiO3‐based ceramics is reported. It is well known that the thermally induced phase transition in these ceramics is accompanied by an anomalous rise in resistivity, an effect referred to as the positive temperature coefficient of resistance. This phenomenon is considered as a grain boundary effect which depends on the behavior of the spontaneous polarization and the relative permittivity of the material with temperature. As the pressure dependence of the relative permittivity and spontaneous polarization in pure BaTiO3 crystals resemble their corresponding behavior with temperature, it was tempting to speculate that the pressure‐induced phase transition in n‐doped BaTiO3‐based ceramics may also be accompanied by a similar rise in resistivity. Preliminary investigations confirming such a prediction were carried out. This behavior may be, appropriately, referred to as the positive pressure coefficient of resistance. A model based on the grain boundary effects has also been proposed to explain the results. This large increase of resistivity with applied pressure may be used for pressure sensing applications.

Lattice, magnetic and transport properties in antiperovskite [formula omitted] compounds

The temperature-dependent magnetization, lattice, and transport properties of Mn 3Sn 1− x Ge x C ( 0 ≤ x ≤ 0.5 ) compounds are systematically investigated. The Mn–Mn atomic distance decreases as Ge content is increased, and the transition temperature from ferromagnetic (or ferrimagnetic) to paramagnetic state decreases too. Mn 3SnC has a large magnetovolume effect (MVE). However, Ge-doping in Mn 3SnC gradually reduces the MVE, till the MVE disappears. Whether there is an abnormal lattice change or not, there always exists an anomalous increase in resistivity near the magnetic phase transition point with decreasing temperature.

Anomalous Increase in Resistivity of Boron-Doped Silicon Film after Solid Phase Crystallization

After the furnace annealing of heavily boron-doped Si film below 650 °C, the electronic properties and relating crystallinity of the Si film were evaluated. The sheet resistance obtained using four-point probe decreases as a result of solid phase crystallization (SPC) at 650 °C for 1 h. With efficient solidified activation, the sheet resistance for the Si film of 50 nm thickness with implantation at a B+ dose of 5 ×1015 cm-2 decreased below 900 Ω/□. By extending annealing time for more than 1 h, resistance increased anomalously. The increase in resistance is mainly due to boron redistribution in the Si film and at the Si/SiO2 interface and to boron deactivation as well, as determined from the secondary ion mass spectrometry (SIMS) profile, which is related to a decrease in carrier concentration.

A study on the early-stage decomposition in the Al–Mg–Si–Cu alloy AA6111 by electrical resistivity and three-dimensional atom probe

Electrical resistivity measurements and three-dimensional atom probe (3DAP) analysis were employed to investigate early-stage decomposition of the Al alloy AA6111 in the temperature range 60–180°C where electrical resistivity initially increased with ageing time. 3DAP measurements provided information on the shape, number density and solute content of the precipitates, as well as the solute concentration of the matrix, for the ageing conditions corresponding to the resistivity maxima. Using the 3DAP results, the precipitate size distributions for these ageing conditions were determined in terms of the measured number of solute atoms per precipitate. The number density and the Cu content of the precipitates decreased with increasing temperature, whereas the Mg/Si ratio increased. The size distribution of precipitates at the higher ageing temperatures showed the addition of larger size precipitates to the precipitate population. A modification to Matthiessen's law was employed to describe the anomalous resistivity increase by considering the effect of solutes and precipitates on the resistivity evolution. Using the 3DAP results in analysing the resistivity anomaly, it was found that the decrease in the resistivity maxima with increasing temperature was associated with the decrease in the number density of precipitates and not the scattering power of precipitates. The 3DAP results were further used to provide information on the mechanisms of early-stage decomposition and the temperature dependence of the nucleation rate. From this, the nucleation rate appeared to be controlled by the migration of solute atoms, which was assisted by quenched-in vacancies.

Magnetic, electronic transport and magneto-transport behaviors of Co xFe 1− xMnP compounds

Magnetic, electronic transport and magneto-transport behaviors of Co x Fe 1− x MnP (0.40 ≤ x ≤ 0.75) compounds have been investigated systematically. Co 0.4Fe 0.6MnP is antiferromagnetic below its Néel temperature of 310 K, while an anomalous increase of resistivity occurs with decreasing the temperature from 350 to 190 K, which is attributed to the effect of critical spin fluctuation on resistivity. Increasing Co concentration gives rise to dramatic changes of magnetic, electronic transport and magneto-transport behaviors. With increasing temperature, a magnetic phase transition from an antiferromagnetic state to a ferromagnetic one takes place at about 280, 218 and 180 K for Co 0.55Fe 0.45MnP, Co 0.65Fe 0.35MnP and Co 0.75Fe 0.25MnP, respectively. Moreover, the compounds experience a metal–insulator transition at 26, 29, 35 and 45 K, respectively, for x = 0.40, 0.55, 0.65 and 0.75. Maximum magnetoresistance ratios of −8.1%, −4.7% and −2.9% are observed in the Co 0.75Fe 0.25MnP, Co 0.65Fe 0.35MnP and Co 0.55Fe 0.45MnP compounds at an external magnetic field of 5 T. The mechanisms of magnetoresistance behaviors are interpreted in terms of the suppression of spin fluctuations in the antiferromagnets by the applied fields.

Temporal evolution of neoclassical tearing modes and itseffect on confinement reduction in ASDEX Upgrade

It is shown that (3,2) neoclassical tearing modes (NTMs) inASDEX Upgrade can, under similar external control parameters, occur atsignificantly different values of βN, with the NTMs occurring athigher βN sometimes having a less detrimental impact on theenergy confinement. This is found to be due to a coupling between the(3,2) NTM and a (4,3) mode, which can either occur continuously andclamp the (3,2) amplitude for the time of the existence of the (4,3) oroccur in bursts on a timescale much shorter than the usual resistivetimescale, where each burst leads to a rapid reduction of the (3,2) NTMcalled an amplitude drop. The amplitude drops may be due tostochastization in the presence of two islands of different helicity andsufficient amplitude, which can act as an anomalous increase inresistivity. These observations point towards the possible existence ofa regime where the energy confinement deterioration due to NTMs isacceptable for reactor scale experiments.

Anomalous increase of resistivity against thermal cycling in some of the phase separated manganites

We investigate the effect of repeated thermal cycles in some of the Pr0.5Ca0.5Mn1−xMxO3 (M=Cr, Co, and Ni and x=0.02–0.05) compounds which undergo a spontaneous (H=0 T) insulator to metal transition below the temperature Tp driven by percolation of ferromagnetic clusters in a charge ordered background. The zero field resistivity (ρ) shows an anomalous behavior upon thermal cycling between a high-(TS)- and a low (TF)- temperature limit: While ρ for T≫Tp is unaffected, it increases significantly for T⩽Tp and Tp shifts down each time upon thermal cycling. In contrast, ρ at a given temperature decreases slowly with time. The anomalous increase of resistivity depends upon the ratio of the charge ordered to ferromagnetic phase fraction and decreases with increasing x and the applied magnetic field (H). We also show that a similar effect can be obtained for Pr0.5Ca0.5Mn0.97Al0.03O3 and Pr0.55Ca0.45MnO3 under H=5 T although these compounds do not exhibit insulator–metal transition in zero field. The low field magnetization study on Pr0.5Ca0.5Mn0.98Cr0.02O3 suggests that the ferromagnetic Curie temperature remains unaffected, whereas the ferromagnetic phase fraction decreases with repeated cycles. We suggest that the observed anomaly is caused by an increase of interfacial strain between charge ordered and ferromagnetic phases.

Pressure dependence of superconducting critical temperature ofSr2RuO4

We studied electrical resistivity of single crystals of an oxide superconductor Sr{sub 2}RuO{sub 4} under hydrostatic pressure up to 12 kbar. The midpoint T{sub c} decreases at the rate of 3{percent}/kbar. Anomalous increase of resistivity along the c axis is observed at room temperature with increasing pressure, whereas that in the ab plane decreased with pressure as normally expected. {copyright} {ital 1997} {ital The American Physical Society}

ELECTRON TRANSPORT PROPERTIES IN FINE-PARTICLE FILMS OF Au EVAPORATED ONTO Si NATIVE OXIDE: THERMAL ANNEALING EFFECTS

We investigated electron transport in fine-particle films of Au prepared onto Si native oxide. Electron transport measurements and TEM observations were carried out for as-deposited and after thermal treatment of the films in air. We observed the anomalous resistance increases in as-deposited fine-particle films of Au and obtained α T =4.5. After 150°C thermal treatment in air, however, these anomalous resistance increases in the Au films disappeared and its topography appeared on the TEM images drastically changed into percolative structure. We found that the size of the Au fine particles causes anomalous resistance increase at low temperature.