Nonmetallic Behavior Research Articles

Magnetotransport of Sm2Ir2O7 across the pressure-induced quantum-critical phase boundary

Rare-earth pyrochlore iridates host two interlocking magnetic sublattices of corner-sharing tetrahedra and can harbour a unique combination of frustrated moments, exotic excitations and highly correlated electrons. They are also the first systems predicted to display both topological Weyl semimetal and axion insulator phases. We have measured the transport and magnetotransport properties of single-crystal Sm2Ir2O7 up to and beyond the pressure-induced quantum critical point for all-in-all-out (AIAO) Ir order at pc = 63 kbar previously identified by resonant X-ray scattering and close to which Weyl semimetallic behavior has been previously predicted. Our findings overturn the accepted expectation that the suppression of AIAO order should lead to metallic conduction persisting down to zero temperature. Instead, the resistivity-minimum temperature, which tracks the decrease in the AIAO ordering temperature for pressures up to 30 kbar, begins to increase under further application of pressure, pointing to the presence of a second as-yet unidentified mechanism leading to non-metallic behavior. The magnetotransport does track the suppression of Ir magnetism, however, with a strong hysteresis observed only within the AIAO phase boundary, similar to that found for Ho2Ir2O7 and attributed to plastic deformation of Ir domains. Around pc we find the emergence of a new type of electronic phase, characterized by a negative magnetoresistance with small hysteresis at the lowest temperatures, and hysteresis-free positive magnetoresistance above approximately 5 K. The temperature dependence of our low-temperature transport data are found to be best described by a model consistent with a Weyl semimetal across the entire pressure range.

Fatigue strength of synthetic rope: experimental methodology

Crane industries and industrial lifting companies aims to reduce the overall weight of the winch and limit the systematic use of steel wire rope in order to increase their competitiveness. This overall weight reduction can result from the lightering of the rope using synthetic material. Metallic rope fatigue behaviors are well documented and criteria for maintenance are established in the ISO 4309 standard unlike non-metallic ropes fatigue behaviors. Many unknowns remain, as failure modes, fatigue strength, ratting criteria, tribological behavior and friction, etc...In this context, CETIM and its industrial partners have launched, within a working group, a research program to evaluate the fatigue performance of synthetic ropes subjected to periodic bending stress. A specific scale 1:1 test bench which simulates the winding of the rope around the pulleys and drums was developed and Fatigue tests was performed on synthetic ropes. This test bench can be used on several rope geometries and dimensions, material (aramid, HMPE…), and loadings.This paper presents the test bench and discusses the experimental methodology developed to test synthetic ropes in fatigue bending mode.

A computational and experimental study in resistance spot welding of thin-gauge and highly conductive dissimilar sheets for battery tab interconnects

We present a combined computational and experimental study of the role of electrical and thermal contact resistances in resistance spot welding of thin-gauge, dissimilar metal sheets with high electrical conductivity, relevant for battery manufacturing for electric vehicles. In this application, the electrical and thermal contact resistances play a dominant role in heat generation and temperature evolution within the work pieces. Previously reported approaching for simulating resistance spot welding have limited capability for representing dissimilar and thin-gauge metal sheets, particularly at higher temperatures when multiple physical phenomena become increasingly interdependent. The approach presented here uses resistivity measurements, combined with thermal modeling and known bulk resistance relationships, to infer the relationship between electrical contact resistance and temperature for different material interfaces. Corresponding thermal contact resistance models are then developed using the Wiedemann-Franz law combined with a scaling factor to account for nonmetallic behavior. The model is validated by comparing experimental and predicted voltage histories and final weld diameters of three- and five-layer stack-ups consisting of alternating aluminum and copper layers. We also analyze heat generation and redistribution during welding to elucidate the dominance of contact resistance over bulk resistivity in these stack-ups as it evolves during the welding process.

Magnetic domain structure and magneto-transport properties of laser ablated Co40Fe40B20 thin films

We report the magnetic domain structure, and electrical and magnetoresistance properties of laser ablated Co40Fe40B20 (CoFeB) (6 to 36 nm) thin films deposited on SiO2 / Si(001) substrates. Magnetic force microscopy performed on annealed CoFeB thin films revealed larger magnetic domains, which are formed due to strong exchange coupling between the grains. The temperature-dependent sheet resistance of as-deposited thin films revealed that the observed non-metallic behavior is due to intragrain-tunneling and SiO2 inclusions in the amorphous matrix. The metallic behavior of annealed CoFeB thin films is due to electron scattering from grain boundaries and granularity correlated to the formation of nano-crystallites. Thickness and field-dependent magneto-transport studies show higher magnetoresistance values for thinner annealed CoFeB films due to more scattering events upon crystallization, which is consistent with the granular nature of the annealed thin films.

Effect of Wettability, Number of Liquid Phases, and Agitation Procedure on Agglomeration/Breakup/Transfer of Fine Particles in Liquid

To discuss nonmetallic inclusion behaviors in a secondary refining process, cold model experiments on agglomeration, breakup, and transfer of fine particles are performed varying the operating factors such as an energy input rate, wettability, agitation practice, and the number of liquid phases. When the other operating conditions are the same, the agglomeration rate of the 1‐particle (isolated particle) with a hydrophobic property is larger than that with a hydrophilic one, and the transfer rate of the 2‐particle (cluster of 2 isolated particles) has the same tendency. The number of the 1‐particle with the hydrophobicity is estimated to increase at the transfer site of the particles from an open eye to a heavy liquid due to a bubble breakup, whereas the 1‐particle with the hydrophilicity shows an opposite trend because of less adhesion on the bubbles. The 1‐particle in the dual phase transfers from the open‐eye spot to a light liquid, although the value is not so much as that of the decrease in the agglomeration. A transfer condition of the inclusion composed of Al2O3 or CaO⋅Al2O3 is calculated when a particle contacts with a solid/liquid interface, and the CaO⋅Al2O3 inclusion is estimated to be engulfed above 3.34 μm in diameter.

Low temperature electrical transport in thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition

In this paper electrical transport studies are performed on thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition (PLD) applying laser ablation of micro-crystalline graphite target. Experiments were carried out on 320 - 420 nm thick SiO2 on Si substrates as well as on hydrogenated diamond-like carbon (DLC) films deposited on SiO2/Si. Structural studies by means of XPS, SEM and Raman spectroscopy revealed that the films can be characterized as nano-sized carbon phases possessing different phase composition (i.e. the ratio sp3/sp2 hybridized carbon, etc.). The electrical conductivity/resistivity of the films was measured in the temperature range 10 K < T < 300 K. Four-contact Van der Pauw method as well as two contact schemes have been applied. Some films have low room temperature resistivity in the range ρ = (0.1–1.5)×10-3 Ω.·m and consist predominantly of sp2 hybridized carbon with Raman spectra, which resemble that of nano-sized graphene depending on the deposition conditions and substrates used. The thinnest only 0.5 nm layer deposited directly on SiO2 exhibits relatively low specific resistance (~10-3 Ω. m), which can be taken as an indication of good deposition conditions of graphene-like layers. The current flow mechanism was explored at temperatures from 300 K down to 10K. The temperature dependence reveals non-metallic behavior - the conductivity decreases at decreasing temperature as opposed to typical metal behaviour. A model of variable range hopping (VRH) mechanism is applied to explain the low temperature conductivity drawn from transport in nanocrystalline disordered systems.

Low temperature electrical transport in microwave plasma fabricated free-standing graphene and N-graphene sheets

In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricated by a microwave plasma-based method is addressed. Temperature–dependent resistivity/conductivity measurements are performed on the graphene/N-graphene sheets compressed in pellets. Different measurement configurations reveal directional dependence of current flow—the room-temperature conductivity longitudinal to the pellet’s plane is an order of magnitude higher than the transversal one, due to the preferential orientation of graphene sheets in the pellets. SEM imaging confirms that the graphene sheets are mostly oriented parallel to the pellet’s plane and stacked in agglomerates. The high longitudinal electrical conductivity with values on the order of 103 S/m should be noted. Further, the current flow mechanism revealed from resistivity-temperature dependences from 300K down to 10K shows non-metallic behavior manifested with an increasing resistivity with decreasing the temperature usually observed for insulating or localized systems. The observed charge transport shows variable range hopping at lower temperatures and thermally activated behaviour at higher temperatures. This allows us to attribute the charge transport mechanism to a partially disordered system in which single graphene sheets are placed predominantly parallel to each other and stacked together.

Structural, magnetic and transport properties of the quaternary Heusler alloy CoFeMnSn

First-principles calculations have been used to study the structure stability, mechanical properties, dynamic stability, electronic structure, magnetic moment, and anomalous Hall conductivity of the quaternary Heusler alloy CoFeMnSn. It is found that the Type Ⅰ structure is the most energetically favorable configuration, which exhibits high mechanical and dynamic stability. The large experimental saturation magnetic moment of 4.16 μB/f.u. and a high Curie temperature well above room temperature facilitate its application in the field of spintronics. The material’s resistivity changes very little with increasing temperature, showing a weak negative temperature coefficient, indicating a non-metallic transport behavior of the alloy. The main carrier of the alloy is hole with a carrier concentration of roughly 2.49 × 1022 cm−3 at 300 K. The analysis of the anomalous transport properties of the alloy indicates that both intrinsic and extrinsic factors contribute to the anomalous Hall effect of the CoFeMnSn alloy. Although it is difficult to distinguish between the side-jump and intrinsic mechanisms, it is shown that the skew scattering associated with phonons plays a significant role in the anomalous Hall effect.

Anomalous Nernst Effect in Perovskite La0.5Ca0.5CoO3

We report the occurrence of the anomalous Nernst effect (ANE) in polycrystalline perovskite La0.5Ca0.5CoO3. The sample is ferromagnetic below TC = 147 K and resistivity shows non-metallic behavior above and below the TC with only a small negative magnetoresistance (~2%) around TC. Field dependence of magnetization at 10 K shows large hysteresis with a coercive field of 6 kOe but a small magnetization ~ 0.64 Bohr magneton/Co even in a field of 50 kOe, which indicates the presence of magnetically heterogeneous ground state consisting of ferromagnetic and non-ferromagnetic phases. The field dependence of the Nernst thermopower (Sxy) at low temperatures shows complete saturation but the magnetization does not. This indicates that the ANE in La0.5Ca0.5CoO3 depends only on the transport properties of the ferromagnetic phase, while it is not affected by the non-ferromagnetic phase. Due to the higher value of remnant Sxy, the magnetized polycrystalline sample exhibits ANE in absence of an external magnetic field.

Temperature Sensing with Thin Films of Flame-Formed Carbon Nanoparticles

A porous nanostructured film of flame-formed carbon nanoparticles has been produced with a one-step procedure. The morphological and structural characteristics of the film have been characterized by atomic force microscopy and Raman spectroscopy. The electrical resistance as a function of the temperature has been investigated in the range from ambient temperature to 120 °C. A nonmetallic behavior has been observed, with a monotonic decrease of the film resistance as temperature increases. Electrical conduction is explained in terms of charge carriers tunneling and percolation between the carbon grains and is not perfectly described by an Arrhenius behavior. A negative temperature coefficient of resistance (TCR) of the order of −100 × 10−4 K−1 has been measured. The high absolute TCR value, together with the ease of material microfabrication processing and biocompatibility of the carbon material make this film ideal for temperature sensing in many environments. A functional relationship between resistance and temperature, which is necessary for practical applications, has been finally derived. A very good agreement between experimental data and fit is obtained with a fifth order polynomial.

Electronic, magnetic, and optical properties in bulk and various (111), (001) surfaces of Sc2CoSn full Heusler compound

The electronic, magnetic, and optical characteristics of the bulk and (111), (001) surfaces of the Sc2CoSn Heusler compound are calculated using first principle calculations. Investigating these properties is performed with FPLAPW, which takes into account the approximate function correlation within the Generalized Gradient Approximation (GGA). The results show that the bulk Sc2CoSn compound achieves a ferromagnetic half-metallic characteristic with an energy gap of 0.54 eV. The density of states for Sc(1)-, Sc(2)-, Co-terminations at the (111) surface, and the Sc(1)Co- and Sc(2)Sn-terminations at the (001) surface show metallic properties at the spin up and spin down channels, whereas the Sn-termination at (111) surface has a half-metallic nature with full spin polarization. A matter that paves the way for many applications related to constructing a massive magnetic resistance. At all ends, the values of magnetic moments of (111) and (001) surfaces demonstrate that Co atoms contribute the most. The optical investigation of the compound shows high reflectivity in the infrared region of the photon energy. The optically non-metallic behavior of the Sc2CoSn compound was revealed by the imaginary component of the dielectric function, with an optical band gap of roughly 1 eV. Based on the obtained results, the investigated material could be utilized in many photo-electronics applications including photo-senses, photo-catalyst, and photo-electrochemical areas.

Numerical simulation for EMS induced solidification and inclusion behavior in bloom caster CC mold with bifurcated SEN

A three-dimensional mathematical model has been developed to investigate solidification and non-metallic inclusions behavior in bloom caster mold with bifurcated submerged entry nozzle (SEN) under the influence of in-mold electromagnetic stirring (EMS). An enthalpy porosity approach is applied for the solidification analysis and the stochastic tracking model is used to track the motion of non-metallic inclusions. A numerical investigation has been carried out to study the influence of the stirrer current intensity on turbulent flow, shell generation and inclusion transport. The complex interplay of the induced flow with the inertial impinging jet from the SEN has been investigated. The effect of inclusion density and size on the removal rate of non-metallic inclusion has also been analyzed. The results show that in-mold EMS plays a significant role in solidification and inclusion behavior. With current intensity of 375 A, the inclusion removal rate is higher than that of 0 A, 300 A and 450 A stirrer current. This research suggests that the optimal current intensity of EMS gives a better internal quality of the continuous casting (CC) bloom mold.

Nonmetallic power-law behavior of conductance in Ni-doped NbSe3 nanowires

We report on diverse transport properties observed in NbSe3 nanowires of dilute Ni concentrations, where the resistance of some nanowires retains metallic behavior with regions of negative absolute resistance and switching transition showing up in current-voltage curve at sufficiently low temperatures, while others demonstrate metal-insulator transitions below the first charge density wave (CDW) transition. The temperature and voltage dependence of the resistance for the nonmetallic samples are governed by power laws; however, the anomalous features of the CDW transitions still retain. The observed transport behaviors are apparently due to the variation of potential along the conducting channel caused by different kinds of nonuniformities. A phenomenological model with one-dimensional phase slippage occurring in the certain segment of the nanowire, where Friedel oscillations-enhanced local CDW domains cluster altogether over the whole cross section, is presented as the possible mechanism for the nonmetallic power-law behavior. Our work sheds new light on the possible origin of nonmetallic power-law behavior in NbSe3, which has been under debate for a long time.

Magnetic glassiness and crystal field effects on thermal and electrical properties of Er5Pd2-type compounds

Magnetic properties, thermal expansion, heat capacity, and electrical resistivity of the cluster-glass compound Er4.8Pd2 and its paramagnetic isostructural counterpart Lu4.8Pd2 have been studied in the temperature range 2–300 K and in applied magnetic fields up to 140 kOe. Short-range antiferromagnetic (AFM) correlations of localized magnetic moments of Er3+ ions were found to develop in Er4.8Pd2 on cooling below T* ≈ 40 K. A cluster-glass magnetic state was observed below freezing temperature Tf ≈ 13.3 K, while Lu4.8Pd2 showed paramagnetic behavior. The crystal electric field (CEF) was found to substantially affect both the heat capacity and the thermal expansion of Er4.8Pd2. The CEF splitting of the Er3+ ion multiplet 4I15/2 was estimated to be as high as 280 K with a doublet ground state. Both the Schottky-type anomaly and short-range antiferromagnetic order contributions were found to give rise to a large volumetric heat capacity of Er4.8Pd2 at low temperatures. High direct magnetocaloric effect with −ΔSM(T)60kOe = 18.8 J mole−1 K−1 was confirmed to exist in Er4.8Pd2 while no inverse magnetocaloric effect was observed at low temperatures. Electrical resistivity of Er4.8Pd2 revealed a non-metallic behavior at low temperatures which was ascribed to an inhomogeneous electronic state due to the formation of clusters with the AFM short-range correlations.

Vanishing of Drude Weight in Interacting Fermions on {mathbb Z}^d with Quasi-Periodic Disorder

We consider a fermionic many body system in {mathbb Z}^d with a short range interaction and quasi-periodic disorder. In the strong disorder regime and assuming a Diophantine condition on the frequencies and on the chemical potential, we prove at T=0 the exponential decay of the correlations and the vanishing of the Drude weight, signaling non-metallic behavior in the ground state. The proof combines Ward Identities, Renormalization Group and KAM Lindstedt series methods.

Investigation of spin gapless semiconducting behaviour in quaternary CoFeMnSi Heusler alloy thin films on Si (1 0 0)

Spin gapless semiconducting (SGS) behaviour of polycrystalline CoFeMnSi (CFMS) Heusler alloy thin films was investigated through structural, magnetic, magnetotransport and electron-transport characterization. In this study, we have tailored the structural ordering in CFMS thin films (∼60 nm) grown at different substrate temperatures (TS) in 150 °C to 550 °C range on Si(100) substrates using pulsed DC magnetron sputtering. All the grown films were polycrystalline in nature, showing an enhancement in structural ordering with TS. Among all the samples, the film grown at 550 °C showed an optimal structure with L21 ordering. The magnetic measurements revealed that saturation magnetization (Ms) of the sample decreased with the an increment in measurement temperature with a value ∼ 3.42 μB/f.u. at 5 K to 3.11 μB/f.u. at 300 K. The Curie temperature (TC) of the sample was estimated to be 778 ± 13 K. The longitudinal resistivity (ρXX) measurements clearly exhibited a negative temperature coefficient of resistivity, indicating the non-metallic behaviour of these CFMS films. The fitting of resistivity curve dig out contribution of electron–phonon scattering and defect scattering to resistivity. Fitting also suggest that holes are the majority charge carriers in optimized CFMS thin film which was further confirmed through positive slope of anomalous Hall resistivity curve. The temperature-dependent anomalous Hall effect (AHE) measurements have also been carried out to identify the different scattering mechanisms responsible for AHE. The results suggested that both the intrinsic as well as extrinsic factors contribute to the AHE of CFMS deposited film with non-zero contribution of phonon-related skew scattering. The carrier concentration (n) and mobility (μ) were found to be nearly temperature-independent, revealing typical SGS characteristics. At room temperature, the n and μ values were found to be 3.91 ± 0.04 × 1021 cm−3 and 88.83 ± 1.58 cm2/Vs, respectively. The value of anomalous Hall conductivity at 5 K is found to be 53.79 S/cm..

Properties of RbHgF3 fluoro-perovskite under growing hydrostatic pressure from first-principles calculations

Mercury fluoro-perovskites based on Rubidium have a lot of technical relevance nowadays, especially in optical and semiconductive applications. A Cambridge Serial Total Energy Package code analysis using the Density Functional Theory was performed to calculate the structural, electronic, elastic, optical, and thermodynamic characteristics as well as the bonding nature of cubic fluoro-perovskites RbHgF3 under various hydrostatic pressures. To determine the total energy, the Perdew–Berke–Ernzerhof generalized gradient approximation was used to manage the exchange–correlation potential. The effects of hydrostatic pressure are studied in the region of 0–20 GPa, which maintains the cubic stable condition of RbHgF3 fluoro-perovskite. Experimental and prior theoretical results agree well with the calculated lattice parameters. When the pressure reached 20 GPa from 0 GPa, the volume, bond length, and lattice constant decreased. The bandgaps demonstrate an indirect band structure, with substantial reductions at various external forces. The total density of states reveals a non-metallic behavior. Mechanical properties satisfy the stability criteria until 20 GPa for this compound, and ductile behavior is also found within that pressure range. External stress modifies the optical characteristics a bit such as the complicated dielectric function, absorption, conductivity, and reflectivity. The presence of blue shift is confirmed by the movement of absorption edges toward higher energies, making this material an intriguing option for optical devices.

Spin gapless semiconductor and nearly spin semimetal antiferromagnets: The case of the inverse Heusler compounds Mn2LiZ (Z = Al and Ga)

Using first-principles calculations, we report the structural, electronic, magnetic and electronic transport properties of the new Heusler compounds Mn2LiZ with Z is Al and Ga. We show that both compounds are more stable in the inverse Heusler structure than in the regular one. The band structure calculations indicate that the Mn2LiAl compound is a spin gapless semiconductor and Mn2LiGa is a nearly spin-semimetal. In agreement with the Slater-Pauling rule, the two compounds are non-conventional antiferromagnets: they show zero spin moment accompanied by the fully spin-polarized charge carriers. Strong direct interaction between the spin moments is obtained. Consequently, the mean-field approximation reveals a high Curie temperature in the two compounds. Within the Boltzmann transport theory, the electrical conductivity shows non-metallic behavior for the two compounds at elevated temperatures, and the Seebeck coefficient appears to be large. In particular, the Mn2LiAl compound has a value greater than 150µV/K in a wide temperature range.

Magnetic frequency identification by quantum interference in magnetoplasmonic carbon/metal nanostructures

The frequency of an alternating magnetic field acting on multiwall carbon nanotubes decorated with Pt nanoparticles was identified as a change in conductance. The samples were prepared in film form using chemical vapor deposition and Pt nanoparticles were grown with acid precursors. Sample characterizations were analyzed by transmission and scanning electron microscopies. In a conductance dependent temperature measurement, the sample exhibits a non-metallic behavior. A Bode analysis shows a relocation on the controllable poles in the magneto-conductive activity. Moreover, optical nonlinearities were studied by single-beam and two-wave mixing configurations in the nanosecond regime. The optical absorbance dependent on irradiance and magnetic field was analytically described. Significant changes in two-wave mixing experiment were observed by magnetic perturbation. Sensitive magnetoplasmonic interactions by adding Pt nanoparticles on carbon nanotubes were responsible for enhancing magnetic and nonlinear optical effects. Immediate applications for scalable magnetophotonic systems in quantum sensing can be contemplated.

Kinetic Modeling of Nonmetallic Inclusions Behavior in Molten Steel: A Review

The kinetic modeling for the nucleation, size growth, and compositional evolution of nonmetallic inclusions in steel was extensively reviewed in the present article. The nucleation and initial growth of inclusion in molten steel during deoxidation as well as the collision growth, motion, removal, and entrapment of inclusions in the molten steel in continuous casting (CC) tundish and strand were discussed. Moreover, the recent studies on the prediction of inclusion composition in CC semiproducts were introduced. Since the 1990s, the development of thermodynamic model and relevant databases for inclusion engineering has been initiated by the steel industry. Later, the commercial software FACTSAGE employing the FACT database was widely used to predict the gas (atmosphere/bubble)–liquid (steel/slag/inclusion)–solid (refractory/slag/steel/inclusion) multiphase equilibria. With the help of the comprehensive thermodynamic database and solution models in conjunction with the development of user-friendly computing packages, the kinetics of inclusion evolution in molten steel can be successfully predicted based on several kinetic models such as the coupled reaction (CR) model, reaction zone model, and tank series recirculation (TSR) model. However, some parameters are needed to represent the real processes according to the model employed at different operational or experimental conditions. The effect of reoxidation on the evolution of inclusions in the ladle and tundish, which was experimentally confirmed, can be simulated by the effective equilibrium reaction zone (EERZ) model. The complex slag–steel interfacial reaction phenomena have been successfully explained by the interfacial kinetic model based on the dynamic interfacial tension and oxygen adsorption/desorption characteristics at the slag-steel interface.