Dependent Resistivity Measurements Research Articles

Temperature dependent partially compensated to nearly fully compensated magnetic state in half-metallic full Heusler alloy, Mn1.2Fe1.18V0.62Al

We report experimental and theoretical studies of magnetization compensation phenomenon in quaternary Heusler alloy Mn1.2Fe1.18V0.62Al by employing dc magnetization, neutron depolarization, neutron diffraction, specific heat, electrical resistivity, and electronic structure calculation. In this ferrimagnetic alloy system with ordering temperature TC = 360 K, the asymmetric thermal variations of the site magnetic moments provide an evidence of the partially compensated magnetic state of the system down to ∼ 48 K. However, below 48 K, the system exhibits its magnetic ground state with the negligibly small ordered moment of 0.05(5) μB/f.u. at 10 K, as obtained from the neutron diffraction study. Nearly full recovery of neutron beam polarization at 4 K in the neutron depolarization study also infers a nearly fully compensated magnetization state in this Heusler alloy. Temperature dependent specific heat and resistivity measurements also corroborate with the dc magnetization study representing 48 K as a turning point at which the system reaches its ground state. The electronic structure calculations, using the SPR-KKR Green’s function approach, verify the half-metallic nature of the present system. The net magnetic moment (0.06 μB/f.u.) obtained from the theoretical calculations as well as neutron diffraction experiments (0.05 μB/f.u.) is in good agreement with the Slater-Pauling rule (0.06 μB/f.u.). This small magnetic moment of the system (Mn0.82Fe1.18)(Mn0.38V0.62)Al proclaims to be a nearly compensated ferrimagnetic system with 23.94 valence electrons. Such magnetically compensated systems with finite spin polarization could be favorable for spintronics applications.

Pressure-Induced Intermetallic Charge Transfer and Semiconductor-Metal Transition in Two-Dimensional AgRuO 3

Pressure-Induced Intermetallic Charge Transfer and Semiconductor-Metal Transition in Two-Dimensional AgRuO ₃

Ca 2 Ga 4 Ge 6 and Ca 3 Ga 4 Ge 6 : Synthesis, Structure, and Electronic Properties

During the search for transition metal-free alkyne hydrogenation catalysts, two new ternary Ca−Ga−Ge phases, Ca2Ga4Ge6 (Cmc21, a=4.1600(10) Å, b=23.283(5) Å, c=10.789(3) Å) and Ca3Ga4Ge6 (C2/m, a=24.063(2) Å, b=4.1987(4) Å, c=10.9794(9) Å, β=91.409(4)°), were discovered. These compounds are isostructural to the previously established Yb2Ga4Ge6 and Yb3Ga4Ge6 analogues, and according to Zintl-Klemm counting rules, consist of anionic [Ga4Ge6]4− and [Ga4Ge6]6− frameworks in which every Ga and Ge atom would have a formal octet with no Ga−Ga or Ga−Ge π-bonding. These compounds are metallic, based on temperature dependent electrical resistivity and thermopower measurements for Ca3Ga4Ge6, along with density functional theory calculations for both phases. Unlike the highly active 13-layer trigonal CaGaGe phase, these new compounds exhibit minimal activity in the semi/full alkyne hydrogenation of phenylacetylene, which is consistent with previous observations that the lack of a formal octet for framework atoms is essential for catalysis in these Zintl-Klemm compounds.

Temperature dependent structural, electrical and electronic investigation of VO2 (B) thin film

Vanadium dioxide can exist in several polymorphs and among these the layered polymorph VO2 (B) with monoclinic symmetry has numerous applications. In this work, VO2 (B) phase thin film was prepared on quartz substrate via sputtering technique and its temperature dependent structural, electrical and electronic properties were investigated. We have witnessed a broader structural phase transition around 220 K; which encounter significant changes in the lattice constants yet the monoclinic symmetry is retained over a temperature range from 100 K to 380 K. Temperature dependent resistance measurement also exhibited a semi-metal to insulator like transition near 220 K displaying over 2 order of magnitude change in resistance across the transition. Small changes in the oxygen K-edge x-ray absorption spectrum were seen with change in temperature. At low temperature, an additional peak (d|| band) has emerged in the XAS spectra at energy higher than the σ* peak. The appearance of d|| band density of states is associated to the enhanced electron correlation effects driven by the localization of V–V pair's interactions at low temperature.

Synthesis and characterisation of a new graphitic C–S compound obtained by high pressure decomposition of CS2

Carbon disulphide (CS2) is, together with its closest analogue CO2, one of the simplest molecular systems made of double covalent bonds. Under high pressure, the molecular structure is expected to break up to form extended crystalline or polymeric solids. Here we show that by compression at 300 K to ∼10 GPa (100 kbar) using large-volume high pressure techniques, a sudden reaction leads to a mixture of pure sulphur and a well-defined compound with stoichiometry close to C2S which can be recovered to ambient pressure. We present neutron and x-ray diffraction as well as Raman data which show that this material consists of sulphur bonded to sp2 graphite layers of nanometric dimensions. The compound is a semiconductor with a gap of 45 meV, as revealed by temperature dependent resistivity measurements, and annealing at temperatures above 200 °C allows to reduce its sulphur content up to C10S. Its structural and electronic properties are fundamentally different to “Bridgman black” reported from previous high pressure experiments on CS2.

Semiconducting nature and magnetoresistance behaviour of ZnO / La0.3Ca0.7MnO3 / SrTiO3 heterostructures

In this report, ZnO /La0.3Ca0.7MnO3 /SrTiO3 (ZnO /LCMO /STO) heterostructures, with various thicknesses of LCMO, were grown successfully using chemical solution deposition (CSD) method. X–ray diffraction (XRD) measurement confirms the presence of LCMO and ZnO phases only without any other unwanted phases. To understand the charge conduction mechanisms across ZnO /LCMO interface as well as for LCMO manganite thin layer, temperature dependent resistivity measurements have been investigated under different applied magnetic fields. The measured ρ (T) data of all the heterostructures in current perpendicular to plane (CPP; for ZnO /LCMO interface studies) mode and current in plane (CIP; for LCMO thin layer studies) mode show the semiconducting behaviour throughout the temperature and magnetic field range studied. The semiconducting state of all the heterostructures have been studied using Mott type variable range hopping (VRH) mechanism to understand the field dependence of charge carrier localization length. Observed negative magnetoresistance (MR) has been discussed in detail with its dependence on applied magnetic field, temperature and manganite layer thickness.

Transport properties, charge conduction mechanism and magnetic behavior of La0.3Ca0.7MnO3:ZnO Nanocomposites

Nanocomposites consist of ZnO and La0.3Ca0.7MnO3 (LCMO) nanoparticles, prepared by cost effective sol–gel method, have been studied for their transport and magnetoresistance (MR) behaviors. Different ZnO nanoparticles contents (weight ratio) were mixed with LCMO nanostructured manganite to understand the possible interactions between ZnO and LCMO nanoparticles. X–ray diffraction (XRD) measurement was performed for all composites and structural quality was verified by performing Rietveld refinements. Variation in an average crystallite size for LCMO and ZnO nanoparticles in different composites has been discussed. Temperature dependent resistivity measurements under different applied magnetic fields suggest the semiconducting nature of all nanocomposites under all applied magnetic fields. Mott type variable range hopping (VRH) mechanism has been employed to understand the dependence of charge carrier localization in LCMO nanostructured manganite lattice on the applied magnetic field and ZnO nanoparticles content within the nanocomposites. Observed MR behavior has been understood under the influence of temperature and ZnO nanoparticles content in the context of spin polarized tunneling (SPT) and magnetic field induced improved conduction across the manganite lattice. Grain and grain boundary contributions to the MR behavior have been explained by using theoretical model fits to obtained MR data at different temperatures for all studied LCMO:ZnO nanocomposites. Magnetic nature of studied LCMO:ZnO nanocomposites has been understood by performing zero field cooled (ZFC) and field cooled (FC) measurement protocols based magnetization and magnetic isotherms measurements that confirm the coexisting magnetic phase in all studied nanocomposites. Magnetic nature has been understood on the basis of weakening of zener double exchange (ZDE) mechanism within the magnetic lattice of LCMO manganite and magnetic contribution from the free charge carriers within the ZnO clusters.

Electron transport characteristics of FeGa, Ni/n-Si junctions by impedance spectroscopy

In this work, we have investigated electron transport across Galfenol (Fe x Ga 1-x ) and Nickel-based Schottky contacts deposited onto n-Si substrates using conventional DC current-voltage (I–V) measurements and have uniquely studied the effects of improper back contact causing additional bias dependent Resistance-capacitance (R–C) components using AC Impedance spectroscopy by choosing proper equivalent circuit models. Junction barrier height and ideality factor were obtained from DC current-voltage characteristics, and bias dependent impedance measurements have been carried out. From Impedance spectroscopy analysis the magnitudes of depletion layer capacitance and barrier height have been calculated and have been compared for both the junctions, and the effect of additional components has been distinguished. Negative capacitance behaviour at lower frequencies and higher forward bias regime has been observed, which might be attributed to interface states in presence of injected charge carriers and by choosing an equivalent circuit having inductor-resistor (R-L) type relaxation, better fit of experimental Nyquist plots of FeGa Schottky junction have been achieved. • FeGa and Nickel based Schottky Junctions have been deposited onto n-Si substrates using RF magnetron Sputtering. • Junction parameters have been calculated using conventional DC and, AC Impedance measurements. • Using equivalent circuit; bias dependency of both Schottky and Ohmic interfaces for has been studied.

Publisher’s Note

Abstract Vanadium dioxide can exist in several polymorphs and among these the layered polymorph VO2 (B) with monoclinic symmetry has numerous applications. In this work, VO2 (B) phase thin film was prepared on quartz substrate via sputtering technique and its temperature dependent structural, electrical, and electronic properties were investigated. We have witnessed a broader structural phase transition around 220 K; which encounter significant changes in the lattice constants yet the monoclinic symmetry is retained over a temperature range from 100 K to 380 K. Temperature dependent resistance measurement also exhibited a semi-metal to insulator like transition near 220K displaying over 2 order of magnitude change in resistance across the transition. Small changes in the oxygen K-edge x-ray absorption spectrum were seen with change in temperature. At low temperature, an additional peak (d|| band) has emerged in the XAS spectra at energy higher than the σ* peak. The appearance of d|| band density of states is associated with the enhanced electron correlation effects driven by the localization of V–V pair's interactions at low temperature.

Effect of Fe Doping on the Structural, Electrical and Magnetic Properties of Perovskite La<sub>0.7</sub>Ca<sub>0.3</sub>Mn<sub>1-</sub><i><sub>x</sub></i>Fe<i><sub>x</sub></i>O <sub>3</sub> (<i>X</i> = 0, 0.01, 0.03 and 0.05)

The effect of Fe-substitution at the Mn-site in La0.7Ca0.3Mn1-xFexO3 (x = 0, 0.01, 0.03 and 0.05) on its structure, electrical and magnetic properties has been studied. These properties were investigated via X-ray diffraction (XRD) analysis, temperature-dependent resistance measurements and temperature-dependent AC magnetic susceptibility measurements. XRD analysis showed all samples are single phase materials. Temperature dependent resistance measurements between 30–300 K showed all samples to undergo insulator-metal transition as temperature decreases. Increase in Fe doping for x = 0, 0.01, 0.03 and 0.05 caused the transition temperature TIM to decrease from 257 K, 244 K, 205 K and 162 K respectively. The magnetic susceptibility measurements showed the samples to exhibit paramagnetic to ferromagnetic transition as temperature decreased. Increase in Fe substitution x at the Mn-site progressively decreased the Curie temperature TC from 250 K at x = 0 to 170 K at x = 0.05.

Electrical resistivity and magnetic susceptibility of substoichiometric CdO and In doped CdO films

Undoped and In doped substoichiometric CdO nanostructured films were prepared via vapor transport method. Mixed phases of hexagonal Cd and cubic CdO were obtained. No peaks related to In or indium oxides were observed in the In doped CdO pattern. Net-like assembles of nanowires were observed for undoped CdO sample whereas a regular morphology of equally shaped grains was observed for In doped CdO sample. The evaluated room temperature electrical resistivity values for undoped and In doped CdO films were 1.56 × 102 and 2.31 × 10–2 Ωcm, respectively. The temperature dependent resistivity measurements elucidated the semiconducting behavior for undoped CdO films, whereas a semiconductor–metal with a transition around 367 K was obtained for In doped CdO film. The magnetic susceptibility showed paramagnetic-antiferromagnetic transition with Neel temperatures of 266 and 308 for undoped and In doped CdO samples, respectively.

5 years of in situ reinforcement corrosion monitoring in the splash and submerged zone of a cracked concrete element

Results of more than 5 years of in situ reinforcement corrosion monitoring are presented including continuous measurements of concrete resistivity, temperature, and open circuit corrosion potential measurements. Depth dependent resistivity and temperature measurements were obtained by means of multi-ring electrodes, while so-called instrumented rebars were used for location- and time-dependent open circuit corrosion potential measurements. The presented results highlight the complex interaction between mass transport, fracture, exposure, and electrochemistry and underline the importance of in situ measurements, which are imperative for model testing to enable accurate and reliable long-term performance predictions of reinforced concrete structures.

Two-transition behavior in Bi0.5Sb0.5SeI crystals

The ions with outer electron configuration of ns2 are often considered key factors for the efficient carrier transport in optoelectronic materials. In many cases precise tuning of the band gap and adjustment of the desired electronic properties achieved through the changes of the chemical environment. Here we investigate BixSb1-xSeI (x = 0.5) mixed crystals that have a one-dimensional structure with intermediate physical parameters between BiSeI and SbSeI compounds. Although crystallographically the substitution appears to be trivial, we found, that it has a rather strong effect on chemical bonds that provoke two-mode Raman behavior as well as two electronic transitions. The temperature dependent electrical resistance and photoluminescence measurements indicated anomalies at ~146 and ~62 K with strong thermal hysteresis loop for Bi0.5Sb0.5SeI. These, mixed samples inherit anisotropic properties, but inhomogeneity prevail the structure. We assert that the difference in masses of bismuth and antimony should be responsible for the observed binary effect.

Suppression of multiple magnetic ordering induced by Nb and Ru substitution in SrCoO3-δ systems

Abstract In this paper, we report detailed study on magnetic behavior of perovskite SrCoO3-δ compound with partial substitution of non-magnetic Nb and magnetic Ru at Co site. All the samples show single-phase nature with tetragonal structure of P4/mmm space group. The semiconducting behavior is evident from temperature dependent resistivity (ρ) measurement. The resistivity exhibits Variable Range Hopping and Small Polaron Hopping mechanisms in different temperature regimes. The magnetoresistance increases with substitution and reaches up to ~35% at 10 K with 70 kOe magnetic field. The samples show weakly ferromagnetic-type transition below room temperature. The saturation magnetization and exchange bias (EB) increase with Nb concentration but the effect is less prominent for Ru substituted samples. Different magnetic properties are explained on the basis of valence states of Nb5+ and mixed valence of Ru4+/5+ replacing Co3+. The existence of ferromagnetic correlated region in antiferromagnetic matrix and irreversible glass state with competing exchange interactions impart the EB effect in these samples. The EB value HEB~7.45 kOe at 10 K is quite significant which might be useful for further technological implementation in electronics/spintronics devices.

Evaluation of magnetotransport properties of Au added YBCO ceramics: combination of experimental and advanced theoretical approaches

The purpose of this work is to investigate the change of flux pinning ability, superconducting and physical properties of gold particle addition in the YBa2Cu3O7-x (YBCO) superconducting matrix using temperature dependent resistivity measurements under different applied magnetic fields; namely 0.0, 0.3, 1.0, 2.0, 5.0 and 7.0 T. The room temperature resistivity, transition temperature (Tc), transition width (∆Tc) and mobile hole carrier concentration values for each sample have separately been determined. In addition, we estimated the field-dependent activation energy (U0), irreversibility field (µ0Hirr), upper critical field (µ0Hc2), penetration depth (λ) and coherence length (ξ) with the quantum mechanical approaches related to the fluxoid mechanism for all the samples prepared. It was found that the flux pinning energy values evaluated by Thermally Activated Flux Creep (TAFC) model were determined to be about 11,455 K, 13,413 K, 10,350 K and 9320 K for the undoped, 1 wt%, 5 wt% and 20 wt% Au doped samples, respectively. Moreover, the results obtained showed that the critical temperature, activation energy, irreversibility and upper critical field values were found to depend strongly on the gold content and applied magnetic field strength. The values of µ0Hirr, µ0Hc2, λ and ξ (∆Tc) initially exhibited a slight increment (decrement) followed by a decrease (increase) for the samples with the higher gold-doping concentrations. The possible reasons regarding the observed changes in flux pinning and fundamental superconducting properties due to gold-doping in YBCO superconductors were discussed in detail. We indicated that a certain amount of gold doping has an effective role to form the nucleation centers that serve as the active flux pinning regions in the YBCO system so that the quality of interaction between the superconducting grains and inter-granular coupling strength in the adjacent multilayers can increase remarkably.

Structural, Optical and Electrical Properties of Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 Pyrochlore Ceramics

Abstract Herein, the structural, morphological, compositional, optical, electrical and dielectric properties of Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 (BZN) solid solutions are reported. Tungsten substituted BZN ceramics which are fabricated by the solid state reaction technique exhibited solubility limits at substitution level below x=0.18. Remarkable engineering in the structural, optical, electrical and dielectric properties of the pyrochlore ceramics is achieved via W substitution. Namely, shrinkage in both of the lattice parameters and in the energy band gap accompanied with decrease in the microstrain, in the dielectric constant and in the electrical resistivity is observed upon increasing the W content below the solubility limit. The increase in the W content in the BZN ceramics enhances the densification of the pyrochlore and leads to higher light absorbability and larger crystallites growth. The temperature dependent electrical resistivity measurements has also shown that the pyrochlore exhibit thermal stability below 380 K.

Investigation of metal-insulator transition temperature and magnetic properties of NdNiO3 nanoparticles

The control of metal–insulator transition (MIT) and magnetic properties of rare-earth nickelates remains a fundamental problem in material science. Here, we report a possible way to tune the MIT as well as the magnetic properties of NdNiO3 by reducing the crystalline size to the nanoscale. NdNiO3 nanoparticles of different sizes have been synthesized by a simple aqueous solution-based chemical method in the atmospheric pressure under oxygen. The x-ray diffraction study shows the formation of orthorhombic nanocrystals of NdNiO3 with Pbnm space group, presence of oxygen vacancies and higher octahedral distortion. The morphology and the particle size distribution have been evaluated by FESEM and TEM. The temperature dependent resistivity measurement shows the metal to insulator transition, which depends on the particle size; lower the particle size, higher the MIT temperature (TMI). Further study on the temperature dependent magnetic susceptibility shows the signature of magnetic phase transition at a temperature (Néel temperature TN), lower than the TMI, which indicates the existence of second order magnetic phase transition in our NdNiO3 nanoparticles. We have attributed the higher TMI and the origin of second order magnetic phase transition predominantly to the higher NiO6 octahedral distortion and the narrowing of bandwidth of the nanocrystalline NdNiO3, which leads to the opening of the charge transfer gap at the temperature higher than the bulk.

Spin valve effect in sputtered FL-MoS2 and ferromagnetic shape memory alloy based magnetic tunnel junction

In the last decade, two-dimensional (2D) transition metal dichalcogenides have been introduced with great significance in the spintronic devices for their extraordinary electrical, optical, and spin-dependent properties. In this work, we have fabricated a few-layer molybdenum disulfide (FL-MoS2) (~6 nm) as a non-magnetic spacer layer in Ni–Mn–In/FL-MoS2/Ni–Mn–In magnetic tunnel junction (MTJ) using DC magnetron sputtering. FL-MoS2 thin film sandwiched between two ferromagnetic shape memory alloy based electrodes exhibit semiconducting behavior, confirmed by current-voltage (I–V) characteristics and temperature dependent resistance measurement. The fabricated MTJ shows spin valve effect in the presence of an external magnetic field. The tunneling magnetoresistance (TMR) has been recorded in 10 K–300 K temperature range. The highest TMR ratio of 0.51% was obtained at a low temperature ~10 K, corresponding to the spin polarization of ~5%. This TMR ratio reduces to a value of 0.032% as the temperature of the device increases up to 300 K, displaying a finite TMR at room temperature. A detailed study of thickness and temperature-dependent magnetization versus magnetic field (M − H) hysteresis loops of Ni–Mn–In thin films has been performed to understand the complex TMR behavior. The present study paves the way for the use of sputtered FL-MoS2 and ferromagnetic shape memory alloy in ultrafast spintronics for advanced magnetic devices application.

Thallium lead iodide (TlPbI3) single crystal inorganic perovskite: Electrical and optical characterization for gamma radiation detection

TlPbI3 has been suggested as a candidate semiconductor material for room temperature gamma ray and charged particle detection, motivated by its wide bandgap (2.17–2.3 eV), and high density (6.6 gm/cm3) required for low noise and high intrinsic detection efficiency. In this work, we studied the optical and electronic properties of Bridgeman-grown TlPbI3 single crystal using ultraviolet–visible–infrared absorption spectroscopy, low temperature cathodoluminescence, temperature dependent current-voltage measurements, and charge carriers’ mobility-lifetime measurements. The fabricated Ag/TlPbI3/Ag device showed Ohmic behavior in temperatures ranging between −7 °C to 22 °C and exhibited high resistivity (~2 × 1011 Ω.cm at RT). Fermi level pinning at 0.72 eV above valence band minimum or below conduction band maximum was calculated from the temperature dependent resistivity measurement, and the 2.17 eV bandgap was determined from ultraviolet–visible–infrared absorption spectroscopy. The cathodoluminescence spectrum of TlPbI3 was resolved to two peaks at 1.45 eV and 1.48 eV indicating deep level traps. The mobility-lifetime product was estimated to be 3.43 × 10−5 cm2/V and 2.29 × 10−6 cm2/V for electrons and holes, respectively. Possible interpretations are presented suggesting the presence of vacancy type defects. Our results provide new essential information for developing such a new class of room temperature radiation detector material for a wide range of applications.

YbCu0.52(2)Sb: Mixed-valent compound with a layered structure

A new ytterbium copper antimonide, YbCu0.52(2)Sb, was synthesized from the Pb-flux reactions, and its crystal structure was determined by the single-crystal X-ray diffraction method. The compound crystallizes in the trigonal space groupR3¯m (No. 166), a = 4.4494(4) Å, c = 33.767(7) Å, which adopts the same structure as Ca0.61(1)Ce0.39(1)Ag0.60(1)Sb. The crystal structure of this compound can be rationalized as a combination of the YbCuSb and YbSb structures. Also, the formula can be written as a sum of these two components, [(Yb2+)(Cu+)(Sb3−)]0.52[(Yb3+)(Sb3−)]0.48. The magnetic susceptibility measurements indicated coexistence of Yb2+ and Yb3+ in the structure, which was further supported by the X-ray photoelectron spectroscopy. The temperature dependent resistivity measurements indicated the metallic nature of the material. Since the Yb-Cu-Sb system contains very limited member compounds, the discovery of this ternary YbCu0.52(2)Sb phase is important, which represents a completely new fashion in stabilizing the crystal structure.