Variable Range Hopping Mechanism Research Articles

Observation of Enhanced Long-Range Ferromagnetic Order in B-Site Ordered Double Perovskite Oxide Cd2CrSbO6.

A B-site ordered double perovskite oxide Cd2CrSbO6 was synthesized under high-pressure and high-temperature conditions. The compound crystallizes to a monoclinic structure with a space group of P21/n. The charge configuration is confirmed to be that of Cd2+/Cr3+/Sb5+. The magnetic Cr3+ ions form a tetrahedral structural frustrated lattice, while a long-range ferromagnetic phase transition is found to occur at TC = 16.5 K arising from the superexchange interaction via the Cr-O-Cd-O-Cr pathway. Electrical transport measurements indicate that Cd2CrSbO6 is an insulator that can be described by the Mott 3D variable range hopping mechanism. First-principles calculations reproduce well the ferromagnetic and insulating ground state of Cd2CrSbO6 with an energy band gap of 1.55 eV. The intrinsic ferromagnetic insulating nature qualifies Cd2CrSbO6 as a promising candidate for possible spintronics applications.

Effect of Ar pressure on phase transition characteristics and charge transport mechanism in VO2 films grown by RF sputtering of V2O5

In this study, we report the growth and characterization of VO2 films deposited on YSZ (001) substrate employing RF magnetron sputtering of vanadium pentoxide (V2O5) target in pure Ar gas ambient. The VO2 film growth has been carried out at ∼700 °C for ∼15 min at ∼100 W RF power with a flow rate of ∼20 sccm at Ar gas deposition pressure of ∼3, ∼6, ∼20, and ∼40 mTorr. x-ray diffractometry and Raman spectroscopy show that the nearly pure VO2 phase achieved at lower Ar pressure, e.g., ∼3 and ∼6 mTorr transform into a multiphase V-O system at ∼20 and ∼40 mTorr. This pattern is also supported by the electrical transport measurements through the occurrence of hysteretic IMT in films grown at ∼3 and ∼6 mTorr and the absence of this signature in these films deposited at ∼20 and ∼40 mtorr Ar pressure. The most pronounced with the strongest hysteresis is seen in the Y6 film, and therefore, the optimum growth pressure in the present study is ∼6 mTorr. The suppression of IMT in Y20 and Y40 is attributed to the appearance of other V-O phases, which smear out the phase transition. The activation energy of the insulating phase is estimated from the Arrhenius fit to the ρ-T data is found to be ∼0.223 eV at ∼3 mTorr Ar pressure which increases to ∼0.311 eV for ∼6 mTorr film in the cooling cycle. The low temperature (120K≤T≤300K) transport conduction in all VO2 films is governed by Efros-Shklovskii’s variable range hopping (ES-VRH) mechanism with a systematic relation between growth conditions and phase transition characteristics. Thus, Argon gas pressure plays a critical role in growth and brings out the feasibility of VO2 films growth by RF sputtering of oxide V2O5 target under Argon ambient only.

Yttrium ion influence on the structural, electrical, dielectric, and magnetic properties of α-Fe2O3 nanoparticles synthesized via Sol-Gel method

In this study, pure and Y3+ substituted Hematite (α-Fe2O3) nanostructure with various compositions, α-Fe2-xYxO3 (x = 0.00, 0.02, 0.05, 0.08 & 0.10), synthesized by using the Sol-Gel method. The X-ray diffraction (XRD) patterns of both pure and Y-substituted α-Fe2O3 samples revealed a rhombohedral phase with the R3¯c space group, having crystallite sizes ranging from 23 to 48 nm. Moreover, the XRD findings align closely with Raman observations. The variation in grain size observed via FE-SEM correlates well with the crystallite size and strain determined by XRD measurements. The resistivity plots exhibited two distinct regions corresponding to two different conduction mechanisms. Analysis of the resistivity data suggests the presence of variable range hopping and nearest-neighbour hopping conduction mechanisms within temperature ranges of 100 K to 300 K and 300 K to 400 K, respectively. The dielectric and magnetic properties exhibit a fluctuating behaviour with the increasing concentration of the Y3+ doping. We observed a shift towards weakly ferromagnetic conduct-like behaviour with the introduction of Y3+ into the hematite nanostructures.

Charge carrier transport in PbS films doped with iodine.

The results of the measurements of electrical and Hall resistivities on polycrystalline PbS films doped with iodine obtained through hydrochemical deposition are presented. The analysis of the temperature dependence of resistivity points out the crossover from the hopping mechanism due to thermal delocalization in the impurity band to the variable range hopping mechanism. The increase in the iodine content in the films leads to an increase in the impurity ionization energy. It has been established that the temperature dependence of resistivity over a wide temperature range obeys the inverse Arrhenius law, which is characteristic of disordered polycrystalline films with different sizes and orientations of crystallites relative to the substrate, as confirmed by AFM topography, Raman spectra and X-ray diffraction measurements. We found that the type of charge carrier changes from electrons to holes with an increase in the iodine content. Additionally, for a wide range of iodine doping, the concentration of charge carriers is low, indicating the possible occurrence of a self-compensation mechanism due to the formation of impurity defects.

Engineering lattice oxygen defects and polaronic transport in vanadium pentoxide via isovalent phosphorus doping

Oxygen vacancies are equilibrium defects in the vanadium pentoxide system that give rise to polaronic hopping transport via V4+ charge compensating defect. In this paper, we report the tunability of polaron formation, the hopping process, and their magnetic signature by substitution of isovalent (5+) phosphorus ions in the V5+ site. The powder x-ray diffraction data show a monotonous shift in lattice parameters with progressive P-doping, confirming the presence of a substitutional dopant. The polaron hopping energy reduced from 0.307 to 0.290 eV depicting a lower defect concentration in P-doping in V2O5. At low temperatures, it is found to obey the Efros–Shklovskii variable range hopping mechanism. The estimated hopping range increased to 1.6 ± 0.1 nm in doped V2O5 in contrast to ∼1.3 nm in the undoped one. The electron spin resonance measurements show a diminishing broad ferromagnetic signal and rising paramagnetic signal (g = 1.97) with progressive P-doping depicting predominant isolated electronic spins in the doped sample. The same is corroborated in room temperature M–H with a distinct hysteresis that diminishes with P-doping and a rise of a paramagnetic slope. Moreover, the reduced oxygen defects and lower V4+ relative occupancy together with fermi level fall toward intrinsic position are substantiated by photoelectron emission studies.

Different reverse leakage current transport mechanisms of planar Schottky barrier diodes(SBDs) on sapphire and GaN substrate

The effects of different substrates on the off-state leakage current in gallium nitride (GaN) planar diodes are experimentally demonstrated and studied by analyzing temperature-dependent current–voltage characteristics. The two devices exhibit different leakage mechanisms despite being subjected to the same process conditions. The device with a sapphire substrate shows a more intricate leakage mechanism, implying the presence of additional leakage channels compared to the device with free-standing substrates. The electrical leakage characteristics in the planar GaN-on-sapphire device (referred to as utemp-SBD) and GaN substrate device (referred to as usub-SBD) Schottky barrier diodes (SBD) can be described by two distinct processes as the reverse bias gradually increases: utemp-SBD go through the thermionic emission (TE), variable range hopping (VRH), Frenkel–Poole (FP) emission and space-charge-limited conduction (SCLC) model; The leakage conduction mechanism of usub-SBD include TE, VRH, and FP emission mechanisms. It is noteworthy that in device 1, there is a rapid increase in leakage current within the voltage range of −36 to −40 V, primarily driven by the SCLC mechanism. This effect arises due to the presence of intrinsic traps in GaN grown on a heterogeneous substrate. Additionally, in the voltage range of −7 to −50 V (348 K to 448 K), the leakage mechanism shifts from FP emission to the VRH model, possibly due to variations in the Schottky barrier height.This study provides an in-depth analysis of the leakage mechanisms observed on different substrates and offers valuable insights for the design of planar gate transistors to minimize or avoid the occurrence of leakage channels.

Layer‐Dependent Optical Modulation and Field‐Effect‐Transistor in Two‐Dimensional 4H‐SnS2 Layers

AbstractTwo–dimensional (2D) 4H‐polytype tin disulfide (SnS2) flakes are synthesized using the chemical vapor transport technique. The weak Van der Waals force between the 2D SnS2 layers offers an easy exfoliation of flakes down to a bilayer of thickness ≈2.02 (±0.1) nm using a mechanical exfoliation technique. The optical and field effect transistor (FET) characteristics of the exfoliated 2D 4H‐SnS2 layers are studied. The exfoliated layers are used to fabricate the ≈13‐layered SnS2 FET. The 4H‐SnS2 exhibits a high on/off ratio of ≈106 and mobility ≈1–4 cm2 V−1 s−1. The low mobility of the 4H‐SnS2 FET devices shows an insulating state concordant with the 2D Motts variable range hopping mechanism at varying temperatures. Moreover, it is found that the optical bandgap of the 2D SnS2 single‐crystal layers is largely widened for the bilayers and tri‐layers. The optical bandgap energies vary in the range of 2.56–1.99 eV. The significant alteration in bandgap energies of ≈0.57 eV offers downscaling of the 2D nanoscale semiconducting devices. Such layer‐sensitive changes in optical transmittance, absorbance, and bandgap energies are reflected in Commission Internationale de L'Eclairage (CIE) chromaticity, showing the distinct color of transmittance through various 2D 4H‐SnS2 layers.

Giant dielectric constant, magnetocaloric effect and spin-phonon coupling in EuTbCoMnO6 semiconductor

Transport, dielectric, magnetic and Raman studies of polycrystalline double perovskite EuTbCoMnO6 have been performed. Temperature-dependent resistivity follows the variable range and small polaron hopping mechanism. The temperature-dependent dielectric study shows the usual frequency-dependent step-like behavior. It also shows thermally activated relaxor peak in loss curves with giant dielectric constant near room temperature. The temperature-dependent magnetization demonstrates a second-order phase transition around 113 K. The critical behavior near the magnetic transition has been systematically investigated. The Widom scaling relation and magnetic entropy change calculation have verified the reliability of critical parameters. Maximum magnetic entropy change around the magnetic transition temperature shows the magnetocaloric effect. The estimated values of critical parameters are close to the value of the theoretical mean-field model. Temperature-dependent Raman study shows spin-phonon coupling in the system. The appearance of the magnetocaloric effect and colossal dielectric constant shows that these materials are interesting for real-life applications.

Electronic transport mechanisms in a thin crystal of the Kitaev candidate α -RuCl3 probed through guarded high impedance measurements

α-RuCl3 is considered to be the top candidate material for the experimental realization of the celebrated Kitaev model, where ground states are quantum spin liquids with interesting fractionalized excitations. It is, however, known that additional interactions beyond the Kitaev model trigger in α-RuCl3 a long-range zigzag antiferromagnetic ground state. In this work, we investigate a nanoflake of α-RuCl3 through guarded high impedance measurements aimed at reaching the regime where the system turns into a zigzag antiferromagnet. We investigated a variety of temperatures (1.45–175 K) and out-of-plane magnetic fields (up to 11 T), finding a clear signature of a structural phase transition at ≈160 K as reported for thin crystals of α-RuCl3, as well as a thermally activated behavior at temperatures above ≈30 K, with a characteristic activation energy significantly smaller than the energy gap that we observe for α-RuCl3 bulk crystals through our angle resolved photoemission spectroscopy (ARPES) experiments. Additionally, we found that below ≈30 K, transport is ruled by Efros–Shklovskii variable range hopping (VRH). Most importantly, our data show that below the magnetic ordering transition known for bulk α-RuCl3 in the frame of the Kitaev–Heisenberg model (≈7 K), there is a clear deviation from VRH or thermal activation transport mechanisms. Our work demonstrates the possibility of reaching, through specialized high impedance measurements, the thrilling ground states predicted for α-RuCl3 at low temperatures in the frame of the Kitaev–Heisenberg model and informs about the transport mechanisms in this material in a wide temperature range.

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.

Electrical transport mechanism and magnetoresistive behavior of trilayer La0.7Sr0.3MnO3/γ-Fe2O3/La0.7Sr0.3MnO3 (FM/FIM/FM) manganites

The magnetization, electrical transport, and magnetoresistance (MR) behavior of Pulsed Laser Deposited polycrystalline tri-layer La0.7Sr0.3MnO3 (LSMO)/γ-Fe2O3/LSMO film and single layer LSMO film on Si (100) substrates are investigated in the temperature range of 5 K–300 K. A magnetic anomaly appears in the magnetization {M(T)} and resistivity {ρ(T)} characterizations of the trilayer film at around 100 K, which is quite robust and is present even at 7 T of the applied magnetic field. The trilayer sample exhibits metal to insulator (MIT) transition at 210 K. The transport behavior of both the films is analysed in the context of nearest-neighbour small polaron hopping model (SPH), Mott variable range hopping (VRH) mechanism as well as thermal activation (TA) model in different temperature ranges for both the films under study. The correlated polarons or less mobile bipolarons exist in the metallic regime of the trilayer sample due to the presence of magnetic inhomogeneities. The low temperature resistivity upturn is observed in LSMO film, which is attributed to the spin fluctuations (Mn3+–O–Mn4+) due to thermal energy. The trilayer sample exhibits a large negative MR of (∼45%) at low temperature (5 K). It manifests consistent negative CMR effect across the whole temperature range of 5 K–210 K (MIT). The improved MR behavior of the trilayer sample as compared to the LSMO film is due to enhanced polycrystalline character of the trilayer film owing to higher grain boundary density and spin dependent scattering at both the interfaces of LSMO/γ-Fe2O3/LSMO structure.

Impurity-related defect complexes-mediated ferromagnetism and impurity band hopping conduction in a highly compensated Zn-doped SnO2

We reported the ferromagnetism (FM) and electrical transport properties induced by donor-acceptor compensated defect complexes and related impurity bands in highly compensated Zn-doped SnO2 thin films. Various characterizations were used to study the optical, electrical, luminescent, and magnetic properties of SnO2 films with Zn dopants. Comparing with the paramagnetic nature of undoped n-type SnO2, we observed a room temperature d0 FM in the highly compensated and p-type Zn-doped SnO2 films with a low conductivity of ∼10−3 Scm−1, suggesting a strong correlation between ferromagnetism and the donor-acceptor compensation. The coercive field, remanent and saturation magnetization for the Zn-doped SnO2 film at 300 K are 310 Oe, 0.8 emu/cm3, and 2.6 emu/cm3, respectively. A detailed analysis for temperature-dependent resistivity indicates that the electrical conduction behavior of Zn-doped SnO2 at low temperatures follows the variable range hopping mechanism proposed by Mott and confirms that impurity bands occur at the Fermi level. As the concentration of Zn dopants increases, the fitting Mott temperature gradually rises, suggesting the contribution of Zn impurities to form the impurity bands where the carriers are localized. First-principles calculations reveal that the Zn substituting Sn site (ZnSn) defect with a low formation energy is responsible for the transformation of the charge carrier type. Furthermore, the oxygen vacancy (VO) between two nearest-neighbor ZnSn defects can stabilize the ferromagnetic coupling and form Mott's variable range hopping conduction derived from the localized carriers in the compensated impurity bands. Our results are of significance for the better understanding of the physical mechanisms underlying the effects of impurity/defect bands on the magnetic and electrical properties of the SnO2 with Zn dopants.

Thickness tuneable dielectric, optical and magnetic response of lithium ferrite thin films deposited by pulsed laser deposition

Spinel ferrite thin films are in demand for efficient device applications due to their promising properties. So, improvement of their magnetic and dielectric behavior for miniaturizing devices is necessary. The lithium ferrite thin films (single phase with a spinel structure space group - P4132) are deposited at 700 °C on Pt(111)/Ti/SiO2/Si and quartz substrates with different thicknesses. The calculated d – spacing of 240 nm from the selected area electron diffraction pattern is in good agreement with the X-ray diffraction results. X-ray photoelectron spectroscopy confirmed the presence of Li, O, and other valance states of Fe ions. The microstructure of the films revealed the formation of uniform grains with well-separated grain boundaries. Further, the root-mean-square surface roughness is decreased from 11 nm (160 nm) to 9 nm (240 nm) and increased only for 300 nm. The optical bandgap is found to be in the range of 2.58 ‒ 2.30 eV and decreaded with the increase in film thickness. The saturation magnetization in-plane and out-of-plane is reduced monotonically with an increase in thickness attributed to the decrease in the compressive strain. The coercivity increased with the increase in film thickness. The dielectric constant improved, whereas dielectric loss decreased with an increase in thickness. The impedance spectra revealed the contribution of grain boundary is reduced with the increase in film thickness and is analyzed using the equivalent circuit model. The involved conduction process is well fitted with the Mott's variable range hopping mechanism. The obtained results demonstrate that desired response can be obtained by tailoring the film thickness for the microwave and magnetic devices such as magnetic oxide semiconductor.

Nature of polaronic hopping conduction mechanism in polycrystalline and nanocrystalline Gd0.5Sr0.5MnO3 compounds

In the present study, we have investigated the structural, electrical and magneto-transport properties of polycrystalline and nanocrystalline Gd0.5Sr0.5MnO3 compounds. The variation of transport properties is modified by tuning the grain size of the material. In the high temperature semiconducting region, temperature dependent resistivity data can be well explained by non-adiabatic small polaron hopping (SPH) mechanism. In addition, the resistivity data for all compounds in the low-temperature paramagnetic region can also be well explained by the variable range hopping (VRH) model. The parameters obtained from SPH and VRH mechanisms are found to be reasonable. In the case of nanocrystalline compounds, there is an overlapping temperature range where both SPH and VRH models are valid simultaneously, and a new conduction mechanism - variable range hopping of small polaron s(VR-SPH) is satisfactorily valid for the whole temperature range of these compounds. However, for the polycrystalline compound, the overlapping temperature region between VRH and SPH models does not exist and the VR-SPH mechanism is not valid here. Thus, polarons play a leading role in selecting different conduction mechanisms in different temperature ranges.

Thickness-tunable magnetic and electronic transport properties of the quasi-two-dimensional van der Waals ferromagnet Co0.27TaS2 with disordered intercalation

The intercalation of magnetic elements in nonmagnetic van der Waals (vdW) materials is an effective way to design different (quasi) 2D magnets and produce exotic properties. More specifically, how exactly the intercalator is distributed within the synthetic crystal can also affect the physical properties substantially. In contrast to conventional $3d$ transition-metal intercalates of niobium and tantalum dichalcogenides, which commonly have $2\ifmmode\times\else\texttimes\fi{}2$ or $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ type ordered intercalation, we report a disordered intercalation of Co atoms between the vdW gaps of $2H$-tantalum disulfide ($2H\text{-Ta}{\mathrm{S}}_{2}$). The obtained quasi-vdW ferromagnet ${\mathrm{Co}}_{0.27}\mathrm{Ta}{\mathrm{S}}_{2}$ shows both perpendicular magnetic anisotropy and thickness-tunable magnetic properties. More interestingly, the temperature dependence of electrical resistivity shows a semiconductorlike behavior, in contrast to the metallic feature of other analogs in this material family. This unexpected phenomenon can be understood through a variable-range hopping mechanism, which is due to highly disordered intercalation. Moreover, ${\mathrm{Co}}_{0.27}\mathrm{Ta}{\mathrm{S}}_{2}$ shows a side-jump scattering dominated anomalous Hall effect, which can also be related to the disordered distribution of Co intercalators.

Rapid Printing of High-Temperature Polymer-Derived Ceramic Composite Thin-Film Thermistor with Laser Pyrolysis.

Polymer-derived ceramic (PDC)-based high-temperature thin-film sensors (HTTFSs) exhibit promising applications in the condition monitoring of critical components in aerospace. However, fabricating PDC-based HTTFS integrated with high-efficiency, high-temperature anti-oxidation, and customized patterns remains challenging. In this work, we introduce a rapid and flexible selecting laser pyrolysis combined with a direct ink writing process to print double-layer high-temperature antioxidant PDC composite thin-film thermistors under ambient conditions. The sensitive layer (SL) was directly written on an insulating substrate with excellent conductivity by laser-induced graphitization. Then, the antioxidant layer (AOL) was written on the surface of the SL to realize the integrated manufacturing of double-functional layers. Through characterization analysis, it was shown that B2O3 and SiO2 glass phases generated by the PDC composite AOL could effectively prevent oxygen intrusion. Therefore, the fabricated PDC composite thermistors exhibited a negative temperature coefficient in the temperature range from 100 to 1100 °C and high repeatability below 800 °C. Meanwhile, it has excellent high-temperature stability at 800 °C with a resistance change of only 2.4% in 2 h. Furthermore, the high-temperature electrical behavior of the thermistor was analyzed. The temperature dependence of the conductivity for this thermistor has shown an agreement with the Mott's variable range hopping mechanism. Additionally, the thermistor was fabricated on the surface of an aero-engine blade to verify its feasibility below 800 °C, showing the great potential of this work for state sensing on the surface of high-temperature components, especially for customized requirements.

Ordered phase transformation and Cu doping effects in room-temperature ferromagnetic Sr3YCo4O10.5+δ.

Sr3YCo4O10.5+δ (314-SYCO), with an unusual ordered structure and a high Curie temperature (Tc ≈ 335K), is attracting increasing attention. Herein, to improve the electrical performance of 314-SYCO, Cu-doped Sr3YCo4-x Cu x O10.5+δ (x = 0-0.8) ceramics were prepared using a solid-state reaction method. Systematic research was conducted on both the ordered phase transformation and the effects of Cu doping on the microstructure, electrical transport characteristics, and magnetic properties. For x = 0-0.4, the (103) and (215) planes were observed and combined with Rietveld refinement results for the X-ray diffraction data, confirming the formation of ordered tetragonal Sr3YCo4-x Cu x O10.5+δ . This phase was formed with a mass gain of ∼0.8% and heat released at ∼1,042°C. With increasing Cu content, the concentration of hole carriers also increased, leading to a substantial reduction in electrical resistivity. The electrical resistivity decreased by 92-99% at 300K. The polycrystalline materials have semiconducting behaviour with a three-dimensional Mott variable-range hopping mechanism. For the magnetic properties, a Hopkinson peak was observed at 319K, and the Tc was approximately 321K for x = 0. The magnetisation and Tc decreased with increasing Cu content, and a G-type antiferromagnetic-to-ferromagnetic phase transition occurred due to the spin state change for some Co3+ ions from high/intermediate spin to low/intermediate spin. These results lay the groundwork for refinement of the sintering procedure and doping parameters to enhance the performance of 314-SYCO in the context of current applications such as microwave absorbers and solid oxide fuel cell cathodes.

Quenching of oxygen-related defects in graphene oxide nanohybrid: Highly selective room-temperature ethanol sensor

The presence of surface defects, such as epoxy and carbonyl groups, is known to control the charge-carrier transport in graphene oxide (GO). In addition, these surface entities also provide an opportunity to synthesize novel hybrid (NH) materials via chemical bonding. These hybrid materials are particularly interesting for sensing as they offer novel properties like larger surface area and improved physical/chemical properties. Herein, we are proposing a novel SiO2@GO–NH based room-temperature (RT) ethanol sensor. The NH is realized from solution-route by following the sol–gel chemistry of tetraethyl orthosilicate. The attachment of SiO2 with the GO network occurs via the formation of Si–O–C bonds, which also leads to the reduction in the atomic percentage of electron-withdrawing groups. This reduction results in the improvement in electron charge transport in GO, which leads to the RT detection of ethanol. Specifically, the charge transport in NH is found to be dominated by a field-driven temperature-independent 2D variable-range hopping mechanism. While the ethanol sensing mechanism is found to be governed by two processes, i.e., via direct interaction of ethanol with NH and interaction with chemisorbed oxygen ions on the Pt/Si@GO–NH interface. Detailed observations reveal that the SiO2–GO NH has great potential to be used as a biomarker for food quality control.

Transition from paramagnetism to ferromagnetism through additional hole doping of non-magnetic antimony in iron doped tellurium alloy

We have found an enhancement in the magnetic ordering of tellurium as a result of doping it with iron along with an additional doping of a non-magnetic element antimony. A weak ferromagnetism is observed from the magnetization hysteresis which can pave the way for new kinds of magnetic semiconductors. Using the modified solid state approach, we synthesized bulk alloys of Fe-doped tellurium with co-doping of Sb having general form Fe0.05(Te)1−xSbx; x = 0 and 0.03 and analyzed the sample for their structural, electrical and magnetic properties. Electrical resistivity measurements with varying external magnetic field has been carried out and it shows semiconducting nature for both samples. The conduction mechanism in the high temperature region follows small polaron hopping (SPH) model whereas in the low temperature region, variable range hopping (VRH) model is found to fit the data. Traditionally, though tellurium is diamagnetic in nature, x = 0 sample presents itself as a paramagnetic material as evident from the magnetization measurements. On the other hand, x = 0.03 sample has a small hysteresis which is brought about by the substitution of Sb. A negative to positive crossover is observed in the magnetoresistance plot of both samples which can be co-related to transition from variable range hopping mechanism to thermally activated hopping mechanism.

Structural, magnetic, and electrical transport properties of half-metallic double perovskite La2CrNiO6 oxides

We report on hydrothermal growth of double perovskite La2CrNiO6 (LCNO) powders, which are theoretically predicted to be half-metallic ferrimagnet. Their structural, magnetic, and electrical transport properties are comprehensively studied. The crystal structure of LCNO powders belongs to an orthorhombic crystal structure with Pbnm space group. The saturation magnetization of the LNCO powders was 0.32 μB/f.u. at 5 K (close to the theoretical value of 0.30 μB/f.u. calculated for a disordered system) and the coercive field was 3000 Oe. The negative Curie-Weiss (CW) temperature (θp = −35 K) indicates the predominant antiferromagnetic (AFM) interactions in the powders and ferrimagnetism with magnetic Curie temperature (TC) of 106 K. A spin glass-like behavior was observed in the LNCO powders as cooling the sample from paramagnetic state to the low-temperature ferro/ferrimagnetic state, which is originated from the magnetic interaction competitions via the AFM (Cr4+−O−Cr4+, Ni2+−O−Ni2+ or Ni2+−O−Cr3+) and FM (Ni2+−O−Cr4+ and Ni3+−O−Cr3+) magnetic paths. The observed sharply down deviation from the Curie-Weiss law below 290 K is decreased with the applied magnetic field increased, which leads to Griffiths-like phase in the powders. XPS spectroscopy reveals dual chemical states of Ni ions (Ni2+ and Ni3+) and Cr ions (Cr3+and Cr4+) in the powders, and two kinds of oxygen species exist in the forms of lattice oxygen and adsorbed oxygen. The electrical transport process of the LCNO powders is governed by small polaron variable range hopping mechanism, where the hopping path of localized electrons are provided by the B-site heterovalent metal Ni and Cr ions.