Mott Variable Range Hopping Research Articles

Electronic and structural properties of the honeycomb iridates A2IrO3 ( A=Na , Li) at elevated pressures

The honeycomb lattice iridates ${A}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$ ($A=\mathrm{Na}$, Li) are spin-orbit assisted Mott insulators proximate to Kitaev's quantum spin liquid. The insulating state as well as the magnetic properties are believed to arise due to a delicate balance of several energy scales. We report on high-pressure electrical transport and x-ray-diffraction measurements on ${A}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$ ($A=\mathrm{Na}$, Li) in an attempt to study their structural and electronic evolution with pressure. We found that while $\mathrm{L}{\mathrm{i}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$ undergoes a structural phase transition into the dimerized state at a pressure of $P$ \ensuremath{\sim} 4 GPa, in $\mathrm{N}{\mathrm{a}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$ the conservation of the original $C2/m$ structure up to at least 58 GPa is observed. In addition, $\mathrm{L}{\mathrm{i}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$ undergoes a sluggish structural rearrangement at the pressure range 20--40 GPa coinciding with a significant decrease in resistance. Despite dissimilar structural evolution and different mechanisms of the electrical conductivity, Arrhenius conductivity for $\mathrm{N}{\mathrm{a}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$ and Mott variable-range hopping in $\mathrm{L}{\mathrm{i}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$, both systems show a very similar $R$($P$) behavior. Namely, after a nonmonotonic decrease of the resistance $R$ and the charge gap \ensuremath{\Delta}, the \ensuremath{\Delta} stabilizes at about 45 GPa and even increases slightly with pressure; the $R$($T$) shows insulating behavior up to the highest pressure measured, 80 and 55 GPa, respectively. This resilient nonmetallic behavior of the studied iridates suggests a formation close to a localized-itinerant crossover of unusual electronic states, whose possible features are discussed. Unforeseeably, the $R$($P$) behavior is not dependent on the buffer element $A$, which seems essential for understanding the nature of the electrical conductivity in iridates.

Enhancing superconductivity of Y5Rh6Sn18 by atomic disorder

For a number of skutterudite-related cage compounds, such as cubic ${R}_{3}{M}_{4}{\mathrm{Sn}}_{13}$ ($R=\mathrm{Ca}$ or La, $M=\text{transition}$ $d$-electron metal) or tetragonal ${\mathrm{Y}}_{5}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$, we have previously reported the impact of various atomic defects in the crystal lattices on the normal-state and superconducting properties of these clathrates. In these quasiskutterudites the nanoscale disorder and/or local inhomogeneity in composition lead to an abnormal increase in the superconducting transition temperature ${T}_{c}$. Here we investigate the impact of atomic defects in the superconductors ${\mathrm{Lu}}_{5\ensuremath{-}\ensuremath{\delta}}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$ (tetragonal symmetry $I{4}_{1}/acd$). We have documented that ${\mathrm{Lu}}_{5}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$ does not crystallize in the assumed stoichiometry but forms a 5-6-18 phase with a Lu deficiency ($\ensuremath{\delta}\ensuremath{\approx}0.5$). Our comprehensive investigations of electronic structure and thermodynamic and electrical transport properties documented a ${T}_{c}$ increase in the more disordered sample (sample 1). The quality of two investigated samples (sample 1 and sample 2) with similar stoichiometry but different local inhomogeneity was obtained by microanalysis and electron transmission microscopy observations. The band structure calculations show a hybridization pseudogap in the electronic bands of stoichiometric ${\mathrm{Lu}}_{5}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$ at about 0.3 eV in respect to the Fermi level ${\ensuremath{\epsilon}}_{F}$. The ab initio calculations predict the scenario that vacancies could shift this pseudogap towards ${\ensuremath{\epsilon}}_{F}$, which is manifested by the Mott variable-range hopping behavior in the resistivity $\ensuremath{\rho}\ensuremath{\sim}{T}^{\ensuremath{-}1/4}$ of more homogeneous sample 2.

Underpinning the conductivity mechanism in wide bandgap metal organic framework through chemical sensing

Metal organic frameworks are an emerging class of materials with a broad range of electronic properties with diverse applications such as sensors, catalysts, and permeable membranes. Here, three isostructural wide bandgap (WB) zeolitic imidazole frameworks (ZIFs) are synthesized having metal ion sites occupied by Zn (ZIF-8, Eg = 5.3 eV), Co (ZIF-67, Eg = 4.3 eV), and both Zn and Co (50%–50% mixture). The conductivity mechanism in these WB ZIFs involves the Mott variable range hopping of charge carriers from one metal site to the other. The hopping probability in the mixture is governed by the constitute having a lesser activation energy. Thus, it reveals that the incorporation of a different metal ion (Co in place of Zn) in the lattice forms a parallel low resistance path through hopping at Co sites and hence reduces the sensor response as well as selectivity toward ammonia. This parallel resistance path of the Co channel does not get affected by ammonia since it is found that ammonia has high affinity toward Zn ions and not toward Co ions. Thus, the incorporation of new metal ions hinders the hopping charge transport mechanisms in ZIFs.

Summerfield scaling model and conduction processes defining the transport properties of silver substituted half doped (La–Ca) MnO3 ceramic

Conductivity spectra of La0.5Ca0.3Ag0.2MnO3 (LCAM) oxide have been investigated in the temperature range [80 K–680 K]. The studied system displays a semiconductor behavior over the explored temperature and frequency ranges. From direct current study, the transport of charge carries is assisted via disorder energy below θD/4. For the temperature range [θD/4- θD/2], the transport properties are governed by activation of Mott-variable range hopping (Mott-VRH) process. Beyond θD/2, the conduction phenomena are assisted through the thermally activation of the small polaron hopping (SPH) mechanism. At high frequencies, the conductivity spectra reveal a dispersive region. They are explained by the double Jonscher response. The latter side was characterized by the appearance of the overlapping-large-polaron-tunneling (OLPT), the correlated barrier hopping (CBH) and the non small polaron tunneling (NSPT) conduction processes. It is found that the calculated disorder energy is frequency independent. At elevated frequencies, the hopping energy is predicted to decrease with increasing frequency which can be related to the change in the Polarons radius. In the temperature range [80 K–220 K], the conductivity spectra follow double Jonscher law. Using the scaling model, the spectra merge into a single master curve, which confirmed the validity of the time temperature superposition principle (TTSP). A confident divergence from the Summerfield is noticed at high frequencies. It proves that the charge mobility is temperature dependant. The Summerfield correction scaling is effectuated by introducing a scaling positive parameter (α = 1.2). An excellent coalescence of conductivity spectra is observed.

Thermoelectric properties of paracostibite fabricated using chemically synthesized Co–Sb–S nanoparticles as building blocks

Paracostibite (CoSbS) is a promising candidate for n-type thermoelectric materials. In this study, a nanostructured CoSbS pellet was fabricated using chemically synthesized Co–Sb–S nanoparticles as building blocks. The CoSbS pellet showed the highest electrical conductivity (σ = 141 S/cm at 661 K) and lowest thermal conductivity [κ ≅ 2 W/(m K)] among the reported CoSbS. Detailed analysis of the electrical transport process in a wide temperature range (3 K–661 K) revealed the existence of a donor level. At a temperature less than 170 K, the resistivity showed Mott variable-range hopping behavior, while the band conduction became dominant as the temperature increased. Nanograins in the pellet significantly enhanced phonon scattering, resulting in suppression of κ. The maximum dimensionless figure of merit value was 0.05 at 661 K, which is comparable with previously reported values for CoSbS TE materials.

Paramagnetism, hopping conduction, and weak localization in highly disordered pure and Dy-doped Bi2Se3 nanoplates

Breaking the topological protection of surface states of topological insulators is an essential prerequisite for exploring their applications. This is achievable by magnetic doping, in reduced dimensions, and predictably by introducing disorder beyond a critical level. In certain cases, the former is also known to induce a transition from weak anti-localization (WAL) to weak localization (WL). Here, we report the occurrence of paramagnetism, hopping conduction, and WL in chemically prepared unannealed DyxBi2−xSe3 (x=0, 0.1, and 0.3) nanoplates primarily via dc magnetization, resistivity, and magnetoconductance measurements. The paramagnetism in the magnetic-atom-free Bi2Se3 nanoplates is ascribed, using density functional theory calculations, to the acquisition of magnetic moments by defects. The defect density in pure Bi2Se3 is estimated to be high (∼1019 defects/cm3). Successive Dy doping brings in further incremental disorder, apart from the Dy atomic moments. The nanoplates are shown to sequentially exhibit thermally activated band conduction, nearest neighbor hopping, Mott variable range hopping (VRH), and Efros–Shklovskii VRH with decreasing temperature. WL is evident from the observed positive magnetoconductance. Annealing converts the WL behavior to WAL, arguably by setting in the topological protection on a substantial reduction of the disorder.

Thickness Effects on Crystal Growth and Metal–Insulator Transition in Rutile‐Type RuO2 (100) Thin Films

The thickness dependence of crystal structure and electrical properties is studied for rutile‐type RuO2 (100) thin films. The island growth mode results in a monotonically varying lattice strain along the a‐axis from negative to positive with increasing thickness. Decrease in the thickness below 20 nm increases the resistivity drastically, resulting in insulating‐like behaviors. The metallic behaviors of the thicker films are well explained by the modified Bloch–Grüneisen function as in bulk RuO2, where the strain has a significant influence on the conduction parameters. The insulating‐like behaviors of the thinner films are assigned to 2D localization and Mott variable range hopping, reflecting the effects of the size and growth mode on electrical conduction.

Dark and photoconductivity of PbS/polystyrene nanocomposite films from 77 to 300 K

The temperature variation of electrical properties of PbS/polystyrene (PS) nanocomposite films has been investigated in dark and under illumination in the temperature range of 77 to 300 K. Dark conductivity of the films is a combination of Mott variable range hopping (M-VRH) from 77 to 125 K, Nearest neighbour hopping (NNH) from 125 to 185 K and thermally activated band conduction (TABC) from 250 to 300 K. The activation energies of NNH and TABC are 17 and 85 meV, respectively. The films are highly photoconducting below 100 K. Photoconductivity of films first increases slowly up to 100 K and then decreases until 300 K. Photoconductivity sensitization centreat 34 meV below LUMO have been identified from quenching of photoconductivity. The results are explained on the basis of interaction between PbS nanoparticles and polystyrene.

Investigation of transport phenomenon and magnetic behavior of Fe doped In[formula omitted]O[formula omitted

In this report the pursuance of Fe concentration on the structural, microstructural, optical, transport and magnetic properties of Indium Oxide (In2O3) have been systematically investigated. Rietveld refined X-ray diffraction, high resolution transmittance electron microscope (HRTEM), selected area electron diffraction (SAED) and Raman patterns substantiated the pure single phase of In2−xFexO3 (x = 0.0-0.4) nanocrystalline cubic bixbyite structure. The average crystallite (grain) size is found to be decreased from ∼ 38.3 to ∼ 27.2 nm with x = 0.0 to 0.4 Fe doping and average particle size of the samples for x = 0.0 and x = 0.2 are measured ∼ 49 nm and ∼ 41 nm respectively from TEM, while the optical band gap stays around ∼ 3.7 eV for each sample. The electrical resistivity is observed to increase with increase in Fe doping which is concomitant with the decrease in oxygen vacancy observed from X-ray photoelectron spectroscopy (XPS) study and photoluminescence (PL). The samples with x = 0.0, 0.01, and 0.2 showed the normal semiconducting behavior and well fitted with thermal activation conduction band (TACB), nearest neighbor hopping (NNH) and Mott-variable range hopping (Mott-VRH) models. The magnetic behavior has a concurrence with the bound magnetic polaron (BMP) model in the vicinity of oxygen vacancies.

Structural and transport properties of composite of La0.8Sr0.2MnO3 and BaTiO3 materials

We studied the effect of BaTiO3 phase on the structural, vibrational, and electrical properties of La0.8Sr0.2MnO3. The parent samples of La0.8Sr0.2MnO3, BaTiO3 and their composite (0.85) La0.8Sr0.2MnO3 + (0.15) BaTiO3 were synthesized by solid-state reaction route. Structural study using X-ray diffraction (XRD) for La0.8Sr0.2MnO3 phase revealed a rhombohedrally distorted (space group R3c) structure, while BaTiO3 compound was found to have crystallized in tetragonal structure (space group P4mm). The XRD results were verified using Rietveld refinement. The composite sample (0.85) La0.8Sr0.2MnO3 + (0.15) BaTiO3 display the presence of both of La0.8Sr0.2MnO3 and BaTiO3 phases. The addition of insulating BaTiO3 phase in the ferromagnetic metallic phase of La0.8Sr0.2MnO3 which exhibits well-characterized metal-to-insulator transition in the vicinity of 350 K enhances the resistivity and shifts the metal–insulator transition temperature TMI towards lower temperature. Further, with the application of magnetic field, resistivity of the composite sample is found to decrease and TMI in composite sample is observed to shift towards higher temperature. The magnetoresistance (MR) of composite sample (0.85) La0.8Sr0.2MnO3 + (0.15) BaTiO3 decreases monotonously in 200–300 K regime under magnetic field of 8 T. The analysis of electrical resistivity data in the metallic region (T TMI) is well described using Small polaron hopping (SPH) and Mott's variable range hopping (VRH) models.

Tunable electron transport with intergranular separation in FePt-C nanogranular films

We report electron transport mechanism in FePt-C granular films as a function of temperature by varying intergranular separation. FePt-C nanogranular films were prepared by sputtering on MgO substrates. From magnetic measurement of the sample, a coercivity of about 3T was found in the perpendicular direction. Above 25 K, the electrical resistivity of the films were found to obey Mott variable range hopping, Efros-Shklovskii variable range hopping and extended critical regime depending on the intergranular separation. However, at lower temperatures it deviates from the above behaviour showing an increase in conductance. Reduced activation energy calculated from resistivity data of these films shows metal-insulator transition. The metallic nature observed at low temperature was attributed to the intergranular ferromagnetic type ordering between granules that enhances the transport of electrons. Intergranular separation, thus, can be used as a tool to engineer the electron transport mechanism to different hopping regimes or extended critical regime in these films.

Comparison of temperature dependences of electrical conductivity of composite rGO-SWNT film with rGO and SWNT films

Temperature dependences of electrical conductivity of reduced graphene oxide composite with single-walled nanotubes (rGO-SWNTs) and rGO films has been studied in the temperature range of 25–290 K. Both films were obtained by vacuum filtration of aqueous suspensions. Temperature dependences of conductivity of films were found similar to the conductivity observed in disordered semiconducting systems. It was demonstrated that the behavior of the conductivity temperature dependence of pure rGO, SWNTs and composite film is different. The temperature dependences of the resistance R(T) of the films were analyzed within the framework of the variable range hopping (VRH) transport in which electron motion is due to the thermo-activated quantum tunneling between localized states. Two-dimensional Mott VRH (Mott 2D VRH) and Efros-Shklovskii VRH (ES VRH) models were applied for analysis. Mott 2D VRH was observed for rGO-SWNT film in the interval of 25–200 K. At higher temperatures R(T) of rGO-SWNT was fitted with Arrhenius-like equation describing electron activation from localized states to delocalized ones. R(T) of the rGO film followed the Mott 2D VRH model from 165 to 290 K, however, at lower temperatures ES VRH model was exploited. From approximation of R(T) by these models the parameters of the electron transport in rGO-SWNT and rGO films were estimated. It was suggested that nanotubes in rGO-SWNT composite serve as conductive bridges among rGO sheets enhancing the conductivity as compared to rGO. The conductivity of rGO also influences on the composite properties because 2D character of electron motion is kept in sharp contrast to SWNT film which demonstrated three-dimensional Mott VRH electron transport in the same temperature range.

Effect of oxygen flow rate on physical properties of Al-doped ZnO transparent conducting films prepared by reactive dc magnetron sputtering using metallic Zn:Al target

In this work, Al-doped ZnO transparent conducting thin films were prepared by a reactive dc magnetron sputtering method on slide glass substrate using single metallic Zn:Al (2 wt.% Al) target with the oxygen flow rate 1, 3, 5, 7 and 9 sccm, respectively. From XRD patterns, the films prepared at R(O2) of 1 sccm showed amorphous characteristics. In contrast, the films prepared at R(O2) of 3, 5, 7 and 9 sccm showed the preferred orientation (002) plane of hexagonal structure. Surface morphology and diameter of nanocolumns of the films were observed by AFM and FESEM. From transmittance spectra, energy gap value was found to vary between 3.24 and 3.32 eV. Electrical resistivity and Hall effect measurements were performed on the films with van der Pauw configuration. The temperature-dependent conductivity was performed in the range 20-300 K. Three types of conduction mechanisms were expected. Thermally activated band conduction at the high temperature range (250-300 K), Mott variable-range hopping (Mott-VRH) at the low temperature range (100-210 K) and Efros-Shklovskii variable-range hopping (ES-VRH) at the very low temperature range (<100 K) can be found in the films prepared with different oxygen flow rate conditions. Except for the oxygen flow rate at 5 sccm, the behavior of weakly localized electrons was observed. Then, the sets of parameters explaining the properties of localized electrons in each conduction regime were determined. The results indicated that the reactive dc magnetron sputtering using a single metallic Zn:Al (2 wt.% Al) target is suitable for TCO films since it can be easily obtained at low temperatures with good physical properties.

Thickness induced metal to insulator charge transport and unusual hydrogen response in granular palladium nanofilms.

This work reports a systematic study of the evolution of charge transport properties in granular ultra-thin films of palladium of thicknesses varying between 6 nm and 2 nm. While the films with thickness >4 nm exhibit metallic behaviour, that at 3 nm thickness undergoes a metal-insulator transition at 19.5 K. In contrast, the 2 nm thick film remained insulating at all temperatures, with transport following Mott's variable range hopping. At room temperature, while the thicker films exhibit resistance decrease upon H2 exposure, the insulating film showed an anomalous initial resistance increase before switching to a subsequent decrease. The nanostructure dependent transport and the ensuing H2 response is modeled on a percolation model, which also explores the relevance of film thickness as a macroscopic control parameter to engineer the desired system response in granular metal films.

Charge transport in pyroprotein-based electronic yarns.

Pyroprotein-based carbon materials produced by heat-treating silk proteins have many potential applications in electronic devices, such as electronic textiles. To further develop potential electronic devices using these pyroproteins, the charge transport mechanism has to be verified. However, the electrical characteristics of the pyroproteins have not been reported yet. In this study, the temperature-dependent charge transport behavior of pyroprotein-based electronic yarns prepared from commercial silks (e-CS yarns) is investigated with respect to various heat treatment temperatures (HTT, 800, 1000, 1200, and 1400 °C). The linear current-voltage properties are shown at a low bias of 100 nA from 9 K to 300 K. The temperature-dependent resistivity of the e-CS yarns can be clearly described by the crossover of 3-dimensional Mott variable range hopping and fluctuation-induced tunneling conduction at the crossover temperature (Tc). These Tc factors are significantly different, due to the structural modulation of the e-CS yarns depending on the HTT, and are characterized by Raman spectroscopy, X-ray diffraction, and transmission electron microscopy. This study is expected to provide a better understanding of the electrical properties of pyroproteins.

The electronics transport mechanism of grain and grain boundary in semiconductive hafnium oxynitride thin film

HfOxNy thin film was deposited on oxidized silicon substrate; its physical structure and chemical composition were studied in detail by X-ray diffractometer, scanning electron microscopy, field emission transmission electron microscope and X-ray photoelectron spectrometer. Microtemperature sensors with high sensitivity based on the film were fabricated. To clarify the conduction process of grain, grain boundary (GB) and the whole film, temperature-dependent AC impedances of a sensor were measured and analyzed in 40–300 K. The results show that at all of the measured temperatures, the resistance of grain is much larger than that of GB, and its rising rates with the temperature reduction are also much larger than that of GB, indicating that the resistive property of HfOxNy thin film is determined by grain. In addition, it has been confirmed that the conduction process of both the HfOxNy film and GB is dominated by thermal activation and Mott variable-range hopping (VRH) in relatively high and low temperature range, respectively. The conduction process of the grain obeys Mott VRH in the whole considered temperature range, while the Mott characteristic temperature is changed. These results provide new insights into the performance enhancement of the transition metal oxynitride-based temperature sensors.

Enhancement of conductivity and transmittance of graphene oxide/PEDOT:PSS electrodes and the evaluation of charge transfer dynamics

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS, is a polymeric composite that can substitute indium tin oxide (ITO), enabling ITO-free organic devices. However, PEDOT:PSS films have conductivities two orders of magnitude lower than ITO due to the presence of PSS, an insulator polymer added to provide water dispersion to PEDOT. To enhance the electrical performance of the films and overcome the insulator limitations, we prepared thin films of graphene oxide (GO) and PEDOT:PSS composites. The dried films were then treated with ethylene glycol (EG). An increment of two orders of magnitude in conductivity values was observed, as well as an increase in transmittance at the visible region. Also, GO:PEDOT:PSS thin films became more hydrophobic due to the partial removal of PSS. The mass ratio that is equal to 0.058 of GO/PEDOT provides higher electrical conductivity due to higher chain orientation of PEDOT as seen in the near edge X-ray absorption fine structure and resonant Auger spectroscopy measurements. The electrical transport follows the Mott Variable Range Hopping model for low temperature, showing that the conduction occurs in three dimensions. The solvent treatment increases the characteristic conductivity and decreases the activation hopping energy, with the characteristic temperature remaining almost unchanged. It indicates that the EG treatment promotes a decrease in charge transfer time and resistivity.

The dependence of fractal figures formed in irradiated germanium on temperature and composition

D C conductivity (σ) measured in the temperature (T) range (300 K–1.7 K) for p-Type Ge irradiated with γ quanta and /or large fluencies of reactor neutrons. The obtained conductivity results reveal that, the activation energies of different conductivity mechanisms are found E1 > E2 > E3 and σo > σ1 > σ2. Also, Meyer- Neldel Rule (MNR) is applicable in different conduction mechanisms. As well as, in hopping conduction mechanisms with different values of Meyer-Neldel Energy (HMNR) for each conductivity mechanism. Mott variable range hopping (VRH) σ = f (T−0.25), and Efros Sholovskii Percolation mechanism of conduction (ESPMC) σ = f (T−0.5) of hopping conduction. Observed a crossover between these two mechanisms of hopping conduction. The scaling theory is applicable in the most temperature ranges of conduction mechanisms. and in the hopping conduction mechanisms as well. The obtained critical exponent for Mott (VRH) is equal to 3.6. For Efros-Shkolovskii (ES) percolation mechanism of conduction (PMC) the critical exponent is equal to 1.74. The Mandelbrot fractal systems formed in the present samples are temperature and compositional dependent. The Scanning electron microscope (SEM) result confirms the dependent the fractal figures formed in irradiated germanium on composition and irradiation fluency.

Crossover between Mott and Efros-Shklovskii variable-range hopping in Sr2IrO4 epitaxial thin films by misfit strain and isovalent doping

We report three-dimensional Mott variable-range hopping (3D Mott-VRH) transport of Sr2IrO4 epitaxial thin films, with a transition to Efros-Shklovskii variable-range hopping (ES-VRH) with increased misfit strain or isovalent doping. We have observed that the characteristic temperature of 3D Mott-VRH transport decreases under increased misfit strain, implying that the density of states near the Fermi energy is reconstructed. With further increased misfit strain (or doping with Ca or Ba ions), a crossover from the 3D Mott-VRH to ES-VRH transport takes place due to increased carrier localization by disorder, opening a Coulomb gap by increasing the effective electron-correlation. The results of magnetoresistance measurements also confirm that the disorder caused by misfit strain or isovalent doping plays an important role in the electronic transport of these Sr2IrO4 thin films. Our experimental observations propose that subtle external stimuli such as structural modifications can modulate the electronic properties of the relativistic Mott insulator, suggesting an unprecedented pathway for electronic device applications.

Electrical conductivity and magnetoresistance in twisted graphene electrochemically decorated with Co particles

Abstract Application of magnetic metal/graphene hybrid structures in magnetosensorics requires the formation of high-quality low-ohmic (barrier-free) contacts and understanding of mechanisms of electric charge transfer near and through the metal/graphene contact area. In present paper we fabricate samples of twisted graphene electrochemically decorated with Co particles (Co- G/SiO2) which demonstrate perfect ohmic electric contact between Co and graphene sheets. Temperature and magnetic field dependencies of surface resistance for pure twisted graphene (G/SiO2) and Co-G/SiO2 samples are considered within the models of 3D Mott variable range hopping and 2D weak-localization quantum corrections to the Drude conductivity . Phenomenological model is proposed explaining the experimentally observed transition from predominantly negative magnetoresistive effect in weak magnetic fields B (below 1–2 T) to positive magnetoresistance (PMR) at B beyond 5 T assuming the growth of PMR due to the distortion of current-conducting routes under the influence of Lorentz force which originates from the enhancement of large-scale potential relief in Co- G/SiO2 sample. This work considers the new approach to the application of G/SiO2 decoration with Co particles for creation both metallic (distributed, defragmented) shunts and high-quality ohmic electrodes in magnetic sensing.