Feature article: Electronic transport in granular metal films†

Sheng, Ping

doi:10.1080/13642819208207638

Cited by 163 publications

(68 citation statements)

References 32 publications

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“…19 In a relatively ordered crystalline material, as in the present case, protonation of polyaniline with sulphonic acid results in a decrease in hopping distance and consequently enhances the hopping mechanism (phonon-assisted tunneling between electronic localized states centered at different positions). 20 It is difficult to distinguish between different conduction mechanisms such as quasi-1D variable range hopping mechanism, 21 3D hopping with electron-electron interaction, 22 tunneling between mesoscopic metallic islands 23 or correlated hopping between polaronic clusters in polyaniline. 24 Nevertheless, experimental investigations show that results can be explained very well in terms of the metallic content as well as in terms of dominant hopping/ tunneling mechanism.…”

Section: Resultsmentioning

confidence: 99%

Thermal characterization of doped polyaniline and its composites with CoPc

et al. 2004

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Thermal diffusivity of the composites of camphor sulphonic acid (CSA) doped polyaniline (PANI) and its composites with cobalt phthalocyanine (CoPc) has been measured using open cell photoacoustic technique. Analysis of the data shows that the effective thermal diffusivity value can be tuned by varying the relative volume fraction of the constituents. It is seen that polaron assisted heat transfer mechanism is dominant in CSA doped PANI and these composites exhibit a thermal diffusivity value which is intermediate to that of CSA doped PANI and CoPc. The results obtained are correlated with the electrical conductivity and hardness measurements carried out on the samples.

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Section: Resultsmentioning

confidence: 99%

Thermal characterization of doped polyaniline and its composites with CoPc

et al. 2004

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“…Conduction through such an array of metallic particles with a random distribution of R ij will be along percolation paths encompassing the lowest resistance contacts. These critical paths include weak conductance links where a single contact connects two larger clusters [19]. The CrO 2 particles are sufficiently small and the contact resistance is sufficiently high for single-particle charging to influence the conductivity.…”

mentioning

confidence: 99%

“…The resistivity is shown in Fig. 1(c); with parameters r`2.09 V m and D 6.0 K, it can be fitted to the expression for granular metals in the dielectric regime [19].…”

mentioning

confidence: 99%

Magnetoresistance of Chromium Dioxide Powder Compacts

et al. 1998

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Cold-pressed powders of the half-metallic ferromagnet CrO 2 are dielectric granular metals. Hysteretic magnetoresistance with maxima at the coercive field arises from interparticle contacts. Dilution with insulating antiferromagnetic Cr 2 O 3 powder reduces the conductivity by 3 orders of magnitude, but enhances the magnetoresistance ratio which reaches 50% at 5K. The negative magnetoresistance is due to tunneling between contiguous ferromagnetic particles along a critical path with a spin-dependent Coulomb gap. [S0031-9007(98)05996-1] PACS numbers: 72.15. Gd, 73.40.Gk, 75.50.Cc, 81.20.Ev Negative magnetoresistance has been widely investigated in ferromagnetic metals and heterostructures. Effects intrinsic to a material are distinguished from extrinsic effects which depend on the direction of magnetization in adjacent ferromagnetic regions. Examples of the former include the anisotropic magnetoresistance of permalloy [1] or the colossal magnetoresistance of nonstoichiometric EuO [2] and mixed-valence manganites [3]. Examples of the latter are the giant magnetoresistance of multilayers [4] and granular metals [5,6] or the behavior of spin-dependent tunnel junctions [7], where resistivity is greatest at the coercive or switching field and decreases as the sample reaches technical saturation. Recent experiments on epitaxial manganite films with a single grain boundary have allowed the high-field, colossal magnetoresistance to be separated from the low-field effect due to heterogeneous magnetization distribution in adjacent grains [8,9]. A characteristic but unexplained feature of the low-field magnetoresistance in manganite ceramics [10], polycrystalline films [11,12], and tunnel junctions [13,14] is its rapid decay with increasing temperature.Here we report a new type of extrinsic magnetoresistance. It is studied in pressed powders of CrO 2 , where it arises from contacts between particles. Chromium dioxide is an ideal material for spin-polarized electron tunneling, as it is a half-metallic ferromagnet where complete spin polarization of the conduction electrons is maintained up to the surface [15]. There are two 3d electrons in spinsplit t 2g subbands, one localized and the other in a halffilled band [16]. The two electrons are strongly coupled by the on-site exchange interaction J H ഠ 1 eV. The intrinsic metallic nature of the oxide is illustrated by the resistivity of an oriented film grown on TiO 2 , shown in Fig. 1(a). It follows Matthiessen's rule with a residual resistivity of 0.1 mV m ͑10 mV cm͒ and a room-temperature value about 30 times greater. The slope dr͞dT remains positive above the Curie temperature ͑T C 396 K͒ [17]. The films exhibit only a small linear intrinsic magnetoresistance effect, ͑1͞m 0 r͒dr͞dH ϳ1%͞T at room temperature.Our samples were made from a commercial CrO 2 powder used for magnetic recording. The powder is composed of acicular single-domain particles with an average length of 300 nm and an aspect ratio of about 8:1. Coercivity is 59 mT (590 G) at room temperature, rising up to ...

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“…An additional issue is that embedding non-metallic particles in a metallic matrix should also cause an increase of the resistivity of the nanocomposite formed (the increase becomes especially pronounced when the particle concentration reaches a level where the particles prevent a full percolation of the metallic matrix. 9 In any case, the Ni-Fe/Si 3 N 4 nanocomposite cannot either have lower resistivity than the bulk Ni-Fe alloy. Based on previously reported experimental and theoretical data for a metal matrix with embedded insulating particles 9 and by taking into account that the present nanocomposites contained about 10% nanoparticle fraction, it can be estimated that the electrical resistivity of Ni-Fe/Si 3 N 4 nanocomposites should be higher by about 30% than that of the bulk Ni-Fe alloy.…”

Section: The Refinement Of Grains and Polycrystalline Nature Is Alsmentioning

confidence: 99%

“…9 In any case, the Ni-Fe/Si 3 N 4 nanocomposite cannot either have lower resistivity than the bulk Ni-Fe alloy. Based on previously reported experimental and theoretical data for a metal matrix with embedded insulating particles 9 and by taking into account that the present nanocomposites contained about 10% nanoparticle fraction, it can be estimated that the electrical resistivity of Ni-Fe/Si 3 N 4 nanocomposites should be higher by about 30% than that of the bulk Ni-Fe alloy.…”

Section: The Refinement Of Grains and Polycrystalline Nature Is Alsmentioning

confidence: 99%

Comment on “Microstructure and Properties of Electrochemically Deposited Ni-Fe/Si₃N₄Nanocomposites from a DMF Bath” [J. Electrochem. Soc., 162, D87 (2015)]

Bakonyi

2015

J. Electrochem. Soc.

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Feature article: Electronic transport in granular metal films†

Cited by 163 publications

References 32 publications

Thermal characterization of doped polyaniline and its composites with CoPc

Thermal characterization of doped polyaniline and its composites with CoPc

Magnetoresistance of Chromium Dioxide Powder Compacts

Comment on “Microstructure and Properties of Electrochemically Deposited Ni-Fe/Si₃N₄Nanocomposites from a DMF Bath” [J. Electrochem. Soc., 162, D87 (2015)]

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Feature article: Electronic transport in granular metal films†

Cited by 163 publications

References 32 publications

Thermal characterization of doped polyaniline and its composites with CoPc

Thermal characterization of doped polyaniline and its composites with CoPc

Magnetoresistance of Chromium Dioxide Powder Compacts

Comment on “Microstructure and Properties of Electrochemically Deposited Ni-Fe/Si3N4Nanocomposites from a DMF Bath” [J. Electrochem. Soc., 162, D87 (2015)]

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Comment on “Microstructure and Properties of Electrochemically Deposited Ni-Fe/Si₃N₄Nanocomposites from a DMF Bath” [J. Electrochem. Soc., 162, D87 (2015)]