Variable-range hopping of spin polarons: Magnetoresistance in a modified Mott regime

Foygel, M.; Morris, Robin D.; Petukhov, A. G.

doi:10.1103/physrevb.67.134205

Cited by 20 publications

(24 citation statements)

References 17 publications

(95 reference statements)

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“…This value is very close to 0.4 and is distinctively different from 0.5 expected for VRH with Coulomb blockade or tunneling transport in granular systems. The 1 / T 0.4 temperature dependence has been predicted by Foygel et al 11 for bound spin ͑magnetic͒ polarons. Traditionally, spin polaron transport has been assumed to follow a simple activation process.…”

supporting

confidence: 53%

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Giant negative magnetoresistance of spin polarons in magnetic semiconductors–chromium-doped Ti2O3 thin films

Wang

Hong

Tang

et al. 2005

Applied Physics Letters

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Epitaxial Cr-doped Ti2O3 films show giant negative magnetoresistance up to −365% at 2K. The resistivity of the doped samples follows the behavior expected of spin (magnetic) polarons at low temperature. Namely, ρ=ρ0exp(T0∕T)p, where p=0.5 in zero field. A large applied field quenches the spin polarons and p is reduced to 0.25 expected for lattice polarons. The formation of spin polarons is an indication of strong exchange coupling between the magnetic ions and holes in the system.

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supporting

confidence: 53%

“…All data analysis and curve fitting were done over the temperature range 2 K Ͻ T Ͻ 15 K. The crossover from p = 0.4 for magnetic polarons to p = 0.25 for standard Mott lattice polarons in high magnetic field has been predicted in Ref. 11. It should be mentioned that the observed field dependence of exponent p is unique for magnetic polarons.…”

mentioning

confidence: 96%

Giant negative magnetoresistance of spin polarons in magnetic semiconductors–chromium-doped Ti2O3 thin films

Wang

Hong

Tang

et al. 2005

Applied Physics Letters

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“…The linearity of ln͑ ͒ as a function of T −1/2 for the entire temperature range is qualitatively consistent with the thermally activated process, = 0 exp͓͑T o / T͒ 1/2 ͔, which is a characteristic of magnetic polaron variable range hopping ͑VRH͒ in the presence of carrier-carrier interaction. 8 The VRH mechanism provides a reasonable explanation of transport behavior in ZnO:C films. Figure 3͑a͒ shows the magnetic-field ͑H͒ dependence Hall resistivity ͑ xy ͒ for the ZnO:C film.…”

mentioning

confidence: 92%

Magnetotransport properties of p-type carbon-doped ZnO thin films

Herng

Lau

Wang

et al. 2009

Applied Physics Letters

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Carbon-doped ZnO ͑ZnO:C͒ thin films exhibiting Curie temperature above room temperature were fabricated using ion beam technique. The magnetic moment of the ZnO:C films was found to be around 1.35 B per carbon atom. The ZnO:C films showed p-type conduction with a hole concentration of ϳ5 ϫ 10 17 cm −3 . In addition, the anomalous Hall effect and negative magnetoresistance can be detected in the ZnO:C films. The magnetotransport properties of the ZnO:C suggested that the films possessed charge carrier spin polarization. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3176434͔In recent years, there has been an intense search for ZnO-based ferromagnetic semiconductors with coexistence of ferromagnetic and spin-transport properties, which are desirable for practical spintronics applications. 1 It was predicted that Mn-doped ZnO could exhibit above room temperature ͑RT͒ ferromagnetism in a hole-rich environment. 2 This prediction initiated intensive experimental work on 3d-transition metals ͑TM͒ doped ZnO. However, the reported results have been receiving skepticism and the origin of the observed ferromagnetism continues to be strongly debated in the literature. 3 As a result, this stimulated an extensive experimental and computational search for non-TM doped ZnO, such as carbon-doped ZnO ͑ZnO:C͒ as alternatives to fabricate an unambiguous and clean ferromagnetic semiconductor. Pan et al. 4 predicted that hole mediation in ZnO:C film could lead to ferromagnetism, but ZnO:C showed n-type behavior experimentally. Thus, the intrinsic ferromagnetism in this carbon system need to be examined carefully before its potential can be explored.The origin of ferromagnetism in ZnO-based semiconductors is the most unsettled question in today's material community. This complication can be partially alleviated if the magnetotransport properties of these materials can be observed. Anomalous Hall effect ͑AHE͒ and magnetoresistance ͑MR͒ are among the most important tools to determine practical functionality of the materials as the spin polarized carrier can be probed and controlled electrically, 5 leading to direct application in electronics. Here, we demonstrate p-type ZnO:C films by investigating its ferromagnetic and magnetotransport properties. By tuning the carbon concentration in the ZnO thin films, one can control the strength of ferromagnetic coupling and its magnetotransport properties.ZnO films with a thickness of 300 nm were prepared on Si substrates at RT using the filtered cathodic vacuum arc technique. The details of ZnO film preparation have been described elsewhere. 6 The ZnO samples were mounted on a water-cooled sample holder and subsequently irradiated by Ar + ions at 45°from the normal to the surface using a Kaufman-type ion gun ͑Iontech Inc. Ltd., model 3-1500-100 FC͒ with a simultaneous supply of C atoms. For the supply of carbon, a graphite plate located perpendicularly near the ZnO sample was cosputtered with the ZnO sample by Ar + ions with an energy of 500 eV at RT. After the fabrication of ZnO:C films, ...

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“…in magnetic systems. In general, the theory of VRH with account for polaronic effect was developed in [17][18][19][20] for different types of polarons.…”

Section: Hard Gap and Polaronic Effect In Homogeneously Disorderedmentioning

confidence: 99%

“…If the distribution of barrier heights has a power-law tail at zero, one can expect the dependence (1) with α = 1. In particular, for homogeneously disordered solids it was shown in [20] that, if the barrier distribution is constant in the vicinity of zero, the Mott conductivity should have the exponent α = 2/(d + 2).…”

Section: Hard Gap and Polaronic Effect In Homogeneously Disorderedmentioning

confidence: 99%

Cotunneling and polaronic effect in granular systems

Ioselevich

Sivak

2017

Phys. Rev. B

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We theoretically study the conductivity in arrays of metallic grains due to the variable-range multiple cotunneling of electrons with short-range (screened) Coulomb interaction. The system is supposed to be coupled to random stray charges in the dielectric matrix that are only loosely bounded to their spatial positions by elastic forces. The flexibility of the stray charges gives rise to a polaronic effect, which leads to the onset of Arrhenius-like conductivity behaviour at low temperatures, replacing conventional Mott variable-range hopping. The effective activation energy logarithmically depends on temperature due to fluctuations of the polaron barrier heights. We present the unified theory that covers both weak and strong polaron effect regimes of hopping in granular metals and describes the crossover from elastic to inelastic cotunneling.

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Variable-range hopping of spin polarons: Magnetoresistance in a modified Mott regime

Cited by 20 publications

References 17 publications

Giant negative magnetoresistance of spin polarons in magnetic semiconductors–chromium-doped Ti2O3 thin films

Giant negative magnetoresistance of spin polarons in magnetic semiconductors–chromium-doped Ti2O3 thin films

Magnetotransport properties of p-type carbon-doped ZnO thin films

Cotunneling and polaronic effect in granular systems

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