Bound magnetic polaron hopping and giant magnetoresistance in magnetic semiconductors and nanostructures

Petukhov, A. G.; Foygel, M.

doi:10.1103/physrevb.62.520

Cited by 38 publications

(52 citation statements)

References 20 publications

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“…In this regime, in contrast to the nearest-neighbor hopping (NNH) of polarons, both the lattice [1,3] or the magnetic ones [10] , the polaron hard gap is washed out by the fluctuations of the polaron shifts (barriers).…”

Section: Qualitative Considerationmentioning

confidence: 99%

“…Several observations of giant and colossal negative VRH magnetoresistance in systems with strong spin disorder such as dilute magnetic semiconductors (DMS) have been reported recently [5,6,7]. It seems rather natural to attribute VRH magnetoresistance to spin polarons that are believed to be a major cause of negative magnetoresistance in DMS [8,9,10]. However, a theory of VRH magnetoresistance has never been addressed in the literature, partially, because of the belief that spin-polaron hopping may lead only to a simple activation dependence of the conductivity which mimics nearest-neighbor hopping [11].…”

Section: Introductionmentioning

confidence: 99%

“…i and j separated by a distance r ij . To find the bound polaron hopping rate in the so called nonadiabatic limit [12,13] one can employ the semiclassical approach developed in [12,13] for the lattice small polarons (SP) or in [10] for the bound magnetic polarons (BMP). In both cases, however, is possible to show (see Appendix) that if i → j tunneling transition is governed either by strong multiphonon coupling (for the lattice SP) or by thermodynamic fluctuations of the local magnetization (for the BMP), when…”

Section: Calculation Of Resistivity a Percolation Theory Ap-proachmentioning

confidence: 99%

“…Bound spin (magnetic) polarons, in contrast to their lattice counterparts, possess polaron shifts that, as well as their distribution, can be tuned by applied magnetic field thus resulting in giant or even colossal magnetoresistance [10,11,14,16]. Externally controlled switching off and on of the magneto-polaron effect also allows one to better identify the hopping mechanism in magnetic materials.…”

Section: Introductionmentioning

confidence: 99%

“…The study of electrical conductivity in solids, which is controlled by polaron hopping, has centered so far on materials where the polaronic part of the activation energy is fixed [1,3,10,11,12,13,14]. Indeed, the lowering of the free energy of the system due to atomic spin alignment [9] ( or lattice polarization [13] ) in the vicinity of the trapped carrier, the so called polaron shift, and its associated hopping barrier are generally determined by the spatial extent of the localized states between which the hopping occurs.…”

Section: Introductionmentioning

confidence: 99%

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

2003

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We analize electrical conductivity controlled by hopping of bound spin polarons in disordered solids with wide distributions of electron energies and polaron shifts (barriers). By means of percolation theory and Monte Carlo simulations we have shown that in such materials at low temperatures, when hopping occurs in the vicinity of the Fermi level, a hard polaron gap does not manifest itself in the transport properties. This happens because as temperature decreases the hopping polaron trades the decreasing electron and polaron barriers for increasing hopping distance.As a result, in the absence of the Coulomb correlation effects, in this variable-range variable-barrier hopping regime, the electrical resistivity, ρ, as a function of temperature, T , obeys a non-activation law: ln (ρ/ρ 0 ) = T /T p with p = 2/(d + 2), where d is the dimensionality of the system. It differs from the standard Mott law for which p = 1/(d + 1). Also, we studied the effects of upper and lower boundaries in the polaron shift distribution on hopping conduction, which may result in a partial re-entrance of the hard polaron gap. We discuss possible applications to the problem of giant negative magnetoresistance in dilute magnetic semiconductors and nanocomposites where for paramanetic materials p = 3/(d + 2).

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Section: Qualitative Considerationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Calculation Of Resistivity a Percolation Theory Ap-proachmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

2003

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Stability of magnetic polarons in magnetic semiconductor single electron transistors: The effect of Coulomb interaction and external magnetic field

Лебедева

Varpula

Новиков

et al. 2012

Physica Status Solidi (b)

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In a magnetic single electron transistor (SET), which consists of a magnetic quantum dot (QD) coupled electrically to nonmagnetic source, drain, and gate electrodes, a magnetic polaron (MP) formation may occur, that is, the charge carrier spin may spin‐polarize the magnetic atoms of the QD and simultaneously the carrier becomes more tightly bound to the QD. We have studied theoretically the effect of the Coulomb interaction and magnetic field on the stability of the MPs in ferromagnetic SETs in the Coulomb blockade regime. The calculated results show that the temperature range, where MP is stable can be controlled by the gate voltage of the SET. At temperatures below the Curie temperature the stability decreases with magnetic field, whereas at higher temperatures the opposite is true. The Coulomb repulsion between two charge carriers separates the spin‐up and spin‐down energy levels, which stabilizes the MP further.

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Magnetic polaron formation in graphene-based single-electron transistor

Savin

Kuivalainen

Новиков

et al. 2014

Phys. Status Solidi B

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We theoretically study the magnetic polaron (MP) formation in a ferromagnetic graphene single-electron transistor (SET), which consists of a graphene quantum dot (QD) between two insulating layers, i.e., a ferromagnetic insulator EuO and a nonmagnetic substrate such as SiC. In the lateral direction the QD is electrically coupled to source, drain and gate electrodes, so that the number of electrons can be controlled by the gate voltage. Due to a proximity effect at the EuO/graphene interface, i.e., the exchange interaction between the charge carriers in graphene and the localized magnetic electrons in EuO, there is a magnetic coupling between the graphene QD and EuO. Using Green's function technique an expression for the total free energy of the SET is derived, which then is minimized at the given temperature and gate voltage. This leads to the MP formation and a consequent local enhancement of the ferromagnetic properties of EuO at the EuO/graphene interface. The MP formation is enforced by the large Coulomb interaction between the carriers in graphene. The spin polarization at the graphene/EuO interface in the QD area can be controlled by the gate voltage of the SET.

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Bound magnetic polaron hopping and giant magnetoresistance in magnetic semiconductors and nanostructures

Cited by 38 publications

References 20 publications

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

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

Stability of magnetic polarons in magnetic semiconductor single electron transistors: The effect of Coulomb interaction and external magnetic field

Magnetic polaron formation in graphene-based single-electron transistor

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