Spin-Spin Interactions in Organic Magnetoresistance Probed by Angle-Dependent Measurements

Wagemans, W Wiebe; Schellekens, A. J.; Kemper, M.; Bloom, Frederick; Bobbert, Peter A.; Koopmans, B.

doi:10.1103/physrevlett.106.196802

Cited by 47 publications

(54 citation statements)

References 25 publications

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“…Also other interactions are easilly added to the spin-pair Hamiltonian, making it possible to study effects like an increased spin mixing due to a difference in g factors of the polarons, and interactions like a dipole coupling or an exchange interaction. 20 A schematic drawing of the two-site model is depicted in Fig. 2.…”

Section: B Two-site Model: Density-matrix Calculationsmentioning

confidence: 99%

“…Adding the first two is a straightforward extension of the polaron-pair Hamiltonian; however, a detailed discussion is given elsewhere. 20 Also the spin-orbit interaction (SOI) could potentially be included in the polaron-pair Hamiltonian; however, we neglected the SOI for two reasons. First, this interaction is expected to be small for the commonly used light organic materials.…”

Section: A Basic Conceptsmentioning

confidence: 99%

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Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

et al. 2011

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The stochastic Liouville equation is applied to the field of organic magnetoresistance to perform detailed microscopic calculations on the different proposed models. By adapting this equation, the influence of a magnetic field on the current in bipolaron, electron-hole pair, and triplet models is calculated. The simplicity and wide applicability of the stochastic Liouville equation makes it a powerful tool for interpreting experimental results on magnetoresistance measurements in organic semiconductors. New insights are gained on the influence of hopping rates and disorder on the magnetoresistance.

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Section: B Two-site Model: Density-matrix Calculationsmentioning

confidence: 99%

Section: A Basic Conceptsmentioning

confidence: 99%

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

et al. 2011

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“…With the increase in dopants, the chance increases for a galvonxyl spin to be within r crit of both bottleneck sites. It is known that strong exchange between the two bottleneck sites quenches OMAR because spin flip-flops occur faster than the hyperfine fields can operate on the spins [18,19]; thus the spin configuration is effectively pinned in their initial state. A similar phenomenon occurs in the doped system under consideration here; the galvinoxyl acts as an intermediary between the bottleneck spins, through which they communicate, and ceases any spin evolution.…”

Section: Published By the American Physical Society Under The Terms Omentioning

confidence: 99%

“…Regime III: Exchange couplings between galvinoxyl and bottleneck spins now dominate the hyperfine interaction. The galvinoxyl acts as an intermediary for exchange interaction between the MEH-PPV sites which is known [18,19] to effectively pin the spins thereby quenching the magnetoconductance. Right: alternative image of the three different regimes.…”

Section: Published By the American Physical Society Under The Terms Omentioning

confidence: 99%

Anomalous organic magnetoresistance from competing carrier-spin-dependent interactions with localized electronic and nuclear spins

et al. 2014

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We describe a regime for low-field magnetoresistance in organic semiconductors, in which the spin-relaxing effects of localized nuclear spins and electronic spins interfere. The regime is studied by the controlled addition of localized electronic spins to a material that exhibits substantial room-temperature magnetoresistance (∼ 20%). Although initially the magnetoresistance is suppressed by the doping, at intermediate doping there is a regime where the magnetoresistance is insensitive to the doping level. For much greater doping concentrations the magnetoresistance is fully suppressed. The behavior is described within a theoretical model describing the effect of carrier spin dynamics on the current. Organic semiconductors (OSC) exhibit intriguing roomtemperature spin-dependent phenomena, including magnetic field effects on "radical pairs" [1][2][3][4][5][6][7][8][9]. Radical pairs, which are spin-carrying excitations that occupy neighboring molecules in an organic film, can consist of electron-hole pairs, electronelectron (or hole-hole) pairs, and mixed pairs consisting of a spin-1/2 polaron and a spin-1 triplet exciton. These radical pairs can undergo spin-dependent reactions, which due to the large on-site exchange energies in OSC, depend sensitively on the pair spin state. The spin-dependent behavior of radical pairs that occupy transport bottleneck sites can have a significant effect on the conductivity [9,10] and electroluminescent efficiency [6,11] of an organic device. The spin dynamics of these radical pairs is sensitive to the presence of magnetic fields, including an applied magnetic field, an exchange or dipolar field with neighboring spins (localized or mobile), and a nuclear (hyperfine) field. Low-field, room-temperature magnetoresistance in OSC with nonmagnetic electrodes, so-called "OMAR," is one consequence. Even though the exact mechanism behind OMAR is still debated [12], it is widely believed to be related to hyperfine interactions and radical pair effects as described above, at least in some materials. The effects of additional radical dopant spins on these phenomena were first studied in the context of organic solar cells [13,14]. The efficiency and short circuit current of doped regio-regular poly(3-hexylthiophene)/1-(3-(methoxycarbonyl)propyl)-1-phenyl)(6,6)C 61 (P3HT/PCBM) solar cells were maximum for a certain doping percentage (∼ 3%), which was suggested to originate from galvinoxyl spins near the PCBM side of the P3HT/PCBM boundary that interacted with electrons to decrease recombination losses by facilitating intersystem crossings to triplet states.* These authors contributed equally to this work. † michael_flatte@mailaps.org Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Here we examine, experimentally and theoretically, the influence of radical doping on the transport characteristics in...

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“…The effect can be tuned by changing the operating conditions, such as voltage, temperature, and angle between the current and magnetic field. [3][4][5][6][7][8][9][10][11][12][13][14][15] Recently, cheap plastic sensor technology has been proposed as an example of its application potential. 16 Nevertheless, a fundamental understanding of the interactions of spins and charges in organic semiconductors currently remains the goal of extensive experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretical [17][18][19] research.…”

Section: Introductionmentioning

confidence: 99%

Unraveling the temperature and voltage dependence of magnetic field effects in organic semiconductors

Janssen¹,

Wouters²,

Cox³

et al. 2013

Journal of Applied Physics

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Articles you may be interested inStudy of poly(3-hexylthiophene)/cross-linked poly (vinyl alcohol) In recent years, it was discovered that the current through an organic semiconductor, sandwiched between two non-magnetic electrodes, can be changed significantly by applying a small magnetic field. This surprisingly large magnetoresistance effect, often dubbed as organic magnetoresistance (OMAR), has puzzled the young field of organic spintronics during the last decade. Here, we present a detailed study on the voltage and temperature dependence of OMAR, aiming to unravel the lineshapes of the magnetic field effects and thereby gain a deeper fundamental understanding of the underlying microscopic mechanism. Using a full quantitative analysis of the lineshapes, we are able to extract all linewidth parameters and the voltage and temperature dependencies are explained with a recently proposed trion mechanism. Moreover, explicit microscopic simulations show a qualitative agreement to the experimental results. V C 2013 AIP Publishing LLC.

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Spin-Spin Interactions in Organic Magnetoresistance Probed by Angle-Dependent Measurements

Cited by 47 publications

References 25 publications

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

Anomalous organic magnetoresistance from competing carrier-spin-dependent interactions with localized electronic and nuclear spins

Unraveling the temperature and voltage dependence of magnetic field effects in organic semiconductors

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