Molecular hyperfine fields in organic magnetoresistance devices

Giro, Ronaldo; Rosselli, F. P.; Carvalho, Rafael dos Santos; Capaz, Rodrigo B.; Cremona, M.; Achete, Carlos A.

doi:10.1103/physrevb.87.125204

Cited by 13 publications

(8 citation statements)

References 26 publications

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“…Furthermore, the overall transmission calculations clarify that the TEMPO-OPE molecules do not work effectively as spin filters because the radical parts are located far from the backbone molecules, resulting in virtually equal transmission probabilities for majority and minority spins (Figure S7). The same conclusion has been pointed out in the theoretical study of the spin-filtering effects of stable radical groups, including nitronyl-nitroxide and tert -butylphenylnitroxide radicals, which are similar to that of our molecule. , However, markedly large positive MRs (10% at 10 mT) have been demonstrated in pure organic thin films and molecular wires with nonmagnetic electrodes such as Au and tin-doped indium oxide electrodes. − In these studies, the positive MRs are interpreted by the hyperfine interaction between conductive electrons and nuclear spins of molecules during the electron-hopping conduction, whereas the MRs appeared at the magnetic field of a few Tesla in our case, and the amplitude is much larger than that of hyperfine fields of typical organic molecules (2–6 mT). , The Zeeman splitting of molecular orbitals also cannot explain the MRs obtained from TEMPO-OPEs because of the marginal change in MRs for OPEs. Hence, a different mechanism from those already proposed for organic molecules is required to explain the origin of the positive MR in our study.…”

supporting

confidence: 83%

“…48−50 In these studies, the positive MRs are interpreted by the hyperfine interaction between conductive electrons and nuclear spins of molecules during the electronhopping conduction, whereas the MRs appeared at the magnetic field of a few Tesla in our case, and the amplitude is much larger than that of hyperfine fields of typical organic molecules (2−6 mT). 48,49 The Zeeman splitting of molecular orbitals also cannot explain the MRs obtained from TEMPO-OPEs because of the marginal change in MRs for OPEs. Hence, a different mechanism from those already proposed for organic molecules is required to explain the origin of the positive MR in our study.…”

mentioning

confidence: 99%

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Large Magnetoresistance in Single-Radical Molecular Junctions

Hayakawa

Karimi²,

Wolf³

et al. 2016

Nano Lett.

118

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Organic radicals are promising building blocks for molecular spintronics. Little is known about the role of unpaired electrons for electron transport at the single-molecule level. Here, we examine the impact of magnetic fields on electron transport in single oligo(p-phenyleneethynylene) (OPE)-based radical molecular junctions, which are formed with a mechanically controllable break-junction technique at a low temperature of 4.2 K. Surprisingly huge positive magnetoresistances (MRs) of 16 to 287% are visible for a magnetic field of 4 T, and the values are at least 1 order of magnitude larger than those of the analogous pristine OPE (2-4%). Rigorous analysis of the MR and of current-voltage and inelastic electron-tunneling spectroscopy measurements reveal an effective reduction of the electronic coupling between the current-carrying molecular orbital and the electrodes with increasing magnetic field. We suggest that the large MR for the single-radical molecular junctions might be ascribed to a loss of phase coherence of the charge carriers induced by the magnetic field. Although further investigations are required to reveal the mechanism underlying the strong MR, our findings provide a potential approach for tuning charge transport in metal-molecule junctions with organic radicals.

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supporting

confidence: 83%

mentioning

confidence: 99%

Large Magnetoresistance in Single-Radical Molecular Junctions

Hayakawa

Karimi²,

Wolf³

et al. 2016

Nano Lett.

118

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“…Quantitative research, for HFI fields in a few molecules frequently employed in studies of spintronics, has already been implemented via first-principle calculations or ab initio calculations (Filidou et al, 2012; Giro et al, 2013; Yu et al, 2013). An effective HFI field for electron and hole polarons in molecular materials with H and deuterium(D)-substituted, have been shown in Yu's research (Yu et al, 2013).…”

Section: Spin Relaxation Mechanism In π-Conjugated Moleculesmentioning

confidence: 99%

Spin Transport in Organic Molecules

Guo

Qin

et al. 2019

Front. Chem.

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Because of the considerable advantages of functional molecules as well as supramolecules, such as the low cost, light weight, flexibility, and large area preparation via the solution method, molecular electronics has grown into an active and rapidly developing research field over the past few decades. Beyond those well-known advantages, a very long spin relaxation time of π-conjugated molecules, due to the weak spin-orbit coupling, facilitates a pioneering but fast-growing research field, known as molecular spintronics. Recently, a series of sustained progresses have been achieved with various π-conjugated molecular matrixes where spin transport is undoubtedly an important point for the spin physical process and multifunctional applications. Currently, most studies on spin transport are carried out with a molecule-based spin valve, which shows a typical geometry with a thin-film molecular layer sandwiched between two ferromagnetic electrodes. In such a device, the spin transport process has been demonstrated to have a close correlation with spin relaxation time and charge carrier mobility of π-conjugated molecules. In this review, the recent advances of spin transport in these two aspects have been systematically summarized. Particularly, spin transport in π-conjugated molecular materials, considered as promising for spintronics development, have also been highlighted, including molecular single crystal, cocrystal, solid solution as well as other highly ordered supramolecular structures.

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“…Thus, the average B 0 value is estimated to be 2.11 ± 0.06 mT, which can be regarded as representative value for all coevaporated Spiro-TTB/HAT-CN compositions. The fit parameter B 0 is often correlated with the strength of the molecular hyperfine fields that affect the magnetosensitive quasiparticles [ 7 , 11 , 20 – 21 ]. Furthermore, it depends on the microscopic details of the underlying model [ 22 ].…”

Section: Resultsmentioning

confidence: 99%

Ultrasmall magnetic field-effect and sign reversal in transistors based on donor/acceptor systems

Reichert¹,

Saragi²

2017

Beilstein J. Nanotechnol.

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We present magnetoresistive organic field-effect transistors featuring ultrasmall magnetic field-effects as well as a sign reversal. The employed material systems are coevaporated thin films with different compositions consisting of the electron donor 2,2',7,7'-tetrakis-(N,N-di-p-methylphenylamino)-9,9'-spirobifluorene (Spiro-TTB) and the electron acceptor 1,4,5,8,9,12-hexaazatriphenylene hexacarbonitrile (HAT-CN). Intermolecular charge transfer between Spiro-TTB and HAT-CN results in a high intrinsic charge carrier density in the coevaporated films. This enhances the probability of bipolaron formation, which is the process responsible for magnetoresistance effects in our system. Thereby even ultrasmall magnetic fields as low as 0.7 mT can influence the resistance of the charge transport channel. Moreover, the magnetoresistance is drastically influenced by the drain voltage, resulting in a sign reversal. An average B 0 value of ≈2.1 mT is obtained for all mixing compositions, indicating that only one specific quasiparticle is responsible for the magnetoresistance effects. All magnetoresistance effects can be thoroughly clarified within the framework of the bipolaron model.

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Molecular hyperfine fields in organic magnetoresistance devices

Cited by 13 publications

References 26 publications

Large Magnetoresistance in Single-Radical Molecular Junctions

Large Magnetoresistance in Single-Radical Molecular Junctions

Spin Transport in Organic Molecules

Ultrasmall magnetic field-effect and sign reversal in transistors based on donor/acceptor systems

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