Distinguishing between tunneling and injection regimes of ferromagnet/organic semiconductor/ferromagnet junctions

Lin, Ran; Wang, F.; Rybicki, James; Wohlgenannt, M.; Hutchinson, K. A.

doi:10.1103/physrevb.81.195214

Cited by 96 publications

(93 citation statements)

References 29 publications

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“…X-ray diffraction measurements showed that the C 60 layers of different thickness were structurally amorphous. The C 60 layer thickness in our devices was far greater than the tunnelling barrier limit that has been reported thus far [7][8][9][10][11][12]35 . Thus, the SDT within the C 60 layer via hopping between localized neighbouring states was mainly considered.…”

Section: Resultsmentioning

confidence: 83%

Observation of a large spin-dependent transport length in organic spin valves at room temperature

et al. 2013

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The integration of organic semiconductors and magnetism has been a fascinating topic for fundamental scientific research and future applications in electronics, because organic semiconductors are expected to possess a large spin-dependent transport length based on weak spin-orbit coupling and weak hyperfine interaction. However, to date, this length has typically been limited to several nanometres at room temperature, and a large length has only been observed at low temperatures. Here we report on a novel organic spin valve device using C 60 as the spacer layer. A magnetoresistance ratio of over 5% was observed at room temperature, which is one of the highest magnetoresistance ratios ever reported. Most importantly, a large spin-dependent transport length of approximately 110 nm was experimentally observed for the C 60 layer at room temperature. These results provide insights for further understanding spin transport in organic semiconductors and may strongly advance the development of spin-based organic devices.

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Section: Resultsmentioning

confidence: 83%

Observation of a large spin-dependent transport length in organic spin valves at room temperature

et al. 2013

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“…Clearly, it is also possible to change the FM-OSC coupling by the use of thin interfacial layers. The effect of a tunnel barrier between the metal and the OSC on the functionality of a spin-valve device has proven to be critical for spin-polarized tunneling [33,37,38,[46][47][48][49]. Dediu and coworkers have demonstrated that the quality of the metalorganic interfaces can be improved by inserting an Al 2 O 3 layer on top of the organic material, prior to growing the top ferromagnetic electrode [50].…”

Section: Magnetoresistance In Organic Spin Valvesmentioning

confidence: 99%

The role of interfaces in organic spin valves revealed through spectroscopic and transport measurements

Drew

Szulczewski

Nuccio

et al. 2011

Physica Status Solidi (b)

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Interfaces between dissimilar materials are critical to the performance of many electronic devices. In electrical devices where the active transport is through an organic semiconductor (OSC) layer there are metallic electrodes to supply and remove the charge carriers. At metal/molecule and molecule/metal interfaces the electrical contact is usually not Ohmic. As a result, in most metal-organic semiconductors-metal devices charge injection is mainly governed by tunneling across the barriers. When the metal electrodes are ferromagnetic the density of occupied and unoccupied electronic states is spindependent, which presents further subtleties to the electron transfer. In this article we summarize some of the important experimental results that have advanced our understanding of spin-polarized electron transfer across ferromagnetic metal (FM)/OSC interfaces. In particular, we highlight key spectroscopic studies that have revealed insights into the nature of the electronic structure between OSCs and FMs, in particular between Alq 3 and Co and Fe surfaces. We discuss the relationship between energy level diagrams for these systems and transport measurements made on spin-valve devices.

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“…To harness the electron spin in organics for spintronic applications, it is mandatory to elucidate the MR, which in turn requires that the device resistance of the OSVs be adequately accounted for. While the large thickness of the organic film in an OSV precludes a direct tunnelling between the electrodes, the observed I-V characteristic is also incomprehensible in terms of electron injection into the organic's lowest unoccupied molecular orbital (LUMO) or hole injection into the highest occupied molecular orbital (HOMO), as commonly assumed in literature [1][2][3][4][5][6][7][8][9] . The two electrodes, labelled 1 and 2, in an OSV have different Schottky barriers, qf 1 oqf 2 (q ¼ |e| is the electron charge), which would give rise to a built-in potential, V bu ¼ f 2 À f 1 , in an undoped organic film at zero bias.…”

mentioning

confidence: 96%

“…The OSVs with a pronounced MR are usually vertical structures [1][2][3][4][5][6][7] , with the top electrode grown after the deposition of the organic. Lateral ferromagnet-organic-ferromagnet devices, where both electrodes are fabricated before the deposition of the organic, however, are much more resistive and seldom exhibit any spin-valve effect 19 .…”

Section: Modelmentioning

confidence: 99%

“…O rganic spintronics has attracted considerable interest since the discovery of large magnetoresistance (MR) in thick (B100 nm) organic spin valves (OSVs) [1][2][3][4][5][6][7] . To harness the electron spin in organics for spintronic applications, it is mandatory to elucidate the MR, which in turn requires that the device resistance of the OSVs be adequately accounted for.…”

mentioning

confidence: 99%

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Impurity-band transport in organic spin valves

2014

Nat Commun

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The central phenomenon in the field of organic spintronics is the large magnetoresistance in thick organic spin valves. A prerequisite for understanding the magnetoresistance is a reliable description of the device resistance, or the I-V characteristics. Here I show that the observed I-V characteristics in the organic spin valves is incompatible with charge injection into the organic's lowest unoccupied molecular orbital or highest occupied molecular orbital but can be explained by electrons tunnelling into a broad impurity band located in the gap between these molecular orbitals. Voltage drop takes place mainly across depletion layers at the two electrode/organic interfaces, giving rise to electrode-limited charge transport. Spin-dependent electron tunnelling into the impurity band from the ferromagnetic electrodes results in spin accumulations inside the organic, which rapidly diffuses through the organic primarily via the exchange between impurity-band electrons. This picture explains the major magnetoresistance features and predicts enhanced capacitance in these devices.

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Distinguishing between tunneling and injection regimes of ferromagnet/organic semiconductor/ferromagnet junctions

Cited by 96 publications

References 29 publications

Observation of a large spin-dependent transport length in organic spin valves at room temperature

Observation of a large spin-dependent transport length in organic spin valves at room temperature

The role of interfaces in organic spin valves revealed through spectroscopic and transport measurements

Impurity-band transport in organic spin valves

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