Low temperature tunneling magnetoresistance on (La,Sr)MnO3∕Co junctions with organic spacer layers

Vinzelberg, H.; Schumann, J.; Elefant, D.; Gangineni, R. B.; Thomas, Jürgen; Büchner, B.

doi:10.1063/1.2924435

Cited by 126 publications

(106 citation statements)

References 21 publications

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“…Finally, there is a clear debate on whether the observed MR in organic spin valves is due to transport within the organic layers or tunneling through thin regions [34,39,66]. For the same arguments as used in Section 6 about ''hot spot'' transport, the LE-mSR measurements appear to show the former is true [43,56].…”

Section: Magnetoresistance In Organic Spin Valvesmentioning

confidence: 93%

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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Section: Magnetoresistance In Organic Spin Valvesmentioning

confidence: 93%

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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“…These donors/acceptors are too small to be directly seen via transmission electron microscopy and other imaging tools. However, Rutherford backscattering and electron energy loss spectroscopy 35 may help to determine the nature of the donors/ acceptors. Another way to detect the impurity band is to measure the device capacitance.…”

Section: Discussionmentioning

confidence: 99%

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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“…12 Most probable candidates for tunneling sites would be pinholes at which the thickness of the OSC is reduced to such an extent that tunneling and thus TMR becomes possible. [8][9][10][11][12][13] Pinholes, however, follow certain statistics resulting in a different resistance change upon downscaling. They vary in size and also exhibit a varying thickness of the remaining OSC layer.…”

Section: Nanosized Vertical Organic Spin-valvesmentioning

confidence: 99%

“…2,4,5,12,13,17,18 We use a similar structure with sputtered MgO as a barrier between the Alq3 and the top electrode. The active device area is defined by a small window in an insulating layer which acts as a kind of nanosized shadow mask.…”

Section: Nanosized Vertical Organic Spin-valvesmentioning

confidence: 99%

Nanosized perpendicular organic spin-valves

Göckeritz

Homonnay

Müller

et al. 2015

Applied Physics Letters

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A fabrication process for vertical organic spin-valve devices has been developed which offers the possibility to achieve active device areas of less than 500x500 nm² and is flexible in terms of material choice for the active layers. Characterization of the resulting devices shows a large magnetoresistance of sometimes more than 100 %, however with equally large variation from device to device. Comparison with large-area spin-valves indicates that the magnetoresistance of both, large and small devices most likely originates from tunneling through pinholes and tunneling magnetoresistance.Organic spin-valve devices are promising candidates for low cost non-volatile electronics, for example for RF-ID tags.1 Nevertheless, a deeper understanding of the underlying device physics is still necessary, especially of the charge transport mechanisms through the organic material and the origin of the magnetoresistance. In vertical organic spin-valves (OSV) an organic semiconductor (OSC) thin film is sandwiched between two ferromagnetic electrodes and the device is operated by a current flow perpendicular through the layers.2 Similar to giant magnetoresistance (GMR) 2-5 and tunneling magnetoresistance (TMR) 6-9 the device resistance depends on the relative magnetization of the two electrodes. However, in contrast to GMR in all-metal structures or TMR in metal/oxide structures it is still an open question whether the origin of the magnetoresistance (MR) effects in OSVs published so far is dominated by spin polarized charge transport through the organic spacer layer or by tunneling processes. 10,11 There is, however, a possible approach to gain deeper insight into this problem which takes into account the scaling of the MR effect with device size. In the case of spin injection and charge transport (GMR) the complete device area is expected to contribute to the current path through the OSC. Reducing the size of the device in this case should keep the resistance area product and the relative magnetoresistance constant. Tunneling processes, however, most likely occur in just a small part of the active area.12 Most probable candidates for tunneling sites would be pinholes at which the thickness of the OSC is reduced to such an extent that tunneling and thus TMR becomes possible. [8][9][10][11][12][13] Pinholes, however, follow certain statistics resulting in a different resistance change upon downscaling. They vary in size and also exhibit a varying thickness of the remaining OSC layer. Each pinhole thus contributes to the total device characteristics by a different resistance and MR contribution. In order to appreciate the necessary density of pinholes we can use results published by Barraud and coworkers.14 They create artificial pinholes in an OSC layer using conducting tip atomic force microscopy (AFM) and study the magnetoresistance after the pinhole is filled up with a ferromagnetic metal. The resistance of the pinholes is typically in the range of 100 MΩ while the magnetoresistance can be as high as 300%. In addition, they ob...

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Low temperature tunneling magnetoresistance on (La,Sr)MnO3∕Co junctions with organic spacer layers

Cited by 126 publications

References 21 publications

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

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

Impurity-band transport in organic spin valves

Nanosized perpendicular organic spin-valves

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