Organic magnetoresistance – Search for the perfect defect

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• Prof. Bert Koopmans, Department of Applied Physics, Eindhoven University of Technology, Netherlands
• Tuesday 01 October 2013, 14:30-15:30
• Microelectronics Research Centre (MRC) Seminar Room, Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Dr. Girish Lakhwani.

Organic spintronics aims at new device functionality by combining the field of spintronics with that of organic electronics. The field covers a broad spectrum of phenomena and devices, including spin-valves based on hybrid organic-ferromagnetic metal junctions, as well as intrinsic magnetoresistance effects in ‘ordinary’ OLE Ds. Such effects can be surprisingly large (> 20%) at room temperature and applying magnetic fields of just a few millitesla. Recent work even reports on 1000’s of percents in molecular wires, while effects at ultra-small fields (< 1 mT) and a dependence on the orientation of the magnetic field have been observed as well Within this presentation it will be shown how different reactions between spin carrying carriers in the presence of local hyperfine fields can explain the effect – very similar to spin-chemical reactions suggested to underlie the navigation ability of migratory birds in the Earth’s magnetic field. In organic devices, the final manifestation of the effect is the result of a subtle interplay between microscopic mechanisms and device physics. In recent work on polymer-fullerene blends we have disentangled the various contributions [1]. Furthermore, we found that trap sites – which are generally considered detrimental for device performance – might be crucial in their explanation. Thus, at present, the quest is for the perfect defect, i.e. the most ideal trap site to boost the magnetic field dependence for future applications.

[1] P. Janssen, M. Cox et al., Nature Communications 4, 2286 (2013)

This talk is part of the Optoelectronics Group series.

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