Efficient spin injection through exchange coupling at organic semiconductor/ferromagnet heterojunction

Yiqiang Zhan 1Xianjie Liu Fenghong Li Elin Carlegrim Mats Fahlman 

1. Department of Physics, Chemistry and Biology, Linköping University, Linköping 58183, Sweden

Abstract

Efficient injection of spin-polarized electrons from a ferromagnetic contact into a semiconductor is an important ingredient in many currently proposed spintronic devices. Such injection has been demonstrated by analyzing the circular polarization of photons that are generated after recombination of the injected electrons with holes in a quantum-well layer inside the semiconductor. The difficulty to achieve coherent spin injection and spin transport above the nanometer scale in normal metals and semiconductors, however, has stimulated the search for new materials. In this context, π-conjugated organic semiconductors (OSCs) have a decisive role, as they are mainly constituted by atoms with low atomic number Z, leading to a low spin–orbit coupling and thus to extremely long spin relaxation times. Despite the advances made in device fabrication, the fundamental knowledge about spin injection at OSCs/ferromagnet heterojunction is still missing. Here we show that the amplified spin polarized charge injection through OSCs/ferromagnet heterojunction by exchange coupling effect. Our results demonstrate that charge transfer (CT) from Fe (or Co) to a π-conjugated orbital of Alq3 at the interfaces not only creates an Ohmic contact, but also induces exchange coupling between Alq3 and the substrate as well as creates spin polarization of a π-conjugated orbital of Alq3. We anticipate our results to be a starting point for fully understanding spin injection and the behavior of organic spin valves, guiding the design of such devices and stimulating new type of applications. 

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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium E, by Yiqiang Zhan
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-06 15:04
Revised:   2009-06-12 13:06
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