Istituto dei materiali per l'elettronica ed il magnetismo     
Bergenti I., Riminucci A., Newby C., Graziosi P., Borgatti F., Casoli F., Pernechele C., Solzi M., Ghidini M., Hueso L. H., Dediu V. Interfaces in organic spintronic devices. In: Joint European Magnetic Symposia 2008 (Dublino, Irlanda, 14 - 19 settembre 2008).
π-conjugated organic semiconductors have emerged as suitable candidates in spintronic devices mainly thanks to their low spin orbit interaction. Magnetoresistive spin valves (SV) based on archetypal organic materials Alq3 and containing half metallic manganite (LSMO) as bottom electrode and Cobalt as the top one have been experimentally obtained[1,2] In such a device, both LSMO/Alq3 and Alq3/Co interfaces play a key role in the spin injection process; the control of their properties is therefore essential in the improvement of device performance. Surface magnetism of the bottom LSMO layer, morphology and disorder of the top Co contact, possible intermixing or interdiffusion at the interface change the magnetic properties of the FM films and affect the intensity of spin valve effect. The introduction of a thin (1-2 nm) Al_2O_3 barrier between the Alq3 and the Co results in a sharper definition of the metal/organic interface. From X-ray reflectivity measurements, the intermixing region at the interface between Alq3 and Co can be estimated to be around 2.5 nm, while the direct interface suffers from a thicker degradation layer. These results have been confirmed by High Energy Photoemission Spectroscopy (HAXPES) measurements, which indicate that the tunnel barrier prevents also the reaction of Co with the organic molecules. Inverse SV effect up to room temperature is routinely found in devices with Al_2O_3 barrier, while scarce control of interfacial layer for the direct deposition of Co on top of Alq3 gives rise to a variety of spurious effect on the device operation such as high closure field and not uniform and defined thickness of organic layer. In this latter condition, the estimation of length over which coherent spin transport is achieved is hardly reproducible. We present a full characterization of ferromagnetic films and their interfaces with Alq3 in presence of buffer insulating layer and we correlate the results with the operation of spin valve device. The presented results clearly indicate that extension of hybrid spintronic devices to practical application requires the engineering of interfaces between organic and the spin polarized materials.[1] Z.H. Xiong, D.Wu, Z.V Vardeny, J.Shi Nature 2004, 427, 821 [2] A. Riminucci, I. Bergenti, L.E. Hueso, M. Murgia, C. Taliani, Y. Zhan, F. Casoli, M.P. de Jong, V. Dediu, arXiv:0701603
Subject Organic Spintronics
Spin-valve effect

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