NANOCON · Nanocontacted Thin Molecular Films for Spintronics

Nanocontacted thin molecular films for spintronics

This proposal is placed in the area of molecular spintronics, a multidisciplinary area of knowledge in between molecular magnetism, molecular electronics and surface science and deals with the integration of molecular materials in spintronic devices. Up to now, most of the work has focused on spin propagation through organic semiconductors not exploiting the unique tailoring opportunity offered by chemistry. For example, it was predicted that the sign and the amplitude of an injected spin current could be controlled through the ferromagnet / molecule electronic coupling strength. Amongst all the existent and promising possibilities, self-assembled monolayers (SAMs) offer the unique opportunity of versatility down to the atomic scale. Through the deposition over surfaces of thin films, their integration into organic molecular tunnel junctions (OMTJs) and the study of the molecule-surface interfaces this project combined chemistry, surface science and spin-transport physics. This proposal has gone beyond the current state-of-the-art in the field of molecular spintronics by using molecular materials as spin barriers in OMTJs. Magnetotransport measurements through conveniently nanostructured thin organic layers and molecular materials have been performed while a special attention has been paid to the molecule-surface interface, critical to correctly interpret transport measurements. During the duration of the project, we have developed the necessary protocols for the integration of these systems into nanocontacs and tried to measure their transport and spin polarised transport properties obtaining uneven results depending on the materials used. In the case of SMM we had to face several problems of compatibility and stability within the different lithographic process involved in device fabrication. And for the moment, we have been unable to obtain better results that in the case of simpler systems like PTF and SAMs. Our best results have been obtained in the case of SAMs. We have successfully deposited SAMs over Co and La2/3Sr1/3MnO3 (LSMO). In the case of LSMO we grated for the first time SAMs over LSMO and integrated them into nanocontacts with Co / SAM / LSMO structure. Tunnel barriers SAMs are special because compared to other systems: (1) SAMs can be easily engineered: they are modular and their parts can be exchanged while keeping the others unchanged. (2) SAMs are intrinsically nanometre thick: the film thickness will be determined by molecule size and SAM structure. (3) SAMs have defined structures: the SAM formation is a self-assembly process, electronic structure is preprogramed. In the case of Co / SAM / LSMO nanocontacts (approximately 20 nm) we have detected (MR) signals up to 50 % at low temperature. The tunnelling magnetoresistance (TMR) in these systems is quite robust against bias, and TMR signals are kept even up to 2 V. The obtained results are quite important because they constitute a building block for molecular / organic spintronic tailoring: the development of the required missing SAM grafting protocols over LSMO. The manganite LSMO is a highly spin polarised (nearly one spin direction at the Fermi level) and air stable ferromagnetic oxide that was promoted as one of the most used electrodes in organic spintronics. However, in contrast to the extensive use of chemisorbed SAMs on coinage non-magnetic metals, proper grafting protocols over LSMO were up to now lacking in the literature and SAMs had not yet been integrated in standard LSMO based molecular spintronic devices. Moreover robust spin injection through the SAMs has been demonstrated in OMTJs unravelling the potential of SAMs for high-voltage spintronic devices on par with MgO (the best available inorganic barriers for spintronics). Beyond the conventional spintronic interest, this could lead to new venues for the injection of spin in organic light emitting devices. Contact details: Sergio Tatay Aguilar Unité Mixte de Physique CNRS/Thales. Associée à l'Université Paris-Sud 1, Av. Augustin Fresnel 91767 Palaiseay Cedex (France) email: sergio.tatay-aguilar@thalesgroup.com

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