DELICE · Device oriented molecular spin filter based interfaces

Device oriented molecular spin filter based interfaces

Progress in information technologies and communication, through the miniaturization and improved performances of electronic devices, has revolutionized the way we live. In order to keep the beat and respond to the demand of our society, there is a necessity to find new innovative and feasible ways to control and manipulate information. Spintronics profits not only from the charge but also from the spin of electrons for information processing, offering the possibility to develop low-power consumption and faster performing devices exhibiting novel functionalities1. Spin valves are prototypical spintronic devices, in which two ferromagnetic (FM) layers are separated by a non-magnetic (NM) or an insulating spacer. As a result of the giant magnetoresistance effect, the trilayer system presents different electrical resistances depending on the relative alignment of the magnetization of the two FM. However, the conservation of the spin information through the NM spacer represents one of the main challenges spintronic devices has to face. Organic semiconductors appear as good NM spacer candidates to overcome this difficulty due to their weak spin-orbit and hyperfine interactions, main responsible for spin decoherence in materials. Still, injecting spins from a FM metal into an organic semiconductor is usually difficult. It was recently spotlighted the relevance of FM/organic semiconductor interfaces on the determination of spin injection and transport in organic spintronics. Therefore it becomes crucial a thorough characterization of the so-called spinterfaces in order to shed light on a poorly understood phenomenon which is limiting the capabilities of organic spintronic devices. The coupling (ex: charge transfer, orbital hybridization) between the organic semiconductors and the surfaces gives rise to new hybrid spinterface states which determine the spin injection and transport properties at the Femi level, modifying the spin polarization and magnetism of surfaces. The presence of these new states has been experimentally verified by spectroscopic investigations, or inferred on the basis of device performances, while combined studies showing how molecular-induced surface modifications impact the magnetoresistance are still lacking. DELICE planned to benefit from the high spin filtering efficiency that had been predicted for some metallocene and porphyrin molecules, holding the promise to either enhance the spin injection from FM surfaces or create spin-polarization on NM metal surfaces. DELICE has studied the still unexplored implementation of such MSF-based spinterfaces in working devices. In parallel, this device-oriented approach has been complemented by a surface science study to obtain a comprehensive, multi-length-scale understanding of the spinterfaces properties. The full exploitation of molecular capabilities in organic spintronic devices, combined with a deeper fundamental understanding of the nano- and microscopic electronic processes taking place at interfaces, will permit the engineering and optimization of devices, giving a new impulse to the field of organic spintronics. The technological potential of such a result in this field represents a major step towards the realization of competitive organic nanodevices.

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