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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - DELICE (Device oriented molecular spin filter based interfaces)

Teaser

Summary

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.

Work performed

At the beginning of the action, September 2017, I started a training on how to use a UHV deposition system to grow different organic and metallic thin films. This system allows to grow devices based on these materials through the use of shadow masks. Simultaneously, I was introduced to different film and device characterization methods.
First, the effect of depositing different organic molecules such as MnPc, H2Pc, PTCDI or C60 on top of very thin ferromagnetic films was investigated. SQUID magnetometry measurements pointed towards a modification of the magnetic properties of the films, but only at low temperature.

Then, a similar study was performed but using thin films of LSMO, which were grown in collaboration with the University of Santiago de Compostela. In this case, a more noticeable magnetic effect was observed when the organic/inorganic interface was formed.

Finally, we implemented some organic spin valve devices including what it was supposed to be a spin filter-based interface. However, we did not see a particular enhancement of the observed magnetoresistances. This is probably linked to the different molecular energy levels, although further work should be done in this regard.

Final results

DELICE provided results with a reasonable scientific and technological impact. The project focused on the role played by the MSF/inorganic spinterfaces in devices, trying to find interfaces which act as a feasible source of highly spin-polarized electrons that can be exploited to fabricate highly performant organic spintronic devices. We studied several spinterfaces from which the field of organic spintronics could actively profit for the development of MSF-based nanodevices.

Ultimately, the project had a societal impact thanks to the specific activities to promote and spread the results obtained within this MSCA action in which the researcher was involved. Such activities include not only other researchers or possible interested technological companies, but also the general public.