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Self-Assembled Monolayers over Ferromagnetic Electrodes for Organic Spintronics

Final Report Summary - SAMSFERE (Self-Assembled Monolayers over Ferromagnetic Electrodes for Organic Spintronics)

The objective of this reporting period was to continue and deepen the study of the Self-assembled Monolayers-based organic magnetic tunnel junctions designed during the first part of the project.
Following our previous pioneering work on the functionalization of LSMO with alkylphosphonic acid, we studied the influence of SAMs grafting on the electronic properties of LSMO using photoemission and absorption spectroscopies (XPS, UPS and XMCD) (Galbiati et al. Appl. Surf. Sci. (2016)). LSMO//SAM/Co, (SAM = alkylphosphonic acid, n = 10, 12, 14, 16, 18) spintronic devices showed an exponential increase of tunnel resistance as a function of alkyl chain length, this is a direct proof of the successful connection of the molecules to the ferromagnetic electrodes. For all the alkyl chains studied we obtained stable and robust tunnel magnetoresistance, with effects up to 250% at low temperature (Tatay et al. J. Phys. Condens. Matter. (2016)).
Using our recently developed method to recover oxidized ferromagnetic metal surfaces (Tatay et al. AIP Advances. (2015)) without altering interfacial properties we have integrated SAMs into organic room temperature MTJs using Py and Co as ferromagnetic electrodes. We have obtained some promising results and measured magnetoresistance signals at room temperature on some of these devices. In general NiFe-based MTJ showed more reliable (less ratio of short-circuited contacts) and displayed higher TMR signals when compared to Co-based MTJs. Moreover, we have integrated some of these SAM-ferromagnetic metal systems into light-emitting diodes. With this aim we designed and studied the electroluminescent devices with ITO/Py//SAM/F8BT/MoOx/Metal structure (M6/M7, F8BT = Poly(9,9-dioctylfluorene-alt-benzothiadiazole)). Similar structures (ITO/ZnO//F8BT/MoOx/Metal (ZnO = Zinc Oxide)) have previously tested at the ICMol and showed low on-set voltages. We first used gold as top electrode. Some of our devices shined light above 4 V, the wavelength of the emitted light closely resembled F8BT emission spectra. The system without SAM showed increased turn-on voltage. These results confirm the feasibility of using SAMs for the construction of spin-OLEDs. The next step will be to include Co as the top ferromagnetic to perform magnectotransport measurements on these devices.