The work performed during the overall duration of the project has encompassed the following tasks:
i) Synthesis of electrically conducting alloys (CuNi, CoPt, etc.) by electrodeposition (using block-copolymer surfactants or colloidal templating), dip coating (evaporation-induced self-assembly method) or dealloying. In addition, the growth of FeRh and FeAl films onto piezoelectric substrates has been also carried out. Finally, we have grown transition metal oxides and nitrides (e.g. Co3O4, CoN, FeN, etc.) using sputtering for voltage-driven magneto-ionic studies. The obtained materials have been thoroughly characterized from a structural point of view using diffraction and electron microscopy techniques. The magnetic properties have been studied using vibrating-sample magnetometry and magneto-optic Kerr effect with home-made capabilities to apply voltage.
ii) Filling of the porous frameworks with a dielectric material. Three approaches have been performed: filling the pores with liquid electrolytes (propylene carbonate), with dielectric polymers (e.g. propylene carbonate) and coating the inner pore walls using atomic layer deposition (basically with Al2O3 and HfO2).
iii) Fundamental studies of electric field actuation on the surface magnetic properties. Interesting results have been obtained in the CuNi, FeCu, FePt and CoPt systems by immersion of the nanoporous film in suitable electrolytes. A reduction of coercivity larger than 30% has been observed in all these systems under applied voltages of the order of 10 V. The maximum effect was encountered for nanoporous CoPt patterned disks with minor amounts of CoO (coercivity reduction by 88%, Fig. 2)). In most cases, the coercivity can be recovered by applying suitable voltage values of opposite polarity. The experimental results are being interpreted with the use of ab-initio calculations and micromagnetic simulations. Interesting results have been obtained by electrolyte-gating paramagnetic Co3O4 and CoN films, where an ON-OFF magnetic transition (from paramagnetic to ferromagnetic and viceversa) can be induced by DC voltage via magnetoionic effects (see Fig. 3).
iv) Implementation of these layers in recording media and memories.
The results obtained in the project have led to around 50 publications in peer reviewed journals (Adv. Funct. Mater., Nat. Commun., Small, ACS Nano, ACS Appl. Mater. Interf., Sci. Rep., Adv.Science J. Mater. Chem. C, APL Mater., etc.). Also, the results have already been presented in several conferences, sometimes as invited talks (e.g. Thermec or the 2nd IEEE Conference on Advances in Magnetics, MMM-Intermag, ISMANAM,etc.). We have also issued three patents (two in PCT stage) related to the results of the project.
