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SPIN-PORICS Report Summary

Project ID: 648454
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - SPIN-PORICS (Merging Nanoporous Materials with Energy-Efficient Spintronics)

Reporting period: 2015-09-01 to 2017-02-28

Summary of the context and overall objectives of the project

This Project aims to integrate engineered nanoporous materials into novel energy-efficient spintronic applications. Magnetic storage and magneto-electronic devices are conventionally controlled by means of magnetic fields (via electromagnetic induction) or using spin-polarized electric currents (spin-transfer torque). Both principles involve significant energy loss by heat dissipation (Joule effect). The replacement of electric current with electric field would drastically reduce the overall power consumption. Strain-mediated magneto-electric coupling in piezoelectric-magnetostrictive bilayers might appear a proper strategy to achieve this goal. However, this approach is not suitable in spintronics because of the clamping effects with the substrate, need of epitaxial interfaces and risk of fatigue-induced mechanical failure. The exciting possibility to control ferromagnetism of metals and semiconductors directly with electric field (without strain) has been recently reported, but most significant effects occur below 300 K and only in ultra-thin films or nanoparticles. This Project tackles the development of a new type of nanocomposite material, comprising an electrically conducting or semiconducting nanoporous layer filled with a suitable dielectric material, where the magnetic properties of the metal/semiconductor will be largely tuned at room temperature (RT) by simply applying a voltage, via electric charge accumulation. The porous layer will consist of specific alloys (Cu-Ni or Fe-Rh) or oxide diluted magnetic semiconductors, where surface magnetic properties have been recently reported to be sensitive to electric field at RT. Based on these new materials, three technological applications are envisaged: electrically-assisted magnetic recording, voltage-driven switching of magnetic random-access memories and spin field-effect transistors. The obtained results are likely to open new paradigms in the field of spintronics and could be of high economic transcendence.

More specifically, the scientific and technological objectives of this project can be summarized as follows:
i) To significantly enhance voltage-driven magnetic effects at RT (not mediated by strain), as compared to the modest changes observed until now in specific alloys and semiconductors of very small thickness.
ii) To use cost-effective approaches to synthesize the target materials. This inherently means to avoid materials where epitaxial growth would be essential (like piezoelectric-magnetostritive composites or sophisticated multiferroic oxides).
iii) To better understand the physical mechanisms governing the observed magnetic changes induced by electric field in metallic alloys and diluted semiconductors.
iv) To integrate the proposed nanoporous materials (filled with suitable dielectrics) into spintronic device configurations, such as tunnel junctions or spin-transistors, and to explore their possible use as electrically-assisted magnetic recording media.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

"The work performed so far since the beginning of the project has focussed in three main key tasks:

i) Synthesis of electrically conducting and semiconducting nanoporous materials: Ni, CuNi, FePt and CoPt by electrodeposition (using block-copolymer surfactants) and Cu- and Ni-doped SnO2 layers by dip coating (evaporation-induced self-assembly method) and Ni-doped SnO2 and Co3O4 impregnated with FexCo(3-x)O4 mesoporous powders (nanocasting technique, see Figure 1). The growth of nanoporous CuNi and FeCu by electrodeposition onto colloidal-templated substrates has been also attempted. Finally, the growth of FeRh, CuNi and FeCu thin films onto piezoelectric substrates has been also carried out. The obtained materials have been thoroughly characterized from a structural point of view using diffraction and electron microscopy techniques. The mechanical integrity of the grown layers has been assessed and modelled using nanoindentation. The magnetic properties have been studied using vibrating-sample magnetometry and magneto-optic Kerr effect.

ii) Filling of the porous frameworks with a dielectric material. Two approaches are being attempted: filling the pores with dielectric polymers and coating the inner pore walls using atomic layer deposition (basically with Al2O3).

iii) Fundamental studies of electric field actuation on the surface magnetic properties. Interesting results have been obtained in the CuNi system by immersion of the nanoporous film in suitable electrolytes to generate an electrical double-layer. A reduction of coercivity larger than 30% has been observed by magneto-optic Kerr effect under applied voltages of the order of 10 V. A decrease of coercivity has been also observed for the nanoporous CoPt system. In some cases, the coercivity can be also increased by applying suitable voltage values. First attemps using a ""dry configuration"" (in porous samples not immersed in liquid electrolytes, but using solid dielectric (polymers or ceramic layers) are being performed now. The experimental results are being interpreted with the use of ab-initio calculations, to assess the changes in the effective magnetic anisotropy energy due to applied electric field. The influence of applied voltage on the strain-mediated metamagnetic transition of FeRh has been also investigated.

The results obtained so far have led to 10 publications and two more have been just submitted (under review). Also, the results have already been presented in a few conferences. We have also issued a patent related to the synthesis of nanoporous metallic alloy films by surfactant-assisted electrodeposition."

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In this Project we aim to study the effects of electric field on the magnetic properties of nanoporous materials and wish to develop the first prototype spintronic devices that incorporate nanoporous conducting or semiconducting layers in their structures (as a proof-of-concept). To this end, the Project seeks new approaches, beyond the state-of-the-art, to merge the advanced synthetic routes for the synthesis of nanoporous materials with the innovative field of spintronics. As examples, we propose voltage-driven MRAM or spin-FET as possible spintronic architectures. The successful implementation of these designs will be a ground-breaking achievement, which would certainly revolutionize the field of spintronics. The foreseen drastic effects of an applied voltage on the magnetic properties of nanoporous frameworks would drastically reduce the energy consumption of miniaturized magnetic memory devices.
So far, much progress (beyond the state-of-the-art) has been achieved in our group in the synthesis of magnetic nanoporous films (both metallic and semiconducting) and their structural and magnetic characterization (using magnetometry and dichroism techniques, at large-scale facilities, like the ALBA or the BESSY synchrotrons). One patent dealing with the synthesis of nanoporous alloys has been submitted and we are drafting a second patent on the magneto-electric effects observed in nanoporous CuNi alloys. Hence, the results from this project are likely to have a strong scientific and technological impact and could be of high economic transcendence.

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