Periodic Reporting for period 4 - SPIN-PORICS (Merging Nanoporous Materials with Energy-Efficient Spintronics)
Reporting period: 2020-03-01 to 2020-12-31
The Project aim is to integrate engineered nanoporous materials into novel energy-efficient magnetic and spintronic applications (Fig. 1). Magneto-electronic devices are conventionally controlled by 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 to operate these devices drastically reduces the 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. 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 are largely tuned at room temperature (RT) by voltage. The porous layer consists of specific alloys (Cu-Ni or Fe-Cu) or magnetic semiconductors, where surface magnetic properties are sensitive to electric field. Based on these new materials, technological applications such as electrically-assisted magnetic recording or magnetic random-access memories are developed. Our technology drastically reduces the energy power consumption (by more than two orders of magnitude) and enhances robustness of data storage systems. This stems from a strong reduction of coercivity with voltage which is ascribed to changes in the electronic band structure of the investigated materials (causing a reduction of the magnetocrystalline anisotropy) and, in some cases (oxide or nitride semiconductors), voltage-driven ion migration. An additional added value of our data storage concept is that the selective application of voltage (instead of magnetic field) to write on the magnetic memory units improves the robustness of the resulting devices. In extreme cases, we have been able to fully remove (and regenerate) magnetism with voltage (depending on the voltage polarity and strength). The obtained results are likely to open new paradigms in the field of spintronics and could be of high economic transcendence.
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.
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.
"In this Project we aimed to study the effects of electric field on the magnetic properties of nanoporous materials and wish to develop the first prototypes of magnetic memories and 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 magnetic memory systems and magneto-electric random access memories as possible spintronic nanoporous architectures. The successful implementation of these designs represents a ground-breaking achievement, which will certainly revolutionize the field of spintronics. The drastic effects of an applied voltage on the magnetic properties of nanoporous frameworks will 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). An important discovery (not initially planned in the proposal) is that voltage can be used to induce (and subsequently suppress, if needed) magnetic properties in transition metal oxide and nitride semiconductors (an effect to which we refer to as ""ON-OFF magnetic switching). This is related to electrically-driven ion migration that allows to locally generate transition metal clusters (with ferromagnetic properties) embedded in the non-magnetic semiconducting matrix. Three patents dealing with (i) the synthesis of nanoporous alloys and (ii) the magneto-electric effects observed in nanoporous alloys, and (iii) the implementation of a new magnetoelectric device with voltage-driven OFF-ON magnetic capabilities have been issued at National and European levels (the third patent being under evaluation). Hence, the results from this project are likely to have a strong scientific and technological impact and could be of high economic transcendence."
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). An important discovery (not initially planned in the proposal) is that voltage can be used to induce (and subsequently suppress, if needed) magnetic properties in transition metal oxide and nitride semiconductors (an effect to which we refer to as ""ON-OFF magnetic switching). This is related to electrically-driven ion migration that allows to locally generate transition metal clusters (with ferromagnetic properties) embedded in the non-magnetic semiconducting matrix. Three patents dealing with (i) the synthesis of nanoporous alloys and (ii) the magneto-electric effects observed in nanoporous alloys, and (iii) the implementation of a new magnetoelectric device with voltage-driven OFF-ON magnetic capabilities have been issued at National and European levels (the third patent being under evaluation). Hence, the results from this project are likely to have a strong scientific and technological impact and could be of high economic transcendence."