Suchergebnisse

Mesoporous Ni and Cu-Ni (Cu20Ni80 and Cu45Ni55 in at. %) films, showing a three-dimensional (3D) porous structure and tunable magnetic properties, are prepared by electrodeposition from aqueous surfactant solutions using micelles of P-123 triblock copolymer as structure-directing entities. Pores between 5 and 30 nm and dissimilar space arrangements (continuous interconnected networks, circular pores, corrugated mesophases) are obtained depending on the synthetic conditions. X-ray diffraction studies reveal that the Cu-Ni films have crystallized in the face-centered cubic structure, are textured, and exhibit certain degree of phase separation, particularly those with a higher Cu content. Atomic layer deposition (ALD) is used to conformally coat the mesopores of Cu20Ni80 film with amorphous Al2O3, rendering multiphase "nano-in-meso" metal-ceramic composites without compromising the ferromagnetic response of the metallic scaffold. From a technological viewpoint, these 3D nanoengineered composite films could be appealing for applications like magnetically actuated micro/nanoelectromechanical systems (MEMS/NEMS), voltage-driven magneto-electric devices, capacitors, or as protective coatings with superior strength and tribological performance. ; Financial support by the European Research Council (SPIN-PORICS 2014-Consolidator Grant, Agreement No 648454), the Spanish Government (Project MAT2017-86357-C3-1-R and associated FEDER) and the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0496), the Generalitat de Catalunya (2017-SGR-292 and 2017-SGR-1519) and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no 665919 is acknowledged. E.P. and M. C. are grateful to MINECO for the "Ramón y Cajal" contract (RYC-2012-10839 and RYC-2013-12448). ; Peer reviewed

The primary advantage of magnetoelectric heterostructures exhibiting direct magnetoelectric effect is the possibility to induce and modulate the electrical response of the ferroelectric phase directly with an external magnetic field (i.e., wirelessly, without applying electric field). Nevertheless, the magnetoelectric coupling in such heterostructures is commonly limited by substrate clamping which hinders effective strain propagation. In this work, 1 μm thick ferromagnetic Fe-Ga layers were electrodeposited onto rigid Si/Cu substrates and subsequently coated with ferroelectric P(VDF-TrFE). Under magnetic field, the (110) textured Fe-Ga alloy is compressed along the z-direction by 0.033%, as demonstrated by X-ray diffraction. The experimental results suggest that while the bottom of the Fe-Ga layer is clamped, its air side exhibits a pronounced tetragonal deformation thanks to the residual nanoporosity existing between the columnar grains, that is, a strain gradient develops across the thickness of the Fe-Ga film. This strain gradient in Fe-Ga induces a change in the piezoresponse of the adjacent ferroelectric P(VDF-TrFE) layer. These results pave the way to the design of high-performance microelectromechanical systems (MEMS) with magnetoelectric response integrated on rigid substrates. ; This work was supported by the Spanish Government (MAT2017-86357-C3-1-R and associated FEDER), the Generalitat de Catalunya (2017-SGR-292), the European Research Council (ERC) under the SPIN-PORICS 2014-Consolidator Grant (Agreement № 648454) and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement nº 665919. Authors also acknowledge networking support by COST Action MP1407-STSM grant COST-STSM-MP1407-43917. J.F. acknowledges the "Juan de la Cierva" (IJCI-2015-27030) contract by the Spanish Government. S.P. acknowledges support from the ERC-2017-CoG HINBOTS Grant No. 771565. ; Peer reviewed

Magneto-ionics is an emerging field in materials science where voltage is used as an energy-efficient means to tune magnetic properties, such as magnetization, coercive field, or exchange bias, by voltage-driven ion transport. We first discuss the emergence of magneto-ionics in the last decade, its core aspects, and key avenues of research. We also highlight recent progress in materials and approaches made during the past few years. We then focus on the "structural-ion"approach as developed in our research group in which the mobile ions are already present in the target material and discuss its potential advantages and challenges. Particular emphasis is given to the energetic and structural benefits of using nitrogen as the mobile ion, as well as on the unique manner in which ionic motion occurs in CoN and FeN systems. Extensions into patterned systems and textures to generate imprinted magnetic structures are also presented. Finally, we comment on the prospects and future directions of magneto-ionics and its potential for practical realizations in emerging fields, such as neuromorphic computing, magnetic random-access memory, or micro- and nano-electromechanical systems. ; Financial support by the European Research Council (SPIN-PORICS 2014-Consolidator Grant Agreement No. 648454, and the MAGIC-SWITCH 2019-Proof of Concept Grant, Agreement No. 875018), the Spanish Government (Nos. MAT2017-86357-C3-1-R, PDC2021-121276-C31, and PID2020-116844RB-C21), the Generalitat de Catalunya (2017-SGR-292 and 2018-LLAV-00032), and the European Regional Development Fund (Nos. MAT2017-86357-C3-1-R and 2018-LLAV-00032) were acknowledged. E.M. acknowledges support as a Serra Húnter Fellow. G.R. acknowledges support from Ayudas Ramon y Cajal No. RYC-2016-21412. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

Among metamagnetic materials, FeRh alloys are technologically appealing due to their uncommon antiferromagnetic-to-ferromagnetic metamagnetic transition which occurs at a temperature T* just above room temperature. Here, a controlled increase of T* (DT* B 20 8C) is induced in pre-selected regions of FeRh films via mechanical strain nanopatterning. Compressive stresses generated at the vicinity of predefined nanoindentation imprints cause a local reduction of the FeRh crystallographic unit cell parameter, which leads to an increase of T* in these confined micro-/nanometric areas. This enhances the stability of the antiferromagnetic phase in these localized regions. Remarkably, generation of periodic arrays of nanopatterned features also allows modifying the overall magnetic and electric transport properties across large areas of the FeRh films. This approach is highly appealing for the design of new memory architectures or other AFM-spintronic devices. ; Dr Patxi Lo´pez-Barbera´ is acknowledged for his assistance with the MOKE experiments. Vicente Garcı´a-Juez from Real Casa de la Moneda – Fa´brica Nacional de Moneda y Timbre is acknowledged for his scientific advice. Dr Florencio Sa´nchez is acknowledged for the growth of the samples. Dr Bernat Bozzo is acknowledged for the electric transport characterization. ALBA synchrotron is acknowledged for the provision of beamtime at the MSPD (proposal number 2017092412) and CIRCE (proposal numbers 2017092462 and 2018022818) beamlines. Financial support from the Spanish Ministry of Economy and Competitiveness, through the ''Severo Ochoa'' Programme for Centres of Excellence in R&D (SEV-2015-0496 and SEV-2017-0706) and the MAT2017-85232-R, RTI2018-095303-B-C53. MAT2014-56063-C2-1- R, MAT2017-86357-C3-1-R (and associated FEDER) and MAT2015- 73839-JIN projects, the Generalitat de Catalunya (2014 SGR 734 and 2017 SGR 292), AGAUR (2018 LLAV 00032 and 2019 LLAV 00050) and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 665919 is acknowledged. This work was supported by the European Research Council under the SPIN-PORICS 2014- Consolidator Grant, Agreement No. 648454 and the MAGICSWITCH 2019-Proof of Concept Grant, Agreement No. 875018. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. I. F. acknowledges his RyC contract RYC-2017-22531. E. C. acknowledges the partial financial support from the National Science Centre of Poland (NCN) by the PRELUDIUM project UMO-2015/17/N/ST5/01988 and the SONATA Project No. UMO-2016/23/D/ST3/02121. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed

The utility of electrical resistivity as an indicator of magnetoionic performance in stoichiometrically and structurally similar thin-film systems is demonstrated. A series of highly nanocrystalline cobalt nitride (Co-N) thin films (85 nm thick) with a broad range of electrical properties exhibit markedly different magnetoionic behaviors. Semiconducting, near stoichiometric CoN films show the best performance, better than their metallic and insulating counterparts. Resistivity reflects the interplay between atomic bonding, carrier localization, and structural defects, and in turn determines the strength and distribution of applied electric fields inside the actuated films. This fact, generally overlooked, reveals that resistivity can be used to quickly evaluate the potential of a system to exhibit optimal magnetoionic effects, while also opening interesting challenges. ; Financial support by the European Research Council (SPIN-PORICS 2014-Consolidator Grant, Agreement No. 648454, and the MAGIC-SWITCH 2019-Proof of Concept Grant, Agreement No. 875018), the Spanish Government (MAT2017-86357-C3-1-R and PID2020- 116844RB-C21), the Generalitat de Catalunya (2017- SGR-292 and 2018-LLAV-00032) and the European Regional Development Fund (MAT2017-86357-C3-1-R and 2018-LLAV-00032) is acknowledged. This work was partially supported by the Impulse-und Net-working fund of the Helmholtz Association (FKZ VH-VI-442 Memriox), and the Helmholtz Energy Materials Characterization Platform (03ET7015). The PALS measurements were carried out at ELBE at the Helmholtz-Zentrum DresdenRossendorf e. V., a member of the Helmholtz Association. L.A. thanks MINECO for a Ramón y Cajal Contract (RYC-2013-12640). J.S. thanks the Spanish Fábrica Nacional de Moneda y Timbre for fruitful discussions. E.M. acknowledges support as a Serra Húnter Fellow. We acknowledge service from MiNa Laboratory at IMNCSIC.

Magneto-ionics allows for tunable control of magnetism by voltage-driven transport of ions, traditionally oxygen or lithium and, more recently, hydrogen, fluorine, or nitrogen. Here, magneto-ionic effects in single-layer iron nitride films are demonstrated, and their performance is evaluated at room temperature and compared with previously studied cobalt nitrides. Iron nitrides require increased activation energy and, under high bias, exhibit more modest rates of magneto-ionic motion than cobalt nitrides. Ab initio calculations reveal that, based on the atomic bonding strength, the critical field required to induce nitrogen-ion motion is higher in iron nitrides (≈6.6 V nm-1) than in cobalt nitrides (≈5.3 V nm-1). Nonetheless, under large bias (i.e., well above the magneto-ionic onset and, thus, when magneto-ionics is fully activated), iron nitride films exhibit enhanced coercivity and larger generated saturation magnetization, surpassing many of the features of cobalt nitrides. The microstructural effects responsible for these enhanced magneto-ionic effects are discussed. These results open up the potential integration of magneto-ionics in existing nitride semiconductor materials in view of advanced memory system architectures. ; Financial support by the European Research Council (SPINPORICS 2014-Consolidator Grant, Agreement No. 648454, and the MAGIC-SWITCH 2019-Proof of Concept Grant, Agreement No. 875018), the Spanish Government (MAT2017-86357-C3-1-R), the Generalitat de Catalunya (2017-SGR-292 and 2018-LLAV-00032), the European Regional Development Fund (MAT2017-86357-C3-1-R and 2018-LLAV-00032), and the French ANR (ANR-18-CE24- 0017 "FEOrgSpin" and ELECSPIN ANR-16-CE24-0018 "ELECSPIN") is acknowledged. This work was partially supported by the Impulse- und Net-working fund of the Helmholtz Association (FKZ VH-VI-442 Memriox) and the Helmholtz Energy Materials Characterization Platform (03ET7015). The PALS measurements were carried out at ELBE at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. We thank the facility staff for assistance. L.A. thanks MINECO for a Ramón y Cajal Contract (RYC-2013-12640).

Magnetic data storage and magnetically actuated devices are conventionally controlled by magnetic fields generated using electric currents. This involves significant power dissipation by Joule heating effect. To optimize energy efficiency, manipulation of magnetic information with lower magnetic fields (i.e., lower electric currents) is desirable. This can be accomplished by reducing the coercivity of the actuated material. Here, a drastic reduction of coercivity is observed at room temperature in thick (≈600 nm), nanoporous, electrodeposited Cu–Ni films by simply subjecting them to the action of an electric field. The effect is due to voltage-induced changes in the magnetic anisotropy. The large surface-area-to-volume ratio and the ultranarrow pore walls of the system allow the whole film, and not only the topmost surface, to effectively contribute to the observed magnetoelectric effect. This waives the stringent "ultrathin-film requirement" from previous studies, where small voltage-driven coercivity variations were reported. This observation expands the already wide range of applications of nanoporous materials (hitherto in areas like energy storage or catalysis) and it opens new paradigms in the fields of spintronics, computation, and magnetic actuation in general. ; Financial support by the European Research Council (SPIN-PORICS 2014-Consolidator Grant, Agreement No. 648454), the Spanish Government (Project Nos. MAT2014-57960-C3-1-R and FIS2015-64886-C5-3-P and associated FEDER) and the Generalitat de Catalunya (Nos. 2014-SGR-1015 and 2014-SGR-301) is acknowledged. E.M. acknowledges the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant Agreement No. 665919. E.P. is grateful to MINECO for the "Ramon y Cajal" contract (No. RYC-2012-10839). E.I.-C. acknowledges the grant awarded by the National Council on Science and Technology in Mexico (CONACYT). R.C., R.R., and P.O. acknowledge support from EU H2020-EINFRA-5-2015 MaX Center of Excellence (Grant 676598). The authors would also like to acknowledge networking support by the COST Action e-MINDS MP1407. ICN2 acknowledges the support from the Severo Ochoa Program (MINECO, Grant No. SEV-2013-0295). ; Peer reviewed

Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room-temperature voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a CoN film. Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics in Co3O4. Both materials are nanocrystalline (face-centered cubic structure) and show reversible voltage-driven ON-OFF ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly creating a plane-wave-like migration front, without assistance of diffusion channels. Remarkably, nitrogen magneto-ionics requires lower threshold voltages and exhibits enhanced rates and cyclability. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. These results may open new avenues in applications such as brain-inspired computing or iontronics in general. ; Financial support by the European Research Council (2014-Consolidator Grant Agreement No. 648454 and 2019-Proof of Concept Grant Agreement N° 875018), the Spanish Government (MAT2017-86357-C3-1-R), the Generalitat de Catalunya (2017-SGR-292 and 2018-LLAV-00032), the French ANR (ANR-18-CE24-0017 Project "FEOrgSpin") and FEDER (MAT2017-86357-C3-1-R and 2018-LLAV-00032) is acknowledged. ICN2 is funded by the CERCA program/Generalitat de Catalunya and supported by the Severo Ochoa Centres of Excellence program (Spanish Research Agency, grant no. SEV-2017-0706). Work at GU has been supported by SMART (2018-NE-2861), one of seven centers of nCORE, a Semiconductor Research Corporation program sponsored by NIST, and NSF (DMR−1905468, DMR−1828420). The PALS measurements were carried out at ELBE at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. We would like to thank A.G. Attallah and E. Hirschmann for assistance during PALS. ; Peer reviewed