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Altres ajuts: CERCA Programme/Generalitat de Catalunya ; the Government of Catalonia's Agency for Business Competitiveness (ACCIÓ) (TECSPR19-1-0021) Soft optomechanical systems have the ability to reversibly respond to optical and mechanical external stimuli by changing their own properties (e.g., shape, size, viscosity, stiffness, color or transmittance). These systems typically combine the optical properties of plasmonic, dielectric or carbon-based nanomaterials with the high elasticity and deformability of soft polymers, thus opening the path for the development of new mechanically tunable optical systems, sensors, and actuators for a wide range of applications. This review focuses on the recent progresses in soft optomechanical systems, which are here classified according to their applications and mechanisms of optomechanical response. The first part summarizes the soft optomechanical systems for mechanical sensing and optical modulation based on the variation of their optical response under external mechanical stimuli, thereby inducing mechanochromic or intensity modulation effects. The second part describes the soft optomechanical systems for the development of light induced mechanical actuators based on different actuation mechanisms, such as photothermal effects and phase transitions, among others. The final section provides a critical analysis of the main limitations of current soft optomechanical systems and the progress that is required for future devices.

New multi-stimuli responsive materials are required in smart systems applications to overcome current limitations in remote actuation and to achieve versatile operation in inaccessible environments. The incorporation of detection mechanisms to quantify in real time the response to external stimuli is crucial for the development of automated systems. Here, we present the first wireless opto-magnetic actuator with mechanochromic response. The device, based on a nanostructured-iron (Fe) layer transferred onto suspended elastomer structures with a periodically corrugated backside, can be actuated both optically (in a broadband spectral range) and magnetically. The combined opto-magnetic stimulus can accurately modulate the mechanical response (strength and direction) of the device. The structural coloration generated at the corrugated back surface enables to easily map and quantify, in 2D, the mechanical deflections by analyzing in real time the hue changes of images taken using a conventional RGB smartphone camera, with a precision of 0.05°. We demonstrate the independent and synergetic optical and magnetic actuation and detection with a detection limit of 1.8 mW·cm-2 and 0.34 mT, respectively. The simple operation, versatility, and cost-effectiveness of the wireless multiactuated device with highly sensitive mechanochromic mapping paves the way to a new generation of wirelessly controlled smart systems., We acknowledge funding from the Generalitat de Catalunya through the 2017-SGR-292 project. The funding from the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN) through the PID2019-106229RB-I00, MAT2016-77391-R, PCIN2016-093 (M-ERA-NET), DPI2015-68197-R, and RTI2018-096786-B-I00 projects and the Ramon y Cajal Fellowship (RyC2013-14479) is acknowledged. The PhD fellowship CIBAE-023-2014 (from SENESCYT) is also acknowledged. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706).

Dense systems of magnetic nanoparticles may exhibit dipolar collective behavior. However, two fundamental questions remain unsolved: i) whether the transition temperature may be affected by the particle anisotropy or it is essentially determined by the intensity of the interparticle dipolar interactions, and ii) what is the minimum ratio of dipole–dipole interaction (Edd) to nanoparticle anisotropy (KefV, anisotropy⋅volume) energies necessary to crossover from individual to collective behavior. A series of particle assemblies with similarly intense dipolar interactions but widely varying anisotropy is studied. The Kef is tuned through different degrees of cobalt-doping in maghemite nanoparticles, resulting in a variation of nearly an order of magnitude. All the bare particle compacts display collective behavior, except the one made with the highest anisotropy particles, which presents “marginal” features. Thus, a threshold of KefV/Edd ≈ 130 to suppress collective behavior is derived, in good agreement with Monte Carlo simulations. This translates into a crossover value of ≈1.7 for the easily accessible parameter TMAX(interacting)/TMAX(non-interacting) (ratio of the peak temperatures of the zero-field-cooled magnetization curves of interacting and dilute particle systems), which is successfully tested against the literature to predict the individual-like/collective behavior of any given interacting particle assembly comprising relatively uniform particles., The authors acknowledge financial support from grant No. MAT2015-65295-R funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”, grant No. PID2019-106229RB-I00 funded by MCIN/AEI/10.13039/501100011033 and the Spanish MEC (through the contract No. BEAGAL18/00095). The authors also acknowledge funding from UCLM's Plan Propio, the Swedish Research Council (VR), the Universidad Pública de Navarra (grant No. PJUPNA2020) and the Generalitat de Catalunya (grant No. 2017-SGR-292). ICN2 is funded by the CERCA program/Generalitat de Catalunya and supported by SEV-2017-0706 grant funded by MCIN/AEI/10.13039/501100011033. K.T., D.P., and M.V. acknowledge support from the European Union's Horizon 2020 Programme: under gran agreement No. 731976 (MAGENTA) and partially the Horizon Europe EIC Pathfinder Programme: under grant agreement No. 101046909 (REMAP).

Interfaces play a crucial role in composite magnetic materials and particularly in bimagnetic core/shell nanoparticles. However, resolving the microscopic magnetic structure of these nanoparticles is rather complex. Here, we investigate the local magnetization of antiferromagnetic/ferrimagnetic FeO/Fe3O4 core/shell nanocubes by electron magnetic circular dichroism (EMCD). The electron energy-loss spectroscopy (EELS) compositional analysis of the samples shows the presence of an oxidation gradient at the interface between the FeO core and the Fe3O4 shell. The EMCD measurements show that the nanoparticles are composed of four different zones with distinct magnetic moment in a concentric, onion-type, structure. These magnetic areas correlate spatially with the oxidation and composition gradient with the magnetic moment being largest at the surface and decreasing toward the core. The results show that the combination of EELS compositional mapping and EMCD can provide very valuable information on the inner magnetic structure and its correlation to the microstructure of magnetic nanoparticles., The authors acknowledge the financial support from the Spanish Minister of Science and Innovation (MICINN) through the projects PID2019-106165GB-C21, PID2019-106165GB-C22, and PID2019-106229RB-I00. They also acknowledge funding from Generalitat de Catalunya through the 2017-SGR-292 and 2017-SGR-776 projects. In addition, research at UCM was supported by MINECO/FEDER MAT2015-66888-C3-3-R and RTI2018-097895-B-C43 grants. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, Grant SEV-2017-0706). M.E. thanks the Spanish MICINN and AEI/FSE for Ramón y Cajal contract (RYC2018-024396-I). A.L.O. acknowledges support from the Universidad Pública de Navarra (Grant PJUPNA2020). STEM-EELS observations carried out at the Centro Nacional de Microscopía Electrónica at Universidad Complutense de Madrid, Spain (ICTS ELECMI).

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 Lopez-Barbera is acknowledged for his assistance with the MOKE experiments. Vicente Garcia-Juez from Real Casa de la Moneda – Fabrica 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).

Electric-field-controlled magnetism can boost energy efficiency in widespread applications. However, technologically, this effect is facing important challenges: mechanical failure in strain-mediated piezoelectric/magnetostrictive devices, dearth of room-temperature multiferroics, or stringent thickness limitations in electrically charged metallic films. Voltage-driven ionic motion (magneto-ionics) circumvents most of these drawbacks while exhibiting interesting magnetoelectric phenomena. Nevertheless, magneto-ionics typically requires heat treatments and multicomponent heterostructures. Here we report on the electrolyte-gated and defect-mediated O and Co transport in a Co3O4 single layer which allows for room-temperature voltage-controlled ON-OFF ferromagnetism (magnetic switch) via internal reduction/oxidation processes. Negative voltages partially reduce Co3O4 to Co (ferromagnetism: ON), resulting in graded films including Co- and O-rich areas. Positive bias oxidizes Co back to Co3O4 (paramagnetism: OFF). This electric-field-induced atomic-scale reconfiguration process is compositionally, structurally, and magnetically reversible and self-sustained, since no oxygen source other than the Co3O4 itself is required. This process could lead to electric-field-controlled device concepts for spintronics., Financial support by the European Research Council (SPINPORICS 2014-Consolidator Grant, Agreement No. 648454), the Spanish Government (Projects MAT2017-86357-C3-1-R and associated FEDER), the Generalitat de Catalunya (2017-SGR-292) and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 665919 is acknowledged. E.P. is grateful to MINECO for the “Ramon y Cajal” contract (RYC-2012-10839). The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. ICN2 also acknowledges the support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295). Work at UCD is supported by the US NSF (DMR1610060 and ECCS-1611424).

The physicochemical properties used in numerous advanced nanostructured devices are directly controlled by the oxidation states of their constituents. In this work we combine electron energy-loss spectroscopy, blind source separation, and computed tomography to reconstruct in three dimensions the distribution of Fe and Fe ions in a FeO/FeO core/shell cube-shaped nanoparticle with nanometric resolution. The results highlight the sharpness of the interface between both oxides and provide an average shell thickness, core volume, and average cube edge length measurements in agreement with the magnetic characterization of the sample., This work has been carried out in the frame of the Spanish research projects MAT2013-41506, MAT2013-48628-R, FIS2013-46159-C3-3-P, and CSD2009-00013, and Catalan Government support from the SGR2014-672 and 2014-SGR1015 projects is acknowledged. We also acknowledge the support received from the European Union Seventh Framework Program under Grant Agreement 312483 - ESTEEM2 (Integrated Infrastructure Initiative-I3). G.S.A. was partially supported by the Knut and Alice Wallenberg Foundation (Project: 3DEMNATUR). M.E. acknowledges the Spanish Ministry of Science and Innovation through the Juan de la Cierva Program. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295). F.d.l.P. and C.D. acknowledge funding from the ERC under grant no. 259619 PHOTO EM. C.D. acknowledges the Royal Society for funding

Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk‐approach based on the combined analysis of synchrotron X‐ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/Fe3O4 core/shell nanocubes is studied at different time intervals. The results indicate that a two‐phase approach (FeO and Fe3O4) is not sufficient to successfully fit the data and two additional interface phases (FeO and Fe3O4) are needed to obtain satisfactory fits, i.e., an onion‐type structure. The analysis shows that the Fe3O4 phases grow to some extent (≈1 nm) at the expense of the FeO core. Moreover, the FeO core progressively changes its stoichiometry to accommodate more oxygen. The temporal evolution of the parameters indicates that the structure of the FeO/Fe3O4 nanocubes is rather stable, although the exact interface structure slightly evolves with time. This approach paves the way for average studies of interfaces in different kinds of heterostructured nanoparticles, particularly in cases where spectroscopic methods have some limitations., R.U.I. acknowledges CAPES and CNPq (No. 206983/2014‐0) Brazilian agencies. A.G.R. and J.N. thanks the support of the Generalitat de Catalunya through the 2017‐SGR‐292 project and the Beatriu de Pinos Program (2011 BPB 00209) and the Spanish Ministerio de Economía y Competitividad (MINECO) through the MAT2016‐77391‐R project. I.P. was supported by the National Research Fund of Luxembourg (Grant No. FNR‐Inter2015/LRSF). A.L.‐O. acknowledges the MINECO through the Juan de la Cierva Program (IJCI‐2014‐21530). X.T. would like to acknowledge the financial support from the MINECO projects MAT2015‐67593‐P and BIA2014‐57658‐C2‐1‐R. The ALBA Synchrotron is acknowledged for the provision of beamtime and the MSPD beamline staff is for their help during the XRD measurements. Dr. Luis G. Martinez from IPEN/CNEN is acknowledged for useful discussions about XRD techniques. Dr. Paolo Scardi from Università degli Studi di Trento is acknowledged for the helpful discussions about WPPM and for providing PM2K v.3 software. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Program (MINECO, Grant No. SEV‐2013‐0295).

Hybrid nanoparticles allow exploiting the interplay of confinement, proximity between different materials and interfacial effects. However, to harness their properties an in-depth understanding of their (meta)stability and interfacial characteristics is crucial. This is especially the case of nanosystems based on functional oxides working under reducing conditions, which may severely impact their properties. In this work, the in-situ electron-induced selective reduction of Mn3O4 to MnO is studied in magnetic Fe3O4/Mn3O4 and Mn3O4/Fe3O4 core/shell nanoparticles by means of high-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Such in-situ transformation allows mimicking the actual processes in operando environments. A multi-stage image analysis using geometric phase analysis combined with particle image velocity enables direct monitoring of the relationship between structure, chemical composition and strain relaxation during the Mn3O4 reduction. In the case of Fe3O4/Mn3O4 core/shell the transformation occurs smoothly without the formation of defects. However, for the inverse Mn3O4/Fe3O4 core/shell configuration the electron beam-induced transformation occurs in different stages that include redox reactions and void formation followed by strain field relaxation via formation of defects. This study highlights the relevance of understanding the local dynamics responsible for changes in the particle composition in order to control stability and, ultimately, macroscopic functionality., Research supported by the European Research Council Starting Investigator Award STEMOX # 239739 (M.R. and J. S.), JSPS Postdoctoral Fellowship for Research Abroad (R.I.) and by Spanish MAT2015-066888-C3-3-R and RTI2018-097895-B-C43 (MINECO/FEDER). Electron microscopy observations at Oak Ridge National Laboratory (ORNL) supported by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Materials Sciences and Engineering Division and through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. A.M. and G.S.A. thank the financial support of the Knut and Alice Wallenberg Foundation through the project 3DEM-NATUR. The work at INC2 has been supported by the 2017-SGR-292 project of the Generalitat de Catalunya and by the MAT2016-77391-R project of the Spanish MINECO. ALO acknowledges the Spanish Ministerio de Economía y Competitividad through the Juan de la Cierva Program (IJCI-2014-21530). ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706). S. J. P. thanks the National University of Singapore for funding. M. E. Acknowledges the Spanish MINECO for her Ramón y Cajal Fellowship (RYC2018-024396-I).

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. Exchange bias effects have been studied in elliptical dots composed of ferromagnetic Ni80Fe20-antiferromagnetic Ir20Mn80 bilayers. The magnetization reversal mechanisms and magnetic configurations have been investigated by magneto-optic Kerr effect and magnetic force microscopy. Although the obtained bias fields in these dots are relatively small, the magnetization reversal is found to be influenced by the ferromagnetic-antiferromagnetic coupling. Namely, for some off-axis angles of measurement, the magnetization reversal mechanism of the Ni80Fe20-Ir20Mn80 ellipses depends on whether exchange bias is induced along the minor or major axis of the ellipses. Hence, exchange bias is shown to be an effective means for tailoring the magnetization reversal of elliptical dots after sample fabrication.

Altres ajuts: ICN2 is funded by the CERCA programme/Generalitat de Catalunya. Ultrabroadband light absorbers are attracting increasing interest for applications in energy harvesting, photodetection, self-regulated devices or soft robotics. However, current absorbers show detrimental insufficient absorption spectral range, or light angle and polarization dependence. Here we show that the unexplored optical properties of highly-damped plasmonic materials combined with the infrared absorption of thin polymer films enable developing ultrabroadband light-absorbing soft metamaterials. The developed metamaterial, composed of a nanostructured Fe layer mechanically coupled to a thin polydimethylsiloxane (PDMS) film, shows unprecedented ultrabroadband and angle-independent optical absorption (averaging 84% within 300-18000 nm). The excellent photothermal efficiency and large thermal-expansion mismatch of the metamaterial is efficiently transformed into large mechanical deflections, which we exploit to show an artificial iris that self-regulates the transmitted light power from the ultraviolet to the long-wave infrared, an untethered light-controlled mechanical gripper and a light-triggered electrical switch.

Recreational fishing is a growing sector of tourism, and in theory, can be done in a sustainable manner such as through catch-and-release where fish are released rather than harvested. In some cases, stakeholders have taken the initiative to develop conservation strategies and management guidelines, as well as establishing monitoring programs of the resources they use. In this work, we provide a case study of a cooperative monitoring program in the Alphonse Group, Republic of the Seychelles, Africa, between a fishing company (Alphonse Fishing Company) and a local non-governmental organization (Island Conservation Society). These efforts have resulted in a code of conduct for the catch-and-release of target species, as well as long-term spatially explicit monitoring of catches, including fish size and catch location for five popular species through catch logs. During three seasons, the five key fish species monitored were giant trevally (Caranx ignobilis, n = 684), moustache triggerfish (Balistoides viridescens, n = 141), Indo-Pacific permit (Trachinotus blochii, n = 99), milkfish (Chanos chanos, n = 55), and yellowmargin triggerfish (Pseudobalistes flavimarginatus, n = 46). We found monthly catch variability across all species and that catches across seasons increased for C. ignobilis (203.8%), T. blochii (45.5%), and B. viridescens (25%), and decreased for C. chanos (-65.6%) and P. flavimarginatus (-10%). Although there are considerations with implementing and maintaining such initiatives, we reviewed the benefits, including how these efforts can serve as the foundation for more thorough scientific research, co-production, and evidence-based management for the most sought-after species, C. ignobilis. We highlight how these cooperative initiatives may lead to formal co-management structures in recreational fishing, and also help to build capacity in government agencies for advancing economic prosperity while establishing sound long-term management and conservation strategies.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

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.

Applications based on aggregates of magnetic nanoparticles are becoming increasingly widespread, ranging from hyperthermia to magnetic recording. However, although some uses require collective behavior, others need a more individual-like response, the conditions leading to either of these behaviors are still poorly understood. Here, we use nanoscale-uniform binary random dense mixtures with different proportions of oxide magnetic nanoparticles with low/high anisotropy as a valuable tool to explore the crossover from individual to collective behavior. Two different anisotropy scenarios have been studied in two series of binary compacts: M1, comprising maghemite (γ-Fe2O3) nanoparticles of different sizes (9.0 nm/11.5 nm) with barely a factor of 2 between their anisotropy energies, and M2, mixing equally sized pure maghemite (low-anisotropy) and Co-doped maghemite (high-anisotropy) nanoparticles with a large difference in anisotropy energy (ratio > 8). Interestingly, while the M1 series exhibits collective behavior typical of strongly coupled dipolar systems, the M2 series presents a more complex scenario where different magnetic properties resemble either “individual-like” or “collective”, crucially emphasizing that the collective character must be ascribed to specific properties and not to the system as a whole. The strong differences between the two series offer new insight (systematically ratified by simulations) into the subtle interplay between dipolar interactions, local anisotropy and sample heterogeneity to determine the behavior of dense assemblies of magnetic nanoparticles., This work was supported by the Spanish Ministerio de Economia y Competitividad (grants MAT2015-65295-R and MAT2016-77391-R). J.N. also acknowledges funding from the Generalitat de Catalunya through the 2017-SGR-292 grant. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centers of Excellence program, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706). M.S.A., R.M., and P.N. acknowledge support from The Swedish Research Council (VR). K.N.T, D.P., and M.V. acknowledge support from the European Union’s Horizon 2020 Research and Innovation Programme: under grant agreement no. 731976 (MAGENTA).

Water remediation and development of carbon‐neutral fuels are a priority for the evermore industrialized society. The answer to these challenges should be simple, sustainable, and inexpensive. Thus, biomimetic‐inspired circular and holistic processes combing water remediation and biofuel production can be an appealing concept to deal with these global issues. A simple circular approach using helical Spirulina platensis microalgae as biotemplates to synthesize Ni@ZnO@ZnS photocatalysts for efficient solar water decontamination and bioethanol production during the recycling process is presented. Under solar irradiation, the Ni@ZnO@ZnS‐Spirulina photocatalyst exhibits enhanced activity (mineralization efficiency >99%) with minimal photocorrosion and excellent reusability. At the end of its effective lifetime for water remediation, the microalgae skeleton (mainly glycogen and glucose) of the photocatalyst is recycled to directly produce bioethanol by simultaneous saccharification and fermentation process. An outstanding ethanol yield of 0.4 L kg−1, which is similar to the highest yield obtained from oxygenic photosynthetic microorganisms, is obtained. Thus, the entire process allows effective solar photocatalytic water remediation and bioethanol production at room temperature using simple and easily scalable procedures that simultaneously fixes carbon dioxide, thereby constituting a zero‐carbon‐emission circular process., The work leading to these results received funding from Metrohm foundation, from the 2017‐SGR‐292 project from the Generalitat de Catalunya, and the PCIN2016‐093 and TEC2017‐85059‐C3‐2‐R projects (co‐financed by the Fondo Europeo de Desarrollo Regional, FEDER) from the Spanish Ministerio de Economía y Competitividad (MINECO). The authors also acknowledge Espirulina Natural (Dra. Ester Falgàs) and Societé Industrielle Lesaffre, Division Leaf for the provision of the microalgae and Ethanol Red yeast, respectively. A.S. would like to acknowledge funding from the EMPAPOSTDOCS‐II program. The EMPAPOSTDOCS‐II programme has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska‐Curie grant agreement number 754364. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV‐2017‐0706).

Fishing has had a profound impact on global reef shark populations, and the absence or presence of sharks is strongly correlated with national socio-economic conditions and reef governance. Decades of overexploitation have devastated shark populations, leaving considerable doubt as to their ecological status(1,2). Yet much of what is known about sharks has been inferred from catch records in industrial fisheries, whereas far less information is available about sharks that live in coastal habitats(3). Here we address this knowledge gap using data from more than 15,000 standardized baited remote underwater video stations that were deployed on 371 reefs in 58 nations to estimate the conservation status of reef sharks globally. Our results reveal the profound impact that fishing has had on reef shark populations: we observed no sharks on almost 20% of the surveyed reefs. Reef sharks were almost completely absent from reefs in several nations, and shark depletion was strongly related to socio-economic conditions such as the size and proximity of the nearest market, poor governance and the density of the human population. However, opportunities for the conservation of reef sharks remain: shark sanctuaries, closed areas, catch limits and an absence of gillnets and longlines were associated with a substantially higher relative abundance of reef sharks. These results reveal several policy pathways for the restoration and management of reef shark populations, from direct top-down management of fishing to indirect improvement of governance conditions. Reef shark populations will only have a high chance of recovery by engaging key socio-economic aspects of tropical fisheries.

On the nanoscale, CoO can have different polymorph crystal structures, zinc blende and wurtzite, apart from rock salt, which is the stable one in bulk. However, the magnetic structures of the zinc blende and wurtzite phases remain virtually unexplored. Here we discuss some of the main parameters controlling the growth of the CoO wurtzite and zinc blende polymorphs by thermal decomposition of cobalt (II) acetylacetonate. In addition, we present a detailed neutron diffraction study of oxygen deficient CoO (CoO0.70–0.75) nanoparticles with zinc blende (∼15 nm) and wurtzite (∼30 nm) crystal structures to unravel their magnetic order and its temperature evolution. The magnetic order of the zinc blende nanoparticles is antiferromagnetic and appears at the Néel temperature TN ∼ 203 K. It corresponds to the 3rd type of magnetic ordering in a face-centered cubic lattice with magnetic moments aligned along a cube edge. The magnetic structure in the wurtzite nanoparticles turned out to be rather complex with two perpendicular components. One component is incommensurate, of the longitudinal spin wave type, with the magnetic moments confined in the ab-plane. In the perpendicular direction, this magnetic order is uncorrelated, forming quasi-two-dimensional magnetic layers. The component of the magnetic moment, aligned along the hexagonal axis, is commensurate and corresponds to the antiferromagnetic order known as the 2nd type in a wurtzite structure. The Néel temperature of wurtzite phase is estimated to be ∼109 K. The temperature dependence of the magnetic reflections confirms the reduced dimensionality of the incommensurate magnetic order. Incommensurate magnetic structures in nanoparticles are an unusual phenomenon and in the case of wurtzite CoO it is probably caused by structural defects (e.g., vacancies, strains and stacking faults)., This work was supported by the Russian grant RFBR 16-02-00058, the MAT2016-79455-P and MAT2015-68200-C2-2-P projects of the Spanish MINECO and by the 2017 SGR 292 and 2017 SGR 776 projects of the Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme funded by the Spanish Research Agency(AEI, grant no. SEV-2017-0706). ALO acknowledges the Juan de la Cierva Program (MINECO IJCI-2014-21530).

The physicochemical properties of spinel oxide magnetic nanoparticles depend critically on both their size and shape. In particular, spinel oxide nanocrystals with cubic morphology have shown superior properties in comparison to their spherical counterparts in a variety of fields, like, for example, biomedicine. Therefore, having an accurate control over the nanoparticle shape and size, while preserving the crystallinity, becomes crucial for many applications. However, despite the increasing interest in spinel oxide nanocubes there are relatively few studies on this morphology due to the difficulty to synthesize perfectly defined cubic nanostructures, especially below 20 nm. Here we present a rationally designed synthesis pathway based on the thermal decomposition of iron(III) acetylacetonate to obtain high quality nanocubes over a wide range of sizes. This pathway enables the synthesis of monodisperse Fe3O4 nanocubes with edge length in the 9–80 nm range, with excellent cubic morphology and high crystallinity by only minor adjustments in the synthesis parameters. The accurate size control provides evidence that even 1–2 nm size variations can be critical in determining the functional properties, for example, for improved nuclear magnetic resonance T2 contrast or enhanced magnetic hyperthermia. The rationale behind the changes introduced in the synthesis procedure (e.g., the use of three solvents or adding Na-oleate) is carefully discussed. The versatility of this synthesis route is demonstrated by expanding its capability to grow other spinel oxides such as Co-ferrites, Mn-ferrites, and Mn3O4 of different sizes. The simplicity and adaptability of this synthesis scheme may ease the development of complex oxide nanocubes for a wide variety of applications., We acknowledge funding from Generalitat de Catalunya through the 2017-SGR-292 and 2017-SGR-776 projects and the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) through the MAT2016-77391-R and MAT2016-79455-P projects. E.F. and F.P. acknowledge the University of Pisa for its funding through the PRA_2017_25 project. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV2017-0706).

The atomic structure of nanoparticles can be easily determined by transmission electron microscopy. However, obtaining atomic-resolution chemical information about the individual atomic columns is a rather challenging endeavor. Here, crystalline monodispersed spinel Fe3O4/Mn3O4 core–shell nanoparticles have been thoroughly characterized in a high-resolution scanning transmission electron microscope. Electron energy-loss spectroscopy (EELS) measurements performed with atomic resolution allow the direct mapping of the Mn2+/Mn3+ ions in the shell and the Fe2+/Fe3+ in the core structure. This enables a precise understanding of the core–shell interface and of the cation distribution in the crystalline lattice of the nanoparticles. Considering how the different oxidation states of transition metals are reflected in EELS, two methods of performing a local evaluation of the cation inversion in spinel lattices are introduced. Both methods allow the determination of the inversion parameter in the iron oxide core and manganese oxide shell, as well as detecting spatial variations in this parameter, with atomic resolution. X-ray absorption measurements on the whole sample confirm the presence of cation inversion. These results present a significant advance toward a better correlation of the structural and functional properties of nanostructured spinel oxides., The authors acknowledge funding from the Spanish Ministerio de Economía y Competitividad (MINECO) through the projects MAT2016-77391-R and MAT2016-79455-P/FEDER (UE). This work has also been carried out in the framework of the projects 2017-SGR-292 and 2017-SGR-776 from the Generalitat de Catalunya. A.L.O. acknowledges the MINECO through the Juan de la Cierva Program (IJCI-2014-21530). M.W. acknowledges the European Union Seventh Framework Programme under grant agreement no. 312483-ESTEEM2. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Program (MINECO, grant SEV-2013-0295).

Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk-approach based on the combined analysis of synchrotron X-ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/Fe

Toxic nitro-compounds, such as 4-nitrophenol, are one of the most common wastewater industrial pollutants. Thus, efficient ways to neutralize them are actively pursued. Here novel procedures to degrade these types of compounds based on the use of mesoporous magnetic nanowires are demonstrated. Fully-mesoporous magnetic narrow (25 nm) CoPt nanowires with an extraordinary effective area are grown using ionic liquid-in-water microemulsions in alumina templates. These mesoporous nanowires are shown to be efficient catalysts for the hydrogenation of 4-nitrophenol by electrocatalysis. Additionally, these nanowires also present exceptional conventional catalytic activity when used in conjunction with NaBH, particularly when magnetic stirring is utilized. In fact, magnetically actuated mesoporous CoPt nanowires drastically outperform all state-of-the-art 4-nitrophenol catalysts. Additionally, given their magnetic character, these nanowires can be easily recycled and reused. Thus, the outstanding catalytic performance of mesoporous CoPt nanowires makes them excellent candidates for wastewater treatment agents., This work was supported by the EU ERDF (FEDER) fund and the Spanish Government grants TEC2014-51940-C2-2-R and MAT2014-57960-C3-1-R from Ministerio de Economía y Competitividad (MINECO) –the latter cofinanced by FEDER. Partial funding from the European Research Council (Consolidator Grant, project n. 648454, SPIN-PORICS) and the Generalitat de Catalunya (2014-SGR-1015 project) is acknowledged. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

Fe–Cu films with pseudo‐ordered, hierarchical porosity are prepared by a simple, two‐step procedure that combines colloidal templating (using sub‐micrometer‐sized polystyrene spheres) with electrodeposition. The porosity degree of these films, estimated by ellipsometry measurements, is as high as 65%. The resulting magnetic properties can be controlled at room temperature using an applied electric field generated through an electric double layer in an anhydrous electrolyte. This material shows a remarkable 25% voltage‐driven coercivity reduction upon application of negative voltages, with excellent reversibility when a positive voltage is applied, and a short recovery time. The pronounced reduction of coercivity is mainly ascribed to electrostatic charge accumulation at the surface of the porous alloy, which occurs over a large fraction of the electrodeposited material due to its high surface‐area‐to‐volume ratio. The emergence of a hierarchical porosity is found to be crucial because it promotes the infiltration of the electrolyte into the structure of the film. The observed effects make this material a promising candidate to boost energy efficiency in magnetoelectrically actuated devices., This work was supported by the SELECTA (No. 642642) H2020‐MSCA‐ITN‐2014 project. Partial financial support by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) (Project Nos. MAT2017‐86357‐C3‐1‐R, MAT2015‐70850‐P and associated FEDER), the Generalitat de Catalunya (2017‐SGR‐292), and the European Research Council (SPIN‐PORICS and FOREMAT, with Agreement Nos. 648454 and 648901, respectively) is acknowledged. E.P. is grateful to MINECO for the “Ramon y Cajal” contract (RYC‐2012‐10839). The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa programme of MINECO, grant no. SEV‐2013‐0295.

A synergetic approach to enhance magnetoelectric effects (i.e., control of magnetism with voltage) and improve energy efficiency in magnetically actuated devices is presented. The investigated material consists of an ordered array of Co–Pt microdisks, in which nanoporosity and partial oxidation are introduced during the synthetic procedure to synergetically boost the effects of electric field. The microdisks are grown by electrodeposition from an electrolyte containing an amphiphilic polymeric surfactant. The bath formulation is designed to favor the incorporation of oxygen in the form of cobalt oxide. A pronounced reduction of coercivity (88%) and a remarkable increase of Kerr signal amplitude (60%) are observed at room temperature upon subjecting the microdisks to negative voltages through an electrical double layer. These large voltage-induced changes in the magnetic properties of the microdisks are due to (i) the high surface-area-to-volume ratio with ultranarrow pore walls (sub-10 nm) that promote enhanced electric charge accumulation and (ii) magneto-ionic effects, where voltage-driven O2– migration promotes a partial reduction of CoO to Co at room temperature. This simple and versatile procedure to fabricate patterned “nano-in-micro” magnetic motifs with adjustable voltage-driven magnetic properties is very appealing for energy-efficient magnetic recording systems and other magnetoelectronic devices., This work was funded by the European Research Council under the SPIN-PORICS 2014-Consolidator Grant (Agreement No. 648454), the Generalitat de Catalunya (2017-SGR292 project), the Spanish Government (MAT2017-86357-C3-1-R, MAT2014-57960-C3-1-R, and associated FEDER projects), and the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 665919. J.F. and E.P. acknowledge the Juan de la Cierva (IJCI-2015-27030) and Ramon y Cajal (RYC-2012-10839) fellowships, respectively, from MINECO. The ICN2 is funded by the CERCA program/Generalitat de Catalunya. ICN2 also acknowledges the support from the Severo Ochoa Program (MINECO, grant SEV-2013-0295)

Nanotherapies require new ways for controlling and improving the delivery of the therapeutic agents to the site of action to maximize their efficacy and minimize the side effects. This control is particularly relevant in photothermal treatments to reduce the required light intensity and amount of injected nanoparticles, and to minimize necrotic cell deaths. Here we present a novel concept for multifunctional nanobiomedical agents: magneto-plasmonic (MP) nanodomes for magnetically guided and amplified photothermal therapies and as contrast agents for multimodal imaging. The MP nanodomes are composed of a Fe/Au bilayer semi-shell deposited on a 100 nm diameter fluorescent polystyrene nanosphere, which gather a unique combination of straightforward functionalization, high colloidal stability, very strong ferromagnetic behavior and intense optical absorption efficiency in the near infrared. We show that the photothermal conversion efficiency of the Fe/Au nanodomes with high Fe ratios is substantially larger than pure plasmonic Au nanodomes and the state-of-art plasmonic nanoheaters, i.e. Au nanorods and nanoshells, by merging strong optical absorption, minimized scattering and low optical anisotropy. Remarkably, the effective magnetophoretic concentration of the Fe/Au nanodomes at the illumination region enables large local increase of the optically induced temperature rise. The Fe semishell also provides very intense T2 contrast in nuclear magnetic resonance, which is at least 15-fold larger per particle than commercial iron oxide contrast agents. Moreover, the fluorescent polystyrene nanosphere and the Au semishell integrate valuable fluorescent and X-ray contrasts, respectively, which we have used to assess the nanodomes internalization by cancer cells. The MP nanodomes are nontoxic to cells even in the case of magnetophoretic local enrichment with initially high particle concentration (100 μg/mL). Remarkably, we demonstrate amplified local photothermal treatments by the magnetic enrichment of the nanodomes at the illumination region, which enables reaching nearly 100% reduction of cell viability with low particle concentration (10 μg/mL) and mild NIR laser intensity (5 W/cm2). These results highlight the high potential of MP nanodomes for magnetically guided and amplified photothermal therapies., This work is supported by Spanish Ministry of Economy, Industry and Competitiveness (MINECO) and European Regional Development Fund (FEDER) (Projects number: MAT2013-48628-R, MAT2016-77391-R, MAT2017-86357-C3-1-R and MAT2017-86357-C3-3-R). Generalitat de Catalunya (2017-SGR-292) is acknowledged. ICN2 is funded by the Centres de Recerca de Catalunya (CERCA) Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295). Zhi Li acknowledges the Chinese Scholarship Council Program (201506950059) for financial support. Jordi Sort acknowledges the financial support by the European Research Council (SPIN-PORICS 2014-Consolidator Grant, Agreement N° 648454).

Nonlinear optical nanostructured materials are gaining increased interest as optical limiters for various applications, although many of them suffer from reduced efficiencies at high‐light fluences due to photoinduced deterioration. The nonlinear optical properties of ferrite core/shell nanoparticles showing their robustness for ultrafast optical limiting applications are reported. At 100 fs ultrashort laser pulses the effective two‐photon absorption (2PA) coefficient shows a nonmonotonic dependence on the shell thickness, with a maximum value obtained for thin shells. In view of the local electric field confinement, this indicates that core/shell is an advantageous morphology to improve the nonlinear optical parameters, exhibiting excellent optical limiting performance with effective 2PA coefficients in the range of 10−12 cm W−1 (100 fs excitation), and optical limiting threshold fluences in the range of 1.7 J cm−2. These values are comparable to or better than most of the recently reported optical limiting materials. The quality of the open aperture Z‐scan data recorded from repeat measurements at intensities as high as 35 TW cm−2, indicates their considerably high optical damage thresholds in a toluene dispersion, ensuring their robustness in practical applications. Thus, the high photostability combined with the remarkable nonlinear optical properties makes these nanoparticles excellent candidates for ultrafast optical limiting applications., The authors acknowledge the support of the 2014‐SGR‐1015 project of the Generalitat de Catalunya. A.L.‐O. acknowledges the Spanish Ministrio de Economía y Competitividad through the Juan de la Cierva Program (Grant No. IJCI‐2014‐21530). ICN2 is founded by the CERCA Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Program (MINECO, Grant No. SEV‐2013‐0295).

Voltage-driven manipulation of magnetism in electrodeposited 200 nm thick nanoporous single-phase solid solution Cu20 Ni80 (at%) alloy films (with sub 10 nm pore size) is accomplished by controlled reduction-oxidation (i.e., redox) processes in a protic solvent, namely 1 m NaOH aqueous solution. Owing to the selectivity of the electrochemical processes, the oxidation of the CuNi film mainly occurs on the Cu counterpart of the solid solution, resulting in a Ni-enriched alloy. As a consequence, the magnetic moment at saturation significantly increases (up to 33% enhancement with respect to the as-prepared sample), while only slight changes in coercivity are observed. Conversely, the reduction process brings Cu back to its metallic state and, remarkably, it becomes alloyed to Ni again. The reported phenomenon is fully reversible, thus allowing for the precise adjustment of the magnetic properties of this system through the sign and amplitude of the applied voltage., The financial support by the European Research Council (SPINPORICS 2014-Consolidator Grant, Agreement No. 648454), the Spanish Government (Projects MAT2017-86357-C3-1-R, MAT2014-57960-C3-1-R and associated FEDER), the Generalitat de Catalunya (2017-SGR-292), and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 665919 is acknowledged. E.P. is grateful to MINECO for the “Ramón y Cajal” contract (RYC-2012-10839). The authors are also indebted to the National Council on Science and Technology in Mexico (CONACYT) for the postdoctoral grant (274347) given to E.I.-C. J.F. acknowledges the Juan de la Cierva Fellowship from MINECO (Grant no. IJCI-2015-27030). The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. ICN2 also acknowledges the support from the Severo Ochoa Program (MINECO, Grant no. SEV-2013-0295).

A crucial challenge in nanotherapies is achieving accurate and real‐time control of the therapeutic action, which is particularly relevant in local thermal therapies to minimize healthy tissue damage and necrotic cell deaths. Here, a nanoheater/thermometry concept is presented based on magnetoplasmonic (Co/Au or Fe/Au) nanodomes that merge exceptionally efficient plasmonic heating and simultaneous highly sensitive detection of the temperature variations. The temperature detection is based on precise optical monitoring of the magnetic‐induced rotation of the nanodomes in solution. It is shown that the phase lag between the optical signal and the driving magnetic field can be used to detect viscosity variations around the nanodomes with unprecedented accuracy (detection limit 0.0016 mPa s, i.e., 60‐fold smaller than state‐of‐the‐art plasmonic nanorheometers). This feature is exploited to monitor the viscosity reduction induced by optical heating in real‐time, even in highly inhomogeneous cell dispersions. The magnetochromic nanoheater/thermometers show higher optical stability, much higher heating efficiency and similar temperature detection limits (0.05 °C) compared to state‐of‐the art luminescent nanothermometers. The technological interest is also boosted by the simpler and lower cost temperature detection system, and the cost effectiveness and scalability of the nanofabrication process, thereby highlighting the biomedical potential of this nanotechnology., This work was supported by the Spanish Ministry of Economy, Industry and Competitivenes (MINECO) projects MAT2013‐48628‐R, MAT2016‐77391‐R, and PCIN‐2016‐093 (H2020 M‐ERA.NET). Z.L. acknowledges the Chinese Scholarship Council (CSC) Program (201506950059) for financial support. The 2017‐SGR‐292 project of the Generalitat de Catalunya is acknowledged. The ICN2 was funded by the Centres de Recerca de Catalunya (CERCA) programme/Generalitat de Catalunya. The ICN2 was supported by the Severo Ochoa programme (MINECO, No. SEV‐2013‐0295). A.L.‐O. and P.V. acknowledge funding from the Basque Government (No. PI2015_1_19), MINECO and the European Regional Development Fund (FEDER) (No. FIS2015 64519 R). A.L.‐O. acknowledges the support from Juan de la Cierva grant. This work was also supported by MINECO under the Maria de Maeztu Units of Excellence (MDM‐2016‐0618). J.S. acknowledges the financial support by the European Research Council (SPIN‐PORICS 2014‐Consolidator Grant, Agreement No. 648454).

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.-- et al., The intimate relationship between stoichiometry and physicochemical properties in transition-metal oxides makes them appealing as tunable materials. These features become exacerbated when dealing with nanostructures. However, due to the complexity of nanoscale materials, establishing a distinct relationship between structure-morphology and functionalities is often complicated. In this regard, in the FexO/Fe3O4 system a largely unexplained broad dispersion of magnetic properties has been observed. Here we show, thanks to a comprehensive multi-technique approach, a clear correlation between the magneto-structural properties in large (45 nm) and small (9 nm) FexO/Fe3O4 core/shell nanoparticles that can explain the spread of magnetic behaviors. The results reveal that while the FexO core in the large nanoparticles is antiferromagnetic and has bulk-like stoichiometry and unit-cell parameters, the FexO core in the small particles is highly non-stoichiometric and strained, displaying no significant antiferromagnetism. These results highlight the importance of ample characterization to fully understand the properties of nanostructured metal oxides., This work was supported by the 2014-SGR-1015 and 2009-SGR-35 projects of the Generalitat de Catalunya, by the MAT2010-20616-C02, MAT2011-27380-C02-01, MAT2010-16407, MAT2013-48628-R and CSD2009-00013 projects of the Spanish Ministerio de Economía y Competitividad (MINECO), the ONDA and COEFNANO projects (no. FP7-PEOPLE-2009-IRSES-247518 and no. FP7-PEOPLE-2012-IRSES-318901) of the European Union, the Russian grants RFBR 13-02-00121, 13-02-12429 and RG 14.B25.31.0025, the Brazilian grants CNPq-304368/2010-5 and FAPEMIG-PPM 00319-11, the Argentine grants PIP 1333 (CONICET) and SECTyP 06/C404 (Univ. Nac. de Cuyo) and the Swedish Research Council (VR). Research at NCSR “D” was supported by the HSF-EU program ARISTEIA, grant COMANA/22. GSA was partially supported by the Knut and Alice Wallenberg Foundation (Project: 3DEM-NATUR). I.V.G. thanks the Generalitat de Catalunya for his sabbatical fellowship (2010 PIV 00096). M.D.B. was partially supported by an ICREA Academia award. M.E. acknowledges the Spanish Ministry of Science and Innovation through the Juan de la Cierva Program. A. G. Roca would like to thank Generalitat de Catalunya for financial support under the Beatriu de Pinós fellowship program (2011 BP_B 00209). ICN2 acknowledges support from the Severo Ochoa Program (MINECO, grant SEV-2013-0295).

© 2017 American Chemical Society. Remanence magnetization plots (e.g., Henkel or δM plots) have been extensively used as a straightforward way to determine the presence and intensity of dipolar and exchange interactions in assemblies of magnetic nanoparticles or single domain grains. Their evaluation is particularly important in functional materials whose performance is strongly affected by the intensity of interparticle interactions, such as patterned recording media and nanostructured permanent magnets, as well as in applications such as hyperthermia and magnetic resonance imaging. Here, we demonstrate that δM plots may be misleading when the nanoparticles do not have a homogeneous internal magnetic configuration. Substantial dips in the M plots of γ-Fe 2 O 3 nanoparticles isolated by thick SiO 2 shells indicate the presence of demagnetizing interactions, usually identified as dipolar interactions. Our results, however, demonstrate that it is the inhomogeneous spin structure of the nanoparticles, as most clearly evidenced by Mössbauer measurements, that has a pronounced effect on the δM plots, leading to features remarkably similar to those produced by dipolar interactions. X-ray diffraction results combined with magnetic characterization indicate that this inhomogeneity is due to the presence of surface structural (and spin) disorder. Monte Carlo simulations unambiguously corroborate the critical role of the internal magnetic structure in the δM plots. Our findings constitute a cautionary tale on the widespread use of remanence plots to assess interparticle interactions as well as offer new perspectives in the use of Henkel and δM plots to quantify the rather elusive inhomogeneous magnetization states in nanoparticles.

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.-- et al., Core–shell nanoparticles attract continuously growing interest due to their numerous applications, which are driven by the possibility of tuning their functionalities by adjusting structural and morphological parameters. However, despite the critical role interdiffused interfaces may have in the properties, these are usually only estimated in indirect ways. Here we directly evidence the existence of a 1.1 nm thick (Fe,Mn)3O4 interdiffused intermediate shell in nominally γ-Fe2O3–Mn3O4 core–shell nanoparticles using resonant inelastic X-ray scattering spectroscopy combined with magnetic circular dichroism (RIXS-MCD). This recently developed magneto-spectroscopic probe exploits the unique advantages of hard X-rays (i.e., chemical selectivity, bulk sensitivity, and low self-absorption at the K pre-edge) and can be advantageously combined with transmission electron microscopy and electron energy loss spectroscopy to quantitatively elucidate the buried internal structure of complex objects. The detailed information on the structure of the nanoparticles allows understanding the influence of the interface quality on the magnetic properties., This work has been supported by the 2014-SGR-1015 and 2009-SGR-35 projects of the Generalitat de Catalunya, by the MAT2010-20616-C02 and MAT2010-16407 projects of the Ministerio de Economía y Competitividad (MINECO). MS acknowledges support from the Polish Ministry of Science and Higher Education. ME acknowledges the Spanish Ministry of Science and Innovation through the Juan de la Cierva Program. MDB acknowledges partial financial support from an ICREA-Academia Award.

Atomic-resolution scanning-transmission electron microscopy showed that barium hexaferrite (BHF) nanoplatelets display a distinct structure, which represents a novel structural variation of hexaferrites stabilized on the nanoscale. The structure can be presented in terms of two alternating structural blocks stacked across the nanoplatelet: a hexagonal (BaFe6O11)2- R block and a cubic (Fe6O8)2+ spinel S block. The structure of the BHF nanoplatelets comprises only two, or rarely three, R blocks and always terminates at the basal surfaces with the full S blocks. The structure of a vast majority of the nanoplatelets can be described with a SR*S*RS stacking order, corresponding to a BaFe15O23 composition. The nanoplatelets display a large, uniaxial magnetic anisotropy with the easy axis perpendicular to the platelet, which is a crucial property enabling different novel applications based on aligning the nanoplatelets with applied magnetic fields. However, the BHF nanoplatelets exhibit a modest saturation magnetization, MS, of just over 30 emu g-1. Given the cubic S block termination of the platelets, layers of maghemite, γ-Fe2O3, (M), with a cubic spinel structure, can be easily grown epitaxially on the surfaces of the platelets, forming a sandwiched M/BHF/M platelet structure. The exchange-coupled composite nanoplatelets exhibit a remarkably uniform structure, with an enhanced MS of more than 50 emu g-1 while essentially maintaining the out-of-plane easy axis. The enhanced MS could pave the way for their use in diverse platelet-based magnetic applications.

The exchange bias properties of 5 nm Co/CoO ferromagnetic/antiferromagnetic core/shell nanoparticles, highly dispersed in a CuxO matrix, have been optimized by matching the lattice parameter of the matrix with that of the CoO shell. Exchange bias and coercivity fields as large as HE = 7780 Oe and HC = 6950 Oe are linked to the presence of a Cu2O matrix (0.3% lattice mismatch with respect to the shells). The small mismatch between Cu2O and CoO plays a dual role: it (i) structurally stabilizes the CoO and (ii) favors the existence of a large amount of uncompensated moments in the shell that enhance the exchange bias effects. The results indicate that lattice matching may be a very efficient way to improve the exchange bias properties of core/shell nanoparticles, paving the way to novel approaches to tune their magnetic properties.

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).

Iron oxides are among the most abundant materials on Earth, and yet there are some of their basic properties which are still not well-established. Here, we present temperature-dependent magnetic, X-ray, and neutron diffraction measurements refuting the current belief that the magnetic ordering temperature of ϵ-FeO is ∼500 K, i.e., well below that of other iron oxides such as hematite, magnetite, or maghemite. Upon heating from room temperature, the ϵ-FeO nanoparticles' saturation magnetization undergoes a monotonic decrease while the coercivity and remanence sharply drop, virtually vanishing around ∼500 K. However, above that temperature the hysteresis loops present a nonlinear response with finite coercivity, making evident signs of ferrimagnetic order up to temperatures as high as 850 K (T). The neutron diffraction study confirms the presence of ferrimagnetic order well above 500 K with Pna'2' magnetic symmetry, but only involving two of the four Fe sublattices which are ordered below T ≈ 480 K, and with a reduced net ferromagnetic component, that vanishes at above 850 K. The results unambiguously show the presence of a high-temperature magnetic phase in ϵ-FeO with a critical temperature of T ∼ 850 K. Importantly, this temperature is similar to the Curie point in other iron oxides, indicating comparable magnetic coupling strengths. The presence of diverse magnetic phases is further supported by the nonmonotonic evolution of the thermal expansion. The existence of a high-temperature ferrimagnetic phase in ϵ-FeO may open the door to further expand the working range of this multifunctional iron oxide.

et al., The combination of lithography and ion implantation is demonstrated to be a suitable method to prepare lateral multilayers. A laterally, compositionally, and magnetically modulated microscale pattern consisting of alternating Co (1.6 µm wide) and Co-CoO (2.4 µm wide) lines has been obtained by oxygen ion implantation into a lithographically masked Au-sandwiched Co thin film. Magnetoresistance along the lines (i.e., current and applied magnetic field are parallel to the lines) reveals an effective positive giant magnetoresistance (GMR) behavior at room temperature. Conversely, anisotropic magnetoresistance and GMR contributions are distinguished at low temperature (i.e., 10 K) since the O-implanted areas become exchange coupled. This planar GMR is principally ascribed to the spatial modulation of coercivity in a spring-magnet-type configuration, which results in 180° Néel extrinsic domain walls at the Co/Co-CoO interfaces. The versatility, in terms of pattern size, morphology, and composition adjustment, of this method offers a unique route to fabricate planar systems for, among others, spintronic research and applications., This work was financed by the Research Foundation-Flanders (FWO), the Concerted Research ActionGOA/14/007, the 2014-SGR-1015 project of the Generalitat de Catalunya, and the European Commission under the 7th Framework Programme through the “Research Infrastructure” action of the “Capacities” Programme, NMI3-II Grant No. 283883. This work is based upon experiments (Proposal Nos. 5928 and 9384) performed at the MARIA instrument operated by JCNS at Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany. The authors would like to thank IMEC for access to its lithography facilities as well as J. Moonens and J. Loo for technical support. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

We study the optimization of the catalytic properties of entirely magnetic Co–Pt compact and mesoporous nanowires of different diameters (25–200nm) by using magnetic actuation. The nanowires are a single-entity, robust, magnetic-catalyst with a huge catalytically-active surface area. We show that apart from conventional parameters, like the size and morphology of the nanowires, other factors can be optimized to enhance their catalytic activity. In particular, given the magnetic character of the nanowires, rotating magnetic fields are a very powerful approach to boost the performance of the catalyst. In particular, the magnetic field induces them to act as nano-stirrers, improving the local flow of material towards the active sites of the catalyst. We demonstrate the versatility of the procedure by optimizing (i) the degradation of different types of pollutants (4-nitrophenol and methylene blue) and (ii) hydrogen production. For example, by using as little as 0.1mgmL−1 of 25nm wide Co–Pt mesoporous nanowires (with ∼3nm pore size) as catalysts, kinetic normalized constants knor as high as 20,667 and 21,750s−1g−1 for 4-nitrophenol and methylene blue reduction, respectively, are obtained. In addition, activity values for hydrogen production from borohydride are as high as 25.0L H2 g−1min−1, even at room temperature. These values outperform any current state-of-the-art proposed catalysis strategies for water remediation reactions by at least 10-times and are superior to most advanced approaches to generate hydrogen from borohydride. The recyclability of the nanowires together with the simplicity of the synthetic method makes this approach (using not only Co–Pt, but also other mesoporous magnetic catalysts) very appealing for very diverse types of catalytic applications. &nbsp

The exchange bias properties of Co/CoO coaxial core/shell nanowires were investigated with cooling and applied fields perpendicular to the wire axis. This configuration leads to unexpected exchange-bias effects. First, the magnetization value at high fields is found to depend on the field-cooling conditions. This effect arises from the competition between the magnetic anisotropy and the Zeeman energies for cooling fields perpendicular to the wire axis. This allows imprinting predefined magnetization states to the antiferromagnetic (AFM) shell, as corroborated by micromagnetic simulations. Second, the system exhibits a high-field magnetic irreversibility, leading to open hysteresis loops attributed to the AFM easy axis reorientation during the reversal (effect similar to athermal training). A distinct way to manipulate the high-field magnetization in exchange-biased systems, beyond the archetypical effects, was thus experimentally and theoretically demonstrated., The work was supported by the 2014-SGR-1015 and 2014-SGR-150 projects of the Generalitat de Catalunya, the Spanish MAT2012-35370 project, European Community’s Seventh Framework Programme (FET-Open/FP7/2007-2013) under grant agreement 296679 (MANAQA), and the Brazilian agency CAPES (BEX 0298/2015-08). G.S.A. thanks the Knut and Alice Wallenberg Foundation (Project 3DEM-NATUR) for the partial financial support. A.S. acknowledges funding from an ICREA Academia award. The authors thank Maria Esther Mata-Zamora and Raul Valenzuela for providing the nanowires. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

We introduce a new perspective on magnetoplasmonics in nickel nanoferromagnets by exploiting the phase tunability of the optical polarizability due to localized surface plasmons and simultaneous magneto-optical activity. We demonstrate how the concerted action of nanoplasmonics and magnetization can manipulate the sign of rotation of the reflected light’s polarization (i.e., to produce Kerr rotation reversal) in ferromagnetic nanomaterials and, further, how this effect can be dynamically controlled and employed to devise conceptually new schemes for biochemosensing. © 2011 American Chemical Society., A.D. and Z.P. acknowledge support from the Swedish Research Council and Swedish Foundation for Strategic Research (Framework program Functional Electromagnetic Metamaterials, project RMA08). J.Å. acknowledges support from the Swedish Research Council, the Swedish Foundation for Strategic Research (Future Research Leader Programme), and the G€oran Gustafsson Foundation. J.Å. is a Royal Swedish Academy of Sciences Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation. V.B. acknowledges the G€oran Gustafsson Foundation and the Blanceflor Boncompagni-Ludovisi Foundation. P.V. acknowledges funding from the Basque Government through the ETORGAI Program, Project No. ER- 2010/00032 and Program No. PI2009-17, the Spanish Ministry of Science and Education under Projects No. CSD2006-53 and No. MAT2009-07980. J.N. acknowledges funding for the Generalitat de Catalunya and the Spanish Ministry of Science and Education through No. 2009-SGR-1292 and No. MAT2010-20616-C02 projects.

The fabrication and subsequent analysis of continuously graded anisotropy films are discussed. During deposition, a compositional gradient is first achieved by varying the Cu concentration from Cu-rich (Fe53Pt47)70Cu30 to Cu-free Fe53Pt47. The anisotropy gradient is then realized after thermal post-annealing, and by utilizing the strong composition dependence of the low-anisotropy (A1) to high-anisotropy (L10) ordering temperature. The magnetic properties are investigated by surface sensitive magneto-optical Kerr effect and alternating gradient magnetometer (AGM) measurements. AGM first-order reversal curve (FORC) measurements are employed in order to provide a detailed analysis of the reversal mechanisms, and therefore the induced anisotropy gradient. At low annealing temperatures, the FORC measurements clearly indicate the highly coupled reversal of soft and hard phases. However, significant interdiffusion results in virtually uniform films at elevated annealing temperatures. Additionally, the A1 to L10 ordering process is found to depend on the film thickness.

The magnetic properties of diluted films composed of nanocomposite Co-CoO nanoparticles (of ∼8 nm diameter) dispersed in a Cu matrix have been investigated. The nanoparticles were formed in an aggregation chamber by sputtering at different Ar/O2 partial pressures (0-0.015). The exchange-bias properties appear to be insensitive to the amount of O2 during their formation. However, the temperature dependence of the magnetization, M(T), exhibits two different contributions with relative intensities that correlate with the amount of O2. The magnetic results imply that two types of particles are formed, nanocomposite Co-CoO (determining the exchange-bias) and pure CoO, as confirmed by transmission electron microscopy observations. Importantly, as the O2 partial pressure during the sputtering is raised the number of nanocomposite Co-CoO nanoparticles (exhibiting exchange-bias properties) is reduced and, consequently, there is an increase in the relative amount of pure, antiferromagnetic CoO particles. © 2011 Springer Science+Business Media B.V.

7 páginas, 6 figuras.-- El pdf del artículo es la versión post-print.-- et al., The fundamental optical properties of pure nickel nanostructures are studied by far-field extinction spectroscopy and optical near-field microscopy, providing direct experimental evidence of the existence of particle plasmon resonances predicted by theory. Experimental and calculated near-field maps allow for unambiguous identification of dipolar plasmon modes. By comparing calculated near-field and far-field spectra, dramatic shifts are found between the near-field and far-field plasmon resonances, which are much stronger than in gold nanoantennas. Based on a simple damped harmonic oscillator model to describe plasmonic resonances, it is possible to explain these shifts as due to plasmon damping., Supported by the European FP7 project ‘Nanoantenna’ (FP7-HEALTH-F5-2009-241818-NANOANTENNA) and the National Project MAT2009 –08398 from the Spanish Ministerio de Ciencia e Innovacion. J.A. acknowledges fi nancial help by the Department of Industry of the Basque Government through the ETORTEK program NANOPHOT. P.V. acknowledges funding from the Basque Government under Programs No. PI2009–17 as well as the Spanish Ministry of Science and Education under Project No. MAT2009–07980. Z. P. acknowledges support from Swedish Foundation for Strategic Research through RMA08–0109 “Functional Electromagnetic Metamaterials” program. J. N. acknowledges funding from the Generalitat de Catalunya and the Spanish Ministry of Science and Education through No. 2009-SGR-1292 and No. MAT2010–20616-C02 projects. A.D. acknowledges support from the Swedish Research Council.

The results of elastic and inelastic neutron scattering in MnF 2 films with orthorhombic crystal structure demonstrate that size-effect for the temperature of the magnetic transition appears for rather thick films 120–1250 nm. This is attributed to the low anisotropy energy in the films inferred from the spin-wave gap.