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CRUE-CSIC (Acuerdos Transformativos 2021) © 2021 The Author(s). Published by Elsevier B.V. We thank 'CAI Difraccion de rayosX' of UCM for Xray diffractometry measurements, and ICTS Centro Nacional de Microscopia of UCM for SEM characterization. We also acknowledge beamtime at BM-25A at the European Synchrotron (ESRF) , and at BL22-CLAESS at ALBA synchrotron. This work has been financially supported through the projects MAT2015-66888-C3-3-R (MINECO/FEDER) and RTI2018-097895-B-C43 of the Spanish Ministry of Economy and Competitiveness. A. P. would like to acknowledge the postdoctoral fellowship granted by Consejea de Educacion, Juventud y Deporte of Comunidad de Madrid and the European Social Fund (grant PEJD-2016/IND-2233 of the YEI program), In this work we present an exhaustive investigation about the possibility of using the electrodeposition technique to grow Ga-Fe-O thin films. The morphological and structural characterization has been performed by means of scanning electron microscopy, X-ray diffractometry and X-ray absorption near edge structure measurements. These results have been complemented with chronoamperometric measurements recorded during growth. We have explored different electrolytes, growth potentials, and pH being observed that it is possible to tune the Fe/ Ga ratio by means of the potential whereas the surface morphology is closely related to the Na_3-citrate content in the electrolyte. The surface roughness is reduced as the Fe content in the layer is increased upon the raise of citrate in the electrolyte composition. X-ray diffractometry indicates that Ga can become partially oxidized, whereas Fe seems to keep its metallic state in its vast majority since we have not obtained clear evidences of oxidation. Thus, this investigation highlights the inherent difficulties to synthetize Ga-Fe-O compounds by means of the electrodeposition technique., Ministerio de Economía y Competitividad (MINECO)/FEDER, Ministerio de Innovación y Ciencia (MICINN)/FEDER, Comunidad de Madrid /FSE, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2021 Elsevier Science We gratefully acknowledge the Spanish CRG at the ESRF for providing beamtime under experiment HC-3343. MS thanks Prof. Monica Dapiaggi for useful discussions. GL thanks Prof. Fabio M. Canepa for illuminating discussions. F.R.-M. gratefully acknowledge the support of the AEI (Spanish Government) Project (No. MAT2017-86450-C4-1-R). F.R.-M. is indebted to MINECO for the "Ramon y Cajal" contract (Ref: RyC-2015-18626), which is co-financed by the European Social Fund., We present an extended X-ray absorption fine structure study at the Mo K-edge of A_2(Mo_(1-y)Mn_y)_2O_7 (A = Gd, Ho; y = 0.05 and 0.10) pyrochlores, as a function of temperature and composition, coupled to diffractometric and magnetic characterizations. Extending the study reported in our previous paper on the pristine A_2Mo_2O_7 compounds to these Mo/Mn partially substituted samples, where we hypothesize a competition between double-exchange and superexchange couplings, we aim to check which structure parameters are related to the nature of the nearest-neighbor magnetic interactions, looking for the presence and evolution of order and structure anomalies. Two Ho samples A_2(Mo_(1-y)Mn_y)_2O_7 (y = 0.05 and 0.10) keep the spin-glass nature of the parent compositions with a strong distortion of the MoO octahedron and of the Mo - Ho and Mo - Mo second shell. On the other hand, two Gd_2(Mo_(1-y)Mn_y)_2O_7 samples, ferromagnetic at low temperature in the undoped case, show the appearance on a local scale of a spin-glass transition mirrored by a quite high structure disorder and by a distortion coherent with a lattice frustration after Mn-doping. Therefore, the Gd and Ho Mn-doped samples display a similar frustrated behavior, differently from the corresponding undoped ones., Ministerio de Economía y Competitividad (MINECO), Centros de Excelencia Ramón y Cajal (MINECO), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Ratchet devices allow turning an ac input signal into a dc output signal. A ratchet device is set by moving particles driven by zero averages forces on asymmetric potentials. Hybrid nanostructures combining artificially fabricated spin ice nanomagnet arrays with superconducting films have been identified as a good choice to develop ratchet nanodevices. In the current device, the asymmetric potentials are provided by charged Néel walls located in the vertices of spin ice magnetic honeycomb array, whereas the role of moving particles is played by superconducting vortices. We have experimentally obtained ratchet effect for different spin ice I configurations and for vortex lattice moving parallel or perpendicular to magnetic easy axes. Remarkably, the ratchet magnitudes are similar in all the experimental runs; i. e. different spin ice I configurations and in both relevant directions of the vortex lattice motion. We have simulated the interplay between vortex motion directions and a single asymmetric potential. It turns out vortices interact with uneven asymmetric potentials, since they move with trajectories crossing charged Néel walls with different orientations. Moreover, we have found out the asymmetric pair potentials which generate the local ratchet effect. In this rocking ratchet the particles (vortices) on the move are interacting each other (vortex lattice); therefore, the ratchet local effect turns into a global macroscopic effect. In summary, this ratchet device benefits from interacting particles moving in robust and topological protected type I spin ice landscapes.

©2020 American Chemical Society We thank ALBA synchrotron for providing time and technical assistance at the BL22 beamline, and Instituto of Sistemas OptoelectrOnicos y Microtecnologia (ISOM) for using some of its facilities. This work has been financially supported through the projects MAT2015-66888-C3-3-R and MAT2015-66726-R (MINECO/FEDER) of the Spanish Ministry of Economy and Competitiveness, RTI2018-097895-B-C43 of the Spanish Ministry of Science, Innovation, and Universities, and Gobierno de Aragon (Grant E10 -17D) and Fondo Social Europeo. A.M.-N. is thankful for the contract from Universidad Complutense and Comunidad de Madrid "Atraccion de Talento" program 2018-T1/IND-10360, and A.B. thanks MINECO for the Ph.D. grant BES-2016-076482., The aim of this work is to clarify how in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with an Fe72Ga28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm. By means of differential X-ray absorption spectroscopy, we have determined the influence of both Ga pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origins for anisotropy and magnetoelasticity open up the possibility to independently tune these two characteristics in Ga-rich FeGa films., Ministerio de Economía y Competitividad (MINECO) / FEDER, Ministerio de Ciencia e Innovación (MICINN), Ministerio de Economía y Competitividad (MINECO), Gobierno de Aragón, Comunidad de Madrid / Universidad Complutense de Madrid, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2020 The author(s). We want to thank Spanish MICINN Grants FIS2016-76058 AEI/FEDER, UE), EU COST-CA16218. IMDEA Nanociencia acknowledges support from the 'Severo Ochoa' Programme for Centres of Excellence in R&D (MICINN, Grant SEV-2016-0686). MCO and AG acknowledges financial support from Spanish MICINN Grant ESP2017-86582-C4-1-R and IJCI-2017-33991; AMN acknowledges financial support from Spanish CAM Grant 2018-T1/IND-10360., Little-Parks effect names the oscillations in the superconducting critical temperature as a function of the magnetic field. This effect is related to the geometry of the sample. In this work, we show that this effect can be enhanced and manipulated by the inclusion of magnetic nanostructures with perpendicular magnetization. These magnetic nanodots generate stray fields with enough strength to produce superconducting vortex-antivortex pairs. So that, the L-P effect deviation from the usual geometrical constrictions is due to the interplay between local magnetic stray fields and superconducting vortices. Moreover, we compare our results with a low-stray field sample (i.e. with the dots in magnetic vortex state) showing how the enhancement of the L-P effect can be explained by an increment of the effective size of the nanodots., Unión Europea. Horizonte 2020, Unión Europea. H2020/COST, Ministerio de Economía y Competitividad (MINECO)/AEI/FEDER, Ministerio de Ciencia e Innovación (MICINN), Comunidad de Madrid, Centros de Excelencia Severo Ochoa (MICINN), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Little–Parks effect names the oscillations in the superconducting critical temperature as a function of the magnetic field. This effect is related to the geometry of the sample. In this work, we show that this effect can be enhanced and manipulated by the inclusion of magnetic nanostructures with perpendicular magnetization. These magnetic nanodots generate stray fields with enough strength to produce superconducting vortex–antivortex pairs. So that, the L–P effect deviation from the usual geometrical constrictions is due to the interplay between local magnetic stray fields and superconducting vortices. Moreover, we compare our results with a low-stray field sample (i.e. with the dots in magnetic vortex state) showing how the enhancement of the L–P effect can be explained by an increment of the effective size of the nanodots.

ZnO has been widely studied in the last decades as an n-type semiconductor due to its wide application range, for example, in optoelectronics, solar cells, light-emitting diodes, thermoelectrics, amongst others. The material efficiency for certain applications is highly dependent on the presenting film morphology. Electrodeposition is well-known as a technique with precise control over the structural and morphological properties of the obtained materials. When the structural and morphological properties are tuned, it is possible to find a wide variety of defects in the ZnO structure. In this study, ZnO films were grown using pulsed electrodeposition with variation of the reduction potential. The crystal order, structural defects and optical emissions of the films have been analyzed by X-Ray Diffraction (XRD), X-ray Absorption Near-Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and Photoluminescence (PL). ZnO film grown at less negative reduction potential presents a stronger texture along [0001] by XRD, higher crystalline order, and more zinc vacancies by XANES and EXAFS. The films obtained at less negative potential present less OH trapped in the ZnO structure and a relatively higher level of defects O, O, O and O than those grown at higher reduction potentials by PL. This will be related to the fact that at less negative potentials there is less concentration of OH at the film surface than at more negative potentials. The combination of X-ray absorption spectroscopy and photoluminescence reveals the complicated nature of the atomic defect in electrodeposited ZnO films. Allowing to evidence the preferential presence of atomic defect as a function of the reduction potential. In this work, we have also compared those defects with reference compounds such as a Zn foil and ZnO polycrystalline powder.

The aim of this work is to clarify how in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with an Fe72Ga28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm. By means of differential X-ray absorption spectroscopy, we have determined the influence of both Ga pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origins for anisotropy and magnetoelasticity open up the possibility to independently tune these two characteristics in Ga-rich FeGa films.

©2019 IOP Publishing We thank support from Spanish MINECO grants FIS201676058 (AEI/FEDER, UE), Spanish CM grant S2013/MIT2850. IMDEA Nanociencia acknowledges support from the 'Severo Ochoa' Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). DG acknowledges RYC-2012-09864, S2013/MIT-3007 and ESP2015-65597-C4-3-R for financial support and AG acknowledges financial support from Spanish MINECO Grant ESP2015-65597-C4-1-R., We have designed, fabricated and tested a robust superconducting ratchet device based on topologically frustrated spin ice nanomagnets. The device is made of a magnetic Co honeycomb array embedded in a superconducting Nb film. This device is based on three simple mechanisms: (i) the topology of the Co honeycomb array frustrates in-plane magnetic configurations in the array yielding a distribution of magnetic charges which can be ordered or disordered with in-plane magnetic fields, following spin ice rules; (ii) the local vertex magnetization, which consists of a magnetic half vortex with two charged magnetic Neel walls; (iii) the interaction between superconducting vortices and the asymmetric potentials provided by the Neel walls. The combination of these elements leads to a superconducting ratchet effect. Thus, superconducting vortices driven by alternating forces and moving on magnetic half vortices generate a unidirectional net vortex flow. This ratchet effect is independent of the distribution of magnetic charges in the array., Ministerio de Economía y Competitividad (MINECO)/AEI/FEDER, Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Centros de Excelencia Severo Ochoa (MINECO), Programa Ramón y Cajal, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2019 The Author(s) This journal is © The Royal Society of Chemistry 2019 Artículo firmado por más de diez autores. Dr Paloma Almodovar is acknowledged for her fruitful discussions about CRM and SEM characterization. The authors also acknowledge the Spanish Ministry of Industry, Economy and Competitiveness for financing the project MAT2015-65445-C2-1-R, MAT2017-86450-C4-1-R, MAT2015-67557-C2-1-P, by the Comunidad de Madrid S2013/MIT-2850 NANOFRONTMAG and H2020 AMPHIBIAN Project ID: 720853. The authors are also grateful to the BM25-SpLine staff for their valuable technical support beyond their duties and for the financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) and The Spanish National Research Council (CSIC) under Grant No. PIE 2010-6OE-013, The ESRF - The European Synchrotron, MICIU and CSIC are acknowledged for provision of synchrotron radiation facilities. A. S. acknowledges the financial support from the Comunidad de Madrid for an "Atraccion de Talento Investigador" contract (No. 2017-t2/IND5395)., The purpose of this work is to fabricate self-assembled microstructures by the sol-gel method and study the morphological, structural and compositional dependence of epsilon-Fe_2O_3 nanoparticles embedded in silica when glycerol (GLY) and cetyl-trimethylammonium bromide (CTAB) are added as steric agents simultaneously. The combined action of a polyalcohol and a surfactant significantly modifies the morphology of the sample giving rise to a different microstructure in each of the studied cases (1, 3 and 7 days of magnetic stirring time). This is due to the fact that the addition of these two compounds leads to a considerable increase in gelation time as GLY can interact with the alkoxide group on the surface of the iron oxide precursor micelle and/or be incorporated into the hydrophilic chains of CTAB. This last effect causes the iron oxide precursor micelles to be interconnected forming aggregates whose size and structure depend on the magnetic stirring time of the sol-gel synthetic route. In this paper, crystalline structure, composition, purity and morphology of the sol-gel coatings densified at 960 degrees C are examined. Emphasis is placed on the nominal percentage of the different iron oxides found in the samples and on the morphological and structural differences. This work implies the possibility of patterning epsilon-Fe_2O_3 nanoparticles in coatings and controlling their purity by an easy one-pot sol-gel method., Unión Europea. H2020, Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Consejo Superior de Investigaciones Científicas (CSIC), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2019 Wiley-V C H VERLAG GMBH We thank Agencia Estatal de Investigacion(AEI)/Fondo Europeo de Desarrollo Regional (FEDER/UE) for funding the project MAT2016-78632-C4-1-R. We acknowledge CSIC, ILL, and ESRF for financial support and facilitated access to the BM25-SpLine line at ESRF and D2B diffractometer at ILL. The authors also thank "Comunidad de Madrid" and the European Structural Funds for their financial support to the ALCCONES (S2013/MAE-2985) and MATERYENER3-CM (S2013/MIT-2753) projects., Materials with the formula Sr_2CoNb_1-xTi_xO_(6-delta) (x=1.00, 0.70; delta=number of oxygen vacancies) present a cubic perovskite-like structure. They are easily and reversibly reduced in N_2 or Ar and re-oxidized in air upon heating. Oxidation by water (wet N_2), involving splitting of water at a temperature as low as 700 ºC, produces hydrogen. Both compounds displayed outstanding H_2 production in the first thermochemical cycle, the Sr_2CoNb_(0.30)Ti_(0.70)O_(6-delta) material retaining its outstanding performance upon cycling, whereas the hydrogen yield of the x=1 oxide showed a continuous decay. The retention of the materials' ability to promote water splitting correlated with their structural, chemical, and redox reversibility upon cycling. On reduction/oxidation, Co ions reversibly changed their oxidation state to compensate the release/recovery of oxygen in both compounds. However, in Sr_2CoTiO_(6-delta), two phases with different oxygen contents segregated, whereas in Sr_2CoNb_(0.30)Ti_(0.70)O_(6-delta) this effect was not evident. Therefore, this latter material displayed a hydrogen production as high as 410 mu molH_2/g_(perovskite) after eight thermochemical cycles at 700 ºC, which is among the highest ever reported, making this perovskite a promising candidate for thermosolar water splitting in real devices., Ministerio de Economía y Competitividad (MINECO) / FEDER, Comunidad de Madrid/FEDER, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2019 American Chemical Society This work has been financially supported through project MAT2015-66888-C3-3-R (MINECO/FEDER) and RTI2018-097895-B-C43 of the Spanish Ministry of Economy and Competitiveness and through PR26/16-3B-2 of Santander and Universidad Complutense de Madrid. We thank "CAI Difraccion de rayos-X" of UCM for the X-ray diffractometry measurements and the "Instituto de Sistemas Optoelectronicos y Microtecnologia" (ISOM) for using its facilities. We also want to thank BM25-Spline, the Spanish CRG at ESRF for providing beamtime., We have investigated the influence of the growth power on the structural properties of Fe_100_(-x)Ga_x (x ca. 29) films sputtered in the ballistic regime in the oblique incidence. By means of different structural characterizations, mainly X-ray diffraction and X-ray absorption spectroscopy, we have reached a deeper understanding about the influence of the local and medium range order on the magnetic behavior of Ga-rich FeGa thin films. On the one hand, the increase of the growth power reduces the crystallite size (medium order) that promotes the decrease of the coercive field of the layers. On the other hand, the growth power also determines the local order as it controls the formation of the A2, B2, and D0_3 structural phases. The increase of the uniaxial in-plane magnetic anisotropy with growth power has been correlated with the enhancement of both Ga pairs and a tetragonal distortion. The results presented in this work give more evidence about the magnetic anisotropy sources in Ga-rich FeGa alloys, and therefore, it helps to understand how to achieve a better control of the magnetic properties in this family of alloys., Ministerio de Economía y Competitividad (MINECO)/FEDER, Ministerio de Economía y Competitividad (MINECO), Universidad Complutense de Madrid/Banco de Santander, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Resumen del trabajo presentado al American Physical Society (APS) March Meeting, celebrado del 4 al 8 de 2019 en Boston, Massachusetts (USA).