Magnetic frustration, phase competition, and the magnetoelectric effect in NdFe3(BO3)4

PACS numbers: 75.85.+t, 75.25. j, 75.30.Et, 78.70.Ck.-- et al.We present an element selective resonant magnetic x-ray scattering study of NdFe3(BO3)4 as a function of temperature and applied magnetic field. Our measurements show that the magnetic order of the Nd sublattice is induced by the Fe spin order. When a magnetic field is applied parallel to the hexagonal basal plane, the helicoidal spin order is suppressed and a collinear ordering, where the moments are forced to align in a direction perpendicular to the applied magnetic field, is stabilized. This result excludes a noncollinear spin order as the origin of the magnetically induced electric polarization in this compound. Instead our data imply that magnetic frustration results in a phase competition, which is the origin of the magnetoelectric response.This work was supported by the DFG through the Emmy Noether Programme (Grant No. GE1647/2-1) and the European Community’s Seventh Framework Program (FP7/2007-2013) under Grant No. 226716.Peer reviewe

On the correlation between the X-ray absorption chemical shift and the formal valence state in mixed-valence manganites

7 páginas, 7 figuras.Here the correlation between the chemical shift in X-ray absorption spectroscopy, the geometrical structure and the formal valence state of the Mn atom in mixed-valence manganites are discussed. It is shown that this empirical correlation can be reliably used to determine the formal valence of Mn, using either X-ray absorption spectroscopy or resonant X-ray scattering techniques. The difficulties in obtaining a reliable comparison between experimental XANES spectra and theoretical simulations on an absolute energy scale are revealed. It is concluded that the contributions from the electronic occupation and the local structure to the XANES spectra cannot be separated either experimentally or theoretically. In this way the geometrical and electronic structure of the Mn atom in mixed-valence manganites cannot be described as a bimodal distribution of the formal integer Mn3+ and Mn4+ valence states corresponding to the undoped references.This work was supported by the Spanish MICINN FIS2008- 03951 project and Diputación General de Aragón (DGACAMRADS). VC thanks the FPU research grant from MICINN.Peer reviewe

Un nuevo rastro lacustre enigmático en el Mioceno superior de la Sierra de las Cabras (Jumilla, Murcia, España)

A new fossil trackway is described in the upper lacustrine Miocene in the Prebetic Zone of the Iberian Peninsula, in town (Murcia region) called Aenigmatichnus jumillensis nov. ichnogen. nov. ichnosp. This trackway consists of a made up of sets of three tracks or triads, which are subparallel to each other, arranged in alternate groups. Each track presents a depression formed by a central body that is three times as long as it is wide, with straight or slightly curved walls, with shorter bodies placed at the ends, one of the ends being shorter and more pronounced than the opposite, which is longer stretched. All the biomechanical possibilities compatible with an anatomical design that could leave the impression of alternate triads of tracks are analysed. The supports are only from the extremities on one side of the organism (left or the displacement being by translation. It is concluded that it had to be a large arthropod (metre scale), with a hexapod decapod (less probably octopod), which had to be dragged laterally by a current in a very shallow lake or wetland environment. To date, no fossil organism is known, nor its current equivalent, that corresponds to these characteristics.Se describe una nueva pista fósil en el Mioceno superior lacustre de la Zona Prebética de la Península Ibérica, en la localidad de Jumilla (Región de Murcia) denominada Aenigmatichnus jumillensis nov. ichnogen. nov. ichnosp. Esta pista presenta un patrón que está formado por conjuntos de tres huellas o tríadas, subparalelas entre sí, y dispuestas en grupos alternos. Cada huella presenta una depresión formada por un cuerpo central que es tres veces más largo que ancho, con las paredes rectas o ligeramente curvadas. Presenta también dos cuerpos más cortos situados en los extremos, siendo uno de ellos más corto y pronunciado que el opuesto, que es más largo y estirado. Se analizan todas las posibilidades biomecánicas compatibles con un diseño anatómico que pudiera dejar la impresión de tres apéndices alternos. Los apoyos son sólo de las extremidades de un lado del organismo (izquierda o derecha), siendo el desplazamiento por traslación. Se concluye que tuvo que tratarse de un artrópodo de gran tamaño (escala métrica), ya fuera un hexápodo o decápodo (menos probablemente octópodo), que tuvo que ser arrastrado lateralmente por una corriente en un entorno lacustre o humedal muy poco profundo. Hasta la fecha, no se conoce ningún organismo fósil, ni su equivalente actual, que responda a estas característicasFunding for open access publishing: Universidad de Huelva/ CBUA. Funding for open access charge: Universidad de Huelva/CBUA. Thanks to Nicholas Minter an anonymous reviewer for comments and suggestions, which improved the manuscript. This study has been partially supported by the project PID2019- 104625RB-100 of the Ministry of Science and Innovation, State Research Agency, and by the Junta de Andalucía to the Research Group RNM276 of the CCTH of the University of Huelva

A new enigmatic lacustrine trackway in the upper Miocene of the Sierra de las Cabras (Jumilla, Murcia, Spain)

Se describe una nueva pista fósil en el Mioceno superior lacustre de la Zona Prebética de la Península Ibérica, en la localidad de Jumilla (Región de Murcia) denominada Aenigmatipodus jumillensis nov. ichnogen. nov. ichnosp. Esta pista presenta un patrón que está formado por conjuntos de tres huellas o tríadas, subparalelas entre sí, y dispuestas en grupos alternos. Cada huella presenta una depresión formada por un cuerpo central que es tres veces más largo que ancho, con las paredes rectas o ligeramente curvadas. Presenta también dos cuerpos más cortos situados en los extremos, siendo uno de ellos más corto y pronunciado que el opuesto, que es más largo y estirado. Se analizan todas las posibilidades biomecánicas compatibles con un diseño anatómico que pudiera dejar la impresión de tres apéndices alternos. Los apoyos son sólo de las extremidades de un lado del organismo (izquierda o derecha), siendo el desplazamiento por traslación. Se concluye que tuvo que tratarse de un artrópodo de gran tamaño (escala métrica), ya fuera un hexápodo o decápodo (menos probablemente octópodo), que tuvo que ser arrastrado lateralmente por una corriente en un entorno lacustre o humedal muy poco profundo. Hasta la fecha, no se conoce ningún organismo fósil, ni su equivalente actual, que responda a estas características.A new fossil trackway is described in the upper lacustrine Miocene in the Prebetic Zone of the Iberian Peninsula, in Jumilla town (Murcia region) called Aenigmatipodus jumillensis nov. ichnogen. nov. ichnosp. This trackway consists of a pattern made up of sets of three tracks or triads, which are subparallel to each other, arranged in alternate groups. Each track presents a depression formed by a central body that is three times as long as it is wide, with straight or slightly curved walls, with two shorter bodies placed at the ends, one of the ends being shorter and more pronounced than the opposite, which is longer and stretched. All the biomechanical possibilities compatible with an anatomical design that could leave the impression of three alternate triads of tracks are analysed. The supports are only from the extremities on one side of the organism (left or right), the displacement being by translation. It is concluded that it had to be a large arthropod (metre scale), with a hexapod or decapod (less probably octopod), which had to be dragged laterally by a current in a very shallow lake or wetland environment. To date, no fossil organism is known, nor its current equivalent, that corresponds to these characteristics

Double stripe ordering in Nd0.5Sr0.5MnO3 determined by resonant soft x-ray scattering

7 pages, 8 figures.-- PACS number(s): 75.47.Lx, 78.70.Ck, 71.30.+hWe have studied the low-temperature ordered phase of Nd0.5Sr0.5MnO3 by resonant soft x-ray scattering at the Mn L2,3 edges. Strong resonances were observed at (0 0) and ( 0 0) reflections, which are resolved in momentum space. Azimuthal scans reveal a periodicity for both resonances, the minimum intensity being almost zero. The two reflections show a very different energy dependence which extends in the whole energy region of the Mn L-edge. The (0 0) reflection originates from the anisotropy induced on the d-symmetry projected density of states owing to the local tetragonal distortion at one of the two crystallographic inequivalent Mn sites (the so-called Mn3+ ions in the conventional ionic description). This is similar to the resonance observed at the Mn K edge. We propose that the ( 0 0) reflection, which has not its counterpart either on the Mn K-edge resonant scattering or on the magnetic scattering, is originated by anisotropy of the d-symmetry projected density of the so-called Mn4+ sublattice. In this way, the latter reflection could denote a pure orbital ordering in this sublattice.We are thankful for the financial support from the Spanish CICyT Project No. MAT2005-04562 and from D.G.A. We also acknowledge ESRF and ID08 beamline for granting beam time.Peer reviewe

Design of a chatbot as a distance learning assistant

Within the process of progressive digitization of materials and tools for teaching and distance learning of a subject of introduction to Microeconomics (quarterly, in year three of the Degree in Social Work), taught by the authors at the National University of Distance Education (UNED), a virtual assistant in the form of chatbot, or conversational robot, called EconBot, has been designed and made available to students from 2017. This paper presents the reasons that led to its adoption, the process of its development, differentiating two phases, its characteristics and functions, the assessment of its usefulness and the role of teachers in the implementation of this type of technological innovation

Electrical sensing of the thermal and light induced spin transition in robust contactless spin-crossover/graphene hybrid devices

Hybrid devices based on spin-crossover (SCO)/2D heterostructures grant a highly sensitive platform to detect the spin transition in the molecular SCO component and tune the properties of the 2D material. However, the fragility of the SCO materials upon thermal treatment, light irradiation or contact with surfaces and the methodologies used for their processing have limited their applicability. Here, we report an easily processable and robust SCO/2D hybrid device with outstanding performance based on the sublimable SCO [Fe(Pyrz)2] molecule deposited over CVD-graphene, which is fully compatible with electronics industry protocols. Thus, a novel methodology based on growing an elusive polymorph of [Fe(Pyrz)2] (tetragonal phase) over graphene is developed that allows us to electrically detect a fast and effective light-induced spin transition in the devices (~50% yield in 5 minutes). Such performance can be enhanced even more when a flexible polymeric layer of PMMA is inserted in between the two active components in a contactless configuration, reaching a ~100 % yield in 5 minutes.Comment: 25 pages, 5 figure

Influence of Syncron® and Nitroactive® on flowering and ripening time in two sweet cherry cultivars

1 Pag. extracted from the Abstracts Book of the International Symposium.In this work, the influence of Syncron® and Nitroactive® on flowering and ripening is evaluated in two sweet cherry cultivars, Earlise and Lapins. A combination of Syncron 2% and Nitroactive 20% were applied at three dates during dormancy in two consecutive years with different winter weather conditions.Peer reviewe

Electrical sensing of the thermal and light induced spin transition in robust contactless spin-crossover/graphene hybrid devices

Hybrid devices based on spin-crossover (SCO)/2D heterostructures grant a highly sensitive platform to detect the spin transition in the molecular SCO component and tune the properties of the 2D material. However, the fragility of the SCO materials upon thermal treatment, light irradiation or contact with surfaces and the methodologies used for their processing have limited their applicability. Here, we report an easily processable and robust SCO/2D hybrid device with outstanding performance based on the sublimable SCO [Fe(Pyrz)2] molecule deposited over CVD-graphene, which is fully compatible with electronics industry protocols. Thus, a novel methodology based on growing an elusive polymorph of [Fe(Pyrz)2] (tetragonal phase) over graphene is developed that allows us to electrically detect a fast and effective light-induced spin transition in the devices (~50% yield in 5 minutes). Such performance can be enhanced even more when a flexible polymeric layer of PMMA is inserted in between the two active components in a contactless configuration, reaching a ~100 % yield in 5 minutes

Double-cell superstructure and vacancy ordering in tensile-strained metallic thin films of P r0.50 C a0.50Co O3 on LaAl O3

The Pr-based cobaltate Pr0.5Ca0.5CoO3 (PCCO) presents in bulk form a singular simultaneous valence and spin-state transition that turns the metallic state into insulator, and displays a large and ultrafast photoresponse in the insulating phase. Epitaxial thin films of PCCO have been grown by deposition on LaAlO3(001) (LAO) substrate, chosen to minimize the mismatch with the film. The films grow epitaxially with two times the substrate periodicity (2a0×2a0×2a0) and the long perovskite axis perpendicular to the surface. We report a reduction of the structural symmetry from Pnma (bulk) to P212121 (film). The P212121 symmetry revealed by synchrotron x ray remains at low temperatures. These PCCO films are metallic, and ferromagnetic below TC=170K, confirming the stabilization of excited Co3+ spin states and the suppression of the concurrent Co spin-state, valence, and metal-insulator transitions. Z-contrast imaging and electron-energy-loss spectroscopy elemental maps reveal long-range ordered oxygen vacancy planes unexpectedly stacking parallel to the interface, in spite of the tensile character of the PCCO/LAO heterostructure. In contrast to the general tendency reported for strained La0.5Sr0.5CoO3-d (LSCO) films, we show that a nominal tensile strain can be also compatible with the presence of alternating O vacancy planes parallel to the interface, instead of perpendicular to it. That occurs thanks to the double cell of the film and the formation of the (1/2, 1/2, 1/2) superstructure studied in this work. These results expand the possibilities of controlling interfacial physical properties via engineering of ordered oxygen-defect structures in strongly correlated oxides