Origin of the large dispersion of magnetic properties in nanostructured oxides: FexO/Fe3O4 nanoparticles as a case study

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).Peer Reviewe

Tunable magnetism in nanoporous CuNi alloys by reversible voltage-driven element-selective redox processes

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

Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks

Golvano-Escobal, Irati et al.Spatio-temporal patterns are ubiquitous in different areas of materials science and biological systems. However, typically the motifs in these types of systems present a random distribution with many possible different structures. Herein, we demonstrate that controlled spatio-temporal patterns, with reproducible spiral-like shapes, can be obtained by electrodeposition of Co-In alloys inside a confined circular geometry (i.e., in disks that are commensurate with the typical size of the spatio-temporal features). These patterns are mainly of compositional nature, i.e., with virtually no topographic features. Interestingly, the local changes in composition lead to a periodic modulation of the physical (electric, magnetic and mechanical) properties. Namely, the Co-rich areas show higher saturation magnetization and electrical conductivity and are mechanically harder than the In-rich ones. Thus, this work reveals that confined electrodeposition of this binary system constitutes an effective procedure to attain template-free magnetic, electric and mechanical surface patterning with specific and reproducible shapes.This work has been partially funded by the 2014-SGR-1015, 2014-SGR-1216 and 2014-SGR-753 projects from the Generalitat de Catalunya, the MAT2014-57960-C3-1-R, MAT2014-51778-C2-1-R and FIS2013-48668-C2-1-P from the Spanish Ministerio de Economía y Competitividad (MINECO) and the ‘Fondo Europeo de Desarrollo Regional’ (FEDER). Dr. Eva Pellicer and Dr. Neus Domingo are also grateful to MINECO for the “Ramon y Cajal” contracts (RYC-2012-10839 and RYC-2010-06365 respectively). ICN2 and ICMAB acknowledge support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295 and Grant SEV-2015-0496, respectively). The PEEM experiments were performed at CIRCE beamline at ALBA Synchrotron with the collaboration of ALBA staff.Peer reviewe

Cantabou : revista del CPR d'Inca

Se trata del proyecto europeo Aprender idiomas cantando, código 03-ESP01-S12CO2-00343-1 y era un proyecto lingüístico de la acción Comenius 1, asociaciones escolares del programa Sócrates. El IES Alcudia actuó de institución coordinadora y se asoció con el Gymnasio Veroias de la ciudad macedónica de Veroias, GreciaResume una experiencia derivada de la realización durante los cursos 2002-2003 y 2003-2004 de un proyecto europeo en el IES Alcudia, relacionado con el aprendizaje de lenguas mediante canciones. Se repasa desde los contactos iniciales con el profesorado de los centros asociados durante la visita preparatoria hasta el intercambio de alumnado participante.BalearesBiblioteca Can Torró; Calle Serra, 15; 07400 Alcúdia; 971-547311;ES

Influence of annealing treatments on crystallization and mechanical properties of a Al-4Ni-6Ce glass

Previous studies of crystallization in Al-based glasses show the early appearance of many nano-sized, pure Al crystals which thereafter grow much more slowly. The present study extends such annealing treatments and examines the early appearance of nano-sized Al crystals and their subsequent growth to very large sizes before, eventually, other intermetallic phases appear. The growth of the Al crystals to very large size appears to take place by a spherulitic destabilization of the Al crystal-glass interface and the formation of a glass-Al mixture. Changes of mechanical properties are discussed in terms of the structural changes. © 2003 Elsevier B.V. All rights reserved.Peer Reviewe

Crystallization of Al-Ni-Ce glass and implications for control of mechanical properties during powder consolidation

Trabajo presentado en el 9th International Symposium on Metastable Mechanically Alloyed and Nanocrystalline Materials (ISMANAM), celebrado en Seúl (Corea del Sur), del 8 al 12 de septiembre de 2002The crystallization behaviour of an Al-based glass is examined looking both at the early stages when nano-sized Al crystals appear and their subsequent growth to very large sizes at longer annealing times before, eventually, other intermetallic phases appear. The growth of the Al crystals to very large size takes place by a dendritic-like destabilisation of the Al crystals-glass interface and the formation of a glass-Al eutectic mixture. Mechanical properties during such annealing have been evaluated by hardness and bend testing on melt-spun ribbons and, where possible, by tensile testing. The changes of properties seen are discussed in terms of the structural changes. Good mechanical behaviour may be controlled by the appearance of many small Al crystals, by the onset of rapid eutectic colony growth, or by changes in the glass matrix.Peer reviewe

Ordered arrays of ferromagnetic, compositionally graded Cu 1-xNix alloy nanopillars prepared by template-assisted electrodeposition

Periodic arrays of compositionally graded Cu-Ni alloy nanopillars (100 or 200 nm in diameter and 450 nm in height) have been fabricated by means of potentiostatic electrodeposition into patterned Au/Ti/Si(111) substrates using a single electrolytic solution. The pillars do not bend after the template removal but remain straight and perfectly attached to the substrate. The average composition of the alloy nanopillars can be tuned between 34 and 70 at% of Ni by varying the applied potential from a [Ni(ii)]/[Cu(ii)] = 95.2 electrolytic solution. The nanopillars are Ni-rich at the bottom with a compositional gradient about ±20-25% above/below the average composition. The magnetic characterization reveals that all the nanopillars are ferromagnetic with coercivity values around 100-150 Oe (in-plane) and 200-500 Oe (out-of-plane), which are larger than those for continuous films of similar average composition. Atom probe tomography of the Cu-rich Cu-Ni nanopillars indicates the segregation of Ni, which would explain their unexpected magnetic character. The graded-anisotropy ferromagnetic Cu-Ni pillars could be potentially applied in several fields including micro/nano-electromechanical systems (MEMS/NEMS), magnetic recording media or spintronics. © The Royal Society of Chemistry 2013.Financial support from the MAT-2010-20616-C02 and MAT-2011-27380-C02-01 research projects and from ICTS-11/07 (Infraestructuras Científicas y Tecnológicas Singulares) of the Spanish MINECO, and the 2009SGR-1292 from the Generalitat de Catalunya are acknowledged. M.D.B. acknowledges partial financial support from an ICREA-Academia Award.Peer Reviewe

The influence of composition and low temperature annealing on hardness and ductility of rapidly solidified Al-Ni-Ce alloys

The crystalline state and mechanical properties of several rapidly solidified Al-Ni-Ce alloys have been examined in both as-solidified materials and after low temperature annealing to crystallise initially amorphous materials. Significant changes in mechanical properties occur due to changes of both chemical composition and of crystalline structure. Further detailed examinations of deformation mechanisms are necessary. © 2002 Published by Elsevier Science Ltd. on behalf of Acta Materialia Inc.Peer Reviewe

Crystallization of a Al-4Ni-6Ce glass and its influence on mechanical properties

The crystallization behaviour of a rapidly quenched, amorphous Al-4Ni-6Ce material has been examined during low temperature annealing, and shown to commence by the nucleation of nanoscale Al crystals, which stop growing once they reach a size of about 10 nm. In a subsequent, second phase of crystallization the dendritic Al crystals grow rapidly with the formation of a crystal-glass eutectic-like mixture. The nanoscale Al crystals lead to some hardening of the glass, but do not modify the good ductility of the material. Subsequent hardening and embrittlement of the glass-nanocrystal composite may depend on slight changes of the extent of crystallization or instead on changes occurring in the glass itself. © 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.Peer Reviewe

Disordering of B2 Intermetallics by Ball Milling, with particular attention to FeAl

Trabajo presentado en el Metastable, Mechanically Alloyed and Nanocrystalline Materials (ISMANAM), celebrado en Oxford (Inglaterra), del 9 al 14 de julio de 2000Our understanding of the disordering, partial or complete, of B2 intermetallics during intense milling is reviewed choosing the FeAl intermetallic as an example, and making especial effort to interpret the changes occurring in terms of the deformation mechanisms during milling and the crystalline and structural changes produced. The ease of disordering can be correlated with the relative energies of possible point defects produced during milling, or by the corresponding types of dislocations. Attempts at modelling structural changes produced by intense deformation appear in good agreement with detailed structural analyses. Many aspects of the processes occurring are still poorly understood, however, and there remains scope for further investigation