Magnetovolume and magnetocaloric effects in Er2Fe17 - Pablo Alvarez-Alonso, Pedro Gorria, Jesus A. Blanco, Jorge Sanchez-Marcos, Gabriel J. Cuello, Ines Puente-Orench, Jose Alberto Rodriguez-Velamazan, Gaston Garbarino, Imanol de Pedro, Jesus Rodriguez Fernandez, Jose L. Sanchez Llamazares, Phys Rev B 86, 184411 (2012).
Understanding the structural and magnetic evolution of superparamagnetic Zn ferrites nanoparticles synthesized by an easy electrochemical process
M. Rivero, A. Serrano, J. A. Rodriguez-Velamazan, A. Munoz-Bonilla, J. Sanchez-Marcos,
J Alloy Compd 881, 160585 (2021).
Abstract
In the present work, a series of zinc ferrite nanoparticles of 11 nm on average size were synthesized following an electrochemical method in aqueous medium. The nanoparticles were structurally characterized by X-ray diffraction (XRD), inductively coupled plasma spectroscopy (ICP), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and neutron diffraction (ND). The magnetic characterization was carried out by vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The electrochemical synthetic methodology used in this paper yields zinc ferrite monocrystalline nanoparticles with a controlled size, shape and composition, in a reproducible manner. The control of such parameters enables obtaining ferrite nanoparticles with tuneable magnetic properties. The results show that the Zn2+ cations are situated in tetrahedral sites in the crystalline spinel structure, which causes a progressive decrease in the magnetic moments of the ferrites with Zn content due to the breakdown of the super-exchange interactions. (C) 2021 Elsevier B.V. All rights reserved.
YBaCuO-type perovskites as potential air electrodes for SOFCs. The case of YSr2Cu2FeO7+delta
Sara A. Lopez-Paz, Rafael Marin-Gamero, Xabier Martinez de Irujo-Labalde, Jorge Sanchez-Marcos, Domingo Perez-Coll, Miguel Angel Alario y Franco, Susana Garcia-Martin,
J Mater Chem A 9, 8554 (2021).
Abstract
The electrochemical properties of YSr2Cu2FeO7+delta with YBaCuO-type structure have been studied. The temperature dependent oxygen content of this oxide has a marked influence on its p-type conducting behavior, since topochemical oxygen release occurs on heating above 673 K while reversible oxygen uptake takes place on cooling. Mixed valence Fe3+/Fe4+ and Cu2+/Cu3+ in combination with anion vacancies within the oxygen-sublattice suggest mixed (electronic and ionic) conductivity in this oxide. Electrochemical measurements indicate that YSr2Cu2FeO7+delta shows high oxygen reduction reaction activity at intermediate temperatures, revealing its potential applications as an air electrode in SOFCs.
Direct 3D printing of zero valent iron@polylactic acid catalyst for tetracycline degradation with magnetically inducing active persulfate.
S. Fernandez-Velayos, J. Sanchez-Marcos, A. Munoz-Bonilla, P. Herrasti, N. Menendez, E. Mazario,
Sci Total Environ , 150917 (2021).
Abstract
Catalyst stability has become a challenging issue for advanced oxidation processes (AOPs). Herein, we report an alternative method based on 3D printing technology to obtain zero-valent iron polylactic acid prototypes (ZVI@PLA) in a single step and without post etching treatment. ZVI@PLA was used to activate persulfate (PS) for the removal of Tetracycline (TC) in recirculating mode under two different heating methodologies, thermal bath and contactless heating promoted by magnetic induction (MIH). The effect of both heating methodologies was systematically analysed by comparing the kinetic constant of the degradation processes. It was demonstrated that the non-contact heating of ZVI by MIH reactivates the surface of the catalyst, renewing the surface iron content exposed to the pollutant solution, which makes the ZVI@PLA catalyst reusable up to 10cycles with no efficiency reduction. In contrast, by using a conventional thermal bath, the kinetic constant gradually decreases over the 10cycles, because of the superficial iron consumption, being the kinetic constant 5 times lower in the 10th run compared to MIH experiment. X-ray diffraction and Mossbauer spectroscopy confirmed the presence of metallic iron embedded in the ZVI@PLA prototype, whose crystalline structure remained unchanged for 10th cycles of MIH. Moreover, it was proven that with no contact heating technology at low magnetic fields (12.2 mT), the solution temperature does not increase, but only the surface of the catalyst does. Under these superficial heated conditions, kinetic rate is increased up to 0.016min-1 compared to the value of 0.0086min-1 obtained for conventional heating at 20°C. This increase is explained not only by PS activation by iron leaching but also by the contribution of ZVI in the heterogeneous activation of persulfate.
Tunneling the size of iron oxide NPs using different alcohols and proportions water-alcohol
FL. Rivera, J. Sanchez-Marcos, N. Menendez, P. Herrasti, E. Mazario,
Adv Nano Res 8, 95 (2020).
Abstract
In this work the properties of iron oxide magnetic nanoparticles (MNPs) synthesized by electrochemical method using different water-alcohol proportions and alcohols have been investigated. The syntheses were carried out using 99% iron foils acting electrodes in a 0.04 M NaCl solutions at room temperature applying 22 mAcm(-2) on the working electrode, mostly obtaining magnetite nanoparticles. The impact of the electrolyte in the size of the synthesized MNPs has been evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), chronopotentiometric studies, and magnetic characterization. The results have shown that nanoparticles can be obtained in the range of 6 to 26 nm depending on the type of alcohol and the proportions in the mixture of water-alcohol. The same trend has been observed for all alcohols. As the proportion of these in the medium increases, the nanoparticles obtained are smaller in size. This trend is maintained until a certain proportion of alcohol: 50% for methanol, and 60% for the rest of alcohols, proportions where obtaining a single phase of magnetite is not favored.
Soft Magnetic Switching in a FeSr2YCu2O7.85 Superconductor with Unusually High Iron Valence
SA. Lopez-Paz, XM. de Irujo-Labalde, J. Sanchez-Marcos, C. Ritter, E. Moran, MA. Alario-Franco,
Inorg Chem 58, 12809 (2019).
Abstract
Ozone oxidation has allowed the stabilization of a very high iron oxidation state in the FeSr2YCu2O7.85 cuprate, in which a long-range magnetic ordering of the high valent iron cations coexists with the superconducting interactions (magnetic ordering temperature T-N = 110 K > superconducting critical temperature T-c = 70 K). The somewhat unexpected A-type AFM structure, with a mu(Fe) similar to 2 mu(B) magnetic saturation moment associated with the hypervalent iron sublattice, suggests an unusual low spin state for the iron cations, while the low dimensionality of the magnetic structure results in a soft switching toward ferromagnetism under small external magnetic fields. The role of the crystal structure and of the high charge concentration in the stabilization of this unusual electronic configuration for the iron cations is discussed.
Toxicity and biodegradation of zinc ferrite nanoparticles in Xenopus laevis
M. Rivero, M. Marin-Barba, L. Gutierrez, E. Lozano-Velasco, GN. Wheeler, J. Sanchez-Marcos, A. Munoz-Bonilla, CJ. Morris, A. Ruiz,
J Nanopart Res 21, 181 (2019).
Abstract
Zn-doped Fe3O4 magnetic nanoparticles have been proposed as the ideal ferrite for some biomedical applications like magnetic hyperthermia or photothermal therapy because of the possibility to adjust their size and chemical composition in order to design tailored treatments. However, reliable approaches are needed to risk assess Zn ferrite nanoparticles before clinical development. In this work, the in vitro toxicity of the nanoparticles was evaluated in five cellular models (Caco-2, HepG2, MDCK, Calu-3 and Raw 264.7) representing different target organs/systems (gastrointestinal system, liver, kidney, respiratory system and immune system). For the first time, these nanoparticles were evaluated in an in vivo Xenopus laevis model to study whole organism toxicity and their impact on iron and zinc metabolic pathways. Short- and long-term in vivo exposure studies provided insights into the contrasting adverse effects between acute and chronic exposure. Quantitative PCR combined with elemental analysis and AC magnetic susceptibility measurements revealed that at short-term exposure (72 h), the nanoparticles' absorption process is predominant, with the consequent over-expression of metal transporters and metal response proteins. At long-term exposure (120 h), there is an upregulation of metal accumulation involved genes and the return to basal levels of both iron and zinc transporters, involved in the uptake of metals. This suggests that at this stage, the nanoparticles' absorption process is residual compared with the following steps in metabolism, distribution and/or excretion processes, indicated by the increase of iron accumulation proteins at both transcriptional and translational level. This testing approach based on a battery of cellular systems and the use of the Xenopus laevis model could be a viable strategy for studying the toxicity, degradability and ultimately the long-term fate of zinc ferrites in the organism.
Cation distribution of cobalt ferrite electrosynthesized nanoparticles. A methodological comparison
J. Sanchez-Marcos, E. Mazario, JA. Rodriguez-Velamazan, E. Salas, P. Herrasti, N. Menendez,
J Alloy Compd 739, 909 (2018).
Abstract
The present work seeks to analyse the structural and magnetic properties of cobalt ferrite nanoparticles obtained by electrochemical synthesis by high-resolution transmission electronic microscopy (HRTEM), X-ray absorption spectroscopy (XAS), Mossbauer spectroscopy (MS), neutron diffraction (ND) and SQUID magnetometer. The cationic distribution is analyzed by different techniques. The inversion degree determined by the most accurate measurements was 0.73(1), and the formula for the nanoparticles therefore was (up arrow Co0.27Fe0.73)[down arrow Co0.73Fe1.27]O-4. The magnetic moment found from DC and Mossbauer spectroscopy measurements was 3.8(3) mu B, and the coercivity was 7870 Oe at 100 K. (c) 2017 Elsevier B.V. All rights reserved.
Compositional Tuning of Light-to-Heat Conversion Efficiency and of Optical Properties of Superparamagnetic Iron Oxide Nanoparticles
M. Rivero, J. Hu, D. Jaque, M. Canete, J. Sanchez-Marcos, A. Munoz-Bonilla,
J Phys Chem C 122, 16389 (2018).
Abstract
Superparamagnetic iron oxide nanoparticles have played a fundamental role in the recent development of nanomedicine as one of the most popular imaging and therapeutic agents. Recently, the ability of iron magnetic nanoparticles for efficient heat generation under infrared optical excitation has even boosted the interest of the scientific community in this family of nanomaterials. The combination of magnetic and optical heating into a single nanostructure makes possible the development of advanced therapy treatments based on synergetic effects between these two heat sources that, in addition, could be combined with high penetration magnetic imaging. Despite its potential, the application of iron oxide nanoparticles in photothermal treatments is limited because the lack of knowledge about the physical mechanisms behind their light-to-heat conversion capacity. In this work, we have systematically investigated the photothermal efficiency of iron oxide nanoparticles with a variable composition achieved by partial replacement of iron by zinc atoms. We have experimentally found that the light-to-heat conversion efficiency gradually increases with the iron content, suggesting a dominant role of iron related transitions in the heating processes. Experimental data included in this work reveal a simple route to tailor the light activated heating processes in iron oxide nanoparticles toward fully controllable treatments.
Microstructural and magnetic characterization of Fe- and Ir-based multilayers
E. Arias-Egido, MA. Laguna-Marco, J. Sanchez-Marcos, C. Piquer, J. Chaboy, M. Avila, JG. Lopez,
Phys Rev Materials 2, 014402 (2018).
Abstract
Nominal [Fe(t)/Ir(t')](n) (M/Mtype), [FeOx(t)/IrOx(t')](n) (O/O), and [Fe(t)/IrOx(t')](n) (M/O) multilayers have been prepared by magnetron sputtering at room temperature. Composition, structure, and magnetic behavior have been analyzed. In the M/M samples, the Fe and Ir phases are identified as bcc and fcc, respectively. The magnetism evolves from bulklike iron to granular behavior as the thickness of the Fe layers decreases. An induced magnetic moment, ferromagnetically coupled to Fe, is observed on Ir by x-ray magnetic circular dichroism (XMCD). Besides, the presence of negative remanent magnetization is observed in the M/M samples. As for the M/O samples, the stronger affinity of iron for oxygen displaces the oxygen atoms giving rise to actual heterostructures that strongly differ from the nominal ones. For similar thickness of the two layers the Fe layer become oxidized while a mixture of metal and oxide phases is found in the Ir layer. The increase of the Fe thickness leads to a metallic Ir layer and a highly coercive (similar to 4.4 kOe) core-shell metal-oxide structure in the Fe layers.
Magnetic Nanoparticles-Based Conducting Polymer Nanocomposites
A. Munoz-Bonilla, J. Sanchez-Marcos, P. Herrasti,
Book , 45 (2017).
Abstract
This chapter reviews the state of art of nanocomposites based on conducting polymers and magnetic nanoparticles. The preparation of hybrid nanocomposites with both magnetic and electrical properties has emerging as attractive alternative in a wide number of applications especially as microwave absorbing material and electromagnetic shielding. An overview of the different synthetic routes of the hybrid nanocomposites is presented, which outlines the most development techniques to prepare homogenous matrix, core-shell nanoparticles, and thin films. This chapter also covers the discussion of both the magnetic and electrical properties of the nanocomposites that significantly vary from the individual components. Finally varies of the most relevant applications of the magnetic nanoparticles-based conducting polymer nanocomposites are highlighted.
Magnetic clusters on the verge of long range ferromagnetism in Lu(Fe0.75Al0.25)(2) and Lu(Fe0.50Al0.50)(2) alloys
C. Piquer, LF. Barquin, J. Chaboy, D. Alba-Venero, MA. Laguna-Marco, R. Boada, J. Sanchez-Marcos, I. Puente-Orench,
J Alloy Compd 695, 704 (2017).
Abstract
Lu(Fe0.75Al0.25)(2) and Lu(Fe0.50Al0.50)(2) alloys have been produced by arc-melting. DC and AC magnetization, Mossbauer spectroscopy, specific heat and neutron diffraction experiments have been performed to determine their magnetic ground state. DC magnetization curves measured at low fields (H < 1 kOe) evidence two peaks, at T-SRO and T-f, and magnetic irreversibility. The peak at T-SRO vanishes and the one at T-f smears out when high fields (H > 1 kOe) are applied. The thermal variation of AC susceptibility shows that both transitions at T-SRO and T-f are frequency dependent. Neither magnetic splitting nor broadening is observed in the Mossbauer spectra of both compounds in the T-f < T < T-SRO thermal range. A magnetically split spectrum is only observed in Lu(Fe0.75Al0.25)(2) for T < T-f. The absence of long range ferromagnetic order in both alloys is confirmed by specific heat and neutron diffraction measurements. The overall interpretation points to a clustered magnetic environment due to the random positions of Fe atoms in the crystallographic cell. At T-SRO a short range ferromagnetic order takes place within the clusters, which become frustrated at T-f, when the random anisotropy of the clusters enables their freezing. (C) 2016 Elsevier B.V. All rights reserved.
Crystal structure and magnetic properties of high Mn-doped strontium hexaferrite
FN. Tenorio-Gonzalez, AM. Bolarin-Miro, F. Sanchez-De Jesus, P. Vera-Serna, N. Menendez-Gonzalez, J. Sanchez-Marcos,
J Alloy Compd 695, 2083 (2017).
Abstract
We present a study on the effect of the substitution of Fe+3 by Mn+3 on the structural and magnetic properties of strontium hexaferrite, SrFe12-xMnxO19 (0 <= x <= 5), which is synthesized by assisted high-energy ball milling. A mechanism of substitution is proposed. Fe2O3, SrCO3 and Mn2O3 powders were mixed in a stoichiometric ratio, milled for 5 h and annealed at 950 degrees C for 2 h. The X-ray diffraction patterns confirm the formation of a hexaferrite structure with small amounts of Fe2O3 as a second phase for low doping levels of Mn3+ and reveal a modification of the lattice parameters as the rate of Mn3+ substitution increases. The magnetic properties demonstrate an important reduction of the magnetic saturation and a significant increase in the coercivity field with cation substitution. The M+ ossbauer results confirm that the Mn3+ ions preferentially occupy the 2a and 12k sites while avoiding the 2b site. (C) 2016 Elsevier B.V. All rights reserved.
Giant direct and inverse magnetocaloric effect linked to the same forward martensitic transformation
JI. Perez-Landazabal, V. Recarte, V. Sanchez-Alarcos, JJ. Beato-Lopez, JA. Rodriguez-Velamazan, J. Sanchez-Marcos, C. Gomez-Polo, E. Cesari,
Sci Rep 7, 13328 (2017).
Abstract
Metamagnetic shape memory alloys have aroused considerable attraction as potential magnetic refrigerants due to the large inverse magnetocaloric effect associated to the magnetic-field-induction of a reverse martensitic transformation (martensite to austenite). In some of these alloys, the austenite phase can be retained on cooling under high magnetic fields, being the retained phase metastable after field removing. Here, we report a giant direct magnetocaloric effect linked to the anomalous forward martensitic transformation (austenite to martensite) that the retained austenite undergoes on heating. Under moderate fields of 10 kOe, an estimated adiabatic temperature change of 9 K has been obtained, which is (in absolute value) almost twice that obtained in the conventional transformation under higher applied fields. The observation of a different sign on the temperature change associated to the same austenite to martensite transformation depending on whether it occurs on heating (retained) or on cooling is attributed to the predominance of the magnetic or the vibrational entropy terms, respectively.
Comparison of ferrite nanoparticles obtained electrochemically for catalytical reduction of hydrogen peroxide
J. Jaime-Gonzalez, E. Mazario, N. Menendez, J. Sanchez-Marcos, A. Munoz-Bonilla, P. Herrasti,
J Solid State Electr 20, 1191 (2016).
Abstract
Fenites of iron, cobalt, and nickel were used as a non-enzymatic sensor for detection of hydrogen peroxide. Xray diffraction (XRD) and transmission electron microscopy revealed that the nanoparticles obtained by electrochemical route and varying the parameters synthesis show similar size of around 20 nm and a relation metal/iron equal to 1/2. The effect of pH, temperature, amount of nanoparticles, and potential has been studied to obtain the best sensor properties in terms of sensitivity and linear response. The mechanism has, CO2, been attributed to the oxidation of Fezand Nit' in the octahedral position of the spinel that enhances the catalytic reduction of hydrogen peroxide. The best sensor has been obtained with magnetite (iron fenite) with a detection limit of 7.3 x 10(6) M and a sensitivity of 4.0 x 10(-4) mu A/M. The magnetite was also applied to determine hydrogen peroxide in commercial contact lens cleaner Novoxy with satisfactory results.
Microstructural, electronic and magnetic characterization of Fe-based nanoparticles embedded in Al matrix
MA. Laguna-Marco, J. Sanchez-Marcos, N. Menendez, J. Chaboy, E. Salas-Colera, C. Prieto,
Mater Design 93, 388 (2016).
Abstract
Nominal granular iron oxide-aluminum thin films have been prepared by simultaneous deposition of iron oxide nanoparticles, grown by the gas-phase aggregation technique, and an aluminium matrix, grown by conventional magnetron sputtering. Composition, structure and magnetic behavior have been analyzed by different techniques including TEM and AFM microscopies, EDX, RBS, X-ray absorption and Mossbauer spectroscopies and SQUID magnetometry. Both, structure and magnetic behavior, are found to be highly dependent on the preparation conditions. In particular, our work shows that for low matrix/nanoparticle ratios the aluminum is able to partially displace the iron oxide and forma core-shell iron metal-iron oxide structure. For higher ratios, on the other hand, the oxygen atoms become very diluted and their role negligible. In this case a core-shell structure consisting of an iron metal core and an iron-aluminum alloy shell is formed. Magnetization measurements indicate that in the first case the core and the shell are magnetically coupled while in the second case the two phases are magnetically uncoupled, the Fe-Al alloy presenting strong coercivity. (C) 2016 Elsevier Ltd. All rights reserved.
Synthesis and characterization of manganese ferrite nanoparticles obtained by electrochemical/chemical method
E. Mazario, A. Mayoral, E. Salas, N. Menendez, P. Herrasti, J. Sanchez-Marcos,
Mater Design 111, 646 (2016).
Abstract
A combined electrochemical/chemicalmethodwas developed in order to synthesize manganese ferrite nanoparticles. The synthesis was carried out in an electrochemical cell containing iron as anode and cathode electrodes and an electrolyte solution of manganese chloride and tetrabutyl ammonium bromide. A usual XRD, STEM compositional mapping images and ICP analysis showed the formation of spinel structure and the presence of Mn, Fe and O in the nanoparticles (NPs) with a stoichiometry Mn0.5Fe2.5O4. The nanoparticle size, shape, and morphology were characterized using electron microscopy and X-Ray absorption spectroscopy, and SQUID measurements were carried out to determine the magnetic behavior. This sample was compared with a same composition manganese ferrite obtained by electrochemical synthesis. (C) 2016 Elsevier Ltd. All rights reserved.
Synthesis and structural characterization of ZnxFe3-xO4 ferrite nanoparticles obtained by an electrochemical method
M. Rivero, A. del Campo, A. Mayoral, E. Mazario, J. Sanchez-Marcos, A. Munoz-Bonilla,
Rsc Adv 6, 40067 (2016).
Abstract
A series of zinc ferrite nanoparticles were synthesized following a single-step electrochemical method in aqueous medium. This strategy allowed the control of both the size and chemical composition of the nanoparticles in an easy and reproducible manner by simply varying the intensity of the applied current. The obtained nanoparticles were morphologically and structurally characterized as a function of the particle size and the Zn content in the sample by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy (ICP) and Raman microscopy. The formation of ZnxFe(3-x)O4 (x = 0.18-0.93) ferrite nanoparticles with crystal sizes in the range of 9 to 18 nm and with a homogeneous distribution of the Zn2+ cation in the crystalline structure was observed. However, following a thermal treatment, a migration of zinc cations was detected that led to the formation of two different crystalline phases, stoichiometric zinc ferrite and hematite. Raman microscopy revealed the formation of segregated micro-domains enriched within these crystalline phases. The study of the magnetic properties of the electro-synthesized ferrite nanoparticles with a homogeneous incorporation of Zn in the structure shows that the saturation magnetization and the coercively values are highly dependent on the chemical composition and crystal size.
High Specific Absorption Rate and Transverse Relaxivity Effects in Manganese Ferrite Nanoparticles Obtained by an Electrochemical Route
Eva. Mazario, Jorge Sanchez-Marcos, Nieves Menendez, Magdalena Canete, Alvaro Mayoral, Sara Rivera-Fernandez, Jesus M. de la Fuente, Pilar Herrasti,
J Phys Chem C 119, 6828 (2015).
Abstract
Superparamagnetic iron oxide-based nanoparticles (SPIONS) have attracted an enormous amount of attention for their potential use in biomedical applications, due to their good biocompatibility and low toxicity. The current study considers citric acid-conjugated manganese ferrite and its synergy to be used in MRI and in hyperthermia treatment, thus showing theragnostic applications. High colloidal stability was obtained with this functionalization. SPIONS with superparamagnetic behavior of crystal sizes of approximately 20 nm were obtained via an electrochemical synthesis method. One of the highest specific absorption rate (SAR) values was achieved in this work (1661 W g(-1)), under a magnetic field of 30 mT at 717 kHz frequency, compared with other magnetic ferrites in the literature. These nanoparticles dissipate heat through Neel relaxation and, together with the high SAR value obtained, indicate an excellent material for hyperthermia treatment of cancer. In addition, these nanoparticles exhibit transverse relaxivity behavior, with an r(2) value of 394 mM(-1) s(-1), i.e., at least two times higher than the value of a commercial magnetic contrast agent based on iron oxides. Finally, no toxicity effects of these nanoparticles are evidenced; as a result, these nanoparticles are appropriate for in vivo application.
Effect of the low magnetic field on the electrodeposition of CoxNi100-x alloys
S. Olvera, E. M. Arce Estrada, J. Sanchez-Marcos, F. J. Palomares, L. Vazquez, P. Herrasti,
Mater Charact 105, 136 (2015).
Abstract
Magnetic, chemical and structural properties of electrosynthesized CoxNi100 - x have been studied. The electrodeposition has been conducted both in the presence and absence of a low magnetic field. The application of a perpendicular magnetic field during the synthesis modified slightly the morphology of the alloys. These changes depend more on the film composition than on the applied field, as demonstrated by AFM images. In the absence of magnetic field, the CoxNi100 - x film grows along the (200) direction. However, when the magnetic field was applied, a preferential orientation along the (111) direction was observed. No important magnetic changes are induced by the presence of the magnetic field during the growth. Based on X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) experiments, the chemical composition of the films was preserved during preparation regardless of whether or not magnetic field is applied. There has been observed an increase in deposition rate in the presence of field even at these low magnetic fields. (C) 2015 Elsevier Inc. All rights reserved.
Gold-coated iron nanoparticles in transparent Si3N4 matrix thin films
J. Sanchez-Marcos, E. Cespedes, F. Jimenez-Villacorta, A. Munoz-Martin, C. Prieto,
J Nanopart Res 15, 1714 (2013).
Abstract
A new method to prepare thin films containing gold-coated iron nanoparticles is presented. The ternary Fe-Au-Si3N4 system prepared by sequential sputtering has revealed a progressive variation of microstructures from Au/Fe/Au/Si3N4 multilayers to iron nanoparticles. Microstructural characterization by transmission electron microscopy, analysis of the magnetic properties and probing of the iron short-range order by X-ray absorption spectroscopy confirm the existence of a gold-coated iron nanoparticles of 1-2 nm typical size for a specific range of iron and gold contents per layer in the transparent silicon nitride ceramic matrix.
Exchange bias and magnetic behaviour of iron nanoclusters prepared by the gas aggregation technique
J. Sanchez-Marcos, M. A. Laguna-Marco, R. Martinez-Morillas, F. Jimenez-Villacorta, E. Cespedes, N. Menendez, C. Prieto,
J Alloy Compd 536, S265 (2012).
Abstract
Iron nanoclusters have been deposited by the gas-phase aggregation technique to form multilayered structures with outstanding exchange-bias (H-E) values up to H-E = 3300 Oe at low temperatures. In order to explain the observed magnetic properties, composition and crystallographic phase have been determined by X-ray absorption spectroscopy. A metal-oxide core-shell arrangement has to be discarded to explain the large obtained values of H-E since structural results show nanoclusters formed by the antiferromagnetic alpha-Fe2O3 oxide. Moreover, nanoparticles of few nanometers formed by substoichiometric alpha-Fe2O3 explain the observed weak ferromagnetism and let to understand the origin of large exchange bias by the interaction between different spin sublattice configurations provided by the low iron coordination at surface. (c) 2011 Elsevier B.V. All rights reserved.
X-Ray Absorption and Mossbauer Spectroscopies Characterization of Iron Nanoclusters Prepared by the Gas Aggregation Technique
J. Sanchez-Marcos, M. A. Laguna-Marco, R. Martinez-Morillas, E. Cespedes, N. Menendez, F. Jimenez-Villacorta, C. Prieto,
J Nanosci Nanotechno 12, 8619 (2012).
Abstract
Partially oxidized iron nanoclusters have been prepared by the gas-phase aggregation technique with typical sizes of 2-3 nm. This preparation technique has been reported to obtain clusters with interesting magnetic properties such as very large exchange bias. In this paper, a sample composition study carried out by Mossbauer and X-ray absorption spectroscopies is reported. The information reached by these techniques, which is based on the iron short range order, results to be an ideal way to have a characterization of the whole sample since the obtained data are an average over a very large amount of the clusters. In addition, our results indicate the presence of ferrihydrite, which is a compound typically ignored when studying this type of systems.
The effect of ball milling in the microstructure and magnetic properties of Pr2Fe17 compound
J. L. Sanchez Llamazares, M. J. Perez, P. Alvarez, J. D. Santos, M. L. Sanchez, B. Hernando, J. A. Blanco, J. Sanchez Marcos, P. Gorria,
J Alloy Compd 483, 682 (2009).
Abstract
The effect of a severe mechanical milling treatment on the microstructure, magnetic and magneto-caloric properties of Pr2Fe17 powders is reported. Bulk alloys showing a rhombohedral Th2Zn17-type crystal structure were mechanically ball milled under Ar atmosphere. After 10 h of milling this crystal structure persists and the mean values of the lattice parameters remain almost unchanged. Average grain sizes around 27 nm were estimated by both, transmission electron microscopy and neutron powder diffraction measurements. While for the starting bulk alloys the low field temperature of the magnetization, M(T), shows a well-defined and sharp decrease at the Curie temperature, T-c = 285(2) K, in ball milled samples the transition becomes broad not allowing an accurate determination of Curie point; in addition, this intrinsic parameter seems to be shifted toward a higher temperature [292(10)K]. The magnetocaloric effect at mu H-o(max) = 5 T was evaluated from the temperature dependence of magnetic entropy change, through the variation of M(H,T) curves. A decrease in the peak value of magnetic entropy change, vertical bar Delta S-M(max)vertical bar, from 5.7 to 3.7 J kg(-1) K-1, and the broadening of the maximum is observed for the milled sample respect to the bulk alloy. (C) 2008 Elsevier B.V. All rights reserved.
Fluorinated tin oxide (FTO) deposited at room temperature: Influence of hydrogen and oxygen in the sputtering gas on the optical and electrical proper
Maria Moran-Pedroso, Jorge Sanchez-Marcos, Alicia de Andres, Carlos Prieto,
Appl Surf Sci 459, 349 (2018).
Abstract
The optical and electrical properties of fluorinated fin oxide (FTO) films deposited at room temperature by sputtering were investigated. In addition to small amount of oxygen to preserve highly transparent films, electrical resistivity become decreased two orders of magnitude by using appropriate hydrogen content in the sputtering gas. Films deposited with Ar-(93%)/O-2((5%))/H-2((2%)) gas mixture show maximal values of conductivity, charge carrier density and mobility as well as excellent transparency. Taking into account the film characterization carried out by Rutherford backscattering spectrometry (RBS), a mechanism is proposed to explain the observed optical and electrical dependence with the hydrogen content in the film.
Indium-tin oxide thin films deposited at room temperature on glass and PET substrates: Optical and electrical properties variation with the H-2-Ar spu
L. Alvarez-Fraga, F. Jimenez-Villacorta, J. Sanchez-Marcos, A. de Andres, C. Prieto,
Appl Surf Sci 344, 217 (2015).
Abstract
The optical and electrical properties of indium tin oxide (ITO) films deposited at room temperature on glass and polyethylene terephthalate (PET) substrates were investigated. A clear evolution of optical transparency and sheet resistance with the content of H-2 in the gas mixture of H-2 and Ar during magnetron sputtering deposition is observed. An optimized performance of the transparent conductive properties ITO films on PET was achieved for samples prepared using H-2/(Ar + H-2) ratio in the range of 0.3-0.6%. Moreover, flexible ITO-PET samples show a better transparent conductive figure of merit, Phi(TC) = T-10/R-S, than their glass counterparts. These results provide valuable insight into the room temperature fabrication and development of transparent conductive ITO-based flexible devices. (C) 2015 Elsevier B.V. All rights reserved.
Huge Photoresistance in Transparent and Conductive Indium Titanium Oxide Films Prepared by Electron Beam-Physical Vapor Deposition
Rocio Martinez-Morillas, Rafael Ramirez, Jorge Sanchez-Marcos, Emiliano Fonda, Alicia de Andres, Carlos Prieto,
Acs Appl Mater Inter 6, 1781 (2014).
Abstract
Transparent and conductive indium titanium oxide (ITiO) films have been obtained by electron beam physical vapour deposition with Ti content from 5 at % up to 28 at %. X-ray absorption spectroscopy techniques have been used to identify the local environment of Ti ions. Even at the lowest concentrations Ti is not incorporated into the In2O3 structure but forms clusters of a Ti-In mixed oxide that present a distorted ruffle TiO2 short-range order. The optical transmittance of the annealed samples reaches 95 % and no significant variation of the gap energy (around 3.7 eV) is observed with Ti content. The electronic conductivity under light irradiation is studied evidencing a huge photo-resistance in the samples with Ti content above 22 at % reaching more than two orders of magnitude for the 26 at % Ti under illumination with few mu W/cm(2) at 365 nm. Hall and conductivity results are analyzed using a model that takes into account both electron and hole carriers as well as the conductivity enhancement by carrier photogeneration. The electron carrier density decreases with Ti content while its mobility increases up to values of 1000 cm(2)/(V s). Oxygen annealed ITiO films obtained by this technique with Ti content below 10 at % have properties adequate as transparent semiconductors and those with Ti content higher than 22 at % have exceptional photoresistive properties relevant for numerous applications.
Raman spectroscopy for the study of reduction mechanisms and optimization of conductivity in graphene oxide thin films
Xavier Diez-Betriu, Susana Alvarez-Garcia, Cristina Botas, Patricia Alvarez, Jorge Sanchez-Marcos, Carlos Prieto, Rosa Menendez, Alicia de Andres,
J Mater Chem C 1, 6905 (2013).
Abstract
Highly reduced few-layer graphene oxide films with conductivities of up to 500 S cm(-1) are obtained. The thin films with an optimized compromise between sheet resistance (3.1 k Omega sq(-1)) and transparency (around 80% to 90%) are suitable for touch screens and transparent electrodes in OLEDs. We discuss the effects of low temperature annealing and chemical reduction on the properties of the films and present an optimized reduction process that allows the original 2D/G Raman intensity ratio of few-layer graphene to be recovered. The Raman spectrum of graphene oxide is found to be only related to oxygen-free graphene-like regions with Raman bands at 1130 and 3155 cm(-1) that probably involve C-H vibrations of rings and edges, while a band at 1700 cm(-1) is assigned to irregular rings such as Stone Wales defects. All the bands involve resonant Raman processes and disappear in highly reduced samples. Clear correlations of the D band width with the sp(2) content in thin films and resistivity have been observed, indicating that this is a good Raman parameter for evaluating the quality of the samples. The structural defects produced by the release of embedded water and some of the oxygen functional groups during annealing are detrimental for intra-grain conductivity but greatly enhance inter-grain connectivity.
Exchange bias and magnetic behaviour of iron nanoclusters prepared by the gas aggregation technique
J. Sanchez-Marcos, M. A. Laguna-Marco, R. Martinez-Morillas, F. Jimenez-Villacorta, E. Cespedes, N. Menendez, C. Prieto,
J Alloy Compd 536, S265 (2012).
Abstract
Iron nanoclusters have been deposited by the gas-phase aggregation technique to form multilayered structures with outstanding exchange-bias (H-E) values up to H-E = 3300 Oe at low temperatures. In order to explain the observed magnetic properties, composition and crystallographic phase have been determined by X-ray absorption spectroscopy. A metal-oxide core-shell arrangement has to be discarded to explain the large obtained values of H-E since structural results show nanoclusters formed by the antiferromagnetic alpha-Fe2O3 oxide. Moreover, nanoparticles of few nanometers formed by substoichiometric alpha-Fe2O3 explain the observed weak ferromagnetism and let to understand the origin of large exchange bias by the interaction between different spin sublattice configurations provided by the low iron coordination at surface. (c) 2011 Elsevier B.V. All rights reserved.
First order ferromagnetic transition in binary CeIn2
D. P. Rojas, J. I. Espeso, J. Rodriguez Fernandez, J. C. Gomez Sal, J. Sanchez Marcos, H. Mueller,
Phys Rev B 80, 184413 (2009).
Abstract
Measurements of the magnetic, thermal, and transport properties of the CeIn2 binary alloy are consistent with a paramagnetic-ferromagnetic transition at T-C=22 K. A discontinuity in the magnetic entropy, electrical resistivity and thermal expansion, and a huge anomaly in the specific heat of 113 J/mol K (Delta c(mag)=103 J/mol K), at the magnetic transition, are observed. In addition, the Arrott plots show negative slope at low fields, the field-cooling and field-warming magnetization present irreversibility, and both the susceptibility and the resistivity evidence a small thermal hysteresis of 0.05 K. Moreover, the values of the entropy change calculated from the magnetization data using the Clausius-Clapeyron equation are in good agreement with those directly obtained from the specific-heat data. The joint analysis of all these results provides evidence for the first order character of this magnetic transition in CeIn2.
Exploring the magneto-volume anomalies in Dy2Fe17 with unconventional rhombohedral crystal structure
Pablo Alvarez-Alonso, Pedro Gorria, Jose L. Sanchez Llamazares, Gabriel J. Cuello, Ines Puente Orench, Jorge Sanchez Marcos, Gaston Garbarino, M. Reiffers, Jesus A. Blanco,
Acta Mater 61, 7931 (2013).
Abstract
We have synthesized the Dy2Fe17 alloy with an unconventional crystal structure (R (3) over barm space group). Neutron powder thermo-diffraction and X-ray powder diffraction under high pressure (up to 15 GPa) show that the rhombohedral crystal structure is stable. Likewise, the alloy with the usual hexagonal crystal structure (P6(3)/mmc), the rhombohedral variant of Dy2Fe17 compound, exhibits a collinear ferrimagnetic order below the Curie temperature (T-C approximate to 363 K), with antiparallel mutual alignment of the Dy and Fe sublattices. Additionally, we have observed two distinctive issues related to magneto-volume anomalies: (i) the pressure dependence of the cell volume at room temperature shows the existence of a critical pressure at which the compound is no longer ferrimagnetic; and (ii) the cell volume shows invar-like behaviour in a wide temperature range (2-290 K), with a minimum at T approximate to 380 K. The spontaneous volume magnetostriction reaches omega(S) = 1.6 x 10(-2) at 2 K that decreases to zero at T approximate to 500 K (approximate to 1.4 T-C), which is associated with the existence of shortrange magnetic correlations. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
The magnetocaloric effect in Er2Fe17 near the magnetic phase transition
Pablo Alvarez-Alonso, Pedro Gorria, Jorge Sanchez Marcos, Jose L. Sanchez Llamazares, Jesus A. Blanco,
J Phys-condens Mat 25, 496010 (2013).
Abstract
Recent investigations in R2Fe17 intermetallic compounds have evidenced that these materials present a moderate magnetocaloric effect (MCE) near room temperature. A series of accurate magnetization measurements was carried out to show that the value of the demagnetizing factor has a significant influence on the absolute MCE value of Er2Fe17. In addition, the critical exponents determined from heat capacity and magnetization measurements allow us to describe the field dependence of the observed MCE around the Curie temperature.
Magnetovolume and magnetocaloric effects in Er2Fe17
Pablo Alvarez-Alonso, Pedro Gorria, Jesus A. Blanco, Jorge Sanchez-Marcos, Gabriel J. Cuello, Ines Puente-Orench, Jose Alberto Rodriguez-Velamazan, Gaston Garbarino, Imanol de Pedro, Jesus Rodriguez Fernandez, Jose L. Sanchez Llamazares,
Phys Rev B 86, 184411 (2012).
Abstract
Combining different experimental techniques, investigations in hexagonal P6(3)/mmc Er2Fe17 showremarkable magnetovolume anomalies below the Curie temperature, T-C. The spontaneous magnetostriction reaches 1.6 x 10(-2) at 5Kand falls to zero well above T-C, owing to short-range magnetic correlations. Moreover, Er2Fe17 exhibits direct and inverse magnetocaloric effects (MCE) with moderate isothermal magnetic entropy Delta S-M, and adiabatic temperature Delta T-ad changes [Delta S-M similar to -4.7 J(kgK)(-1) and Delta T-ad similar to 2.5 K near the T-C, and Delta S-M similar to 1.3 J(kgK)(-1) and Delta T-ad similar to -0.6 K at 40 K for Delta H = 80 kOe, respectively, determined from magnetization measurements]. The existence of an inverse MCE seems to be related to a crystalline electric field-level crossover in the Er sublattice and the ferrimagnetic arrangement between the magnetic moments of the Er and Fe sublattice. The main trends found experimentally for the temperature dependence of Delta S-M and Delta T-ad as well as for the atomic magnetic moments are qualitatively well described considering a mean-field Hamiltonian that incorporates both crystalline electric field and exchange interactions. Delta S-M (T) and Delta T-ad(T) curves are essentially zero at similar to 150 K, the temperature where the transition from direct to inverse MCE occurs. A possible interplay between the MCE and the magnetovolume anomalies is also discussed.
Crystal structure, magnetocaloric effect and magnetovolume anomalies in nanostructured Pr2Fe17
Pedro Gorria, Pablo Alvarez, Jorge Sanchez Marcos, Jose L. Sanchez Llamazares, Maria J. Perez, Jesus A. Blanco,
Acta Mater 57, 1724 (2009).
Abstract
Using high-energy ball milling, nanostructured Pr2Fe17 powders can be obtained from their arc-melted bulk alloys. High-resolution X-ray and neutron powder diffraction experiments reveal that the Th2Zn17-type rhombohedral crystal structure is maintained, after milling for 10 h, with almost unchanged values for both crystalline lattice parameters (Delta a; Delta c < 0.05%) and vanishing mechanically induced microstrain (< 0.1%). Although the mean crystalline size decreases down on 20 +/- 3 nm, magnetovolume anomalies observed in pure Pr2Fe17 are still present with a significant volume decrease on heating front 5 up to 320 K. After the milling, a significant increase in the magnetic anisotropy, due to the drastic reduction in crystalline size, is observed, while the value of the magnetic moment seems to be increased slightly (5%). In addition, the magnetocaloric effect of bulk and nanostructured Pr2Fe17 has been investigated. The magnetic entropy change, |Delta S-M|, decreases from 6.3 to 4.5 J kg(-1) K-1 under an applied magnetic field mu H-0 = 5 T after the milling process. However, the width of the |Delta S-M|(T) curve is substantially enlarged and hence the refrigerant capacity is enhanced. These findings make the iron-based nanostructured Pr2Fe17 powders interesting for applications in magnetic refrigeration at around room temperature. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
The effect of ball milling in the microstructure and magnetic properties of Pr2Fe17 compound
J. L. Sanchez Llamazares, M. J. Perez, P. Alvarez, J. D. Santos, M. L. Sanchez, B. Hernando, J. A. Blanco, J. Sanchez Marcos, P. Gorria,
J Alloy Compd 483, 682 (2009).
Abstract
The effect of a severe mechanical milling treatment on the microstructure, magnetic and magneto-caloric properties of Pr2Fe17 powders is reported. Bulk alloys showing a rhombohedral Th2Zn17-type crystal structure were mechanically ball milled under Ar atmosphere. After 10 h of milling this crystal structure persists and the mean values of the lattice parameters remain almost unchanged. Average grain sizes around 27 nm were estimated by both, transmission electron microscopy and neutron powder diffraction measurements. While for the starting bulk alloys the low field temperature of the magnetization, M(T), shows a well-defined and sharp decrease at the Curie temperature, T-c = 285(2) K, in ball milled samples the transition becomes broad not allowing an accurate determination of Curie point; in addition, this intrinsic parameter seems to be shifted toward a higher temperature [292(10)K]. The magnetocaloric effect at mu H-o(max) = 5 T was evaluated from the temperature dependence of magnetic entropy change, through the variation of M(H,T) curves. A decrease in the peak value of magnetic entropy change, vertical bar Delta S-M(max)vertical bar, from 5.7 to 3.7 J kg(-1) K-1, and the broadening of the maximum is observed for the milled sample respect to the bulk alloy. (C) 2008 Elsevier B.V. All rights reserved.
Microstructural and magnetic characterization of Nd2Fe17 ball milled alloys
P. Alvarez, J. L. Sanchez Llamazares, M. J. Perez, B. Hernando, J. D. Santos, J. Sanchez-Marcos, J. A. Blanco, P. Gorria,
J Non-cryst Solids 354, 5172 (2008).
Abstract
Microstructural and magnetic changes induced by ball milling in Nd2Fe17 alloy have been investigated. X-ray and neutron powder diffraction studies have shown that the main crystalline phase present in the as-cast Nd2Fe17 compound is the rhombohedral Th2Zn17-type crystal structure. Contrary to other materials, the crystal structure does not change after milling, and the crystal lattice parameters slightly increases while the induced strain is less than 0.1%. It has been observed from SEM and TEM images that the microstructure consists of agglomerates of nanoparticles with a mean size around 20 nm, and from magnetic measurements a broadening of the temperature range in which ferromagnetic to paramagnetic transition takes place. (C) 2008 Elsevier B.V. All rights reserved.
Relative cooling power enhancement in magneto-caloric nanostructured Pr(2)Fe(17)
Pedro Gorria, Jose L. Sanchez Llamazares, Pablo Alvarez, Maria Jose Perez, Jorge Sanchez Marcos, Jesus A. Blanco,
J Phys D Appl Phys 41, 192003 (2008).
Abstract
The magneto-caloric effect (MCE) of arc-melted bulk and 10 h ball-milled nanostructured Pr(2)Fe(17) powders has been investigated. The maximum value for the magnetic entropy change, vertical bar Delta S(M)vertical bar, in the milled alloy is 4.5 J kg(-1) K(-1) for mu(0)H = 5T, at around room temperature. The full width at half maximum, delta T(FWHM), of vertical bar Delta S(M)vertical bar(T) for the nanostructured powders is about 60% greater than that of the starting bulk alloy, thus giving rise to large relative cooling power values of 573 J kg(-1) (4.5 J cm(-3)) for mu(0)H = 5T estimated from the product of vertical bar Delta S(M)vertical bar(max) x delta T(FWHM). These results have been compared with those of well-known magnetic materials that exhibit a large or giant MCE effect. The potential for using these low-cost iron based nanostructured Pr(2)Fe(17) powders in magnetic refrigeration at room temperature is also discussed.
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