Differently shaped nanocrystalline (Fe, Y)3O4 and its adsorption efficiency toward inorganic arsenic species

Herein we report effects of partial substitution of Fe3+ by Y3+ in magnetite (Fe3O4) on morphology and inorganic arsenic species adsorption efficiency of the Fe3−x Y x O4 nanoparticles formed. The series of Fe3−x Y x O4 (x = 0.00, 0.042 and 0.084, labeled as Y00, Y05 and Y10, respectively) was synthesized using co-precipitation followed by microwave-hydrothermal treatment (MW) at 200 °C. With increase of yttrium content (x value), both the morphological inhomogeneity of the samples and the fraction of spinel nanorods as compared to spinel pseudospherical particles increased. By both transmission electron microscopy and x-ray powder diffraction analyses, it was determined that the direction of growth of the spinel nanorods is along the [110] crystallographic direction. The Fe3−x Y x O4 affinities of adsorption toward the inorganic arsenic species, As(III) (arsenite, AsO3 3−) and As(V) (arsenate, AsO4 3−), were investigated. Increased Y3+ content related to changes in sample morphology was followed by a decrease of As(III) removal efficiency and vice versa for As(V). The increase in Y3+ content, in addition to increasing the adsorption capacity for As(V), significantly expanded the optimum pH range for the maximum removal and decreased the contact time for necessary 50% removal (t 1/2) of As(V) (Y00: pH 2–3, t 1/2 = 3.12 min; Y05: pH 2–6, t 1/2 = 2.12 min and Y10: pH 2–10, t 1/2 = 1.12 min). The results point to incorporation of Y3+ in the crystal lattice of magnetite, inducing nanorod spinel structure formation with significant changes in sorption properties important for the removal of inorganic arsenic from waters.This is the peer-reviewed version of the article: Nanotechnology, 2019, 30, 47, 475702, [https://dx.doi.org/10.1088/1361-6528/ab3ca2]Published version: [http://cer.ihtm.bg.ac.rs/handle/123456789/3243

Structure and Magnetic Properties of Intermetallic Rare-Earth-Transition-Metal Compounds: A Review

This review discusses the properties of candidate compounds for semi-hard and hard magnetic applications. Their general formula is R1−sT5+2s with R = rare earth, T = transition metal and 0≤s≤0.5 and among them, the focus will be on the ThMn12- and Th2Zn17-type structures. Not only will the influence of the structure on the magnetic properties be shown, but also the influence of various R and T elements on the intrinsic magnetic properties will be discussed (R = Y, Pr, Nd, Sm, Gd, … and T = Fe, Co, Si, Al, Ga, Mo, Zr, Cr, Ti, V, …). The influence of the microstructure on the extrinsic magnetic properties of these R–T based intermetallic nanomaterials, prepared by high energy ball milling followed by short annealing, will be also be shown. In addition, the electronic structure studied by DFT will be presented and compared to the results of experimental magnetic measurements as well as the hyperfine parameter determined by Mössbauer spectrometry

Etude de petites particules metalliques incluses dans une matrice d'alumine: interactions dipolaires entre particules, calcul du temps de relaxation dans le modele de Brown

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 78347 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Effect of M Substitution on Structural, Magnetic and Magnetocaloric Properties of R₂Fe_17-x M_x (R = Gd, Nd; M = Co, Cu) Solid Solutions

The structure, magnetic and magnetocaloric properties of Nd2Fe17−xCox (x = 0; 1; 2; 3, 4) and Gd2Fe17-xCux (x = 0, 0.5, 1 and 1.5) solid solutions have been studied. For this purpose, these samples were prepared by arc melting and subsequent annealing at 1073 K for a 7 days. Structural analysis by Rietveld method on X-ray diffraction (XRD) have determined that these alloys crystallize in the rhombohedral Th2Zn17-type structure (Space group R¯3 m) and the substitution of iron by nickel and copper leads to a decrease in the unit cell volume. The Curie temperature (TC) of the prepared samples depends on the nickel and copper content. Based on the Arrott plot, these analyses show that Nd2Fe17-xCox exhibits a second-order ferromagnetic to paramagnetic phase transition around the Curie temperature. These curves were also used to determine the magnetic entropy change ∆SMax and the relative cooling power. For an applied field of 1.5 T, ∆SMax increase from 3.35 J/kg. K for x = 0 to 5.83 J/kg. K for x = 2. In addition the RCP increases monotonously. This is due to an important temperature range for the magnetic phase transition, contributing to a large ∆SMax shape. Gd2Fe17-xCux solid solution has a reduction of the ferromagnetic phase transition temperature from 475 K (for x = 0) to 460 K (for x = 1.5) is due to the substitution of the magnetic element (Fe) by non-magnetic atoms (Cu). The magnetocaloric effect was determined in the vicinity of the Curie temperature TC. By increasing the Cu content, an increase in the values of magnetic entropy (∆SMax) in a low applied field is observed

Étude de nouveaux matériaux de type La(Fe1-xSix)13 pour la réfrigération magnétique à température ambiante

La première partie des travaux réalisés a été dédiée à l' élaboration de composés LaFe13-xSix (1,3 ¡U x ¡U 2,2) par broyage à haute énergie. Il a fallu déterminer les conditions de synthèse et de recuit optimales pour l'obtention d'échantillons monophasés. Leur homogénéité a été analysée par diffraction des rayons X et microsonde électronique. Les résultats ont montré qu'une microstructure plus fine favorise la formation de la phase désirée : un recuit de 30 min (au lieu de 30 jours pour les massifs) à 1373K suffit à l'obtention d'un composé quasi-monophasé. D'après les mesures magnétiques effectuées, les composés synthétisés par broyage mécanique ont des proprié tés magnétiques et magnétocaloriques similaires aux massifs. Ils présentent une transition métamagnétique des électrons itinérants induite par le champ ou la température. Leur température de Curie augmente avec le Si, variant de 200K à 235K pour x = 1,4 à 2,0 alors que leur variation d'entropie magnétique diminue de 20 J/kg K à 4 J/kg K sous une variation de champ de 0-2 T. La deuxième partie de l'étude a consisté à améliorer les propriétés magnétocaloriques des intermétalliques par l'insertion d'atomes interstitiels (H, C). Les mesures magnétiques ont montré une nette augmentation de la température de transition (jusqu'à Tamb.) par effet magnétovolumique tout en conservant un effet magnétocalorique important. Les analyses par diffraction des neutrons en température effectuées sur les composés deutérés ont permis de suivre l'évolution des données cristallographiques et des moments magnétiques par Fe. Il ressort de cette étude que ces composés présentent un grand intérêt dans la recherche de futurs matériaux magnétocaloriques pour la réfrigération magnétique à température ambiante. Dans le cadre de l'exploration de nouveaux systèmes, les propriétés magnétocaloriques des composés Y1-xRxFe2D4,2 (R = Er, Tb) ont également été étudiés en couplant les études magnétiques avec des mesures de diffraction des neutronsThe first part of this work was devoted to the elaboration of the LaFe13-xSix (1.3 ¡Ü x ¡Ü 2.2) alloys by high energy ball-milling. The synthesis and annealing conditions were defined in order to obtain single phase samples. Their homogeneity was checked by X ray diffraction and electron microprobe analysis. The results show that a finer microstructure is convenient for the formation of the NaZn13 phase and that only a 30 minutes heat treatment at 1373K is sufficient to obtain almost single phase LaFe13-xSix compounds. This means that this way of synthesis is cost-effective, and interesting for industrial production. According to the magnetic measurements, the annealed ball-milled compounds show similar magnetic and magnetocaloric properties than the bulk ones. They exhibit an itinerant electron metamagnetic transition induced by a magnetic field or a temperature change. Their Curie temperatures increase with the Si content from 200K to 235K wh en x = 1.4 and 2.0 respectively, while their magnetic entropy variation decreases from 20 J/kg K to 4 J/kg K under a magnetic field change of 0-2 T. The second part of this study consisted to improve the magnetocaloric properties of the intermetallic compounds by the insertion of light elements (H and C). According to the literature, the magnetic measurements show a clear increase of the transition temperature until room temperature in both cases. Moreover, the giant magnetocaloric effect is maintained. The evolutions of the crystallographic data and the magnetic moment by Fe atom were analyzed by neutron powder diffraction in temperature. This work brings out how interesting are those compounds for their application in room temperature magnetic refrigeration devices. In the framework of new magnetocaloric systems investigation, the magnetic and magnetocaloric properties of the Y1-xRxFe2D4,2 (R = Er, Tb) compounds were studied. Neutron powder diffraction measurements were pe rformed in complement to magnetic measurementsPARIS-EST-Université (770839901) / SudocSudocFranceF

Intermétalliques magnétiques praséodyme-cobaltnanostructurés (étude multiéchelle et optimisation)

Ce travail s'inscrit dans le cadre général de l'étude structurale et magnétique de nanomatériaux magnétiques à base de terres rares (R) et de métaux de transition (T) dont le domaine d'application concerne les aimants permanents ou l'enregistrement magnétique à haute densité. Dans la recherche de nouvelles phases aux caractéristiques magnétiques performantes, nous nous sommes intéressés à l'alliage Pr2Co7 . Ce composé a des propriétés magnétiques dures intéressantes : température de Curie élevée et une anisotropie magnéto-cristalline uniaxiale importante. Du point de vue magnétique, les interactions d'échange Co-Co sont les plus fortes, suivies par les interactions R-Co, tandis que les interactions R-R sont très faibles. La dominance des interactions Co-Co induit des températures de Curie assez élevée dans les composés Pr2Co7 . L'anisotropie magnétocristalline résulte de la combinaison de deux anisotropies uniaxiales des réseaux de praséodyme et de cobalt. Afin de renforcer ces interactions, il s'avère nécessaire de substituer partiellement le cobalt dans les composés Pr2Co7 par un élément approprié tel que le fer qui a un rayon légèrement plus gros que celui du cobalt ou par insertion d'un élément léger tel qu hydrogène ou le carbone qui peuvent augmenter les distances interatomiques et renforcer le moment magnétique. De plus, parallèlement à des propriétés magnétiques intrinsèques performantes, il est nécessaire d'optimiser les propriétés magnétiques extrinsèques de l'alliage par la recherche d'un état nonocristallin convenable correspondant aux applications potentielles. Les propriétés extrinsèques des composés Pr2Co7 n'ont été que très peu étudiées. Plusieurs méthodes ont été utilisées pour l'élaboration des nanomatériaux. Dans notre étude, nous avons mis en œuvre la technique de broyage à haute énergie suivie d'une recristallisation contrôlée, méthode de synthèse qui jusque-là n'avait pas encore été utilisée pour synthétiser ce type de composé. À cette échelle, la taille des grains devient de l'ordre de grandeur de la longueur d'échange. Cette méthode qui constitue un processus de synthèse hors équilibre, permet l'obtention de poudres nanostructurées métastables à partir d'un mélange de poudres élémentaires. Cette technique est particulièrement efficace dans le cas des alliages à base de terre rares (Pr, Sm...) qui sont extrêmement volatil. En effet, elle permet d'éviter l'état liquide puisque la réaction a lieu en dessous de la température de fusion et conduit à des quantités importantes reproductibles et homogènes d'alliages. Nous avons utilisé différentes méthodes de caractérisation à savoir : la diffraction de rayon X (DRX), la microscopie électronique à transmission (MET) couplée avec l'analyse EDX,la Magnéto/susceptométre Manics DSM-8This work falls within the general framework of the structural and magnetic nanomaterials based magnetic rare earth (R) and transition metal (T) whose domain of application concerns the permanent magnets or magnetic recording high density. In search of new magnetic phases in performance characteristics, we were interested in the alloy Pr2Co7. This compound has interesting hard magnetic properties: high Curie temperature and uniaxial magnetocrystalline anisotropy important. From the perspective of magnetic exchange interactions Co-Co are the strongest, followed by R-Co interaction, while the RR interactions are very weak. The dominance of Co-Co interactions induces relatively high Curie temperatures in compounds Pr2Co7.The magnetocrystalline anisotropy results from the combination of two networks uniaxial anisotropy praseodymium and cobalt. To strengthen these interactions, it is necessary to partially substitute cobalt in compounds Pr2Co7 by an appropriate element such as iron which has a radius slightly larger than that of cobalt or by insertion of a light element the hydrogen and carbon that can increase the interatomic distances and enhance the magnetic moment. Moreover, along with intrinsic magnetic properties improves, it is necessary to optimize the extrinsic magnetic properties of the alloy by the search for a suitable nanocrystalline state corresponding to the potential applications. The extrinsic properties of compounds Pr2Co7 have been little studied.Several methods were used for the development of nanomaterials. In our study, we have W arranty the technique of high energy milling followed by recrystallization controlled synthesis method which until then had not yet been used to synthesize this type of compound. At this scale, the grain size becomes of the order of magnitude of the exchange length. This method which is a non-equilibrium synthesis process, allows the production of nanostructured powders metastable from a mixture of elemental powders. This technique is particularly effective in the case of alloys based on rare earth (Pr, Sm ...) that are extremely volatile. Indeed, it avoids the liquid state since the reaction takes place below the melting temperature and led to reproducible and large quantities of homogeneous alloys. We used different characterization methods, namely: the X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled with EDX analysis, the magneto / susceptometer Manics DSM-8PARIS-EST-Université (770839901) / SudocSudocFranceF

Etude expérimentale et théorique des propriétés structurales et magnétiques des nanomatériaux Pr(Co,Fe)3

Les composés intermétalliques à base d'éléments de terres rares et de métaux de transition présentent des propriétés magnétiques intéressantes pour les applications technologiques (aimants permanents, enregistrement magnétique,...). Ce travail est dédié à l'étude des propriétés structurales et magnétiques des nanomatériaux de type PrCo(3-x)Fex, dérivant de la structure PuNi3. L'état nanocristallin a pour but d'optimiser les propriétés magnétiques extrinsèques, il a été obtenu par broyage à haute énergie suivi d'un recuit. Les composés PrCo3 ont une anisotropie uniaxiale, une aimantation très importante et un champ coercitif de 12 kOe à température ambiante et de 55 kOe à T = 10 K. L'analyse des données de diffraction des rayons X par affinement Rietveld a montré que le système PrCo3-xFex est mono-phasé de type PuNi3 pour x < 1. La substitution du Co par Fe induit des améliorations significatives sur les propriétés magnétiques intrinsèques. Cette amélioration est due d'une part au renforcement du moment magnétique moyen 3d des composés substitués, et d'autre part à l'effet magnétovolumique. Parallèlement, nous avons complété cette étude expérimentale par deux études théoriques. La première approche, à l'échelle atomique, consiste à faire des calculs de type DFT des structures électroniques et des propriétés magnétiques intrinsèques des intermétalliques RCox, (R = Y, Pr et x = 2, 3, 5) et PrCo(3-x)Fex. La seconde approche correspondant à l'échelle mésoscopique a pour but d'interprêter le lien entre les propriétés magnétiques extrinsèques et la structure à l'échelle nanométrique. Elle est menée dans le cadre du micromagnétisme par une méthode de type éléments finisThe intermetallic based on rare earth and transition metal compounds present interesting magnetic properties for the technological applications (permanent magnets, magnetic recording,...). This work is dedicated to the study of the structural and magnetic properties of nanocrystalline PrCo(3-x)Fex, described in the PuNi3 type structure. The nanocrystalline state leads to optimize the extrinsic roperties, it has been obtained by high energy milling technique following by subsequent annealing. The compound PrCo3-xFex presents a very high uniaxial magnetocrystalline anisotropy, a very important magnetization and a coercive field of 12 kOe at room temperature and 55 kOe at T = 10 K. The analysis result of X-ray diffraction pattern of PrCo(3-x)Fex using the Rietveld refinement showed that these compounds are single phase with the rhombohedral PuNi3-type structure for x < 1. The substitution of the Co by Fe leads to significant improvement on the intrinsic magnetic properties. This improvement comes from on the one hand the increase of average 3d magnetic moment on substituted compounds, and on the other hand the magnetovolumic effect. We have completed this experimental study by two theoretical investigations. The first approach, at the atomic scale, with DFT based calculations of the electronic structure and intrinsic magnetic properties of RCox (R = Y, Pr and x = 2, 3, 5) and PrCo3-xFex intermetallics. The second approach is the simulation of the extrinsic magnetic properties in the framework of micromagnetism. It has been performed in order to get a qualitative picture of the microstructure effect on the macroscopic magnetization curve, this model is treated by using the finite elements methodPARIS-EST-Université (770839901) / SudocSudocFranceF

Tuning the Magnetocaloric Properties of the La(Fe,Si)13 Compounds by Chemical Substitution and Light Element Insertion

International audienc

A single integral expression for the magnetisation of a textured superparamagnetic system

A superparamagnetic system consists of many single domain particles with relaxation times smaller than the time of measurement (t=100 s), with the result that thermal agitation leads to zero magnetisation in zero field,M(H=0)=0 for t>100 s. For particles in a fluid, an external field will result in a magnetisation given by the Langevin function as inparamagnetism. However, particles fixed into position in the presence of a field, obtain an orientational texture. We still find M(H=0)=0, but the magnetisation is not given by the Langevin function. The model of Chantrell et al. can yield an expression for M capable of including texture. This requires the calculation of the partition function of the system which is a double integral in the coordinate system used. Here we reduce this double integral to a single integral

Series expansions for the magnetisation of a solid superparamagnetic system of non-interacting particleswith anisotropy

The calculation of the magnetisation curve of an assembly of non-interacting fine superparamagnetic particles, with uniaxial anisotropy and easy axes fixed in a solid non-magnetic matrix is considered. The presence of anisotropy complicates the calculation which otherwise would result in the Langevin function. The calculation for particles with anisotropy and easy axes fixed at arbitrary angles to the external field, requires the calculation of the partition function, which has previously been expressed exactly as a double integral or as a sum of single integrals. We have recently shown how the partition function can be reduced to a single integral and here we show how this can be expressed as a double infinite series containing known functions. Special cases are considered, some existing analytic formulae are reobtained, and some new analytic formulae are presented. For identical particles the deviation from the Langevin function is known to be considerable. The formulae presented should facilitate the incorporation of the effects of anisotropy