Structural and magnetic properties of nanocrystalline ZnFe2O4 powder synthesized by reactive ball milling

International audienceThe zinc ferrite (ZnFe2O4) has been obtained in nanocrystalline state by reactive milling in a high energy planetary mill from a stoichiometric mixture of oxides (ZnO and α-Fe2O3). A post milling annealing promotes the solid state reaction, improves the ferrite crystalline state and removes internal stresses. The formation of zinc ferrite was studied by X-ray diffraction and magnetic measurements. The chemical homogeneity and morphology of the powders were studied by X-ray microanalysis and scanning electron microscopy. The mean crystallite size after 16 h of milling was found to be 18 ± 2 nm. The lattice parameter of the obtained ferrite depends on the milling time and subsequent annealing treatment. It is lower than that of zinc ferrite obtained by the ceramic method. The evolution of the magnetization versus milling time is discussed in terms of milling induced cations reorganisation into the spinel structure

Synthesis, structural and magnetic characterization of nanocrystalline nickel ferrite-NiFe2O4 obtained by reactive milling

International audienceNanocrystalline nickel ferrite (NiFe2O4) has been synthesized from a stoichiometric mixture of oxides NiO and alpha-Fe2O3 in a high energy planetary mill. An annealing at 350 degrees C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 +/- 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure

Elaboration et étude de poudres magnétiques douces (Ni-Fe, Ni-Fe-X, Ni-Fe-X-Y) à l'état nanocristallin par broyage mécanique de haute énergie

Le composé intermétallique Ni3Fe et les alliages 79Ni16Fe5Mo et 77Ni14Fe5Cu4Mo (% massique) ont été élaborés par broyage mécanique de haute énergie. Le temps minimum pour leur obtention a été établi. La formation de ces alliages a été suivie par diffraction de rayons X, de neutrons et analyses thermomagnétiques. Pour le composé intermétallique, l effet bénéfique de recuits (à 400 et 450 C) sur la formation de l alliage et des propriétés magnétiques a été mis en évidence. La température de recristallisation et l enthalpie de formation de Ni3Fe ont été déterminées par analyses calorimétriques différentielles. L évolution du champ coercitif en fonction du temps de broyage et de la taille de grain est aussi présentée. La formation des alliages à base de nickel au cours de recuits a été analysée. Le diagramme broyage recuit transformation pour le composé Ni3Fe a été étendu. Pour l alliage NiFeMo, l évolution de l aimantation en fonction du temps de broyage est présenté, ainsi que la reproductibilité des propriétés magnétiques de diverses séries d échantillons. La sensibilité de la diffraction neutronique a été utilisée pour mettre en évidence la présence de contamination par les jarres et/ou les billes lors de broyage long. Pour l alliage NiFeCuMo, l évolution de l aimantation spontanée en fonction du temps de broyage est analysée. L influence du temps de broyage sur la composition de l alliage est montrée. Pour les longs temps de mécanosynthèse, une différence entre les températures de Curie mesurées en montée et en descente est alors observée et discutée.The Ni3Fe intermetallic compound and the 79Ni16Fe5Mo and 77Ni14Fe5Cu4Mo (wt. %) alloys have been obtained by high energy mechanical milling. For the given conditions, the minimum time needed for theirs formation has been established. The alloys formation has been followed by X-ray and neutron diffraction and thermomagnetic analyses. For the Ni3Fe intermetallic compound the annealing effect on his formation has been proved; the annealing temperatures were 400 C and 450 C. The recrystallization temperature and formation enthalpy of Ni3Fe have been obtained by differential scanning calorimetry. The coercitive field evolution with milling time and crystallite size is also discussed. A formation mechanism of the Ni-Fe alloys under the temperature and magnetic field is proposed. A extended milling annealing transformation diagram for the Ni3Fe formation is given. For the NiFeMo alloy, the magnetisation evolution with the milling time is showed; also the reproductibility of magnetic properties for different alloys series is discussed. The sensibility of neutron diffraction has been used to show the iron contamination by the containers and/or balls for the long milling times. For the NiFeCuMo alloy, the spontaneous magnetisation evolution with the milling time is analyzed. The long time milling influence to the alloy composition is showed. For the long milling times, a difference between the Curie temperature at heating and cooling is observed and discussed.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Synthesis, structural and magnetic characterization of nanocrystalline CuFe2O4 as obtained by a combined method reactive milling, heat treatment and ball milling

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Structural and magnetic properties of the copper ferrite obtained by reactive milling and heat treatment

International audienceCopper ferrite (CuFe2O4) was synthesised from an equimolar mixture of copper and iron oxides by mechanosynthesis and subsequent heat treatment. After mechanosynthesis, depending on the milling time, the powder consists in a mixture of phases. The heat treatment at 600 degrees C did not lead to a complete reaction of the mechano-activated precursors. After the heat treatments at 800 and 1000 degrees C, the complete formation of copper ferrite for almost all the milling times was noticed. The crystal structure of the copper ferrite was found to be cubic for all the samples heat treated at 1000 degrees C and a mixture of tetragonal and cubic for the samples heat treated at 800 degrees C. The amount of copper ferrite with cubic structure predominates in the samples with prolonged milling duration and a decrease of the tetragonal distortion by increasing the milling time occurs. The crystallisation of CuFe2O4 in cubic structure for the samples milled for prolonged time is influenced by the powder contamination with iron. The magmetisations of the samples obtained after heat treatment at 1000 degrees C were found to be larger compared to the ones of the samples heat treated at 800 degrees C. The iron contamination, milling duration and heat treatment temperature influence the cations distribution, thus leading to the saturation magnetisation of the copper ferrite samples ranging from 11.9 mu(B)/f.u. to 16.4 mu(B)/f.u

Influence of the heat treatment conditions on the formation of CuFe2O4 from mechanical milled precursors oxides

International audienceStoichiometric mixture of CuO and alpha-Fe2O3 milled in air up to 30 h was subjected to different heat treatments. The evolution of the heat treated milled powders was investigated by X-ray diffraction (XRD). The CuFe2O4 was partially obtained by milling, the material consisting in a mixture of phases. By applying different heat treatments in air and in vacuum, for 2-6 h, in 500-800 A degrees C temperature range the phases composition of the milled samples is changed. A heat treatment at 500 A degrees C in vacuum favours the formation of delafossite (CuFeO2) and tenorite (CuO) phases. If the same heat treatment is made in air, the CuFe2O4 phase formation with a cubic structure is favoured. Differential scanning calorimetry (DSC) investigation realised in Ar atmosphere revealed two large exothermic peaks. The first one is associated with the formation of the delafossite and tenorite phases and the second one with the formation of CuFe2O4. The XRD patterns of the samples subjected to the DSC measurements present maxima corresponding to the delafossite and cuprospinel (CuFe2O4) phases. For the heat treatment at 600 A degrees C in air the phases present in the sample are the same as for the annealing performed at 500 A degrees C: CuFe2O4, alpha-Fe2O3 and CuO. The heat treatment in air at 800 A degrees C leads to the complete reaction between the different phases and the formation of CuFe2O4 phase in whole the sample volume. The CuFe2O4 ferrite crystallises after this heat treatment in two crystal systems: cubic and tetragonal

AlSb intermetallic semiconductor compound formation by solid state reaction after partial amorphization induced by mechanical alloying

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Modulated magnetic structures for vortex pinning in high temperature superconductors

Cette thèse porte sur la réalisation et l'étude de systèmes hybrides d'interface entre une couche magnétique et un supraconducteur. Tout d'abord, nous avons réalisé et étudié des structures magnétiques mésoscopiques dont les propriétés magnétiques ont été modulées par l'effet de la dimensionnalité du système (épaisseur et taille latérale). Deux types des structures ont été considérés. La première est constituée par des couches minces de pérovskite LaSrMnO. Par une étude complexe nous avons réussi à démontrer la corrélation directe entre l'incorporation de l'oxygène dans le LaSrMnO et l'évolution de ses propriétés structurales, magnétiques et électriques. Une deuxième classe de matériaux magnétiques étudiés est constituée des métaux de transition (Co) et des alliages (Ni80Fe20). Les couches ont étés structurées par lithographie optique et gravure ionique sous forme d'objets de taille micronique. Par la suite, ces structures ferromagnétiques ont été interfacées avec des films minces constitués d'un supraconducteur à haute température : YBaCuO. L'objectif ultime de cette étude a été le contrôle de la dynamique des vortex dans le supraconducteur par deux types de mécanismes: intrinsèque ou les centres de pinning sont les défauts structuraux dans le film supraconducteur et un mécanisme extrinsèque lié à l'influence des modulations du champ magnétique généré par la structure magnétique mésoscopique adjacente.The present thesis deals with the fabrication and study of hybrid, ferromagnetic/superconducting, interface systems. Magnetic mezoscopic systems, whose magnetic properties were modulated by the dimensionality (thickness and lateral size) of the systems was studied. Two types of structures were considered. The first consisted of perovskite-like epitaxial LaSrMnO thin films. We have demonstrated the direct correlation between oxygen incorporation in the LaSrMnO lattice and the evolution of its structural, magnetic and electric properties. A second class of magnetic materials that has been studied consisted of transition metals (Co) and alloys (Ni80Fe20). We have defined micronic objects from the as-deposited films, by means of optical lithography and ion beam etching. These structures were then integrated to form an interface with thin epitaxial high Tc superconducting films: YBaCuO. The ultimate goal of the above studies was the control of vortex dynamics within the superconducting layer by two mechanisms: the first, intrinsic, in which flux pinning is achieved by structural defects within the superconducting film, and a second one, extrinsic, correlated with influence of the magnetic field modulations created by the adjacent mezoscopic magnetic structure.NANCY1-Bib. numérique (543959902) / SudocSudocFranceF

MATÉRIAUX COMPACTS MAGNÉTIQUES DOUX OBTENUS À L'ÉTAT NANOCRISTALLIN À PARTIR DE POUDRES D'ALLIAGES Ni-Fe-X ISSUES DE MÉCANOSYNTHÈSE

Cette thèse est consacrée à 1) la préparation d'alliages magnétiques base nickel à l'état nanocristallin 2) à l'élaboration de compacts nanocristallins 3) la caractérisation des propriétés physiques et particulièrement magnétiques douces des poudres et des compacts en fonction des paramètres d'élaboration. L'élaboration des alliages magnétiques doux a été réalisée par broyage mécanique de haute énergie à sec ou en utilisant le benzène comme agent de contrôle, conduisant à des matériaux nanocristallins. Les conditions optimales de synthèse des poudres ont été déduites pour les systèmes Ni3Fe, 79Ni16Fe5Mo et 77Ni14Fe5Cu4Mo et un protocole contenant broyage mécanique par voie humide suivi d'un traitement thermique est proposé. Ce protocole a permis de préparer des cristallites de taille ajustable de 12 à 30 nm selon la durée et le mode de broyage choisi. La taille des particules obtenues a pu être contrôlée par le choix de la quantité de benzène utilisée. Les propriétés intrinsèques des poudres tant microstructurales que structurales, magnétiques et thermiques ont été analysées en fonction des conditions d'élaboration. Une combinaison de techniques (DSC, TG, IR et MS) nous a permis d'expliquer la présence et la décomposition de benzène sur la surface des poudres broyées. Deux méthodes ont été mises en oeuvre pour élaborer des compacts nanocristallins magnétiques doux : le frittage plasma et la préparation de matériaux composites. Les conditions optimales de compactage de poudres magnétiques ont été déterminées en variant la pression de compactage, le taux de polymère, la méthode de polymérisation, la taille de particules, etc. Les propriétés physiques dynamiques ont été étudiées jusqu'à des fréquences de 100 kHz et une induction maximale de 0,05 et 0,1 T. Des valeurs typiques de la perméabilité relative initiale comprises entre 30 et 50 et des pertes comprises entre 300 et 7000 W/kg (f = 50 kHz et Bmax = 0,1 T) ont été obtenues et ont été discutées en fonction des paramètres de compactage. Pour les compacts obtenus par frittage plasma, des perméabilités relatives maximales comprises entre 200 et 900 ont été obtenues en variant la température et la durée du processus. Un traitement thermique post frittage (450 C/4 h) sous H2 conduit à une diminution du champ coercitif d'environ 50 % et une augmentation de la perméabilité de jusqu'à 600 % en conservant la structure nanocristalline de compacts. Les propriétés magnétiques des compacts composites ont été modélisées sur la base du modèle de Bruggemann.This thesis is devoted to 1) the preparation of magnetic nickel-based alloys in nanocrystalline state 2) the preparation of nanocrystalline compacts 3) the characterization of physical and in particularly soft magnetic properties of the powder and compacts as a functions of their elaboration parameters. The development of soft magnetic alloys has been achieved by dry or wet high energy milling using benzene as process control agent, leading to nanocrystalline materials. The optimum conditions for powder synthesis have been derived for systems Ni3Fe, 79Ni16Fe5Mo and 77Ni14Fe5Cu4Mo and a protocol containing mechanical milling followed by heat treatment is proposed. This protocol has allowed the preparation of powder having crystallite size tunable from 12-30 nm depending on the milling time and chosen milling method. The as obtained particles size could be controlled by choosing the amount of benzene used. The intrinsic properties of powders as microstructural and structural, magnetic and thermal have been analyzed according to the preparations conditions. A combination of (DSC, TG, IR and MS) techniques has allowed us to explain the presence and decomposition of benzene on the milled powders surface. Two methods have been implemented to develop nanocrystalline soft magnetic compact: spark plasma sintering and preparation of composite materials. The optimum conditions for compaction of magnetic powders were determined by varying the compaction pressure, the polymer quantity, the polymerization method, the particle size, etc.. The dynamic physical properties have been investigated up to frequencies of 100 kHz and a maximum induction level of 0.05 and 0.1 T. Typical values of initial relative permeability between 30 and 50 and core losses between 300 and 7000 W/kg (f = 50 kHz and Bmax = 0.1 T) were obtained and have been discussed in terms of compaction parameters. For the spark plasma sintered compacts, maximum relative permeability between 200 and 900 were obtained by varying the sintering temperature and process duration. A post sintering heat treatment (450 C/4 h) under H2 leads to a decrease in the coercive field of about 50% and increased permeability of up to 600 % conserving the nanocrystalline structure of the compacts. The magnetic properties of the composite compacts were modeled on the basis of the Bruggemann model.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Magnetic and structural properties of SmCo5/alpha-Fe nanocomposites

International audienceSmCo5/alfa-Fe magnetic nanocomposites have been obtained by mechanical milling in a planetary mill and subsequent annealing. Under all experimental conditions, only the pure SmCo5 phase and the alfa -Fe one were observed by X-ray diffraction. In the as-milled state, a significant remanence-enhancement effect is already found in a reference sample made of SmCo5 nanograins. In nanocomposites, the coercive field, µ0Hc, is below 0.1 T. After annealing, coercivity develops, up to a maximum value µ0Hc = 0.36T under optimal conditions. The associated remanent magnetization reaches 69Am2/kg