Дисертації з теми "Propriétés et matériaux magnétiques"
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Folcke, Emeric. "Structure et magnétisme d'alliages nanostructurés FePt et FeAu." Rouen, 2013. http://www.theses.fr/2013ROUES054.
This thesis focuses on synthesis and characterization of FePt and FeAu nanostructured equiatomic alloys, in the search for new functional alloys for magnetic recording. First, the FePt alloy has been investigated as thin layers (thickness 100 nm). The effects of thermal annealing and Pb heavy ion irradiation (900 MeV) on the degree of crystallographic order and, therefore, on the magnetic properties were studied. Second, ordered FePt nanoparticles of about 5 nm in diameter were obtained and analysed by atom probe tomography. We also investigated both structural and magnetic nanoparticles of FeAu nanoparticles, less than 10 nm in size, coated or not in a metal matrix. The structural diversity of the nanoparticles was demonstrated by transmission electron microscopy. This diversity is accompanied by a variety of magnetic behaviours, revealed by the presence of the metal matrix. The influence of a structural change, obtained after thermal annealing or Pb heavy ion irradiation was also studied. This work highlighted the importance of the degree of structural order of FePt and FeAu phases on their magnetic properties. We also showed the influence of the matrix coating the nanoparticles on their structural and magnetic properties. We showed the existence of an anisotropic exchange coupling between nanoparticles dispersed in a metal matrix. The existence of this coupling has been correlated with the presence of different magnetic behaviours in relation with the dispersion of crystallinity
Vitucci, Francesco Maria. "Propriétés optiques et magnétiques de matériaux multiferroïques : gaFeO3 et LuFe2O4." Thesis, Tours, 2010. http://www.theses.fr/2010TOUR4017/document.
We present a contribution to the study of structural, electronic and magnetic propertiesof multiferroic compounds. These materials – characterized by the coexistence and coupling of different types of long-range orders, such as magnetic and ferroelectic – have recently become a subject of great importance because of their academic interest and their significance for potential applications. In this context we have studied the two compounds GaFeO₃ and LuFe₂O₄. The study involved the use of several techniques : electronic spin resonance (ESR), magnetic measurements by magnetometry and infrared spectroscopy (IR).Local and macroscopic magnetic measurements reveal an anomalous paramagnetic phase in GaFeO3. This is attributed to the existence of short-range magnetic correlations in a wide temperature range above the ordering temperature. On the other hand, the analysis of IR phonon spectra recorded at different temperatures (10 ≤ T ≤ 1000 K) shows that the ordering of magnetic moments does not affect the structural properties of GaFeO₃ For LuFe₂O₄, conversely, the magnetic degrees of freedom are coupled to the structural properties via the charge ordering of Fe³+/Fe²+ ions, as suggested by ESR and IR spectroscopy
Setifi, Fatima. "Synthèse, structures et propriétés physiques de matériaux moléculaires conducteurs et magnétiques." Rennes 1, 2003. http://www.theses.fr/2003REN10030.
Dos, Santos Maria Elenice. "Mise en forme et propriétés magnétiques de manganites multiferroïques." Phd thesis, Université Rennes 1, 2014. http://tel.archives-ouvertes.fr/tel-01059303.
Ban, Voraksmy. "Matériaux magnétoréfrigérants à large zone de travail." Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10005/document.
The global warming by its scale and its complexity puts several questions on the future of our planet. One of the ways proposed to slow down this process is the reduction of the production of greenhouse gases. The domains of the refrigeration try to be renewed to answer the new ecological standards and one of the most promising alternatives is the magnetic refrigeration based on the magnetocaloric effect. This report concerns the research of new magnetorefrigerants with large temperature span and joins directly in this environmental and economic stake which aims at replacing the classic systems of refrigeration in a near future. At first, this research works focused on Gd-Tb alloys: various nuances of these alloys would allow to widen the temperature range. Their magnetocaloric properties were determined and a first study on their behavior in corrosion was begun in various coolants. Finally, the optimization of their shaping was realized for their use in the prototype of Cooltech Applications company. Secondly, we studied single-phase compounds as derivatives of Mn3GaC or Mn3Sn2 which present several successive magnetic transitions and thus a large temperature span. A lot of substitutions were simultaneously realized on the Mn and Sn sites of the compound Mn3Sn2 continuing the works led within the team on Mn3Sn2 and its derivatives since 2006
Bounour-Bouzamouche, Wafa. "Matériaux hybrides nanotubes de carbone/ferromagnétiques : élaboration et propriétés magnétiques statiques." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCD095/document.
Hybrid materials as carbon nanotubes filled with ferromagnetic materials (FMCNT) have great potential for spintronic applications. Their magnetic properties strongly depend on their density,orientation and filling efficiency. Two preparation methods of (FMNTC) were used: i) ex-situ synthesis where mechanical opening of the nanotubes produced by electrical arc is first achieved and in-situ during the synthesis by electrical arc discharge, ii) synthesis by chemical vapor deposition enhanced by plasma (PECVD) in the presence of cobalt Co and Co / Pd catalysts. Our results showed that the arc in-situ approach is more effective especially with the addition of a filling promoter such as yttrium (Y) and sulfur (S). Different proportions of catalyst were varied and their influence on the yield of hybrid nanotubes studied. The quality and quantity of obtained nanotubes as well as their yields and magnetic properties were improved. The PECVD synthesis revealed that the addition of a thin layer of palladium (~6 nm) as a co catalyst with the cobalt leads to a significant improvement inthe density of the filler and the alignment of the nanotubes. Magnetic measurements thereby demonstrated the contribution of a shape anisotropy that can be associated with a better geometric orientation of the nanotubes to the substrate
Mallet, Jérémy. "Electrodéposition et propriétés magnétiques de nanofils d'alliage CoxPt1-x." Reims, 2004. http://theses.univ-reims.fr/exl-doc/GED00000023.pdf.
The constant drive in the fabrication of magnetic recording media to increase the aerial density has implied to use another storage process such as perpendicular recording. To this end, new materials with strong perpendicular anisotropy, high coercive field and nanoscaled grain size are required. CoxPt1-x alloy is an excellent candidate due to the large magnetocrystalline anisotropy associated with its ordered face centred tetragonal phase (L10). CoxPt1-x nanowires have been electrodeposited into the nanopores of two different substrates: polycarbonate membranes or alumina membranes supported on doped Si wafers. The properties of the nanowires have been studied in both their as-deposited and annealed states. The crystalline structure and alloying composition have been systematically analyzed by X-Ray diffraction, TEM and EDX. The magnetic properties have been measured by VSM and SQUID magnetometers. The as-deposited nanowires have a metastable fcc structure and exhibit a quite hard ferromagnetic behavior. Magnetic characteristics, such as saturated magnetization, coercive field or magnetic reversal process, have been determined. The annealed nanowires can show different crystalline structures (fcc, L10 or L12) depending on both the alloy composition and the heat treatment processing. Influence of several factors on the magnetic properties of the nanowires, such as substrate nature, annealing conditions and measurement temperature, has been investigated. Very promising results were obtained with nanowires of 80 nm in diameter embedded in the alumina membrane, which exhibit a coercive field higher than 10 kOe at room temperature
Gout, Delphine. "Relations entre propriétés optiques et structures électroniques dans de nouveaux matériaux des familles Ln-M-S-X (Ln=La, Ce, M=P, Si, Ge, Sb et X=Cl, Br, I)." Nantes, 2000. http://www.theses.fr/2000NANT2121.
The aim of this work was the study of cerium and lanthanum compounds belonging to the Ln-M-Q-X, Ln-P-Q and Ln-Sb-S-Br (Ln=La, Ce, M=Si, Ge, X=Cl, Br, I) systems. These compounds present a rich structural chemistry and widely varying physical properties related to a high coordination number of the LnIII cations and the occurrence of very localized 4f orbitals
Bloyet, Clarisse. "Métallophosphates bidimensionnels luminescents et magnétiques : relation structure-propriétés." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC241/document.
This PhD work deals with the study of new lamellar magnetic and luminescent organic-inorganic hybrid materials synthesized by hydrothermal process. These materials were obtained from 3d transition metal salts (Cu2+, Co2+, Mn2+, Zn2+) and low symmetric organic molecules bearing at least one phosphonic acid function grafted onto a rigid aromatic platform (phenyl or naphthalene). The choice of the metal cation as well as additional functions (halogen: F, Cl, Br, I, carboxylic acid or methyl) on these cyclic systems led to two-dimensional hybrid materials with various architectures and physical properties (luminescence, magnetism and/or magnetoelectric coupling). Understanding the interconnections between the structural and physical properties of these metal phosphonates paves the way for the design of novel multifunctional materials
Rache, Salles Benjamin. "Propriétés magnétiques, électriques et structurales et transport polarisé en spin dans des structures hybrides MnAs-GaAs." Paris 6, 2010. http://www.theses.fr/2010PA066328.
Pain, Damien Michel Marcel. "Relations entre les propriétés magnétiques statiques et les propriétés en hyperfréquence de couches minces ferromagnétiques." Versailles-St Quentin en Yvelines, 1999. http://www.theses.fr/1999VERS0014.
Les materiaux ferromagnetiques ont beaucoup d'applications dans l'industrie, de l'electrotechnique a l'enregistrement magnetique. Le travail porte sur l'etude des proprietes statiques et dynamiques des couches minces ferromagnetiques, deposees sur substrat souple par procede pvd. Les modeles classiques du gyromagnetisme rendent bien compte du comportement en hyperfrequence de certains de ces materiaux. Nous nous interessons plus particulierement aux cas atypiques. Pour realiser cette etude, nous avons etendu la gamme de frequence d'un permeametre jusqu'a 6 ghz. Nous pouvons ainsi realiser des mesures de susceptibilite transverse. Les theories d'hoffmann sont en plus etendues aux frequences de resonance sous champ magnetique statique. Certains films presentent spontanement des domaines en bandes tres etroites, inferieures au micrometre. Un modele energetique adapte rend a la fois compte des cycles d'hysteresis mesures et des proprietes hyperfrequences. La finesse des pics de resonance est mise en evidence. Pour les films a faible anisotropie, nous avons montre que les modeles classiques du gyromagnetisme sont applicables. L'influence des domaines est egalement analysee. Une etude qualitative aborde les effets des inhomogeneites du champ demagnetisant sur les spectres de permeabilite. L'etude des recuits thermo-magnetiques montre une propriete nouvelle. Les films presentent en epaisseur une division en deux zones d'anisotropie differente, en valeur et en direction. L'influence du champ de recuit sur la rotation de l'anisotropie ne se fait donc pas de maniere uniforme. Une approche energetique, prenant en compte le couplage des deux populations, modelise correctement les cycles d'hysteresis de ces echantillons recuits et les spectres de permeabilite, en particulier l'apparition de deux modes de resonance bien distincts sous champ statique
Karboul, Trojet Wiem. "Etude statique et dynamique de matériaux ferromagnétiques soumis in situ à des contraintes extérieures : Application aux massifs et aux films minces." Paris 13, 2012. http://scbd-sto.univ-paris13.fr/intranet/edgalilee_th_2012_karboul.pdf.
Feldner, Hélène. "Propriétés magnétiques de systèmes à deux dimensions : système frustré de spins sur réseau carré et propriétés magnétiques de systèmes finis de graphènes." Strasbourg, 2011. http://www.theses.fr/2011STRA6180.
This thesis is about the magnetic properties of two different two dimensional systems. The first one corresponds to vanadates or cuprate crystals, which can be studied by a spin system on square lattice and a Heisenberg model with three couplings, a ferromagnetic first neighbor coupling and antiferromagnetic second and third neighbor couplings. This system is frustrated and lead to a non trivial classical phase diagram. We have studied the influence of quantum fluctuation using a Holstein-Primakov approach and the Schwinger bosons model. The second system studied corresponds to graphene of finite size. To study this system we use a mean field approximation of the Hubbard model. In a first step we recover within our method well known results and check that the model has been correctly implemented. In a second step, in order to assess the accuracy of this method, we perform complementary exact diagonalization calculations, and compare our results with quantum Monte Carlo simulations. And in the last part we will show evidence of a dynamical signature of the zigzag edge magnetization of finite sample of graphene
Fellah, Farid. "Microstructure et propriétés magnétiques et mécaniques du cobalt nanostructuré consolidé à partir de nanoparticules synthétisées par chimie douce." Paris 13, 2009. http://www.theses.fr/2009PA132019.
Nanostructured materials exhibit physical and mechanical properties significantly different from the corresponding bulk part. In this context, this work is a study of magnetic and mechanical properties of cobalt nanostructured materials. A bottom up approach, combining polyol process and either Hot Isostatic Pressing or Spark Plasma Sintering, was chosen to elaborate nanostructured materials. First, the synthesis of particles resulted in 50 and 240 mn cobalt nanoparticles with a faced centered cubic structure (fcc). Secondly, the consolidation gave mixture of fcc and hexagonal closed packed (hcp) materials with mean grains sized varying from 235 to 340 nm. Grains materials are observed to be subdivided by a lamellar structure corresponding to the fcc and hcp phases. The growth substructure seems to be dependant of the material density. Magnetic properties show an evolution with the grains size whereas mechanical properties show lamellar density dependence. In one hand we measured coercive fields characteristic of soft magnetic materials but still higher than amorphous materials. And in another hand, mechanical stresses reach 1200 MPa which are obviously better than amorphous materials. More over, the elongation to failure is still in a good range compared to nanocrystalline materials
Abdel, Samad Bassel. "Elaboration, étude et caractérisation de couches minces dans les grenats de fer et d'yttrium : applications dans le domaine télécommunication." Saint-Etienne, 2009. http://www.theses.fr/2009STET4007.
The thesis work began with the preparation of thin films of yttrium iron garnet (YIG) in DIOM Laboratory at Saint-Etienne, by radio frequency sputtering. Hundreds of samples was elaborated by varying the deposition conditions : argon flow, oxygen flow, heating the substrate during deposition and annealed in air and vacuum. The magneto-optical and magnetic characterization samples was performed by studying the Faraday effect, the Kerr effect, and the VSM to check the magnetic properties of the films. The surface samples were analyzed by scanning electron microscopy. Measuring the thickness of the films was achieved by a profilometer. The technique of characterization by Rutherford backscatter (RBS) performed at CNRS team in Lebanon, was determined the stoichiometry of samples. The crystalline state of samples was performed by X-ray diffraction ; this work has resulted in some improvments. This work also presente the design of a coplanar circulator, development of the magnetic films, the elaboration of its structure in a clean room (Hubert Curien Laboratory) and finally on the characterization of the devices. The circulator that we've made presente an interesting non-reciprocal effect, for small ferrite films thicknesses of (8µm)
Claiser, Nicolas. "Densités électroniques et densités de spin de matériaux magnétiques moléculaires." Nancy 1, 2003. http://www.theses.fr/2003NAN10188.
We have studied the electron density of molecular magnetic materials, either purely organic (nitronyle-nitroxyde radicals) or heavy atom complexes (Y and Gd, semiquinone radical). Using the topological analysis obtained by high resolution X-rays diffraction, we characterised the intra and intermolecular interactions involved in the control of the macroscopic properties. For the nitronyle-nitroxyde radicals, we have demonstrated the close relationship between the electron density distributions and the magnetic properties. For the heavy atom complexes, the electron and spin densities (obtained by polarised neutron diffraction) completed by ab initio calculations allow a precise description of the semiquinone and hydrotrispyrazolylborate ligands and the determination of the charges and spin transfers, which are fundamental in the understanding of the exchange mechanisms. A fundamental problem on the calculation of the atomic form factors, pointed out on the gadolinium complex, is discussed
Ramanatha, Dayalu Anand Theerthan. "Effet des contraintes électriques et magnétiques sur des cristaux simples ferroélectriques et céramiques." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2012. http://tel.archives-ouvertes.fr/tel-00914178.
Rafhii, Ahmad El. "Étude de l'évolution des propriétés diélectriques et magnétiques des matériaux sous champ microonde." Toulouse, INPT, 1997. http://www.theses.fr/1977INPT026H.
Santos, Maria Elenice dos. "Mise en forme et propriétés magnétiques de manganites multiferroïques." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S017/document.
Structural and magnetic properties of Co2MnO4, an inverse spinel structure with spatial group Fd3m and cubic symmetry, were investigated by X-Ray Diffraction (DRX) and using a SQUID magnetometer. Co2MnO4 is a multiferroic compound presenting electrical and magnetic properties due to the presence of the Co and Mn elements, which are distributed on tetrahedral and octahedral sites of the AB2O4 structure. Valence fluctuations of Co and Mn (Co2+/Co3+ and Mn2+/Mn3+/Mn4+) can easily occur and depend on the synthesis procedures and thermal processes, which can change the oxidation states of the metallic cations. In this work, samples of BixCo2-xMnO4 (0.0 ≤ x ≤ 0.3) were synthesized, partially replacing Co by Bi, a non magnetic element. A soft chemical route, the modified polymeric precursors method (MPPM) was used. All samples were heat-treated in similar conditions, under a temperature of 1100 ºC (24h). DRX results, associated with Rietveld refinements, showed crystalline materials with similar crystallographic data. The cell parameter of the cubic structure increased with the Bi content. SEM images showed that Bi presence altered the grains sizes (~1 - 10 µm). A spurious phase, rich in Bi, was formed due to both the solubility limit of Bi and the ionic radii of Co (0,65Å) and Bi (1,17Å). In order to solve these questions, synthesis of a new solid solution, the CoxBi2-xMnO4 (0.0 ≤ x ≤ 1.7), by the MPPM route was attempted. In parallel, a novel elaboration method, the mechanochemical route (MS), was used to synthesize the BixCo2-xMnO4 (0.0 ≤ x ≤ 0.3) series. The magnetic results, MxT (Zero‑Field–Cooled / Field–Cooled) cycles, 1/χ-versus-T curves and MxH hysteresis loops, revealed important information about the magnetic nature and oxidation states of the Co and Mn cations. The ferrimagnetic behavior of Co2MnO4 was preserved, with the ZFC/FC curves exhibiting well-defined magnetic transitions and strong irreversibility below TC. Several magnetic parameters, such as TC, Tmax, MFC (extrapolation of the FC curve to T=0), the coercive field HC and MS (saturation magnetization to H= 50 kOe) changed significantly with the Bi content. According to the structural and magnetic results, a charge balance is proposed, (Co2+)[Co2+x(Bi3+,CoIII)1-xMn3+1-xMn4+x]O4, where Co2+ occupies the tetrahedral positions “( )” and is responsible of the antiferromagnetic interactions, all others cations occupying the octahedral sites “[ ]” and are responsible of ferromagnetism. The CoIII cations at the octahedral sites are on a low-spin non-magnetic configuration (S = 0) and they are partially substituted by Bi, also a non-magnetic ion, resulting on an effective moment μeff ~ 8,2 µB, with no change as a function of the Bi content
As propriedades estruturais e magnéticas do composto Co2MnO4, uma estrutura espinélio inversa de grupo espacial Fd3m e simetria cúbica, foram investigadas por difração de raios X e usando um magnetômetro SQUID. Co2MnO4 é um composto multiferróico, exibindo propriedades elétricas e magnéticas devido à presença dos elementos Co e Mn, distribuídos nos sítios tetraédricos e octaédricos da estrutura AB2O4. A flutuação das valências Co2+/Co3+ e Mn2+/Mn3+/Mn4+ podem ocorrer facilmente e estão sujeitas aos processos de síntese e efeitos térmicos, podendo ser associados a estes variações nos estados de oxidação de Co e Mn devido à substituições parciais destes elementos. Neste trabalho foram sintetizadas amostras BixCo2-xMnO4 (0,0 ≤ x ≤ 0,3), sendo o Bi um elemento não magnético. Para tal, uma rota de síntese química, o método MPPM, foi utilizada. Todas as amostras foram submetidas a tratamentos térmicos em condições idênticas, na temperatura de estabilização da fase BixCo2-xMnO4 igual a 1100ºC (24h). Os resultados de DRX e refinamentos de Rietveld mostraram que o método MPPM produziu amostras cristalinas com informações cristalográficas idênticas, exceto no caso do parâmetro de rede que aumentou em dependência ao percentual de Bi. As imagens morfológicas destes materiais mostraram que o Bi alterou a forma e o tamanho dos grãos variando entre (~0,5 – 1,7 µm). Devido ao limite de solubilidade do Bi dentro da rede espinélio e à diferença entre os raios iônicos do Co (0,65Å) e Bi (1,17Å), a formação de uma fase espúria rica em Bi ocorreu. No sentido de solucionar questões como esta, a síntese do sistema CoxBi2-xMnO4 (0,0 ≤ x ≤ 1,7) pela rota MPPM e de BixCo2-xMnO4 (0,0 ≤ x ≤ 0,3) por método de mecanosíntese foram realizadas. Os resultados magnéticos, curvas MxT (Zero Field – Cooled ZFC e Field – Cooled FC); 1/χ versus T e MxH, revelaram informações importantes sobre a disposição dos cátions presentes. O comportamento ferrimagnético de Co2MnO4 foi mantido, com as curvas ZFC e FC mostrando irreversibilidade e transições bem definidas abaixo de TC. No entanto, os valores de TC, Tmáx e MFC (extrapolação da curva FC para T = 0) obtidos por MxT, assim como ΘCW obtidos por 1/χ versus T, e HC e MS (magnetização de saturação para H= 50 kOe) obtidos por MxH sofreram mudanças significativas, as quais foram associadas ao Bi que alterou o ambiente magnético dos materiais. De acordo com os resultados estruturais e magnéticos, um balanço de cargas foi proposto para BixCo2-xMnO4: (Co2+)[Co2+x(Bi3+, CoIII)1-xMn3+1-xMn4+x]O4, sendo os cátions Co2+ nas posições ( ), responsáveis pelas interações AFM e todos os cátions posicionados em [ ] na relação acima, responsáveis pelo caráter FM destes materiais. Os valores de μef = ~ 8,2µB, para todas as amostras BixCo2-xMnO4 (0,0 ≤ x ≤ 0,3), não sofreram alterações. Os cátions CoIII, presentes nos sítios octaédricos, possuem uma configuração de baixo spin (S = 0), o que não implicou em qualquer mudança na soma total dos μef quando da substituição de Co por Bi, uma vez que ambos não são elementos co momentos magnéticos
Berezovsky, Florence. "Matériaux moléculaires à base de donneurs organiques et d'anions inorganiques magnétiques : synthèses, structures et propriétés." Brest, 2000. http://www.theses.fr/2000BRES2001.
Demessence, Aude. "Matériaux hybrides multifonctionnels : Elaboration et propriétés d'hydroxydes lamellaires de métaux de transition magnétiques et luminescents." Strasbourg 1, 2006. http://www.theses.fr/2006STR13199.
Khalil, Ismaïl. "Caractérisation magnétique basse fréquence par la méthode de nappe de courant : conception et fabrication d'un prototype composé de couches minces de Cu et de YIG élaborées par pulvérisation cathodique RF." Saint-Etienne, 2009. http://www.theses.fr/2009STET4011.
The ferrite materials are widely used today in the electromagnetic devices of different applications (inductors, transformers, recording heads. . . ). In a permanent context of reduction in size of components and improving their performance, new magnetic materials including thin films makes interest. Therefore this work concern the realization of a micro-inductor based on ferrite thin film (YIG) and its magnetic characterization at low frequency (f<1MHz) to determine the value of the initial relative permeability µr of these films. This study begins by presenting the different elaboration techniques of thin films and the methods to determine µr. A choice of characterization method (current sheet method) is then adopted. Before preparing the samples, a bench of 4 probes is employed and verified for passive components on L and C. This bench has led to a protocol of measurements and a protocol for evaluating the uncertainty measurement. A work devoted to the elaboration of multilayer (Cu and YIG on substrate) and their characterization by various methods is made. After studying the influence of various parameters on the morphological, crystallographic and magnetic layers, a protocol of developping a sample to obtain multilayers with good magnetic and mechanical properties is established. Two types of prototypes are produced (with a commercial thick layer and with thin films prepared in the DIOM laboratory). The comparison between simulation and experimental results in the case of thick layers is needed to validate and analyze the limitations of the adopted method. This study has identified the dimensional characteristics of micro-inductors, thin films of YIG and extracts a value of µr (around 32) after the comparison between simulations and experiments
Wacquant, François. "Elaboration et étude des propriétés de réseaux de fils magnétiques submicroniques, obtenus par multi-extrusions." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10058.
Jeannot, Cécile. "Synthèse et étude des propriétés structurales, magnétiques et chimiques de ferrates (IV), (V) et (VI) alcalins." Nancy 1, 2000. http://www.theses.fr/2000NAN10132.
Synthesis, magnetic and chemical properties of alkaline ferrate (IV), (V) and (VI) have been investigated. The first part of this report is devoted to the study of the K-Fe -O system. After a bibliographical review of potassium oxides, the syntheses carried out by. , solid-state reaction between KO2 and an iron oxide have showed that it is possible to synthesise K2FeO4 at 350°C under atmospheric pressure of oxygen, or at 450°C in a sealed "Pyrex" tube. Ferrate (V) was only detected in some of mixtures, the oxidation step (IV) was never found. The study of the Na-Fe -O system lead to evidence the existence of sodium ferrate (IV) Na4FeO4. This phase crystallises in the triclinic system and belong to the Na4MO4 series (M = transition element). In this compound, iron is in a tetrahedral site. Na4FeO4 is aritiferromagnetic below 16 K. The study of the magnetic structure shows that the exchange interactions may form via Fe-O-Na-O-Fe superexchange ways. Na4FeO4 is the first example of material which stabilises Fe (IV) in a tetrahedral site. With our experimental conditions, it was not possible to stabilise the oxidation step (VI), whereas a ferrate (V) could be detected while operating in presence of oxygen generated in-situ in the sealed Pyrex tube or in presence of hydroxide. The study of the Na-K-Fe-O system evidenced the existence of the oxidation step (V) in a compound with the K2NaFeO4 formula. Isotypic with K2NaMnO4, iron (V) is tetrahedrally co-ordinated. Paramagnetic until 6 K, the Mössbauer parameters ofthis Fe (V) high spin have been specified for the first time. The optimization of the synthesis of ferrate (VI) by electrochemical way is also described. Ferrate (IV) and (V) di sproportionate to give Fe (VI) and Fe (III). The last part of this work is devoted to the chemical propel1ies of ferrate (VI) which has potential industrial applications in the field of energy and environment
Recour, Quentin. "Étude des propriétés structurales, magnétiques et magnétocaloriques de Mn3Sn2 et de ses dérivés." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0272/document.
Not available
Cleuziou, Jean-Pierre. "Synthèse et étude des propriétés de nanoparticules magnétiques de type coeur-coquille." Toulouse 3, 2007. http://thesesups.ups-tlse.fr/156/.
Molecular electronics and spintronics are both rapidly emerging fields of nanoelectronics with a strong potential impact for the realization of new functions and devices helpful for information storage as well as quantum information. My thesis aimed at the merging of the two fields by the realization of molecular junctions that involves magnetic nanostructures. We chose two different approaches: (i) electronic transport through carbon nanotubes filled with magnetic material (hybrid carbon nanotubes), and (ii) development of a nano-SQUID with carbon nanotube Josephson junctions, which should be sensitive enough to study individual magnetic molecules that are attached to the carbon nanotube
Eyraud, Franck. "Contribution à l'élaboration et à la caractérisation de céramiques magnétiques de structure spinelle pour l'absorption d'ondes électromagnétiques." Lyon 1, 1995. http://www.theses.fr/1995LYO19007.
Orveillon-Dubajic, Glenn. "Verres métalliques : conception, synthèse et caractérisation des propriétés magnétiques et de transport." Bordeaux 1, 2008. http://www.theses.fr/2008BOR13566.
On one hand, this work deals with development and the characterisation of metallic glasses dedicated to magnetocaloric cooling or thermoelectric applications. These alloys have been designed and elaborated taking on board both application's criteria and criteria liked to the glass forming ability. On the other hand, this work has demonstrated that glass forming ability and glass forming range can be quite well predicted using thermodynamical data to evaluate the kinetics of crystallisation
Millot, Nadine. "Synthèse et propriétés de ferrites nanométriques : influence de la taille des grains et de la nature de la surface sur les propriétés structurales et magnétiques de ferrites de titane synthétisés par chimie douce et mécanosynthèse." Dijon, 1998. http://www.theses.fr/1998DIJOS053.
Maalej, Wassim. "Synthèse, caractérisations physicochimiques et structurales, propriétés et structures magnétiques de séléniates et molybdates basiques de métaux de transition." Strasbourg, 2011. https://publication-theses.unistra.fr/public/theses_doctorat/2011/MAALEJ_Wassim_2011.pdf.
Hydrothermal synthesis has been used to prepare materials based on transition metal hydroxides, synthetic analogues of minerals, for the study of their magnetic properties and structures. After a first part devoted to some general considerations, the second one shows the results obtained on compounds exhibiting the natrochalcite structure type, NaCu2H3O2(SO4)2, where the alkali metal can be Na or K, the transition metal Mn, Fe, Co or Ni, the tetrahedral anion SeO42- or MoO42-. The synthesis process was optimized in order pure samples with a good yield to be obtained. DT-TGA traces allow one to confirm the formulation and IR spectroscopy is used to identify the constituting groups. Determination of the crystalline structure from single-crystal X-ray data or neutron powder diffraction data confirms that the compounds are isostructural with natrochalcite. The structure contains infinite chains of edge-shared MO6 octahedra (M = Mn, Fe, Co, Ni). All the compounds order antiferromagnetically at low temperature. The corresponding magnetic structures appear different from one compound to another. A peculiar result is evidenced for NaFe2D3O2(MoO4)2 with the concomitant presence of two magnetic structures. The third part concerns a similar study for Co5(OH)6(SeO4)2(H2O)4 and Na2Ni(HPO3)2. The first one orders ferromagnetically at TC = 9 K, the magnetic moments being oriented along the b axis, and the second one orders antiferromagnetically at TN = 6 K. The conclusion evidences the main results and give some perspectives for further work
Gutium, Ababei Rodica. "Synthèses et études de nouveaux matériaux magnétiques et photomagnétiques." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14238/document.
The exponential growth of technological demands for information storage capacity is at the origin of the nanosciences and the development of the molecular electronics. Since more than 40 years, the main objective in this field of research is mainly to store as fast as possible more information in a smaller volume. Nowadays, chemists know how to create molecules with remarkable properties, such as Single–Molecule Magnets (SMMs) and Single–Chain Magnets (SCMs), which show magnetic bistability at low temperature (T < 10 K) providing a memory effect. Therefore, the design of novel materials with original physical properties, based on molecular magnetic objects, became the focus of many researches around the world. Following this approach, the design of SMM linked by active bridges that can switch between two magnetic states under external stimuli (temperature, pressure, light...), should favor additional properties and allow an external control (by irradiation) of the magnetic properties of the final SMM-based materials. The goal of this thesis is to organize SMMs by assembling them with two types of linkers: electron-transfer building blocks (Na2[Fe(CN)5NO]) and spin-crossover complexes ([Fe(LN5)(CN)2] and [Fe(LN3O2)(CN)2]). Three new materials obtained from the organization of [MnIII(BS)]+ complexes with the [Fe(CN)5NO]2- building-block, showed no significant photoactivity unlike the Na2[Fe(CN)5NO] precursor. Nevertheless, one of these organized systems exhibits Single-Molecule Magnet behaviour. The employed strategy to link [MnIII(BS)]+ units with photomagnetic [Fe(LN5)(CN)2] and [Fe(LN3O2)(CN)2] spin-crossover complexes, leads to nine new interesting compounds. The most significant novelty from a structural point of view is the various topologies of compounds obtained from molecular complexes to one-dimensional architectures with different arrangements. All compounds exhibit interesting magnetic properties. For example, one of the unidimensional networks shows an antiferromagnetic order followed by a slow relaxation of the magnetization that has been observed for the first time in a canted system. On the other hand, magnetic investigations under light irradiation have revealed remarkable photoinduced properties in the case of five systems based on FeII units in their low spin state. In conclusion, the synthetic strategy used in this thesis has been experimentally validated and opens new perspectives for future photomagnetic SMM and SCM systems
Leclercq, Bastien. "Unités ferromagnétiques « basse D » : frustration et transitions méta-magnétiques pour la mise en place de couplages magnétoélectriques." Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1R078.
Despite their immense interest, scope and applications of magnetoelectrics materials are still a rarity, their use has been hindered by the weakness of the polarization generated by magnetoelectric effect (e.g. BiFeO3) or the low working temperature (e.g. TbMnO3). In these compounds there is a coupling between the ferroelectric and magnetic properties that coexist simultaneously. By the existence of these couplings, these materials are of great interest in particular for electronics applications (sensors, switch, etc) and data storage, allowing to take advantages of both the electrical and magnetic properties. The capacity can thus be doubled, the information can be written electrically taking advantage of the low energy consumption, and read magnetically in a non-destructive way. However, the actual development strategy too often relies on optimization of the few well-known exploitable compounds in the literature, which does not lead to great improvement of the properties. Here we propose an original and thoughtful approach for designing magnetoelectric properties in inorganic compounds, dealing with low dimensional ferromagnetic units (0D blocks, 1D chains, 2D layers) and their alignment under field through metamagnetic transitions. Our candidates possess collinear or canted macrospins of high spin magnetic cations (M = Fe2+, Co2+, Mn2+), separated by non-magnetic and electrical insulating spacers XO4 or X2O7 (X=P, As) or large cations (A=Ba2+, Sr2+) building up the insulating properties. We give particular interest to AM2X2O8 polymorphs and their frustrated network including the first Ising 2D FM oxide BaFe2P2O8, some rare example of low-D ferromagnetic compound with incommensurate structures such as BaMX2O7, but also the M-type Hexaferrites AM12O19. We paid particular attention to the creation of intrinsic magnetic frustrations (triangular lattice and/or cationic substitution), and magnetization steps where the creation of frustrations and magnetic domains during the reorientation of spins under field is expected to be at the origin of enhanced magnetoelectric properties
Aronica, Christophe. "Ingénierie des matériaux magnétiques à base moléculaire : synthèses, structures et propriétés magnétiques de complexes de coordination d'éléments de transition d et f." Lyon 1, 2006. http://www.theses.fr/2006LYO10126.
Baazaoui, Mohamed. "Elaboration et étude des propriétés structurales, magnétiques, électriques et magnétocaloriques d’oxydes mixtes type Pérovskites." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENI106/document.
Manganites of formula La0.67Ba0.33Mn1-xFexO3 and Pr0.67Ba0.33Mn1-xFexO3 were synthesizedby ceramic route and their structural and physical properties were studied. The samples exhibit aparamagnetic-ferromagnetic transition for Fe rate £ 10% (resp. 5%) for the La (resp. Pr) series,while a typical behavior of spin glass is observed beyond this rate. This ferromagneticparamagnetictransition is associated to a metallic-semiconductor transition and a semiconductorbehavior throughout the whole temperature range is observed when there is no ferromagnetictransition. The physical properties can be interpreted by the double exchange mechanism whichweakens for increasing rates of substitution. The metallic conduction is due to electron scattering(by phonon and grain boundaries), while the semiconductor character is due to the presence ofpolarons.Magnetocaloric study for Pr0.67Ba0.33MnO3, Pr0.67Ba0.33Mn0.95Fe0.05O3, La0.67Ba0.33MnO3 andLa0.67Ba0.3Mn0.95Fe0.05O3 shows that our materials are promising to be used in magneticrefrigeration technology
Ajroudi, LIlia. "Ferrites de cobalt nanostructurés ; élaboration, caractérisation, propriétés catalytiques, électriques et magnétiques." Electronic Thesis or Diss., Toulon, 2011. http://www.theses.fr/2011TOUL0017.
This work is devoted to the synthesis and the study of the physical properties of cobalt ferrite nanomaterials. Thecobalt ferrite nanopowders (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) were synthesized by a new solvo thermal chemical route.The nanopowders are highly crystallized, very homogeneous in size and chemical composition. The nanopowderssizes are ranged from 4 nm for high cobalt content to 7 nm for low cobalt content. They are single phased, with thespinel structure, and a cell parameter varying with the cobalt content. The cobalt ferrites do not oxidize, when heatedunder air. For compositions near x=1, the cobalt ferrites are stable when heated under air up to 900°C, as for the othercompositions, phase transformations occur above 550°C.The catalytic measurements have shown the oxidation of CH4 into CO2 in presence of the catalyst for all thecompositions. Cobalt ferrite with composition x=1.8, presents the lowest activation energy and the best catalyticefficiency; this can be related to the great specific surface and the high rate of active sites for this composition.Concerning the conduction properties, the cobalt ferrites exhibit a semiconductor character up to 500-600 ° C and ametallic one above. Changes in conductivity from a composition to another are explained by changes in the number ofpairs [Co2+, Fe3+].A superparamagnetic behaviour was evidenced whatever the composition. This is due for one part to a size and shapeeffect and for the other part to different cationic distribution between tetrahedral and octahedral sites. These ferriteshave a saturation magnetization close to that of the massive state, because of the high crystallinity of the nanopowders,attributed to the synthesis method developed in this work
Mur, Jacques. "Corrélations entre propriétés structurales et magnétiques : cas d'identités quasi-isolées à faible interaction d'échange intracluster." Bordeaux 1, 1985. http://www.theses.fr/1985BOR10584.
Gercsi, Zsolt. "Influence de la structure et de la température sur les propriétés magnétiques douces de matériaux nanostructuré à base de fer et de cobalt." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2004. http://tel.archives-ouvertes.fr/tel-00133083.
Giang, Do Thi Huong. "Elaboration et étude de couches minces et multicouches à magnétostriction géante à base du composé TbFeCo." Rouen, 2005. http://www.theses.fr/2005ROUES022.
This thesis deals with the magnetostriction of the sputtered films based on the new composition Tb(Fe0. 45Co0. 55)1. 5. For the single film, a magnetostriction as high as 1140x10-6 was obtained. In Fe/Tb(Fe0. 45Co0. 55)1. 5(600nm)/Fe sandwich films, further improvement of magnetostrictive characteristics thanks to the interfacial coupling was observed. Optimal behaviors were found in 250°C-annealed sandwich with 15nm thick Fe-layer: high magnetostriction, high magnetostrictive susceptibility and low coercivity. The best performances were obtained for “Spring Magnets” magnetostrictive {Tb(Fe0. 55Co0. 45)1. 5(12nm)/Yx(Fe0. 7Co0. 3)1-x(10nm)}50 multilayers. The microstructure of the individual soft magnetic Fe or FeCo-layer depends on the Y-concentration and/or heat treatments. An excellent magnetostrictive softness with low magnetic coercivity (0. 4mT), large magnetostrictive susceptibility (29. 7x10-2 T-1) and large magnetostriction (720x10-6) was obtained in the sample with nanocrystalline soft layers (x=0. 1) named as discontinuous exchange-spring multilayers. For this system, models of the magnetization process at low and room temperature, including the interfacial domain wall, have been proposed. Using these magnetostrictive films, magnetoelectric (ME) Tb(Fe0. 45Co0. 55)1. 5/PZT composites have been fabricated that exhibit a maximum ME voltage coefficient as large as 9650 (V/m)(kA/m). Based on this ME composite, we have successfully manufactured a promising magnetic sensor with a very high ME voltage response (130mV/mT), which allows to determine not only the strength of the magnetic field but also its direction
Chausson, Sophie. "Synthèse et utilisation de matériaux hybrides lamellaires pour l'élaboration et la caractérisation de nanocomposites polymères." Caen, 2009. http://www.theses.fr/2009CAEN2047.
The aim of this work is to elaborate original lamellar hybrid materials and disperse them in a polymer matrix to obtain nanocomposites. They have been prepared using two different matrixes, one apolar (polyethylene) and one polar (polyamide-12). The two lamellar hybrid systems have been dispersed in these matrixes and studied as part of the hybrid nature. The first one, the lamellar oxide KTiNbO5, has been chemically modified with alkylamines having different carbon chain lengths in order to be compatible with the different polymer matrixes. The dispersion of such materials has allowed improving several properties like thermal stability, mechanical resistance and fire resistance. The second family studied is the copper alkylphosphonate one. They have been prepared with different alkyl chain lengths. The aim of this study is to prepare a hybrid material with a transition metal and to disperse it in the polymer matrixes. A deep structural study of the homologue series has revealed two types of compounds: hydrated for the short alkyl chains (number of carbon atoms≤10) and dehydrated for the alkyl chains with n≥10. These two structural types have shown different magnetic behaviours. Finally, the incorporation of these fillers in polyethylene and polyamide-12 has revealed that the chemical nature of the bond which links the organic part to the inorganic one of the hybrid does not allow obtaining an efficient exfoliation mechanism
Presmanes, Lionel. "Couches minces de ferrites mixtes de cobalt-manganèse et de cobaltites mixtes de fer-manganèse pour l'enregistrement magnéto-optique." Toulouse 3, 1995. http://www.theses.fr/1995TOU30162.
Chahine, Joe. "Matériaux moléculaires à propriétés multiples (transition de spin, conductivité électrique et photochromisme) : synthèse et mise en forme." Toulouse 3, 2011. http://thesesups.ups-tlse.fr/1312/.
The aim of this work is to "build" multifunctional molecular materials, by combining two molecular building blocks. The first one brings magnetic properties, like spin transition and the second one electrical or photochromic properties. These materials will also be used in devices and therefore we will focus on their processing. In this work, the spin transition compounds are FeIII complexes bearing Schiff based ligand (sal2trien, qsal, salEen) or FeII complexes containing triazoles (trz) or bi(pyrazol-1-yl)pyridyne (bpp) ligands. Electrical properties are brought by the bisdithiolene units Ni(dmit)2 (dmit = 1,3-dithia-2-thione-4,5-dihiolate) or by a coordination polymer with the linking polydentate ligands ethylenetetrathiolate (MC2S4)nx- (M = NiII, CuII, FeIII, ZnII, CoII). Photochromic mononitrosyl complexes [Fe(CN)5NO]2- or [RuCl5NO]2- are used in this work. Complexes [CTS][Ni(dmit)2]x (CTS) [FeII({4'-R}2-1-bpp)2]2+ (R = H, Br) or [FeII(3-bpp)2]2+ with x > 1 are synthesized by the combination of [Ni(dmit)]n- (n = 1, 2) with various spin transition complexes. The magnetic behavior of these compounds depends on the charge of the counter ion in the corresponding starting materials. Their electrical properties are studied: they all show semi conductive behavior. In order to resynthesize [Fe(sal2trien)][Ni(dmit)2] (a complex which presents a full spin crossover with a pronounced hysteresis loop of 30 K, centered at 245 K), five novel polymorphs were obtained. The influence of angular distortions and the nature of intermolecular contacts on the magnetic response are highlighted in these compounds. The combination of spin transition entities ([FeIII(qsal)2)]+ or [FeIII(R-salEen)2]+ (R = H ; 3-MeO)) with photochromic entities ([Fe(CN)5NO]2- or [RuCl5NO]2-) led to various compounds with remarkable magnetic properties (such as LIESST and reverse-LIESST effect). Processing of molecular materials is an important challenge. In order to obtain the material in a useable form, the spin crossover coordination polymer [Fe(Htrz)2(trz)](BF4) has been embedded in a silica matrix. The complex has been obtained as nanoparticles and retained its magnetic properties in the composite. The use of ionic liquid as structuring agent in the synthesis of (NiC2S4)n resulted in the first conductive coordination polymer as nanoparticles. We prepared stable colloid solutions containing nanoparticles with adjustable size, (unlike the "bulk" polymer) which will therefore offer new perspectives on their applications in devices and nanoelectronics industry
Dupuy, Alexandre. "Amplificateurs de puissance en technologie MIC à très haute efficacité et forte linéarité." Nice, 2006. http://www.theses.fr/2006NICE4022.
The different works conducted on this thesis were to design power amplifiers with high efficiency and high linearity by using different schemes. A power combining methods for tunnel diode oscillators using the infinite wavelength phenomenon was also realized. The first project had presented a new technique called the “Enveloppe Delta Sigma Modulation (EDSM)”, which only retains the advantages of two well known techniques, the Kahn technique (EER) and the Sigma-Delta modulation. The EDSM can achieve a high efficiency and a high linearity, and a low pulse sampling rate. In the second project, high efficient power amplifiers were realized using the interesting properties of metamaterials. The use of these metamaterial permits a size reduction of the power amplifiers and consequently of the associated losses. A class F and inverse class F power amplifier were presented different power combining methods for tunnel diode oscillators using the infinite wavelength phenomenon. Two different structures based on metamaterial were used to design the oscillator, one uses a zero-degree lines and the other one uses a zeroth order resonator
Mougin, Alexandra. "Nanosystèmes magnétostrictifs de TRFe2(110) (TR=terre rare) : croissance, morphologie et propriétés magnétiques." Nancy 1, 1999. http://docnum.univ-lorraine.fr/public/SCD_T_1999_0122_MOUGIN.pdf.
Brymora, Katarzyna. "Modélisation des propriétés magnétiques et optiques de nanoparticules d’intérêt médical." Thesis, Le Mans, 2013. http://www.theses.fr/2013LEMA1015/document.
This thesis concerns the ab initio modeling of ligands and magnetic nanoparticles used in medicine (magnetic hyperthermia, medical imaging). Calculations are performed by the Quantum Espresso software based on density functional theory and LDA+U. The goal is first to understand the binding of ligands on magnetic nanoparticles, the nature of ionicity in the particles, then to describe the change in magnetic anisotropy due to the chemical bondings on surface, and finally to describe the change in optical properties due also to the bonding of various ligands or clusters on the surface of hybrid gold and iron oxide nanoparticles
Serres, Arnaud. "Synthèse de nanoparticules magnétiques par implantation ionique de manganèse dans le GaAs : étude structurale et propriétés magnétiques." Toulouse 3, 2004. http://www.theses.fr/2004TOU30110.
Ciuculescu, Eliza-Diana. "Synthèse et étude des propriétés de nanoparticules magnétiques de type coeur-coquille." Toulouse 3, 2007. http://thesesups.ups-tlse.fr/155/.
Bimetallic magnetic nanoparticles (NPS) of core-shell type exhibit a huge potential of application due to the wide range of possible applications which can be envisaged for this type of objects. Each potential application requires particles of specifically optimised properties which requires on one hand, the development of synthesis methods and on the other, a thorough study of their properties. In this thesis we have developed methods allowing the direct synthesis of 3d/4d NPS (here Fe/Rh) of core-shell 3d@4d and 4d@3d type by reversing the kinetics of reduction of the 3d and 4d elements precursors. Under dihydrogen, iron atoms are produced faster than Rh atoms (hence formation of Rh@Fe NPs). The contrary is observed in the presence of an amine-borane complex (hence Fe@Rh NPs are formed). For these systems, which combine a magnetic metal (Fe) and a magnetically polarisable one (Rh), we have been able to study the influence of the chemical order and structure (evidenced by WAXS, XANES and EXAFS) on the magnetic properties of the NPs through SQUID, Mössbauer and XMCD measurements. In a second part we have developed the synthesis of NPs of CoAl alloy and used the higher reactivity of aluminium towards dioxygen to induce the segregation of Co and the formation of alumina in order to obtain in fine systems of Co@Al2O3 type. This segregation was followed by magnetisation measurements with a SQUID magnetometer
Desmarest, Cyrille. "Propriétés électromagnétiques de matériaux superparamagnètiques : préparation, et caractérisation magnétique et optique." Versailles-St Quentin en Yvelines, 2000. http://www.theses.fr/2000VERSA011.
Santamaria, Clément. "Phenomenes induits par les interactions en competition : coexistence de l'ordre et du desordre, ordre orientationnel dans des films minces magnetiques." Cergy-Pontoise, 1998. http://www.theses.fr/1998CERG0051.
Ajroudi, LIlia. "Ferrites de cobalt nanostructurés ; élaboration, caractérisation, propriétés catalytiques, électriques et magnétiques." Thesis, Toulon, 2011. http://www.theses.fr/2011TOUL0017/document.
This work is devoted to the synthesis and the study of the physical properties of cobalt ferrite nanomaterials. Thecobalt ferrite nanopowders (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) were synthesized by a new solvo thermal chemical route.The nanopowders are highly crystallized, very homogeneous in size and chemical composition. The nanopowderssizes are ranged from 4 nm for high cobalt content to 7 nm for low cobalt content. They are single phased, with thespinel structure, and a cell parameter varying with the cobalt content. The cobalt ferrites do not oxidize, when heatedunder air. For compositions near x=1, the cobalt ferrites are stable when heated under air up to 900°C, as for the othercompositions, phase transformations occur above 550°C.The catalytic measurements have shown the oxidation of CH4 into CO2 in presence of the catalyst for all thecompositions. Cobalt ferrite with composition x=1.8, presents the lowest activation energy and the best catalyticefficiency; this can be related to the great specific surface and the high rate of active sites for this composition.Concerning the conduction properties, the cobalt ferrites exhibit a semiconductor character up to 500-600 ° C and ametallic one above. Changes in conductivity from a composition to another are explained by changes in the number ofpairs [Co2+, Fe3+].A superparamagnetic behaviour was evidenced whatever the composition. This is due for one part to a size and shapeeffect and for the other part to different cationic distribution between tetrahedral and octahedral sites. These ferriteshave a saturation magnetization close to that of the massive state, because of the high crystallinity of the nanopowders,attributed to the synthesis method developed in this work
Villette, Carole. "Elaboration et caractérisation de fines particules de ferrites spinelles substitués (cuivre/cobalt/manganèse) : relations structure-propriétés magnétiques." Toulouse 3, 1995. http://www.theses.fr/1995TOU30286.