Dissertations / Theses on the topic 'Mossbauer spectroscopy'
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1
Cowie, Bruce C. C. "Novel applications of Mossbauer spectroscopy." Thesis, Heriot-Watt University, 1988. http://hdl.handle.net/10399/934.
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Sheen, Nicholas I. "Mossbauer spectroscopy of linear chain systems." Thesis, University of Canterbury. Physics, 1994. http://hdl.handle.net/10092/8074.
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Since the prediction by Villain in 1975 of moving magnetic domain walls (or solitons) in 1-dimensional Ising-like antiferromagnets, there has been interest in compounds with these properties. Mössbauer spectra of CsCo₀.₉₉Fe₀.₀₁Cl₃ in the magnetically ordered phases below TN₁ = 21.2 K were analysed by Ward et al (1987) assuming that only the two lowest energy electronic states of the ⁵⁷Fe⁺ ion were significantly occupied (the 2-level relaxation model). This assumption is unreliable above approximately 18 K because it was estimated that the third lowest-lying electronic state of Fe⁺ was significantly occupied at those temperatures. Nevertheless, it was found that two relaxation processes were present, one attributed to moving domain walls, and the other to transitions between the low-lying electronic states of the Fe⁺ ion.
In this work the 2-level relaxation model was extended to include the third lowest-lying electronic state of the Fe⁺ ion. A further extension, the combined relaxation model, enables Mössbauer spectra to be fitted when both 3-level electronic relaxation and relaxation due to moving domain walls occur with similar rates at the same ⁵⁷Fe⁺ site. The quasi 1-dimensional Ising-like antiferromagnetic salt NH₄CₒCl₃ doped with less than 1 atomic % ⁵⁷Fe⁺ was synthesised, and Mössbauer spectra were taken at temperatures between 1.3 and 250 K. The Mössbauer spectra of both CₛC₀₁₋ₓFeₓCl₃ and NHâ‚„Coâ‚ -â‚“Feâ‚“Cl3 in the magnetically ordered phases were analysed using the 2-level, 3-level and combined relaxation models. Although good fits to the Mössbauer spectra of CₛC₀₁₋ₓFeₓCl₃ and NH₄FeₓCl₃ were obtained using all the relaxation models, the combined relaxation model was the most satisfactory since the assumptions of this model were not invalidated by the parameters obtained from the fits. The soliton relaxation rates obtained were much slower than those predicted theoretically and found from other experiments on CsCoCl3.
One reason for this which is examined in this thesis is that the determined rates are unduly affected by the approximations made in the relaxation models. Another possible explanation of the discrepancy is that the presence of iron in the cobalt chains changes the soliton dynamics.
In order to study the effect of doping NNH₄FeₓCl₃with Fe⁺, the isomorphous crystal NH₄FeₓCl₃ was grown. The magnetic structure of NH₄FeₓCl₃ is expected to be governed by ferromagnetic intra-chain interactions and weaker antiferromagnetic inter-chain interactions. The linewidth broadening of the Mössbauer spectra of NH₄FeₓCl₃ at temperatures up to 10 K is evidence for the existence of magnetic correlations above the Neel temperature (1.7 K). The 4.2 and 1.3 K spectra show that a distribution of magnetic hyperfine fields B are present, possibly due to incommensurate magnetic ordering. At 4.2 K the main components of the Mössbauer spectrum are approximately 79 % with B = 0 and 21 % with B = 5.32 T. At 1.3 K the main components of the Mössbauer spectrum are approximately 72 % with B = 5.2 T and 28 %with B = 0. The non-magnetic subspectrum at 1.3 K may be caused by cancellation between the different components of the magnetic hyperfine field.
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Thorpe, Stephen C. "Surface corrosion studies by Mossbauer spectroscopy." Thesis, Sheffield Hallam University, 1987. http://shura.shu.ac.uk/20440/.
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Transmission [57]Fe Mossbauer Spectroscopy has been used to investigate two standard iron oxides and two environmental corrosion products in the temperature range 10-300 Kelvin. This was achieved using a specially developed Air Products cryogenic refrigeration system using gaseous helium as the refrigerant - thereby removing the requirement of an expensive liquid helium facility normally required for low temperature work. Characteristic spectra and transitions were observed for both the standard oxides. The environmental corrosion products demonstrated the differences in observed spectra between a sample which exhibits only bulk properties and one in which the particle size distribution within the sample is such that relaxation phenomena become important. The interpretations-made from the variable temperature Mossbauer data were confirmed by the complementary technique of X-ray diffraction. Conversion electron Mossbauer spectroscopy (C.E.M.S.) and conversion X-ray Mossbauer spectroscopy (C.X.M.S.) backscatter techniques have also been developed and are now routinely available in our laboratory. The greater escape depth of the conversion X-ray allows the C.X.M.S. method to be used to record spectra from samples to which a protective layer such as a paint, varnish, grease or oil layer has been applied. To ensure a surface sensitive signal, the substrate surfaces had to be enriched in the Mossbauer isotope 57Fe. This was achieved by vacuum evaporation of 57Fe onto the substrate surface and subsequent diffusion of the 57Fe into the near surface region - this diffusion had to be accomplished without oxidising the surface. Samples thus prepared were subsequently exposed to aggressive atmospheres and their CXM spectra recorded. The limitation of the method is that only room temperature spectra can be recorded at present and difficulties are encountered in the assignment of spectra that contain only quadrupole doublets.
4
Al-Rawwas, Ahmed Dhofar. "A Mossbauer spectroscopy study of strontium iron oxides." Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385228.
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Younis, Adbelhamid Mohamed. "Characterisation of iron in Libyan soil using Mossbauer spectroscopy." Thesis, University of St Andrews, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.731715.
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Abrahams, I. "Mossbauer spectroscopic and structural studies of tin materials." Thesis, City University London, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375839.
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Moody, Kevin L. "Moessbauer spectroscopy on the Apple computer." Virtual Press, 1988. http://liblink.bsu.edu/uhtbin/catkey/543988.
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Software for Moessbauer spectroscopy has been developed for use on the Apple computer. This software is capable of collecting and fitting Moessbauer data when the Apple computer is interfaced with the ND2200 series multichannel analyzer. The software was tested in a study of the feasibility of using Moessbauer spectroscopy to study glass. Results indicate that iron in brown commercial glass and the volcanic glasses behaves similarly. This study concludes that Moessbauer spectroscopy is a promising method for the study of natural and archeological glasses and quality control in the manufacture of commercial glass.Department of Physics and Astronomy
8
Skinner, Stephen John. "Synthesis and characterisation of metal oxides and metal doped variants." Thesis, Open University, 1997. http://oro.open.ac.uk/57713/.
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Kurokuzu, Masayuki. "Studies on Iron Chalcogenide by Mossbauer Spectroscopy and Nuclear Resonant Inelastic Scattering." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188478.
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McLean, Andrew Lister. "Applications of maximum entropy data analysis." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319161.
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Arelaro, Amanda Defendi. "Síntese e caracterização de nanopartículas de ferritas." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-10032009-124743/.
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Nanopartículas magnéticas têm sido extensamente estudadas não só pelas inúmeras possibilidades de aplicações nas áreas tecnológica e biomédica, mas também do ponto de vista acadêmico, visando a uma compreensão das alterações de suas características físicas nesta escala de tamanhos. Sintetizar nanopartículas com baixa dispersão de tamanhos e homogeneidade morfológica, estrutural e estequiométrica é de grande importância para o estudo de suas características magnéticas. No presente trabalho, amostras de diferentes ferritas (MeFe2O4, M = Fe, Co e Ni) foram produzidas por um método de síntese química que envolve a decomposição do acetilacetonato de Fe em altas temperaturas na presença de um álcool de cadeia longa e dos surfactantes e estabilizantes oleilamina e ácido oléico. Como o objetivo deste trabalho é estudar a variação das propriedades magnéticas em função do metal M, foi selecionada uma amostra de cada material com diâmetros médios próximos entre si (entre 5,7 e 8,1 nm). A caracterização estrutural foi feita por microscopia eletrônica de transmissão de baixa e alta resolução, além de difração de raios-X. As propriedades magnéticas foram caracterizadas por medidas de susceptibilidade ac em função da freqüência e temperatura, magnetização em função do campo magnético e espectroscopia Mössbauer em campos magnéticos aplicados entre 0 e 12 T. As amostras apresentaram estreita distribuição de tamanhos, ausência de aglomerados, homogeneidade morfológica e altíssima cristalinidade. Das medidas magnéticas foram obtidos, por dois métodos distintos, valores da constante de anisotropia magnética de 2,56,1 para M = Ni, 23,019,3 para M = Fe e 50,042,3 para M = Co (valores em 105 erg/cm3). Estes valores estão acima do esperado para os respectivos materiais bulk, indicando uma contribuição à anisotropia além da magnetocristalina. Os valores de magnetização de saturação a 4,2 K (17,1, 74,0 e 30 emu/g para M = Fe, Co e Ni) estão em geral abaixo do valor esperado para os respectivos materiais massivos. Curvas MH obtidas acima da temperatura de bloqueio mostram o comportamento superparamagnético das partículas. Espectros Mössbauer coletados sob altos campos confirmaram a alta cristalinidade das partículas, excluindo a existência de uma camada superficial de spins desalinhados.Magnetic nanoparticles have been extensively investigated, motivated by their potential technological and biomedical applications as well as in search of a better understanding of the physical properties modifications induced by nanoscale size. Synthesizing nanoparticles with a narrow size dispersion and good morphological, structural and stoichiometric homogeneity is an important requisite for such studies. In this work, nanocrystalline samples of different ferrites MFe2O4 (M = Fe, Co and Ni) have been prepared by a chemical synthesis method involving high-temperature decomposition of Fe acetylacetonate in the presence of a long-chain alcohol and of surfactant and stabilizing agents oleylamin and oleic acid. The main objective of this work being a comparative study of the effect of the M element on the magnetic properties, one sample was selected for each compound, with close mean diameters (5.7-8.1 nm). The structural characterization was carried out by low and high-resolution TEM and x-ray diffraction. Magnetic properties were characterized by frequency and temperature dependent ac susceptibility, magnetization vs. field measurements, and Mössbauer spectroscopy in applied magnetic fields ranging from 0 to 12 T. All samples exhibited narrow size distributions, no particle agglomeration, morphological homogeneity, and an excellent crystallinity. Magnetic anisotropy constants were obtained from magnetic data by two different methods, giving 2.5-6.1 for M = Ni, 23.0-19.3 for M = Fe, and 50.0-42.3 for M = Co (all data in 105 erg/cm3). These results are higher than those expected for the respective bulk materials, indicating an additional contribution to purely magnetocrystalline anisotropy. Saturation magnetization values at 4.2 K (17.1, 74.0 and 30 emu/g por M = Fe, Co and Ni) are generally below the corresponding bulk values. Magnetization curves above the blocking temperature exhibit superparamagnetic behavior. High-field Mössbauer spectra do not show a superficial shell of misaligned spins, thus confirming the high crystallinity of the nanoparticles.
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Tabbakh, Shabani Amir Ali. "Mineral chemistry and Mossbauer spectroscopy of micas from granitic rocks of the Canadian Appalachians." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0018/NQ45196.pdf.
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El, Khalifi Mohammed. "Étude théorique des matériaux d'électrode positive négative pour batteries Li-ion." Thesis, Montpellier 2, 2011. http://www.theses.fr/2011MON20200.
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Ce mémoire est consacré à l'étude théorique des matériaux de cathode pour batteries Li-ion de structure olivine LiMPO4 (M=Mn, Fe, Co, Ni), des phases délithiées MPO4 et des phases mixtes LiFexMn1-xPO4, FexMn1-xPO4 et LiFexCo1-xPO4. La stabilité des phases magnétiques et les paramètres de maille théoriques ont été déterminés par la méthode des pseudopotentiels et comparés aux données expérimentales. Les structures électroniques ont été calculées par une méthode « tout électron » et analysées en termes d'hybridation des orbitales atomiques Ces résultats ont permis d'interpréter les spectres de photoélectrons X et d'absorption des rayons X, en particulier les modifications réversibles associées aux cycles de lithiation/délithiation. Les effets de la polarisation de spin et de la corrélation électronique ont été discutés. Enfin, le calcul des paramètres Mössbauer du 57Fe a montré qu'un accord quantitatif entre les résultats théoriques et les données expérimentales nécessitait la prise en compte de ces deux effets. Ce type de calcul a permis de prédire et d'expliquer que la transformation LiFePO4FePO4 s'accompagnait de la variation du gradient de champ électrique Vzz d'une extrémité à l'autre de l'échelle Mössbauer pour 57FeThis thesis is devoted to the theoretical study of the cathode materials for Li-ion batteries with olivine structure LiMPO4 (M=Mn, Fe, Co, Ni), the delithiated phases MPO4 and the mixed phases LiFexMn1-xPO4, FexMn1-xPO4 and LiFexCo1-xPO4. The magnetic phase stability and lattice parameters were theoretically determined from pseudopotential calculations and the results have been compared with experiments. Electronic structures were obtained from all electron calculations and analyzed in terms of orbital hybridization. The results have been used for the interpretation of X-ray photoemission and X-ray absorption spectra, especially changes due to lithiation/delithiation cycles. Effects of spin polarization and electronic correlation on the electronic structures have been also discussed. It has been shown that ab initio calculations of the 57Fe Mössbauer parameters also require these two effects in order to obtain a quantitative agreement with experiments. Finally, it was found that LiFePO4FePO4 transformation involves a dramatic change of the electric field gradient VZZ from one end to the other of the 57Fe Mössbauer scale
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Elwell, S. "A study of europium compounds in unusual oxidation states by Mossbauer spectroscopy and other techniques." Thesis, University of Kent, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235331.
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Hudder, Brandon Neal. "Spectroscopic and analytical characterization of the distribution of iron in intact mitochondria from Saccharomyces cerevisiae." Diss., Texas A&M University, 2006. http://hdl.handle.net/1969.1/4342.
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Electron paramagnetic resonance (EPR) and Mössbauer spectroscopy were used to examine the distribution of iron in mitochondria from Saccharomyces cerevisiae. These organelles were packed into EPR and Mössbauer cuvettes, affording spectra with unprecedented signal/noise ratios. EPR spectra of as-isolated intact mitochondria exhibited fourteen distinct signals, some of which were assigned according to previously reported g-values obtained using isolated proteins. Signals from adventitious manganese (II) and iron (III) were largely removed when mitochondria were isolated in buffers supplemented with the metal chelators EDTA or EGTA. Signals were simulated and intensities were quantified to afford spin concentrations and estimates of the concentration of EPR-active species in mitochondria. The effects of treating samples with chemical modifiers were examined. Packed samples were analyzed for protein and metal content, affording averaged values of 50 mg/mL [protein], 590 õM [Fe], 340 õM [Cu], and 17 õM [Mn]. 57Fe-enriched intact mitochondria isolated in the presence of metal chelators exhibited Mössbauer spectra dominated by three components. Approximately 60% of the 57Fe in the sample gave rise to a quadrupole doublet, most of which was diamagnetic. The parameters of this doublet are typical of S = 0 [4Fe-4S]2+ clusters and S = 0 ferrous heme groups. Spectra of samples reduced with dithionite, pH 8.5, suggested that at least half of this doublet arose from [4Fe-4S]2+ clusters. The second major component exhibited in the Mössbauer spectra arose from high-spin ferrous ions (10%-30%). The third major component (15%) came from iron exhibiting magnetic hyperfine interactions and is likely reflected in the Fe-containing species observed by EPR. The results presented here suggest that mitochondria contain ~ 600 õM of Fe overall, ~ 200 â 400 õM organized as [4Fe-4S]2+ clusters, with about 25 õM due to the [4Fe-4S]2+ cluster of aconitase. Approximately 60 õM â 200 õM of the Fe in mitochondria is high-spin ferrous ions, ~ 40 õM as the Rieske S = 1/2 [2Fe-2S]+ cluster of cytochrome bc1, and ~20 õM as the S = 1/2 [2Fe-2S]+ cluster of succinate dehydrogenase. The high-spin ferric hemes of the a3:CuB site of cytochrome oxidase and cytochrome c peroxidase each account for ~ 4 õM of Fe.
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Piilonen, Paula C. "Crystal chemistry, Mossbauer spectroscopy and paragenesis of astrophyllite group minerals from over- and undersaturated alkaline rocks." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/9322.
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The crystal-chemistry and paragenesis of astrophyllite group minerals (AGM) from over- and undersaturated alkaline rocks has been documented by a combination of electron microprobe analyses, single-crystal and powder X-ray diffraction, Mossbauer spectroscopy, Fourier-transform infrared spectroscopy, nuclear reaction analysis, thermal gravitational analysis, thermal decomposition, wet-chemical methods and optical measurements. A standardized general formula for AGM has been developed, based on 31 anions, and is of the form A2BC7D 2T8O26(OH)4X 0-1, where [10]--[13]A = K, Rb, Cs, H3O+, H2O, or □; [10] B = Na or Ca; [6]C = Mn, Fe2+ Fe3+ Na, Mg, or Zn; D = [6]Ti, Nb, or Zr; [4]T = Si or Al and X = &phis; = F, OH, O, or □. Results from Mossbauer spectroscopy, bond valence sums and thermodynamic calculations indicate F to order at X [&phis;(16)] whereas the monovalent anion sites in the O-sheet are host solely to OH- . On this basis, eight species and two AGM polytypes are recognized, the most recent, niobokupletskite, identified from Mont Saint-Hilaire during the course of this study. The AGM heterophyllosilicate structure consists of two composite sheets stacked along [001] in a 2:1 ratio resulting in a layered HOH structure. Single-crystal X-ray refinements indicate the existence of two kupletskite polytypes, kupletskite-1A and kupletskite-Ma2b2c, the result of polytypic stacking of identical HOH layers. Mossbauer spectroscopy indicates all Fe to be present in the O-sheet, and Fe3+/Fe tot ratios in AGM to range from 0.01 to 0.21, corresponding to 0.05 to 0.56 apfu Fe3+, confirming that Fe 2+ is the dominant valence state for iron in the AGM structure. AGM from oversaturated alkaline intrusions are characterized by a restricted range of Mn/Mn+Fetot (0.03 to 0.69) and enrichments in K, Rb, Ti (with positive values of Nb-Zr) and Si. AGM from undersaturated intrusions display a wide range in Mn/Mn+Fetot, (0.09 to 1.00) and have been further subdivided into a kupletskite subgroup (Mn/Mn+Fetot ≥ 0.50) and an astrophyllite subgroup (Mn/Mn+Fetot < 0.50). Kupletskite subgroup samples are enriched in Na, Mn, Zn, Fe3+, Nb and Zr (with positive values of Nb-Zr), whereas astrophyllite subgroup samples are enriched in K, Ca, Fe2+, Ti, Zr (with negative values of Nb-Zr) and F. Crystal-chemical parameters in AGM (such as Mn/Mn+Fetot and Nb/Nb+Zr) can be used as petrogenetic indicators. At Mont Saint-Hilaire (Quebec), two distinct paragenetic trends are recognized in the AGM population: (1) an oxidizing magmatic to post-magmatic oxidizing trend resulting in enrichment of the AGM in Na, Mn, Fe3+ and Nb, and (2) a reducing trend resulting in enrichment in Ca, Fe2+, Zr and F by hydrothermal or metasomatic processes. The second evolutionary trend is thought to be the result of interaction of an exsolved magmatic fluid with either meteoric waters or sediments. Both trends lend evidence for late-stage mobilization and concentration of high field-strength elements (such as Nb and Zr) in highly alkaline systems.
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Evans, James R. "The electric field gradient of octahedral iron in layer silicates: theory with applications to Mossbauer spectroscopy." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/22144.
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Zagorskiy, D. L., V. V. Korotkov, V. N. Kudryavtsev, S. A. Bedin, S. N. Sulyanov, K. V. Frolov, A. I. Vilenski, and B. V. Mchedlishvili. "Metallic Nanowires on the Base of Porous Matrixes: Obtaining by Galvanic Replication, Structure and Some Properties." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/34949.
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In this work nanowires (Co, Ni and Fe) were obtained via template synthesis, using etched track polymer matrix. The peculiarity of electrodeposition of Co and Ni was investigated and discussed: When filling
the pores of a small diameter (0.1 and 0.2 microns) the dependence of current on time passes through a
minimum. It can be supposed that the difficulties, appearing while filling nanosized pores, are related to
the peculiarities of diffusion in narrow channels. The electrolyte for Fe deposition into nanosized pores was
selected, the necessity of agitation was demonstrated. The results of X-rays analysis demonstrate that obtained wires have polycrystalline structure, which slightly depends on the deposition voltage. Mossbauer
spectroscopy was used for investigation of Fe samples. The obtained sextet corresponds to α-Fe with polycrystalline structure. Two types of Fe atoms were found. The presence of two types of oxides was also detected.
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Dou, Lixin. "Applications of Bayesian inference methods to time series data analysis and hyperfine parameter extractions in Mossbauer spectroscopy." Thesis, University of Ottawa (Canada), 1999. http://hdl.handle.net/10393/8483.
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The Bayesian statistical inference theory is studied and applied to two problems in applied physics: spectral analysis and parameter estimation in time series data and hyperfine parameter extraction in Mossbauer spectroscopy. The applications to spectral analysis and parameter estimation for both single- and multiple-frequency signals are presented in detail. Specifically, the marginal posterior probabilities for the amplitudes and frequencies of the signals are obtained by using Gibbs sampling without performing the integration, no matter whether the variance of the noise is known or unknown. The best estimates of the parameters can be inferred from these probabilities together with the corresponding variances. When the variance of the noise is unknown, an estimate about the variance of the noise can also be made. Comparisons of our results have been made with results using the Fast Fourier Transformation (FFT) method as well as Bretthorst's method. The same numerical approach is applied to some complicated models and conditions, such as periodic but non-harmonic signals, signals with decay, and signals with chirp. Results demonstrate that even under these complicated conditions the Bayesian inference and Gibbs sampling can still give very accurate results with respect to the true result. Also through the use of the Bayesian inference methods it is possible to choose the most probable model based on known prior information of data, assuming a model space. The Bayesian inference theory is applied to hyperfine parameter extraction in Mossbauer spectroscopy for the first time. The method is a free-form model extraction approach and gives full error analysis of hyperfine parameter distributions. Two applications to quadrupole splitting distribution analysis in Fe-57 Mossbauer spectroscopy are presented. One involves a single site of Fe3+ and the other involves two sites for Fe3+ and Fe2+. In each case the method gives a unique solution to the distributions with arbitrary shape and is not sensitive to the elemental doublet parameters. The Bayesian inference theory is also applied to the hyperfine field distribution extraction. Because of the complexity of the elemental lineshape, all the other extraction methods can only use the first order perturbation sextet as the lineshape function. We use Blaes' exact lineshape model to extract the hyperfine field distribution. This is possible because the Bayesian inference theory is a free-form model extraction method. By using Blaes' lineshape function, different cases of orientations between the electric field gradient principle axis directions and the magnetic hyperfine field can be studied without making any approximations. As an example the ground state hyperfine field distribution of Fe65Ni35 Invar is extensively studied by using the method. Some very interesting features of the hyperfine field distribution are identified.
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Zagorskiy, D. L., V. V. Korotkov, V. N. Kudryavtsev, S. A. Bedin, S. N. Sulyanov, K. V. Frolov, V. V. Berezkin, and B. V. Mchedlishvili. "Matrix Synthesis of Magnetic Nanowires." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35260.
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In this work nanowires of magnetic metals (Co,Ni and Fe) were obtained via matrix synthesis, using etched track polymer template. The new data on electrodeposition of Ni was obtained. Two effects- the growth rate decrease (while the growing metal nanowires are filling the pores) and current density in-crease were investigated and discussed.
The results of X-rays analysis obtained using synchrotrone source demonstrated the dependence of structure and composition of nanowires on the deposition voltage. Mossbauer spectroscopy was used for in-vestigation of Fe samples. The obtained data are in good agreement with X-rays results.
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Oudah, Mohamed. "Antiperovskite Oxide Sr3-xSnO: Discovery of Superconductivity and Its Evolution with Deficiency." Kyoto University, 2018. http://hdl.handle.net/2433/232225.
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Schaefer, Michael Vernon. "Spectroscopic evidence for interfacial Fe(II)-Fe(III) electron transfer in clay minerals." Thesis, University of Iowa, 2010. https://ir.uiowa.edu/etd/596.
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Although interfacial electron transfer has been shown to occur for sorbed Fe(II) and Fe-oxides, it is unclear if a similar reaction occurs between sorbed Fe(II) and Fe(III)-bearing clay minerals. Here, we use the isotope specificity of 57Fe Mössbauer spectroscopy to demonstrate electron transfer between sorbed Fe(II) and structural Fe(III) in a nontronite clay mineral (NAu-2). Appearance of an Fe(II) doublet in the NAu-2 spectra after reaction with aqueous 56Fe(II) (56Fe is transparent in Mössbauer spectra) provided evidence for reduction of structural Fe(III). Mössbauer spectra using enriched 57Fe(II) reveal that Fe(II) is oxidized upon sorption to NAu-2, and the oxidation product of this reaction is a ferric oxide with spectral parameters similar to lepidocrocite. The reduction of structural Fe(III) by Fe(II) induces electron delocalization in the clay structure, which we observe by variable-temperature Mössbauer spectra and macroscopic color change indicative of Fe(II)-Fe(III) pairs. The extent of structural Fe(III) reduction in NAu-2 is equal to the amount of Fe(II) sorbed until approximately 15% reduction, after which point reduction is no longer concomitant with the amount of sorbed Fe(II).
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Sheffer, Abigail Anne. "Chemical Reduction of Silicates by Meteorite Impacts and Lightning Strikes." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/194729.
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A suite of lightning strike glasses and unmelted starting materials has been studied by electron microscope and Mossbauer spectroscopy to determine Fe oxidation states. Nine of eleven samples are reduced compared to the starting materials; four of the glasses contain Fe0. Only one sample contained evidence of reduction by carbon, and the results support the reduction of Fe as intrinsic to the rapid, high temperature processing during lightning strikes.A thermodynamic modeling code is used to model the formation of moldavite tektites and the reduction of Fe from sediments around the Ries crater. During isentropic cooling from a strong shock, Fe3+ is reduced to Fe2+ at all modeled conditions. The best matches to an average moldavite composition and the compositions of the Bohemian and Bohemian:Radomilice sub-strewn fields occur with a mixture of surface and subsurface sands along a 4500 J/kg-K isentropic cooling path, consistent with an asteroid impact. The Lusatian and Moravian sub-strewn fields are better represented by starting materials of entirely surface sands, consistent with the uppermost layers of surface material having traveled the farthest from the impact.The thermodynamic code is also used to investigate the formation of lunar regolith agglutinates and reduction of Fe to Fe0. Forming Fe0 requires assuming Fe0 is miscible in silicate liquid at elevated temperatures and pressures. When Fe0 is included in the liquid solution, it is stable at modeled conditions. Simple separation of liquid from vapor is not sufficient to reproduce agglutinate glass. When the vapor phase is allowed to partially redeposit and some Fe0 is directly condensed from vapor, the resulting liquid better reproduces mare agglutinate glasses. This model cannot reproduce highland agglutinate glass, because the Al concentration remains too high in the liquid. The best match to mare glass is produced using the <10 µm fraction of the mare soil along the 8000 J/kg-K cooling isentrope at 100 bars, 4370 K with 95% vapor redeposition and 50% of the Fe(g) directly condensed as Fe0. The reduced fulgurite samples and the results of the impact models suggest that Fe reduction is intrinsic to the rapid, high temperature processing of silicates.
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Voyer, Christian. "A 119Sn and 155 Gd Mossbauer spectroscopy and neutron diffraction study of R3T4X4 (R=rare-earth, T=Cu,Ag, X=Sn, Ge) compounds." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104480.
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The isostructural R3T4X4 (R: rare earth, T:Mn,Pd,Cu,Ag, X:Si,Ge,Sn) family of compounds have been extensively studied recently due to the rich variety of magnetic behaviour exhibited: the two rare earth sublattices often order with quite different moment values and distinct magnetic structures. In some cases the rare earth sites will also have quite different ordering temperatures. Several of the series, R3Cu4Sn4, R3Ag4Sn4 and R3Cu4Ge4, appear not to follow the expected de Gennes scaling law of transition temperatures despite the structural uniformity of the system. Moreover, the system suffers from a common problem in rare earth intermetallic systems: an important lack of data and understanding of the Sm and Gd members.Capitalizing on the presence of Sn in many of these compounds, we have used 119Sn Mossbauer spectroscopy as a probe of local magnetism at the Sn sites in the structure. Although Sn carries no magnetic moment, a transferred field from the rare earth neighbours is observed, as both Sn sites in the structure have nearest neighbours from both rare earth sublattices. We also performed 155Gd Mossbauer spectroscopy on three Gd compounds, probing the local magnetism at the 155Gd nuclei directly. Using the newly developed flat plate mounting for highly absorbing samples, we performed neutron diffraction on several Sm and Gd compounds to probe the long range spatial symmetry of the rare earth magnetic moments. The Mossbauer spectroscopy and neutron scattering results were then combined as verification of consistency, but more importantly as complementary sources of magnetic information allowing us to draw conclusions that otherwise could not be drawn with either of the experimental techniques alone.We find that a simple isotropic hyperfine field transfer model successfully describes the 119Sn Mossbauer spectra of several R3T4Sn4 (T:Cu,Ag) compounds. 119Sn Mossbauer spectroscopy also reveals important magnetic interactions previously missed: Nd3Cu4Sn4 data exhibits a clear magnetic contribution at temperatures at which neutron diffraction data did not, while Ho3Cu4Sn4 exhibited magnetic interactions above the ordering temperature determined by neutron diffraction. The Sm3Ag4Sn4 and Sm3Cu4Sn4 compounds proved to behave entirely differently than previously thought: the former undergoes magnetic ordering at 26K rather than 9K, and shows evidence of anisotropic field transfer, while Sm3Cu4Sn4 fails to order and instead exhibits slow moment dynamics. The Gd compounds also yield surprising results as Gd3Cu4Ge4 and Gd3Ag4Sn4 order at far higher temperature than previously thought, while Gd3Cu4Sn4 exhibits the most complex 119Sn Mossbauer spectrum due only to the moments at the Gd-2d site. The R3T4X4 system remains highly magnetically complex and diverse, however the magnetic landscape has been significantly altered. The flat plate mounting technique for neutron diffraction, especially when combined with Mossbauer spectroscopy data, allows for the determination of the magnetic structures of Sm3Ag4Sn4 as well as Gd3Ag4Sn4 and partially of Gd3Cu4Sn4, showing great promise as an important new experimental tool.La famille de composés R3T4X4 (R: terre rare, T: Mn, Pd, Cu, Ag, X: Si, Ge,Sn) adopte uniformément la structure orthorhombique de type Gd3Cu4Ge4 (groupe d'espace Immm, # 71). Ces composés ont été étudiés récemment en raison de la riche variété de comportements magnétiques observés: chaque sous-réseau de terre rare s'ordonne avec des valeurs de moment magnétique très différentes et adoptent des structures magnétiques distinctes. Dans certains cas, les deux sites de terres rares auront également des températures d'ordre magnétique très différentes. Plusieurs membres de la série, R3Cu4Sn4, R3Ag4Sn4 et R3Cu4Ge4, ne semblent pas suivre la loi d'échelle de de Gennes des températures de transition magnétique, malgré l'uniformité structurelle du système. De plus, le système souffre d'un problème commun parmi les systèmes intermétalliques de terre rare: un manque important de mesures et compréhension des membres Sm et Gd du système.Capitalisant sur la présence de Sn dans plusieurs de ces composés, nous avons effectué des mesures de spectroscopie Mossbauer 119Sn comme une sonde locale du magnétisme aux sites Sn dans la structure. Bien que le Sn ne comporte pas de moment magnétique, un champ transféré des terres rares voisines est observé, vu que les deux sites Sn dans la structure ont des voisins proches des deux sous-réseaux de terres rares. Nous avons également effectué des mesures de spectroscopie Mossbauer 155Gd sur trois composés de Gd, pour sonder le magnétisme local aux noyaux 155Gd directement. En utilisant la plaque de montage nouvellement mise au point pour des échantillons hautement absorbants, nous avons procédé à la diffusion neutronique sur plusieurs composés de Sm et Gd pour sonder la symétrie spatiale à longue portée des moments magnétiques des terres rares. La spectroscopie Mossbauer et les résultatsde diffusion neutronique ont ensuite été combinés premièrement pour une vérification de cohérence, mais avant tout comme des sources complémentaires d'information magnétique qui nous permettent de tirer des conclusions qui ne pourraient autrement pas être établies avec l'une ou l'autre de ces techniques à elles seule.Nous constatons qu'un simple modèle de transfer isotropique de champ magnétique hyperfin décrit avec succès les spectres Mossbauer 119Sn de plusieurs composés R3T4Sn4 (T: Cu, Ag). La spectroscopie Mossbauer 119Sn révèle aussi d'importantes interactions magnétiques inconnues auparavant: la présence d'une contribution magnétique claire de Nd3Cu4Sn4 à des temp ératures auxquelles la diffusion neutronique n'en detecte aucune, tandis que Ho3Cu4Sn4 exhibe des interactions magnétiques au dessus de la température d'ordre magnétique déterminée par diffusion neutronique. Il s'avère que les composés Sm3Ag4Sn4 et Sm3Cu4Sn4 ont un comportement très différent de ce qui était cru auparavant: le premier subit un ordonnement magnétique à 26K au lieu de 9K, et montre des signes de transfert de champ magnétique hyperfin anisotrope, alors que le deuxième ne parvient pas à l'ordre magnétique mais exhibe une dynamique de moment magnétique lente. Les composés de Gd révèlent aussi des résultats surprenants alors que Gd3Cu4Ge4 et Gd3Ag4Sn4 ont une température d'ordonnement magnétique beaucoup plus élevée qu'on ne le pensait, et que Gd3Cu4Sn4 exhibe lesspectres Mossbauer 119Sn les plus complexes du uniquement aux moments magnétiques du site Gd-2d.Le système R3T4X4 reste très complexe et diversifié d'un point de vue magnétique, mais le paysage magnétique a été significativement modifié. La technique de plaque de montage pour la diffusion neutronique, en particulier lorsqu'elle est combiné avec les données de spectroscopie Mossbauer, permet la détermination des structures magnétiques des composés Sm3Ag4Sn4 et Gd3Ag4Sn4, et partiellement du composé Gd3Cu4Sn4, et reste prometteuse comme un nouvel outil expérimental important.
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Kuznetsova, Yelena Anatolyevna. "Atomic and nuclear interference phenomena and their applications." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2428.
Full textAbstract:
In this work, interference and coherence phenomena, appearing in atomic and
molecular ensembles interacting with coherent light sources, as electromagnetically
induced transparency (EIT), coherent population trapping (CPT), and slow group
velocity of light are investigated. The goal of the project is to make the steps towards
various applications of these phenomena, first, by studying them in solid media (which
are the most advantageous for applications), second, by suggesting some novel applications
such as CPT-based plasma diagnostics, and realization of new types of
solid-state lasers (based on suppression of excited-state absorption via EIT). The
third goal of the project is extension of coherence and interference effects well-known
in optics to the gamma-ray range of frequencies and, correspondingly, from atomic to
nuclear transitions. A particular technique of chirped pulse compression applied to
M??ossbauer transitions is considered and the possibility of compression of M??ossbauer
radiation into ultrashort gamma-ray pulses is analyzed.
The theoretical treatment of the interference and coherence effects is based on
the semiclassical description of atom-light interaction, which is sufficient for correct
analysis of the phenomena considered here. Coherent media are considered in two-,
three-, and four-level approximations while their interaction with light is studied both
analytically and numerically using the Maxwell-Bloch set of equations.
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Venturini, Junior Janio. "Síntese por sol-gel de ferrita de cobalto e sua caracterização microestrutural e de propriedades magnéticas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/148043.
Full textAbstract:
Neste trabalho, estudou-se a síntese por sol-gel da ferrita de cobalto (CoFe2O4), variando-se a temperatura de tratamento térmico do xerogel. Nitrato de ferro e nitrato de cobalto foram utilizados como fonte de cátions e ácido cítrico como mineralizador. Os produtos obtidos, tratados a 750, 800 e 850°C, tiveram sua microestrutura e propriedades magnéticas investigadas no intuito de encontrar correlações entre as condições de síntese, as posições ocupadas pelos cátions dentro da estrutura espinélio do composto e as propriedades magnéticas medidas. Estudos de difratometria de raios X exibiram reflexões características da estrutura espinélio, o que sugere que o tratamento térmico não afetou significativamente a estrutura cristalina do material. Uma fração secundária de hematita também foi observada. As ferritas apresentaram área superficial específica (por BET) de aproximadamente 4 m².g-1. Imagens por MEV indicam que o material apresenta-se aglomerado. Quanto às propriedades magnéticas, um máximo de coercividade de 1405.2 Oersted foi encontrado para a amostra tratada a 800°C. Espectros Mößbauer indicaram um baixo grau de inversão nos espinélios formados, o que é incomum para a ferrita de cobalto. Subtraindo do espectro obtido por Mößbauer o excesso de ferro na forma de hematita, há um forte indicativo que a ferrita foi sintetizada de maneira sub-estequiométrica deficiente em ferro.We herein report a study on the sol-gel synthesis of cobalt ferrite (CoFe2O4) and the effect of treatment temperature on the product outcome. Iron nitrate and cobalt nitrate were used as cation sources and citric acid as mineralizer. Products treated at 750, 800 and 850°C had their microstructure and magnetic properties assessed in order to correlate their synthesis conditions, the positions in which the cations are inserted in the spinel structure and the magnetic behavior displayed by the ferrites. X-ray diffractometry studies exhibit the characteristic reflections of spinel group materials, suggesting that the thermal treatment does not sensibly affect the crystalline structure of the material. A secondary fraction of hematite was also observed. The ferrites exhibit a specific surface area (from BET) of approximately 4 m².g-1. SEM images indicate the material forms agglomerates. As to the magnetic properties, a maximum of 1405.2 Oersted was achieved for the sample treated at 800°C. Mößbauer spectra indicate a fairly low inversion degree in the synthesized materials, which is rather unusual for cobalt ferrite. After deducting the iron fraction present in the form of hematite, there are strong indications that cobalt ferrite was synthesized as a substoichiometric iron-deficient spinel.
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Dang, Mei-Zhen. "Interplay of spin structures, hyperfine magnetic field distributions and chemical order-disorder phenomena in face centered cubic Fe-Ni alloys studied by Mossbauer spectroscopy measurements and Monte Carlo simulations." Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10020.
Full textAbstract:
The magnetic properties of fcc Fe-Ni alloys are studied by Mossbauer spectroscopy and Monte Carlo (MC) simulations. Both macroscopic (magnetization, paraprocess susceptibility, Curie points, etc.) and microscopic properties (hyperfine fields) are used to test simple local moment models under various assumptions. A non-linear composition dependence of the average hyperfine field is observed by Fe-57 Mossbauer spectroscopy. A microscopic vector hyperfine field model is proposed and used to model the measured average hyperfine fields and hyperfine field distributions (HFDs) in the collinear ferromagnetic Fe-Ni alloys (y $\le$ 0.45 in Fe$\sb{y}$Ni$\sb{1-y}).$ Modeling the liquid helium temperature average hyperfine fields and HFDs resolves the coupling parameters in the proposed hyperfine field model:$$\langle\vec H\sb{k}\rangle\sb{T}=A\langle\vec\mu\sb{k}\rangle\sb{T}+ B\sum\sb{j}\langle\vec\mu \sb{j}\rangle\sb{T}.$$To the extent that chemical short range order can be neglected in our rapidly quenched samples, the coupling parameters are $\rm A=A\sb0+A\sb1y\ (A\sb0=89$ kOe/$\mu\sb{B},$ A$\sb1={-}20$ kOe/$\mu\sb{B})$ and B = B$\rm\sb0=B\sb1y\ (B\sb0=4.4$ kOe/$\mu\sb{B},$ B$\sb1=3.2$ kOe/$\mu\sb{B}).$ MC simulations show the success and the limits of a simple local moment model, in characterizing the bulk magnetic properties of Fe-Ni. A new approach for simulating HFDs is developed. It combines MC simulation for the spin structure and the above phenomenological hyperfine field model for the site-specific hyperfine field values. Using this method, we calculated spin structures and HFDs in Fe-Ni alloys at different compositions and temperatures. Finally, interplay between the magnetic and the atomic ordering phenomena is studied in FeNi$\sb3,$ FeNi and Fe$\sb3$Ni, by considering the magnetic and chemical interactions simultaneously using MC simulations. Serveral new features that are not predicted by mean-field theory or MC simulations with chemical interactions only arise: (1) chemical order can be induced where using chemical interactions only leads to the prediction of no chemical order (2) chemical segregation can be induced where using chemical interactions only leads to the prediction of no chemical segregation, (3) FeNi$\sb3$ and Fe$\sb3$Ni are found to have significantly different chemical ordering temperatures where chemical interactions only lead to equal ordering temperatures, (4) chemical ordering temperatures are significantly shifted from their chemical interactions only values, even when the chemical ordering temperature is larger than the magnetic ordering temperature, (5) abrupt steps can occur in the spontaneous magnetization at the chemical ordering temperature, when the latter is smaller than the magnetic ordering temperature, and (6) nonlinear relations arise between the chemical ordering temperature and the chemical exchange parameter U $\equiv$ 2U$\sb{FeNi}-{\rm U}\sb{FeFe}-{\rm U}\sb{NiNi},$ where the U$\sb{ij}$ are the near-neighbour pair-wise chemical bonds.
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Miola, Eduardo José. "Espectroscopia e difração de raios X aplicadas ao estudo de ferro e aço nitretados por plasma." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-31082012-120244/.
Full textAbstract:
Este trabalho apresenta um estudo sobre a formação e evolução da camada de nitretos sobre substrato de ferro com pureza de 99,83% e do aço AISI H12, nitretados por plasma. As camadas foram obtidas com a variação sistemática das condições de nitretação, como temperatura, tempo e frequência do plasma. A atmosfera de trabalho empregada foi a de uma mistura gasosa de 20% N2 + 80% H2, mantida à pressão constante de 6 mbar, sob fluxo. Uma investigação detalhada da camada nitretada das amostras de ferro foi feita através de desgaste mecânico em passos sucessivos e após cada desgaste, as novas camadas foram analisadas por espectroscopia Môssbauer de elétrons de conversão (CEMS) auxiliadas por outras técnicas, como difração de raios X, microdureza e microscopia ótica e eletrônica. As análises superficiais demonstraram que a camada nitretada é formada por uma mistura de nitretos γ-Fe4N, ε-Fe3N e-ε-Fe3,2N, que variam suas proporções com as condições de nitretação. Abaixo desta camada outros nitretos são formados como e ε-FeXN (2≤X≤3,2) e α-Fe16N2. No aço H12, foi estudada a influência da nitretação por plasma em correntes contínua e pulsada. As amostras foram caracterizadas quanto ao perfil de microdureza, perfil de concentração de nitrogênio, difração de raios X e espectroscopia Môssbauer de elétrons de conversão (CEMS) e de raios X de conversão (CXMS). A camada composta próxima à superfície, como vista por CEMS, consiste de uma mistura de γ-Fe4N e ε-FeX(N, C) enquanto a camada próxima à zona de difusão, investigada por CXMS, consiste de uma mistura de fases γ-Fe4N, ε-FeX(N, C) Fex(N, C), α-Fe16N2 e γ-austenita. O crescimento da camada nitretada quando difundida utilizando corrente contínua segue uma lei parabólica, o que não ocorre com o processo com corrente alternada. Este efeito deve ser devido à taxa de \"sputerring\" do catodo e da difusão auxiliada por radiação, que são mais acentuadas no caso de corrente alternada, para tempos de nitretação t ‹ 2h. A situação é revertida para t › 3h.This work investigates the formation and evolution of nitride layers on a 99.83% pure iron and a AISI H-12 steel substrates by using plasma nitriding processoThe layers were obtained by systematic variation of the nitriding conditions, such as temperature, time and plasma frequency. The employed atmosphere consisted of a gaseous mixture of H2-20% N2, at a constant pressure of 6.0 mbar in f1ux.A detailed investigation of the nitrided layer on iron samples was performed through surface mechanical wear in successive steps. After each step the layer was analysed by Conversion Electron Mõssbauer spectroscopy (CEMS), as well as by other techniques, as X-ray diffraction, microhardness and optical and electronic metallography. The surface analysis of iron samples showed that the nitrided layers are formed bya mixture of γ-Fe4N, ε-Fe3N e-ε-Fe3,2N nitrides, whose proportions have varied with the nitriding conditions. Below this layer, different nitrides are formed, ε-FeXN (2≤X≤3,2) e α-Fe16N2. For H-12 steel substrates it was also studied the influence of direct and pulsed current on the layer. The samples were characterized related to the microhardness profile, nitrogen concentration profile, Xray diffraction and Conversion Electron and X-ray Mõssbauer spectroscopy (CEMS) and (CXMS). The near-surface compound layer, as probed by CEMS, consisted of a mixture of γ-Fe4N e ε-FeX(N, C) phases. The near-diffusion zone compound layer, as probed by CXMS presented a mixture of γ-Fe4N , e ε-FeX(N, C) Fex(N, C), α-Fe16N2e γ and- e γ-austenite phases. For the plasma process, the growth of the nitride layers in direct current follows the parabolic law, what does not occur when process with pulsed current is used. This effect is probably due to cathode rate sputtering and radiation-enhanced diffusion, the latter being more accentuated in the case of pulsed current, for nitriding times t ‹ 2h. The situation is reversed for t › 3h.
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Hneda, Marlon Luiz. "Effets de basse dimensionnalité et de la frustration magnétique dans les composés du type AB2O6." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/143196.
Full textAbstract:
Cette tbese comprend une étude sur les composés AB2O6 qui ont attiré un large intérêt ces dernieres années grâce à leurs propriétés de magnétisme de basse dimensionalité. Pour mieux étudier les propriétes magnétiques et les parametres qui les influencent oous oous sommes appuyé sur une bonne connaissance de la stmcture cristalline. Tous les écbantillons ont été étudié par diffraction de rayons X (pression ambiante ou sous hautes pressions) et neutroDique (basse et/ou baute température). Nous avons également effectué d'autres caractérisations, telles que mesures de susceptibilité, de cbaleur spécifique et spectroscopie Mossbauer. Nous avons produit la série MnNb2_6 V 80 6 afio de faire varier les distances intercbaines magnétiques et donc la nature des interactions d'échanges. Ces composés sont intéressants pour préseoter une faible anisotropie et un couplage des moments magnétiques dans les chaines en zig-zag le long de l'axe c, ce qui leur confere un caractere unidimensionnel et un couplage antiferromagnétique entre les chames. Nous avons fait une comparaison avec le modele théorique de la chaine d'Heisenberg classique et obtenu des constantes d'échange intra et intercbatnes, J et J', et sa dépendance par rapport à la teneur 8. Ensuite, nous avons fait une étude des séries MnxAt-xNb206 avec A = Fe, Co et Ni. Notre but a été de vérifier comment la nature et la différence de rayons atomiques peuvent influer sur le comportement structural et magnétique de ces composés. Pour ceux qui n'ont pas présenté de mise en ordre magnétique à 1,5 K nous avons fait une étude des corrélations à courtes distances en utilisant le modele de Bertaut La mise en reuvre de synthese HP et HT nous a permis de stabiliser une phase Mn V 20 6 en symétrie orthorhombique et de mettre en jour ses propriétés physiques. Nous avons ensuite comparé avec le MnV 20 6 monoclinique et également avec le MnNb20 6 orthorhombique. Les comportements magnétiques des composés isostructuraux sont tres similaires mais dans le cas de MnNb20 6, les moments magnétiques forment des chaí'nes du type + - + - et dans la pbase Mo V 20 6 nous observons des cbalnes du type + + - -, stmct.ure inédite dans ces composés.Esta tese compreende um estudo sobre os compostos AB2O6 que chamaram a atenção nos últimos anos graças às suas propriedades de magnetismo de baixa dimensionalidacle. Para melhor entender as propriedades magnéticas e os parâmetros que as influenciam, nos apoiamos no conhecimento da estrutura cristalina. Todas as amostras foram estudadas por difração de raios X (pressão ambiente e sob altas pressões) e de nêutrons (em baixa e em alta temperatura). Também fizemos outras caractetizações como medidas ele susceptibilidade magnética, calorespecífico e espectroscopia Mossbauer. A sé ti e MnNb2_6 V 60 6 foi produzida a fim de variar as distâncias entre as cadeias magnéticas e, com isso, a natureza das interações de troca. Estes compostos são interessantes por apresentarem baixa anisotropia, um acoplamento dos momentos magnéticos nas cadeias em zig-zag ao longo elo eixo c, conferindo-lhe o caráter unidimensional, e ainda um acoplamento antiferromagnético mais fraco entre as cadeias. É feita uma comparação com o modelo teórico de cadeia de Heisenberg clássica e são obtidas as constantes ele troca intra e intercadeias, J e J', e sua dependência em relação à ó. Em seguida, foi feito um estudo das séries MnxAt-xNb20 6 com A = Fe, Co e Ni, com o objetivo de verificar como a natureza e a diferença dos raios atômicos podem influenciar o comportamento estrutural e magnético destes compostos. Para aqueles que não apresentaram ordem magnética à l ,5 K, foi feito um estudo das conelações ele curta distância utilizando o modelo de Bertaut. Graças a síntese AP e AT conseguimos estabilizar o MnV 20 6 em simetria ortorrômbica e determinar suas propriedades físicas. Fizemos então uma comparação com o polimorfo monoclínico Mn V 206 e também com o composto ortonômbico MnNb20 6 . Os comportamentos magnéticos macroscópicos dos compostos isoestruturais são muito similares, porém no caso ela fase MnNb20 6, os momentos magnéticos formam cadeias elo tipo +- + - e na fase Mn V 20 6, as cadeias são do tipo + + - -, estrutura inédita, até então não observada nestes compostos.
This thesis comprises a study of tbe compounds of AB20 6 type that have attracted wide interest in recent years due to tbeir low-dimensional magnetism properties. To better understand tbeir magnetic properties and tbe parameters lhat influence it, we have relied on a good knowledge of lhe crystal stmcture. Ali samples were studied by X-ray diffraction (ambient pressure or under hlgh pressure) and neutron diffraction (low and/or high temperature). We also performed other cbaracterizations, such as magnetic susceptibility, specific heat and Mbssbauer spectroscopy measurements. We have produced tbe MnNb2_6 V 60 6 serie in order to vary the distances between magnetic interchains and thus the nature of lhe excbange interactions. Tbese compounds are interesting due to tbe presence of Jow anisotropy and a coupling of magnetic moments in zigzag cbains along the c-axis, whlch gives lhem a one-dimensional character, and ao antiferromagnetic coupling between cbains. We made a comparison wilh the theoretical modei of the classical Heisenberg chain and obtained the exchange constants intra- and inter-cbain, J and J', and its dependency on the content b. Then we made a study o f MnxA1_.,Nb20 6 series with A = Fe, Co and Ni. Our aim was to check how the nature and tbe difference in atomic radii can influence the stmctural and magnetic properties of tbese compounds. For those whlcb sbowed no magnetic ordering at 1.5 K we made a study of correlations at short distances using Bertaut's model. Thanks to tbe use of HP and HT synthesis we managed to stabilize MnV20 6 in orthorbombic symetry and determine its physical properties. We then performed a comparison witb the monoclinic MnV20G and with tbe 011horbombic MnNb206 compound as well. Macroscopic magnetic behaviour o f isostructural compounds are ve1y similar but in the case of MnNb20 6, the magnetic moments form + - + - type chains while the Mn V 20 6 presents cbains of + + - - type, a structure never observed before in tbis family o f compounds.
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Bull, James. "Application of Quantum Mechanics to Fundamental Interactions in Chemical Physics: Studies of Atom-Molecule and Ion-Molecule Interactions Under Single-Collision Conditions: Crossed Molecular Beams; Single-Crystal Mössbauer Spectroscopy: Microscopic Tensor Properties of ⁵⁷Fe Sites in Inorganic Ferrous High-Spin Compounds." Thesis, University of Canterbury. Department of Chemistry, 2010. http://hdl.handle.net/10092/4292.
Full textAbstract:
As part of this project and in preparation for future experimental studies of gas-phase ion-molecule reactions, extensive modification and characterization of the crossed molecular beam machine in the Department of Chemistry, University of Canterbury has been carried out. This instrument has been configured and some
preliminary testing completed to enable the future study of gas-phase ion-molecule collisions of H⁺₃ and Y⁻ (Y
= F, Cl, Br) with dipole-oriented CZ₃X (Z = H, F and X = F, Cl, Br). Theoretical calculations (ab initio
and density functional theory) are reported on previously experimentally characterized Na + CH₃NO₂, Na + CH₃NC, and K + CH₃NC systems, and several other systems of relevance. All gas-phase experimental and theoretical studies have the common theme of studying collision orientation dependence of reaction under singlecollision
conditions. Experimental measurements, theoretical simulations and calculations are also reported on some selected ferrous (Fe²⁺) high-spin (S=2) crystals, in an attempt to resolve microscopic contributions of two fundamental macroscopic tensor properties: the electric-field gradient (efg); and the mean square displacement (msd) in the case when more than one symmetry related site of low local point-group symmetry contributes to the same quadrupole doublet. These determinations have been made using the nuclear spectroscopic technique of Mössbauer spectroscopy, and complemented with X-ray crystallographic measurements.
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Houlton, Andrew. "Mossbauer spectroscopic studies of iron(II) sandwich compounds." Thesis, University of Essex, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252634.
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Alnjiman, Fahad. "ZnSnN2 thin films for photovoltaic applications." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0296/document.
Full textAbstract:
Des films de nitrure de zinc et d’étain (ZnSnN2) ont été élaborés par co-pulvérisation magnétron réactive à des températures proches de l’ambiante. La composition chimique des revêtements a été optimisée en ajustant les paramètres de dépôt comme la tension appliquée aux cibles métalliques, la pression de travail et la composition du gaz plasmagène. Dans les conditions optimisées, les films sont fortement cristallisés sur les différents types de substrats testés. Une étude approfondie sur la structure des films a été entreprise par microscopie électronique en transmission. Nous avons ainsi pu montrer que nos films de ZnSnN2 cristallisent dans le système hexagonal. Toutefois, cette structure diffère de celles présentées dans la littérature pour le nitrure de zinc et d’étain. Des études sur l’environnement chimique des éléments constitutifs des revêtements ont également été menées par spectrométrie Mössbauer et par photoémission X. Elles montrent que l’étain est présent dans nos films sous forme de Sn4+ en configuration tétraédrique. Nous avons également pu montrer que l’oxygène présent dans nos films est principalement localisé dans les zones inter-colonnaires. Enfin, les propriétés optiques et électriques de nos films ont été estimées en fonction de leur composition chimique. L’ensemble des résultats obtenus durant ce travail démontre la pertinence de ZnSnN2 pour des applications futures en tant que couche absorbante dans les cellules photovoltaïquesZinc tin nitride (ZnSnN2) thin films have been deposited by reactive magnetron co-sputtering at room temperature. The stoichiometry of the films has been controlled by optimizing the deposition conditions such as the voltage applied to the metallic targets, the deposition pressure and the composition of the gas mixture. By using the optimized parameters, the deposited films are highly crystallized on the different used substrates. A special attention has been devoted to the determination of the film structure. Among the various structures reported in the literature, we have shown by transmission electron microscopy that the films crystallised in a hexagonal structure. Nevertheless, the structure of our films does not fit with that reported in the literature for the hexagonal ZnSnN2 material. In addition to this structural study, we have performed fine characterization using conversion electron Mossbauer spectrometry and X-ray photoemission spectroscopy. Both methods show that the optimized films contain Sn4+ ions in tetrahedral configuration. Nevertheless, oxygen contamination at the column boundaries has been evidenced. The electrical and optical properties of the films have been determined has a function of the film composition. The results obtained in this PhD work clearly evidence that ZnSnN2 is a suitable material for photovoltaic applications
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Matthews, D. P. "Ion exchange and Mossbauer spectroscopic studies of zeolite ZSM5." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37777.
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Lussier, Aaron J. "Zonation in tourmaline from granitic pegmatites & the occurrence of tetrahedrally coordinated aluminum and boron in tourmaline." Mineralogical Society of Great Britan and Ireland, 2008. http://hdl.handle.net/1993/5043.
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[1] Four specimens of zoned tourmaline from granitic pegmatites are characterised in detail, each having unusual compositional and/or morphologic features: (1) a crystal from Black Rapids Glacier, Alaska, showing a central pink zone of elbaite mantled by a thin rim of green liddicoatite; (2) a large (~25 cm) slab of Madagascar liddicoatite cut along (001) showing complex patterns of oscillatory zoning; and (3) a wheatsheaf and (4) a mushroom elbaite from Mogok, Myanmar, both showing extensive bifurcation of fibrous crystals originating from a central core crystal, and showing pronounced discontinuous colour zoning. Crystal chemistry and crystal structure of these samples are characterised by SREF, EMPA, and 11B and 27Al MAS NMR and Mössbauer spectroscopies. For each sample, compositional change, as a function of crystal growth, is characterised by EMPA traverses, and the total chemical variation is reduced to a series of linear substitution mechanisms. Of particular interest are substitutions accommodating the variation in [4]B: (1) TB + YAl ↔ TSi + Y(Fe, Mn)2+, where transition metals are present, and (2) TB2 + YAl ↔ TSi2 + YLi, where transition metals are absent. Integration of all data sets delineates constraints on melt evolution and crystal growth mechanisms.
[2] Uncertainty has surrounded the occurrence of [4]Al and [4]B at the T-site in tourmaline, because B is difficult to quantify by EMPA and Al is typically assigned to the octahedral Y- and Z-sites. Although both [4]Al and [4]B have been shown to occur in natural tourmalines, it is not currently known how common these substituents are. Using 11B and 27Al MAS NMR spectroscopy, the presence of [4]B and [4]Al is determined in fifty inclusion-free tourmalines of low transition-metal content with compositions corresponding to five different species. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well-resolved, allowing detection of very small (< ~0.1 apfu) amounts of T-site constituents. Results show that contents of 0.0 < [4]B, [4]Al < 0.5 apfu are common in tourmalines containing low amounts of paramagnetic species, and that all combinations of Si, Al and B occur in natural tourmalines.
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Irwin, Mark Robert Floyd. "The synthesis and characterisation of metal complexes containing chemically reduced bipyridyl ligand systems." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:44dd8d43-01cf-4a2a-ab66-c7cab1d9201f.
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This thesis describes the synthesis and characterisation of metal complexes that contain chemically reduced bipyridyl ligands. The crystal structures of twenty-six novel complexes are reported alongside detailed discussions on the electronic and spectroscopic effects and trends associated with the different oxidation states within these species. Chapter One introduces the isomers of bipyridine and their redox chemistry, the concept of non-innocent ligands and the spectroscopic techniques that are currently used in determining ligand oxidation states. Subsequently, examples of main group, transition metal, lanthanide and actinide species that contain or may contain reduced forms of the ligand are discussed. Chapter Two details the synthesis and structural characterisation of alkali metal salts of singly and doubly reduced forms of the three commercially available bipyridine isomers. The effects of this reduction are investigated with the aim of developing diagnostic fingerprints for each of the ligand oxidation states. Chapter Three discusses the synthesis of an homologous series of compounds of the form [M(2,2'-bipy)(mes)2]n– where M = Cr, Mn, Fe, Co, Ni and n = 0, 1. Trends in magnetism, bonding and electronic structure are investigated with reference to theoretical calculations and the diagnostic fingerprints identified in the previous chapter. Chapter Four describes the synthesis and characterisation of three compounds containing the isostructural motif [Zn2(4,4'-bipy)(mes)4]n– where n = 0, 1, 2. Structural and spectroscopic changes are discussed and com- pared to theoretical calculations. Chapter Five contains descriptions of the spectroscopic techniques employed in the above research and synthesis routes to all compounds featured in this thesis.
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Johnson, J. A. "Mossbauer spectroscopic studies of linear and non-linear magnetic excitations in crystals." Thesis, University of Liverpool, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356272.
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Alnjiman, Fahad. "ZnSnN2 thin films for photovoltaic applications." Electronic Thesis or Diss., Université de Lorraine, 2018. http://www.theses.fr/2018LORR0296.
Full textAbstract:
Des films de nitrure de zinc et d’étain (ZnSnN2) ont été élaborés par co-pulvérisation magnétron réactive à des températures proches de l’ambiante. La composition chimique des revêtements a été optimisée en ajustant les paramètres de dépôt comme la tension appliquée aux cibles métalliques, la pression de travail et la composition du gaz plasmagène. Dans les conditions optimisées, les films sont fortement cristallisés sur les différents types de substrats testés. Une étude approfondie sur la structure des films a été entreprise par microscopie électronique en transmission. Nous avons ainsi pu montrer que nos films de ZnSnN2 cristallisent dans le système hexagonal. Toutefois, cette structure diffère de celles présentées dans la littérature pour le nitrure de zinc et d’étain. Des études sur l’environnement chimique des éléments constitutifs des revêtements ont également été menées par spectrométrie Mössbauer et par photoémission X. Elles montrent que l’étain est présent dans nos films sous forme de Sn4+ en configuration tétraédrique. Nous avons également pu montrer que l’oxygène présent dans nos films est principalement localisé dans les zones inter-colonnaires. Enfin, les propriétés optiques et électriques de nos films ont été estimées en fonction de leur composition chimique. L’ensemble des résultats obtenus durant ce travail démontre la pertinence de ZnSnN2 pour des applications futures en tant que couche absorbante dans les cellules photovoltaïquesZinc tin nitride (ZnSnN2) thin films have been deposited by reactive magnetron co-sputtering at room temperature. The stoichiometry of the films has been controlled by optimizing the deposition conditions such as the voltage applied to the metallic targets, the deposition pressure and the composition of the gas mixture. By using the optimized parameters, the deposited films are highly crystallized on the different used substrates. A special attention has been devoted to the determination of the film structure. Among the various structures reported in the literature, we have shown by transmission electron microscopy that the films crystallised in a hexagonal structure. Nevertheless, the structure of our films does not fit with that reported in the literature for the hexagonal ZnSnN2 material. In addition to this structural study, we have performed fine characterization using conversion electron Mossbauer spectrometry and X-ray photoemission spectroscopy. Both methods show that the optimized films contain Sn4+ ions in tetrahedral configuration. Nevertheless, oxygen contamination at the column boundaries has been evidenced. The electrical and optical properties of the films have been determined has a function of the film composition. The results obtained in this PhD work clearly evidence that ZnSnN2 is a suitable material for photovoltaic applications
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Guillot-Deudon, Catherine. "Les Conducteurs ioniques... études physico-chimiques par spectroscopie Mossbauer et résonance magnétique nucléaire." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb375981604.
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Jasmin-Lebras, Guénaëlle. "Etude des reseaux kondo magnetiques ybp, ybn, ybpdsb par spectroscopie mossbauer sur #1#7#0yb." Paris 11, 1994. http://www.theses.fr/1994PA112277.
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Cette these est consacree a l'etude des reseaux kondo d'ytterbium ybp, ybn et ybpdsb par les techniques suivantes: spectroscopies mossbauer et de muons, mesures de chaleur specifique, magnetiques et de diffusion de neutrons. Sur le site de la terre rare, la presence des fluctuations de spin, inherentes a l'etat kondo (t#k) tend a contrecarrer l'effet de l'echange rkky (t#r#k#k#y). Cette competition, modelisee par doniach, confere aux reseaux kondo des phases magnetiques anormales dont les caracteristiques dependent de l'importance relative des deux interactions antagonistes t#k et t#r#k#k#y. Dans ybp, ybn et dans un premier echantillon de ybpdsb, nous avons observe un ordre magnetique a longue distance au dessous d'une temperature de neel bien plus faible que t#r#k#k#y et des moments magnetiques fortement reduits. Nous rendons assez bien compte de ces proprietes magnetiques a l'aide de modeles theoriques approches de resolution du hamiltonien d'anderson dans lesquels on peut inclure les levees de degenerescence dues a l'interaction de champ cristallin et aux interactions zeeman et d'echange. Le calcul variationnel et les mesures de chaleur specifique nous ont permis d'estimer que le couplage kondo est du meme ordre de grandeur que l'interaction d'echange rkky dans les trois composes. Ceci signifie qu'ils sont proches du point critique x#c du diagramme de doniach. Cette propriete rend ces materiaux tres sensibles aux perturbations susceptibles de modifier la densite d'etats de la bande de conduction n(e#f). C'est ce que nous avons observe dans un second echantillon de ybpdsb qui, contrairement au premier, ne presente pas de transition de phase mais des fortes correlations dynamiques a courte distance entre les moments d'ytterbium. Cette difference de comportement entre les deux echantillons est certainement due a d'une difference de stoechiometrie en ytterbium qui modifie n(e#f)
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Chamas, Mohamad. "Électrodes négatives pour batteries Li-ion à base de FeSn2 : performances, Mécanismes et Vieillissement." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20189.
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Comme dispositif de stockage de l'énergie, les batteries Li-ion possèdent de nombreux avantages et en particulier une densité d'énergie élevée. Toutefois, la recherche de nouveaux matériaux d'électrode reste nécessaire pour améliorer les performances. Ce travail concerne les matériaux d'électrode négative avec pour objectif l'augmentation de leur capacité. Dans ce but nous nous sommes intéressés à un composé intermétallique à base d'étain : FeSn2. Nous avons effectué la synthèse de ce matériau par différents procédés afin d'obtenir des microparticules et un matériau nanostructuré. L'étude des mécanismes électrochimiques a montré que pour ces deux types de matériaux la première décharge constituait une étape essentielle de restructuration de l'électrode aboutissant à la formation in situ d'un nanocomposite Fe/Li7Sn2. Le suivi quantitatif de la réaction de conversion, responsable de cette transformation, a été effectué par spectrométrie Mössbauer in situ et operando grâce à une nouvelle cellule électrochimique que nous avons développée. D'autres techniques ont été utilisées : DRX et spectrométrie d'impédance in situ, SQUID et XPS. En associant ces différentes techniques nous avons montré que les cycles de charge/décharge étaient basés sur une réaction réversible entre Li7Sn2 et LixSn riche en étain sans reformation de FeSn2. Ce résultat diffère des mécanismes observés pour CoSn2 et Ni3Sn4 et pourrait expliquer la perte progressive de capacité généralement observée avec FeSn2. Toutefois, les performances sont intéressantes avec une capacité de 400-500mAh/g sur 50 cycles entre C/10 et 10C. Enfin, nous avons mis en évidence un phénomène de vieillissement de l'électrode en fin de décharge qui provoque sa délithiation irréversibleLi-ion batteries are rechargeable energy storage systems with high energy density. However, new electrode materials are needed in order to improve the electrochemical performances. This thesis is devoted to a tin based intermetallic compound as negative electrode for Li-ion batteries: FeSn2. Different synthesis methods were used in order to obtain microsized particles and nanostructured materials. The study of the electrochemical mechanisms shows that for both types of materials the first discharge is an essential restructuring step leading to the in situ formation of a Fe/Li7Sn2 nanocomposite. This transformation is due to a conversion reaction that was quantitatively characterized by Mössbauer spectroscopy from in situ and operando measurements. A new cheap and reliable electrochemical cell was developed for these measurements. Other techniques have also been used: in situ XRD and impedance spectroscopy, XPS and SQUID. By combining these tec hniques we have shown that the charge/discharge cycles were based on a reversible reaction between Li7Sn2 and tin-rich LixSn without back reaction with iron nanoparticles. This result is rather surprising because it differs from the mechanisms observed for CoSn2 and Ni3Sn4 but could explain the progressive loss of capacity usually observed with FeSn2. However, interesting performances were obtained with a capacity of 400-500mAh/g for 50 cycles and lithium rates between C/10 and 10C. Finally, we have identified aging process for the electrode at the end of discharge that causes irreversible delithiation
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Thévenin, Thierry. "Étude par spectroscopie Mossbauer (#2#3#7np) et diffraction x de chalcogénures et oxychalcogénures de neptunium." Paris 6, 1988. http://www.theses.fr/1988PA066562.
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Cette these presente une contribution a l'etude de la structure electronique de chalcogenures et oxychalcogenures de neptunium par spectroscopie mossbauer (sm) de np-237. Au cours de ce travail, six phases nouvelles ont ete identifiees dans les systemes np-y (y=s, se), np-o-y (y=se, te) et np-mo-y (y=s, se). Nous avons etudie l'influence de l'environnement du neptunium, et de la nature du ligand, sur le deplacement isomerique (di). De facon, systematique, le di (lie a la densite electronique au noyau de np) diminue avec l'electronegativite de l'ion chalcogene et augmente avec la distance moyenne neptunium-ligand dans les composes de neptunium tetravalent. L'influence de l'environnement est beaucoup plus limitee dans le cas des composes de neptunium trivalent. Dans une seconde partie, nous avons synthetise les premiers chalcogeno-halogenures d'actinides. Dans une troisieme partie, nous avons evalue la premiere valeur experimentale du coefficient de sternheimer pour l'ion np(4+)
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Lacroix, Lise-Marie. "Nanoparticules de fer de taille contrôlée pour l’hyperthermie : synthèse par voie organométallique, caractérisations magnétiques et mesures de puissance dissipée." Toulouse, INSA, 2008. http://eprint.insa-toulouse.fr/archive/00000240/.
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Les nanoparticules magnétiques présentent un fort potentiel pour le traitement de tumeurs par hyperthermie ; leur efficacité dépend de la taille, de l’état de surface et de la nature du matériau. Nous avons réalisé une étude fondamentale de la synthèse par voie organométallique de nanoparticules de fer métallique, de leurs propriétés magnétiques intrinsèques et de leur réponse en hyperthermie. Des particules de taille contrôlée (entre 1. 5 à et 90 nm ont été obtenues par décomposition du dimère (Fe{N[Si(CH3)3]2}2)2. Leur croissance a été suivie par TEM, Mössbauer et SQuID et a révélé les rôles clés de mésophases lamellaires et de l’acide. Une méthode innovante de synthèse par mûrissement de germes est développée. La surface des nanoparticules n’est pas oxydée (Ms = 220 Am2. Kg-1), mais une exaltation de la constante d’anisotropie (Keff) a été mesurée pour de petites particules (10 pour 1. 5 nm et 3 pour 5. 5 nm). Holographie électronique et calculs micromagnétiques ont permis d’étudier quantitativement une configuration vortex dans un cube de 30 nm. Un banc de mesure d’hyperthermie ajustable en fréquence a été mis en place et a permis de caractériser des particules superparamagnétiques de fer (de 5. 5 et 7. 5 nm). Des particules de FeCo de 14. 2nm ont également été testéesMagnetic nanoparticles are of great interest for hyperthermia treatment of tumours. Their efficiency depends on their size, their surface state and the material used. We realised a fundamental study of the iron nanoparticles synthesis, of their specific magnetic properties and of their hyperthermia response. A detailed analysis of theoretical models could enlighten the optimised properties (superparamagnetism/ferromagnetism transition, high saturation magnetisation MS ). Monodisperse iron nanoparticles are synthesized by the decomposition of the organometallic precursor (Fe{N[Si(CH3)3]2}2)2. The growth mechanism was studied by kinetic studies using electronic microscopy, Mössbauer spectrometry and SQuID measurements. The key role of lamellar structures and acid concentration was described. A new approach, never reported so far, based on the ripening of small iron germs was used for the first time. Particle with tuneable sizes ranging from 1. 5 to 11. 2 nm were obtained with Ms = 220 Am2. Kg-1. An increase of the anisotropic constant was reported for small particles regarding bulk iron (10 for 1. 5 nm and 3 for 5. 5 nm). Magnetic configurations have been directly imaged in 30 nm nanocubes thanks to the electronic holography technique. Micromagnetic simulations coupled with holography permit to quantitatively analyse a vortex structure in an isolated cube. A frequency adjustable electromagnet was designed. The first hyperthermia measurements are reported for superparamagnetic iron (of 5. 5 and 7. 5 nm). A ferromagnetic behaviour corresponding to Stoner-Wohlfarth model was for the first time observed for 14. 2 nm FeCo nanoparticles
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Colineau, Eric. "Etude des propriétés magnétiques et électroniques de composés de neptunium NpX3 et Np2T2X par spectroscopie Mossbauer, diffraction de neutrons et magnétométrie SQUID." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10107.
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Le travail presente dans cette these est une contribution a l'etude des proprietes magnetiques et electroniques des composes intermetalliques npx#3 (x=al, ga, in, sn) et np#2t#2x (t=co, ni, ru, rh, pd, pt ; x=in, sn) par spectroscopie mossbauer, diffraction de neutrons et magnetometrie squid. L'interet de ces series est de presenter une hybridation progressive des electrons 5f du neptunium avec les orbitales des ligands et une reduction concomitante du magnetisme lorsque le numero atomique des elements x ou t diminue. Il est donc possible d'observer, le long d'une meme serie isostructurale, l'evolution des proprietes magnetiques et electroniques, de l'ordre magnetique avec des electrons 5f localises, jusqu'au paramagnetisme de pauli avec des electrons 5f totalement delocalises. Pour chaque famille de composes etudies, est etablie une comparaison avec les familles homologues ou le neptunium est remplace par l'uranium ou le cerium. La serie npx#3 a fait l'objet d'un certain nombre d'etudes depuis une vingtaine d'annees, et les resultats presentes ici completent et precisent les connaissances anterieures de ces composes. Les diagrammes de phases et les structures magnetiques de npal#3, npga#3 et npin#3 ont ete completes et precises. Le facteur de forme et la carte de densite d'aimantation de npsn#3 ont ete mesures. L'etat de charge et l'etat fondamental du neptunium dans ces composes sont discutes. La serie np#2t#2x a ete recemment decouverte et les resultats exposes dans ce memoire constituent la premiere etude des proprietes magnetiques et electroniques de ces composes. Les mesures de spectrometrie mossbauer ont permis d'etablir que huit de ces composes s'ordonnent et trois ne s'ordonnent pas. Nous avons determine les temperatures de mise en ordre, la valeur du moment a saturation porte par le neptunium et l'etat de charge du neptunium
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CHAQOUR, SIDI MOHAMED. "Synthese et etude structurale des combinaisons ternaires soufrees formees par le fer et l'ytterbium. Etude par diffraction des rayons x, spectroscopie mossbauer et microscopie electronique." Paris 6, 1996. http://www.theses.fr/1996PA066079.
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Plusieurs echantillons du pseudobinaire fes-yb#2s#3 ont ete synthetises et analyses par diffraction des rayons x, microscopie electronique et spectroscopie mossbauer. L'analyse des cliches de poudre des differentes compositions de la ligne fes-yb#2s#3 montre qu'il existe un domaine de phases de symetrie cubique, type nacl, dans la region riche en fer 0,50n<0,75 ; n = fe/(fe+yb). Quand la teneur en ytterbium augmente, nous avons un domaine de symetrie cubique, type spinelle (0,33n,,475). Les cliches de diffraction electronique des echantillons de ces differentes compositions montrent l'existence conjointe de domaines de type spinelle ordonnes et de type nacl desordonnes. La presence de trainees selon la direction <111>* et de satellites diffus a ete interpretee a l'aide d'images haute resolution par une distribution irreguliere de defauts planaires, disposes parallelement aux plans 111. Par ailleurs, la spectroscopie mossbauer a ete utilisee pour suivre l'evolution du fer en sites octaedrique et tetraedrique. Tous les spectres mossbauer obtenus confirment l'etat de valence (+2) du fer dans ces echantillons. Pour des valeurs de n = 0,273 ; 0,25 et 0,222, trois phases homogenes ont ete obtenues. L'etude structurale sur monocristal de ces composes montrent que ces structures presentent des caracteristiques communes. Les cations yb#3#+ occupent des sites prismatiques et partagent les sites octaedriques, en desordre statistique, avec les cations fe#2#+. Ces structures peuvent etre decrites a partir de deux motifs de base. Une relation entre la formule chimique du compose et sa structure geometrique a ete etablie
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VAAST, PACI CHRISTINE. "Etude de l'induction locale dans le compose supraconducteur yba#2cu#3o#7#-# par spectroscopie mossbauer sur la sonde #1#7#0yb#3#+ : methodologie et resultats." Paris 11, 1997. http://www.theses.fr/1997PA112413.
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Cette these est consacree a l'etude de la distribution de l'induction dans yba#2cu#3o#7#-#
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Nouri, Kamal. "Contribution à l'étude des diagrammes des phases ternaires R-Fe-X (R : Y, Sm; X : Ni, Ga) : Elaborations, études structurales, magnétiques et magnétocaloriques des composés intermétalliques dans les systèmes (Sm,Y)-Fe-(Ni,Ga)." Thesis, Paris Est, 2016. http://www.theses.fr/2016PESC1139.
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Depuis quelques dizaines d’années, l’étude de composés intermétalliques à base des métaux de transition 3d, et d’éléments de terres rares 4f, présente un vif intérêt tant d’un point de vue fondamental qu’appliqué. Les propriétés remarquables de ces matériaux magnétiques proviennent de la présence, dans le même composé, de métaux de transition 3d, caractérisés par un magnétisme itinérant donné par les électrons de la bande externe 3d, et de métaux de terres-rares 4f qui, eux, présentent un magnétisme localisé dû aux électrons de la couche interne 4f. La recherche présentée ici se concentrera sur deux diagrammes des phases ternaires alliant samarium, fer et nickel et l’yttrium, fer et Gallium dans le deuxième système. Ces types d’intermétalliques sont aussi potentiellement caractérisés par un effet magnétocalorique (EMC) défini par le réchauffement ou le refroidissement de ces matériaux magnétiques sous l’application ou la suppression d’un champ magnétique extérieur.Le but de la thèse est la construction des deux diagrammes ternaires qui n’ont jamais été publiés et étudier les propriétés physicochimiques dans les systèmes (Sm,Y)-Fe-(Ni,Ga). Cette recherche aboutira à la détermination des diagrammes ternaires Sm-Fe-Ni et Y-Fe-Ga expérimentales (section isotherme à 800°C) et d’étudier les propriétés structurales de ces composés intermétalliques. Les propriétés magnétiques et magnétocaloriques ont également été étudiées en couplant les analyses magnétiques avec les mesures par diffraction des rayons X et par spectroscopie Mössbauer. Ces travaux ont mis en évidence l’influence importante de la nature et du taux de fer substitué au nickel et au gallium dans les deux systèmes sur les propriétés magnétiquesIn recent decades, the study of intermetallic compounds containing 3d transition metals and 4f rare earth elements presents great interest both from a fundamental point of view and in its various applications. The remarkable properties of these magnetic materials come from the presence, in the same compound, of 3d transition metal, characterized by an itinerant magnetism given by the electrons in the 3d external band, and 4f rare-earth which themselves have a localized magnetism due to the electrons of the 4f inner layer. The research presented here will focus on the construction of two ternary phase diagrams combining [Sm-Fe-Ni] in the first system and [Y-Fe-Ga] in the second one. These types of intermetallics are also characterized by a magnetocaloric effect (EMC) defined by the heating or cooling of these magnetic materials under the application or removal of an external magnetic field.The aims of the thesis are the construction of two ternary phase diagrams that have never been published before and the study of the physicochemical properties in the (Sm, Y) -Fe- (Ni, Ga) systems. This research will lead to the determination of experimental ternary phase diagrams Sm-Fe-Ni and Y-Fe-Ga (isothermal section at 800°C) and to study the structural properties of some intermetallic compounds.The magnetic and magnetocaloric properties were also studied by coupling magnetic analysis with the X-ray diffraction and Mössbauer spectroscopy measurements. This work has highlighted the important influence of the nature and rate of iron substituted by nickel and gallium in both systems on the magnetic properties
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Baranov, Alexeï. "Apport de la spectroscopie Mössbauer à l'étude des phénomènes électroniques et structuraux au sein de réseaux oxygénés renfermant un élément de transition à un degré d'oxydation élevé." Bordeaux 1, 2007. http://www.theses.fr/2007BOR13449.
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Le dopage (1% atomique) par une sonde Mössbauer (57Fe) a permis –au sein de réseaux oxygénés dérivés de la structure perovskite renfermant le nickel trivalent (RNiO3 : R=terre rare ou Tl), le cuivre trivalent (LaCuO3, SrCuO4, La2Li0. 50Cu0. 50O4) et la valence mixte III/IV du manganèse (CaMn7O12)- de mettre en évidence divers phénomènes électroniques (ordre orbitalaire, transition métal-isolant, dismutation) et structuraux. La spectroscopie Mössbauer conduit à préciser divers paramètres caractérisant l’environnement local de la sonde et apporte ainsi une approche nouvelle par rapport aux techniques basées sur les interactions à longue distance (techniques de diffraction notamment)This thesis is devoted to the study of electronic phenomena, structural and magnetic transitions through Mössbauer Spectroscopy using 57Fe as local probe (1 to 2% at. ). Three different matrixes have been selected: (i) the nickelates TNiO3 with the perovskite structure (T=rare-earth, Y, Tl), (ii) the copper 3+ oxides: LaCuO3 with the perovskite structure, SrLaCuO4 and La2Li0. 50Cu0. 50O4 with the K2NiF4-type structure, (iii) the oxide CaMn7O12 with a structure derived from the perovskite (CaMn )(Mn Mn4+)O12 where a Jahn-Teller cation (Mn3+) can occupy the A site. Mössbauer spectroscopy has allowed to underline the following electronic and structural phenomena: (i) for the TNiO3 matrixesthe insulationmetal transition, the disproportionation, the magnetic ordering involving two Ni3+ electronic configurations; (ii) for the Cu3+ Oxides: the charge transfert Cu3+ O Cu2+ OL; (iii) in the case of CaMn7O12 matrix two phenomena: a second order structural transition (rhomboedral cubic) (387T455 K), a second order magnetic transition close to 90 K
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Sousa, Eduardo Carvalho. "Désordre de spins, anisotropie magnétique et magnéto-optique de nanoparticules de ferrites." Paris 6, 2007. http://www.theses.fr/2007PA066678.
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Des nanoparticules de ferrites mixtes, obtenues par chimie douce, sont dispersées en milieu acide grâce à une stratégie coeur/couronne protégeant les particules de leur dissolution. Leur composition chimique, inhomogène, est bien décrite par un coeur de ferrite stoechiométrique et une couche surfacique de composition chimique moyenne Fe3O4. Les distributions de tailles des particules sont caractérisées à l’ambiante par aimantation, biréfringence magnéto-induite et rotation Faraday. A basses températures, des mesures d’aimantation permettent de distinguer le coeur monodomaine ordonné des spins de la couronne gelant de façon désordonnée. Des mesures de spectroscopie Mössbauer sous champ montrent l´évolution du modèle coeur -couronne en fonction dún champ externe. Lánisotropie magnétique des nanoparticules, étudiée par magnétométrie, spectroscopie Mössbauer et biréfringence en champs croisés est dominée par la forte contribution des spins de surface, faiblement couplés à ceux du coeur.
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Bahamida, Saida. "Etude des propriétés structurales et magnétiques des alliages FePd en couches minces par spectrométrie Mossbauer et diffraction de rayons X." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMR116/document.
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Dans ce travail, nous nous intéressons à l’étude des propriétés structurales et magnétiques de films déposés sur des substrats de silicium et de verre, qui sont : Fe85Pd15, Fe80Pd20, Fe64Pd36 et Fe56Pd44, ainsi qu’aux corrélations qui peuvent être déduites de ces propriétés. Ces films minces sont élaborés par la technique d’évaporation thermique par effet Joule. Par ailleurs, ces films ont été analysés par plusieurs techniques, à savoir: la diffraction des rayons X (DRX), la microscopie électronique à balayage (MBE), la microscopie à force atomique (AFM), la spectrométrie Mössbauer, la magnétométrie SQUID, la magnétométrie à gradient de champ alternatif (AGFM) et la microscopie à force magnétique (MFM). L’analyse de DRX a révélé que les échantillons Fe80Pd20, Fe64Pd36 sont bi-phasiques et constitués d’une phase (Fe,Pd)-α cubique centrée (cc) et d’une phase FePd cubique à faces centrées (cfc). Par ailleurs, les échantillons Fe85Pd15 et Fe56Pd44 se sont avérés monophasiques et formés de la phase (Fe, Pd)-α, et de la phase FePd respectivement. Concernant les alliages, Fe85Pd15, Fe80Pd20et Fe64Pd36, nous avons trouvé, que la phase (Fe, Pd)-α se saturait à 20 % de Pd; et la phase ‘FePd’ apparaissait à ce même pourcentage. Ensuite, l’alliage Fe56Pd44 déposé sur le silicium a subit un recuit isotherme, à 550°C à différents temps de maintien, dans le but d’induire une transformation de la phase FePd désordonnée en la phase L10FePd ordonnée. La variation, en fonction du temps, de la fraction transformée de la phase ordonnée, révélée par la DRX et le SQUID, s’est avérée obéir à la loi d’Avrami. Concernant les propriétés magnétiques, nous avons trouvé que l’alliage Fe64Pd36, était également le siège de la transformation de la phase FePd désordonnée en la phase L10FePd ordonnée. Cette transformation est marquée par l’existence d’un couplage d’échange entre la phase douce (Fe, Pd)-α et la phase dure L10FePd. Ce phénomène a été mis en évidence par plusieurs techniques révélant, par exemple, la forme du cycle d’hystérésis caractérisée par un champ coercitif élevé et une aimantation à saturation élevéeIn this work, we are interested in the study of the structural and magnetic properties of thin films deposited on silicon and glass substrates which are: Fe85Pd15, Fe80Pd20, Fe64Pd36 and Fe56Pd44, as well as in the correlations which can be deduced from these properties. These thin films are prepared using the thermal evaporation technique by Joule effect. Moreover, these films have been analyzed by several techniques, namely: X-rays diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Mössbauer spectrometry, SQUID magnetometer, alternating field gradient magnetometer (AFGM) and magnetic force microscopy (MFM). The XRD analysis revealed that the Fe80Pd20 and Fe64Pd36 samples are biphasic, and present a body centered cubic (bcc) α-(Fe, Pd) and a face centered cubic (fcc) FePd structure respectively. Furthermore, the samples Fe85Pd15 and Fe56Pd44 were observed to be monophasic and formed of a body centered cubic α-(Fe, Pd) phase and a face centered cubic FePd phase respectively. Concerning the Fe85Pd15, Fe80Pd20 and Fe64Pd36 alloys, we found that the α-(Fe, Pd) phase saturated at 20% of Pd and that the FePd phase appeared at this same concentration. Then, the Fe56Pd44 alloy deposited on silicon substrates was subjected to isothermal annealing, at 550 ° C for different holding times, in order to induce a transformation of the disordered FePd phase into the ordered L10FePd phase. The variation, as a function of time, of the transformed fraction of the ordered phase, revealed by XRD and SQUID, was found to obey to Avrami's law. Concerning the magnetic properties, we have found that the Fe64Pd36 alloy was also observed to present a transformation of the disordered FePd phase into the ordered L10FePd phase. This transformation is marked by the existence of an exchange coupling between the soft α-(Fe, Pd) phase and the hard L10FePd phase. This phenomenon has been confirmed by several techniques revealing, for instance, the shape of the hysteresis cycle characterized by a high coercive field and a high saturation magnetization
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Appert, Florian. "Conception et réalisation de détecteurs dédiés à l'analyse de couches minces par spectrométrie Mossbauer : application à l'étude des propriétés magnétiques de films d'oxydes multiferroïques." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMR133/document.
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Ce travail de thèse porte sur la réalisation de deux instruments adaptés à l’étude de couches minces par spectrométrie Mössbauer du 57Fe par électrons de conversion (CEMS) et à leur utilisation pour la caractérisation de films épitaxiés de ferrite de bismuth BiFeO3 (BFO). Le premier dispositif est constitué d’un compteur proportionnel couplé à un module thermoélectrique. Il permet l’acquisition de manière simple et économique de spectres Mössbauer sur une gamme de température variant de 245 à 375K et sous une induction magnétique externe allant jusqu’à 1,4 T. Un second dispositif a été développé sur la base d’un channeltron™et d’un cryostat à circulation d’hélium pour des acquisitions allant jusqu’à 4 K. Les analyses CEMS ont été réalisées sur des couches minces de différentes épaisseurs de BFO (110) et (001) épitaxiées sur LaAlO3 et SrTiO3. Au-delà d’une épaisseur critique, les couches de BFO (110) présentent un mélange de phases magnétiques colinéaire et cycloïdale. La phase colinéaire présente un axe d’anisotropie suivant [001] dans le plan de la couche et lamodulation cycloïdale se propage dans un plan perpendiculaire à celui-ci. Des effets combinés de contraintes et dimensionnalité ont été avancés pour expliquer la déstabilisation de la cycloïde pour les couches les plus fines. Dans les couches minces de BFO (001) présentant une phase tétragonale de BFO, les mesures CEMS ont montré que la température de mise en ordre magnétique se rapproche de l’ambiante lorsque l’épaisseur des couches diminueThis work is devoted to the development of two Mössbauer detectors dedicated to thin films studies by conversion electron Mössbauer spectrometry (CEMS), and to their use for the characterization of bismuth ferrite BiFeO3 (BFO) epitaxials thin films. The first designed instrument is composed of a proportional counter and a thermoelectric module. It allows CEMS acquisitions of Mössbauer spectra from 245 to 375K with an external magnetic field upto 1.4 T. The second device is based on a commercial channeltron™ and a continuous flow cryostat allowing measurements downto 4 K. The CEMS measurements have been performed on (110) and (001) oriented BFO layers with various thickness deposited on LaAlO3 et SrTiO3 substrates. Beyond a critical thickness, the (110) BFO exhibits a mixing of collinear and cycloidal magnetic phases. The collinear phase shows an anisotropy axis [001] direction which is located in the sample plane. The cycloid propagation plane have been found to be perpendicular to the sample plane. Both epitaxial strain and size effects have been proposed to explain the cycloid destabilization in the thinner films. In (001) BFO thin films, exhibiting a BFO tetragonal phase, the CEMS measurements have shown that the magnetic ordering temperature tends to decrease with the layer thickness