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Dissertations / Theses on the topic 'Magnetic properties of solids'
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1
Obertelli, S. D. "Magnetic properties of low-dimensional solids." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305925.
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Coomber, Andrew Treeve. "Magnetic and electrical properties of low dimensional molecular solids." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387616.
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Harrison, W. T. A. "Structural and magnetic properties of some mixed metal oxides." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379947.
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Ranmohotti, Kulugammana G. S. "Synthesis, structure and magnetic properties of oxy-anion based magnetic solids containing transition metal oxide nanostructures." Connect to this title online, 2008. http://etd.lib.clemson.edu/documents/1233347528/.
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Harrison, Richard John. "Magnetic properties of the magnetite-spinel solid solution." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603779.
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The intrinsic magnetic properties of Fe-bearing solid solutions with the "spinel" crystal structure are determined to a large extent by the processes of non-convergent cation ordering and subsolvus exsolution. The aim of this dissertation is to investigate the interaction between these processes and the magnetic properties of the magnetite-spinel solid solution, with a view to assessing how these factors might influence the acquisition of natural remanent magnetization in other Fe-bearing solid solutions. Temperature and compositional variations in the state of non-convergent cation order are determined using a macroscopic thermodynamic theory, which is calibrated using cation ordering and phase equilibrium constraints from the literature. The cation distribution in the solid solution is calculated for various temperatures and used to derive the ideal variation in saturation magnetization as a function of composition. A compensation point is predicted at approximately 70 mol% MgA1<SUB>2</SUB>O<SUB>4</SUB>, which is confirmed by experimental measurement of the saturation magnetization in synthetic samples. The magnetic properties of synthetic samples are sensitive to rapid changes in the distribution of Fe<SUP>2+</SUP> and Fe<SUP>3+</SUP> cations which occur during quenching. The kinetics of this ordering process are investigated using the Ginzburg-Landau rate law, which is used to calculate the ordering behaviour during quenching, isothermal annealing and temperature ramp experiments. The calculations show that rapid relaxation of the Fe<SUP>2+</SUP>-Fe<SUP>3+</SUP> distribution occurs when intermediate members of the solid solution are heated above 400°C, and there is hysteresis in the degree of order during repeated heating and cooling cycles. Both these effects are confirmed by measurements of magnetic susceptibility versus temperature.
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Petit, Leon. "Screened real-space Korringa-Kohn-Rostoker description of the magnetic properties of solids." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310727.
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Bertrand, Renee. "Magnetic properties of asbestos." Thesis, Open University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235729.
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Horsfall, Alton Barrett. "Electrical and magnetic properties of II-VI diluted magnetic semiconductors." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4984/.
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The electrical and magnetic properties of MOVPE grown epitaxial layers of Hg(_1-x)Mn(_x)Te layers has been investigated using a number of techniques. The samples have been grown by the Inter Diffused Multilayer Process, (IMP) on (100) semi insulating GaAs substrates with ZnTe and CdTe buffer layers. The samples have been shown to show a number of phenomena nopt observed in the bulk material, such as an anomaly in the resistivity, rnagnetoresistance related to the intrinsic magnetism of the material, and saturation of the room temperature magnetisation. In general the samples are of a highly compensated nature with the value of |R(_H)e|(^-1) varying between l0(^14) and 5xI0(^17) cm(^-3) at 20K, the Hall mobilities varying between 8 and 3.5x10(^5) cm(^2)V(^-1)s(^-1) at 20K. Magnetically, the samples generally show a paramagnetic signal that is swamped by the diamagnetic background of the substrate and buffer layers. The paramagnetisrn can be well modelled using a Curie Weiss fit. A number of the samples show a saturation in the magnetisation, which, has been explained via the use of vacancy ordering within MnTe regions in the sample. The susceptibility of the samples has been investigated using a Faraday balance system, and this data has been fitted using; a cluster model for Mn ions within the sample. The photomagnetisation of Cd(_0.9)Mn(_0.1)Te:In has been investigated using a faraday balance system, and modelled using the work of Dietl and Sample, to calculate the number of polarons that had formed on donors in the sample, ΔN(_D)(^MAG) = 1.28x10(^15)cm(^-3). The number of donors in the sample has been measured by means of the Hall effect, ΔN(_D)(^ELEC) = 1.92x10(^15)cm(^-3), and this value compared to that obtained from the model. We have proposed a model to explain this discrepancy based on the concept of band tails in the impurity band.
9
Lambrick, David Brynne. "Magnetic properties of metallic fine particle systems." Thesis, Durham University, 1986. http://etheses.dur.ac.uk/7087/.
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A study of the magnetic properties of metallic fine particle systems in the form of magnetic fluids has been made. The fluids were prepared utilising the organometallic decomposition route (detailed separately by N. Mason, Ph.D. thesis, Durham University 1986) and single metal systems containing Fe, Co and Ni were prepared from new precursors. The properties of the first hydrocarbon based mixed metal particle systems are also reported. For systems prepared with Fe precursors it is thought that the fine particles are not in the α-Fe phase but may be amorphous and/or consist of iron carbides. Co and Ni systems result in particles with bulk-metal like structures although Co usually forms in the f.c.c. phase. The h.c.p. is also observed. The mixed metal systems were of FeCo and Ni(_3)Fe and a tendency to form the superlattice or ordered structures was observed. In both cases Fe has been lost to the particles and this is thought to be due to the formation of volatile iron compounds during preparation and/or surfactant complexes. Narrow size distributions have been obtained in all cases with mean particle diameters in the range 4-10 nm and standard deviations of between 0.8 and 1.9. The form of the size distribution has been found to be Gaussian. A study of the anisotropy of the particles using torque and magnetisation measurements has found uniaxial anisotropy with the first anisotropy constant of the order lO(^5)Jmֿ(^3).The values observed are too large to be ascribed solely to shape anisotropy. Low temperature magnetisation measurements have revealed the existence of a paramagnetic component in the fluids. Loss of magnetisation has occurred in all systems and is thought to be due to oxidation of the metal.
10
Thompson, Sarah M. "The magnetic properties of plastically deformed steels." Thesis, Durham University, 1991. http://etheses.dur.ac.uk/3600/.
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This study concentrates on low carbon pearlitic steels. Two sets of experiments are carried out, the first on a section of semi-killed gas pipe and the second on specially prepared alloys of iron and carbon with pearlite fractions varying from 0.19% to 100%. Their magnetic properties are studied both in the as received state and after tensile plastic deformation. In addition, four different heat treatments are applied to the low carbon steel. Standard magnetisation and fluxmeter techniques are used to determine the bulk magnetic properties, with further use of a vibrating sample magnetometer for coercivity measurements. The Barkhausen noise of the samples is also recorded and High Voltage Lorentz Electron Microscopy used to directly observe the domain configurations and the interaction of the domain walls with dislocation tangles. The changes in the magnetic properties after tensile deformation are similar to those due to elastic compressive stress, with an additional increase in the coercivity. For the initial magnetisation curve initial permeability (J-Li) and maximum relative permeability both decrease, while the field at which the latter occurs (Hm) increases. The hysteresis curve shears over reducing the maximum differential permeability and the remanence and also increasing the coercivity. These results and the change in the shape of the hysteresis curve, most noticeable in the low carbon steels, are explained in terms of the reduction in easy domain wall movement due to the dislocation tangles, as observed under the electron microscope, and to the magnetostrictive effect of the compressive residual stress. Inter-relationships are found between coercivity and both J-Li and Hm. The coercivity io also found to vary linearly with both Vickers Hardness and Yield Stress. The Kneppo formula for the initial magnetisation curve is found to hold better for the higher carbon content steels with the fit deteriorating with increasing plastic deformation.
11
Stanley, H. B. "Magnetic properties of rare-earth single crystals." Thesis, University of Southampton, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356720.
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Simpson, John Andrew. "Magnetic properties of rare-earth elements and superlattices." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308539.
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Cook, A. J. "Electrical and magnetic properties of high temperature superconductors." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240538.
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Bentall, Mark J. "Structure and magnetic properties of thin films and superlattices." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269864.
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15
Walker, Michelle. "Modelling of the magnetic properties of fine particle systems." Thesis, Bangor University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303081.
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Gregory, Christopher Ian. "Magnetic properties of the itinerant helimagnets MnSi and FeGe." Thesis, Durham University, 1992. http://etheses.dur.ac.uk/6057/.
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This thesis describes high quality magnetisation measurements made on single crystals of MnSi, FeGe and ZrZn(_2) using a vibrating sample magnetometer. The measurements on MnSi have also been complemented with neutron scattering experiments. MnSi is a heavily investigated itinerant helimagnet which exhibits a variety of interesting phenomena associated with formation of a helical spin density wave propagating along < 111 > directions. Magnetisation measurements were performed as a function of magnetic field at fixed temperatures stepping through the magnetic transition observed at 29.1 ± 0.05K. These were found to be highly anisotropic and included observation of the so-called 'Phase A' consistent with measurements using other techniques and providing explanation of apparent anomalies in previous magnetisation data (Kadowaki et al. (1981)). Further investigation of 'Phase A' using small angle neutron scattering (SANS) was successful in determining the magnetic state of MnSi within this regime in terms of helix reorientation which is shown to be broadly consistent with the expression for the free energy derived by Bak and Jensen (1980) and Plumer and Walker (1981). Reorientation of the helical spin density wave as a function of magnetic field was also studied using SANS to complement the magnetisation measurements. The second order process observed is similar to that predicted by Plumer and Walker (1981) and the form of their model for the magnetisation of is compared with the experimental results. Finally, anomalous magnetisation measurements close to the magnetic transition were further explored through neutron scattering. The results suggest a possible isotropic phase pre-empting the helical spin density wave formation. Cubic FeGe is also capable of supporting a static helical spin density wave and has a critical temperature of 278.7K with helix propagating along < 100 > directions above 211K and along < 111 > directions below 211K (for decreasing temperatures). Magnetisation measurements were made on cubic FeGe with magnetic field applied parallel to the < 100 > direction and the magnetic phase diagram determined. Coupled with the SANS data of Lebech et al. (1989) it shows similar processes in terms of helix reorientation in an applied magnetic field occur for both FeGe and MnSi. The magnetic phase diagram is in good agreement with that predicted by Plumer (1990) for magnetic field applied parallel to the < 100 >
17
Al-Jiboory, Muhammed Mekki. "Magnetic and microstructural properties of single crystal terfenol-D." Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333993.
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Yoshizawa, Kazunari. "STUDIES ON ELECTRONIC AND MAGNETIC PROPERTIES IN SOLID STATE CHEMISTRY." Kyoto University, 1992. http://hdl.handle.net/2433/168752.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである<br>Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(工学)<br>甲第5090号<br>工博第1211号<br>新制||工||864(附属図書館)<br>UT51-92-J137<br>京都大学大学院工学研究科分子工学専攻<br>(主査)教授 山邊 時雄, 教授 清水 剛夫, 教授 藤本 博<br>学位規則第4条第1項該当
19
Bouvier, Philippe. "The magnetic and magneto-optic properties of sputtered granular layers." Thesis, Coventry University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318531.
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Pollard, Robert James. "The microstructure and magnetic properties of NdFeB based permanent magnets." Thesis, University of Salford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328260.
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Bryn-Jacobsen, Caelia. "The structural and magnetic properties of rare-earth alloys and superlattices." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361887.
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Chapman, James R. "Optical properties of highly correlated electron systems in a magnetic field." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389008.
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Lawless, Martin John. "Magneto-optical properties of strained layer and dilute magnetic semiconductor superlattices." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334257.
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Greaves, Simon John. "Magnetic, magneto-optic and microstructural properties of Pt/Co multilayer films." Thesis, University of Salford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333969.
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Purdy, Jonathan Harry. "The magnetic and magnetoelastic properties of amorphous rare earth metal metal alloys." Thesis, University of Hull, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259781.
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Butler, David. "The preparation and magnetic properties of melt spun terbium-iron-boron alloys." Thesis, University of Hull, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328839.
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Hawton, M. J. "An investigation of anisotropic magnetic properties of rare earth iron boron alloys." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6758/.
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In 1983 Sumitomo in Japan and General Motors in the USA both announced the production of new 'super magnets' based on a rare earth iron boron mixture. The Sumitomo magnets are based on an intermetallic compound with a composition Nd(_2)Fe(_14)B. This thesis describes an Investigation towards understanding the reason why permanent magnets made from this material have such favourable magnetic properties. A description is given of a new type of torque magnetometer designed to operate within the bore of a superconducting solenoid to make measurements at a field high enough for this type of material. The construction and testing of the instrument are described. Results are presented of uniaxial magnetocrystalllne anisotropy values calculated from torque measurements and also of magnetisation measurements for R(_2)Fe(_14)B, R=Nd,Ho,Gd and Dy from 4.2K to room temperature. The basal plane anisotropy calculated from torque measurements for Gd(_2)Fe(_14)B from l00K to 300K is also reported. These anisotropy results are related qualitatively to the crystal structure and electronic structure of the rare earth ions. Observations of regions of uniform magnetization, domains, within the material are also described, and the movement of the boundaries between such domains, domain walls, under varying magnetic fields. These movements’ characterise the material and help In understanding the processes Involved in making a magnet resistant to demagnetisation. From the observation of equilibrium domain wall patterns domain wall energies and domain wall thicknesses have been calculated.
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Papakonstantinou, Pagona. "Magnetic, optical and magneto-optical properties of Co/Ti substituted barium hexaferrite." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241427.
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Williams, Paul Ieuan. "The magnetic and magnetostrictive properties of rare earth - transition metal alloy films." Thesis, University of Salford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315402.
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Baskar, Dinesh. "High temperature magnetic properties of transition metal oxides with perovskite structure /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/9812.
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Tzou, Der-Lii M. "Solid state 13C NMR studies of the Morphology and orientational order of polymer fibers." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/30276.
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El-Hilo, Mohammad. "The effects of magnetostatic interactions on the properties of magnetic fine particle systems." Thesis, Bangor University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276175.
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Yi, Zhu-an. "The preparation and magnetic properties of melt-textured RBaâ†2Cuâ†3Oâ†x superconductors." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261621.
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Yamada, Takashi. "Basic properties of Dual Reciprocity Boundary Element Method and applications to magnetic field analysis." Thesis, University of Portsmouth, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240420.
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Atzori, Matteo. "Anilate-based Functional Molecular Materials with Conducting and Magnetic Properties." Thesis, Angers, 2015. http://www.theses.fr/2015ANGE0009/document.
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Ce travail de thèse explore la capacité des ligands anilates d’être employés pour la préparation de nouveaux matériaux moléculaires fonctionnels avec des propriétés magnétiques et de conduction électrique. Les anilates, qui sont les dérivés du 2,5-dihydroxy-1,4- benzoquinone substitués sur les positions 3 et 6, ont été sélectionnés comme ligands puisque leurs caractéristiques électroniques et structurales, leurs modalités de coordination et leur capacité de médiation des interactions de super-échange magnétique en font d’excellents ligands pour la préparation de ces matériaux. Plusieurs ligands anilates ont été utilisés pour le design et la préparation d'une nouvelle classe de complexes paramagnétiques octaédriques tris-chélates de formule générale [MIII(X2An)3]3- (MIII = Cr, Fe; X = Cl, Br, I, H, Cl/CN, An = C6O4 2- = anilate). Ces complexes métalliques paramagnétiques ont été complètement caractérisés et utilisés comme briques moléculaires pour la préparation de i) une nouvelle classe de ferriaimants moléculaires, dans laquelle la modification des substituants sur le ligand permet de modifier les interactions entre les centres métalliques, et, par conséquent, les propriétés magnétiques, ii) des conducteurs paramagnétiques moléculaires obtenus par combinaison avec le donneur organique BEDT-TTF, iii) une série de conducteurs moléculaires chiraux obtenus par combinaison du donneur organique TM-BEDT-TTF avec des couches hétéro-bimétalliques anioniques obtenues par association in situ de complexes tris(chloranilate)ferrate(III) et des ions potassium. En outre, ont été synthétisés de nouveaux dérivés anilates avec des propriétés electroactives et de luminescence, afin de démontrer la capacité du motif anilate d’être fonctionnalisé avec différents substituants comme porteurs de propriétés physiques spécifiques<br>This work explores the potential of anilate-based ligands in the synthesis of new rational designed functional molecular materials exhibiting improved magnetic and conducting properties. Anilates, namely 3,6-disubstitued 2,5-dihyroxy-1,4- benzoquinones in their dianionic form, have been selected as ligands since their electronic/structural features, coordination modes and ability to mediate magnetic exchange interactions between coordinated metal centers make them potential candidates for the preparation of theabove-mentioned materials. Various anilate derivatives have been used for the preparation of a family of rationally designed tris-chelated octahedral paramagnetic metal complexes of general formula [MIII(X2An)3]3- (MIII = Cr, Fe; X = Cl, Br, I, H, Cl/CN, An = C6O4 2- = anilate). These paramagnetic metal complexes have been thoroughly characterized and used, in turn, as molecular building blocks for the preparation of i) a family of molecule-based magnets, where subtle changes in the nature of the substituents on the anilate moiety were employed as “adjusting screws” in tuning the magnitude of the magnetic interaction between the metals, and thus, the magnetic properties, ii) hybrid paramagnetic molecular conductors in combination with the BEDT-TTF organic donor, iii) a complete series of isostructural chiral molecular conductors obtained by combining the TMBEDT- TTF chiral donor with 2D heterobimetallic anionic layers obtained in situ by the self-assembling of tris (chloranilato)ferrate(III) metal complexes and potassium cations.Moreover, novel anilate derivatives showing electroactive and luminescent properties have been further synthesized, highlighting the versatility of the anilate moiety to be functionalized with suitable substituents carrying selected physical properties
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Newnham, Sharon. "Studies of the microstructure and magnetic properties of Nd-Fe-B based permanent magnet materials." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260188.
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Adnan, Johari Bin. "Development of instruments for the study of magnetic properties of recording materials, minerals and rocks." Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316241.
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Marques, Marcelo. "Estudo teórico das ligas quaternárias semicondutoras AlxGayIn1-x-yX (X=As, P ou N) e do sistema semicondutor magnético (Ga,Mn)N." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-07032014-145041/.
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Este trabalho pode ser dividido em duas partes. Na primeira, estudamos a série de ligas quaternárias \'Al IND. x\'\'Ga IND. y\'\'In IND. 1-x-y\'As, \'Al IND. x\'\'Ga IND. y\'\'In IND. 1-x-Y\', e \'Al IND. x\'\'Ga IND. y\'\'In IND. 1-x-y\'N. Estes sistemas são muito importantes do ponto de vista tecnológico, principalmente na optoeletrônica. O estudo é feito através de cálculos de estrutura eletrônica baseados na teoria do funcional da densidade (TFD) (com o uso de pseudopotenciais ultrasuaves) combinados com métodos estatísticos, como o Monte Carlo e o método da Abordagem Quase-Química Generalizada. Estes últimos foram desenvolvidos neste trabalho para descrição adequada de sistemas complexos como estas ligas semicondutoras. Obtemos suas propriedades eletrônicas, estruturais e termodinâmicas em função da composição dos átomos da liga e da temperatura de crescimento do sistema. Por último neste estudo, propomos um modelo que descreve o mecanismo de emissão de luz na liga quaternária de nitreto AlGaInN, sendo este assunto ainda bastante controverso na literatura. O modelo é baseado na formação de aglomerados de InN e GaInN, e explica as diferentes emissões no ultravioleta e no verde observados na liga AlGaInN. Na segunda parte, estudamos o sistema semicondutor magnético diluído (Ga,Mn)N que é muito promissor para futuras aplicações na nova tecnologia da spintrônica. Para isto, utilizamos também a TFD, mas dependente de spin e com o uso do método Projector Augmented Wave-PAW. Inicialmente, estudamos o MnN nas estruturas dos nitretos, que são a zincblende (zb) e a wurtzita (w). Obtemos um estado fundamental antiferromagnético (AFM) para o MnN-zb e ferromagnético (FM) para o MnN-w. No entanto, verificamos que o estado fundamental é muito suscetível à aplicação de uma tensão hidrostática, que nos levou a sugerir um modelo em que o magnetismo observado na liga GaMnN pode estar relacionado com inclusões de MnN tensionadas, com estado fundamental AFM, ou inclusões relaxadas, com estado fundamental FM. Em seguida, estudamos super-redes do tipo GaN-w/MnN-w formadas a partir de duas até seis camadas de MnN. Obtivemos um estado fundamental FM, o que é muito interessante para aplicações em spintrônica. Por último, estudamos o caso de apenas uma camada de \'Mn IND. x\'\'Ga IND. 1-x\'\'N\', imersa em GaN. Este sistema tem estado fundamental AFM e metálico para 100 % de Mn, o qual, entretanto, muda para FM e meio-metálico à medida que a concentração de Ga aumenta. Iniciamos o estudo desta liga bidimensional, propondo um Hamiltoniano modelo de Ising para descrever as interações neste sistema.<br>This work can be divided in two parts. In the first part, we studied the series of AlxGayIn1-x-yAs, AlxGayIn1-x-yP, and AlxGayIn1-x-yN quaternary alloys. These systems are very important in a technological point of view, mainly for optoelectronic applications. We performed band structure calculations based on Density Functional Theory (DFT) (employing ultrasoft pseudopotentials) combined with statistical methods, as the Monte Carlo and the Generalized Quasi-Chemical Approach. These two latter methods were developed in this work, in order to have a suitable description of quaternary alloys, which are very complex systems. We obtained their structural, thermodynamic, and electronic properties as a function of the atomic composition in the alloy and the growth temperature of the system. At the end of this first part, we propose a model to describe the emission mechanism in the AlGaInN quaternary alloys. This subject is still a matter of controversy in the literature. Our model is based on the formation of InN and GaInN clusters, and it explains the different light emissions in the ultraviolet and green regions of the spectrum, observed in the AlGaInN samples. In the second part of the work, we studied the diluted magnetic semiconductor system (Ga,Mn)N, which is one of the main candidates for the future applications in the spintronic new technology. For this study, we used spin DFT, solving the Kohn-Sham equations with the Projector Augmented Wave (PAW) method. Firstly, we studied the MnN in the nitrides (AlN, GaN, and InN) structures, which are the zincblende (zb) and the wurtzite (w). We obtained an antiferromagnetic (AFM) ground state for the zb-MnN, and a ferromagnetic (FM) ground state for the w-MnN. However, we verified that the ground state is very sensitive to the application of a hydrostatic strain. These results, led us to suggest that maybe the magnetism observed in the GaMnN alloys can be related with relaxed inclusions of MnN (with a FM ground state) or strained inclusions of MnN (with an AFM ground state). After this, we studied w-GaN/w-MnN superlattices, with the MnN layer formed by 2, 4, and 6 monolayers of w-MnN. We obtained a FM ground state for this system, which is very interesting for spintronic applications. Finally, we studied the case of only one monolayer of MnxGa1-xN in w-GaN. This system presents an AFM ground state for 100 % of Mn, but changes to a FM half-metalic state as the Ga composition increases. In this work we started the study of the MnxGa1-x \"bidimensional alloy\" system, proposing an Ising model Hamiltonian to describe the interactions among the Mn atoms in the system.
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Dungate, David George. "A theoretical study of the magnetic and superconducting properties of strongly interacting d and f electron systems." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239615.
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Richard, Laura Amanda. "A study of the crystallographic, magnetic and electronic properties of selected ZrM2-H systems." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:276c59fe-cf45-42d2-a5a0-8c534c8b46bd.
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Dissolution of hydrogen into intermetallic compounds characteristically occurs at interstitial sites, causing little alteration to the base metal substructure but often bringing about substantial electronic and magnetic changes to the material. These hydrogen-induced alterations in the intermetallic hydrides are of interest both on a fundamental research level and in terms of technological applications; however, there exists no general theory as to how and why these alterations arise. The objective of this research is to elucidate to general effect of hydrogen on intermetallic compounds through the study of crystallographic, magnetic and electronic properties. An investigation has been carried out on the properties of three intermetallic compound - hydrogen systems of general formula ZrM₂, where M = V, Cr, Mn. All three compounds reversibly absorbed hydrogen with no change in crystal symmetry: powder diffraction studies showed that hydrogen was accommodated in interstitial sites of the existing metal sublattice via lattice expansion. The measurement of the magnetic properties of these systems was combined with the determination of conductivity and dielectric properties in order to describe the electronic e¤ects of hydrogen absorption. Despite the lack of signi
cant structural alteration in these systems, electron transfer between the metal sublattice and hydrogen may occur, as manifested in the appearance/disappearance of magnetic phenomena and the increase/decrease of electrical conductivity. Whilst the hydrogen addition in ZrM₂-H occurs simply via an expansion of the crystal structure, hydrogen does not act purely as null dilutant - there exist subtle electronic changes connected with the hydriding process as well.
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Pan, Genhua. "Investigation into the microstructure, magnetic properties and read/write performance of thin-film media for perpendicular recording computer disks." Thesis, University of Plymouth, 1993. http://hdl.handle.net/10026.1/2363.
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Pronounced effect of under layers on the squareness and slope T of the perpendicular loops of very thin CoCr films was observed. Experimental and theoretical studies suggest that, depending on the film microstructure, there are two origins on the anomalous shearing of perpendicular loops of Cc-based perpendicular films: the columnar shape anisotropy and the wall-motion-like magnetization reversal process. For films with larger intercolumnar separation, the contribution of the columnar shape anisotropy to the total demagnetizing factor is mainly responsible for the deshearing of the loops. For continuous perpendicular films, the intergranular exchange coupling controls the magnetization reversal process and the wall-motion-like reversal explains the anomalous shearing of the hysteresis loop. The square and desheared perpendicular loops of very thin CoCr films originated from their strong perpendicular anisotropy and large intergranular nonmagnetic separation. Study of the orientation relationship between the Co-based films and their underlayers suggested that the texture of the very thin CoCr and CoCrTa films is determined by the thermodynamic nature of hcp Co crystal itself and the nature of the underlayers or substrates on which it grows. Amorphous underlayers provide "neutral" substrate surfaces for. the [0002] self-oriented growth of hcp Co-based films. Hcp Ti and [111] textural fee Pt, Au underlayers favour the [0002] oriented epitaxial growth. [100] or [110] textural bee Cr underlayers favour the [1010] oriented growth. The perpendicular coercivity of a Co-based medium is determined by its crystalline anisotropy and intergranular exchange coupling, and can be largely affected by the morphology of its underlayers. The larger perpendicular coercivity of the CoCrTa films on Ti underlayers was mainly due to the large grain diameter which results in a reduction in the intergranular exchange coupling constant. The difference between the surface and bulk coercivity of the CoCrTa films on Ti underlayers was attributed to the improvement of the crystallographic orientation of the hcp Co crystals and the development of large grains as the film grows thicker, which causes the reduction in the surface intergranular exchange coupling due to large grains as well as large intergranular separation. Co84Nb12Fe4 amorphous films were investigated as back-layers for double layer media. Very low coercivity down to 0.0125 Oe was achieved for films of 10000 Å-thick with a saturation magnetic induction of 11 kG. The thickness dependence of coercivity follows the Neel formula for films thicker than 400 Å. A D5o density of 160 KFRPI was achieved for the 2000 Å-thick medium on Pt underlayers using MIG heads of gap length 0.15 µm. Experimental and theoretical analyses of the read/write processes show both the achieved D5o density and the reproduced output level for these media were head field and head-medium spacing limited. Lower medium noise and higher SNR were achieved by the media with Ti underlayers, which supports the intergranular exchange coupling noise theory.
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Huang, Mantao. "Voltage control of electrical, optical and magnetic properties of materials by solid state ionic transport and electrochemical reactions." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127898.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, May, 2020<br>Cataloged from the official PDF of thesis.<br>Includes bibliographical references (pages 139-153).<br>Reversible post-fabrication control of material properties enables devices that can adapt to different needs or environmental conditions, and brings additional levels of functionality, paving the way towards applications such as reconfigurable electronics, reconfigurable antennas, active optical devices and energy efficient data storage. One promising way of achieving the controllability is through solid-state ionic transport and electrochemical reactions in thin film structures, where the properties of materials can be electrically controlled by a gate voltage in an addressable way. Here we explore using such ionic gating method to control the electrical, optical and magnetic properties of solid-state thin film layers, and show that large modification can be achieved for a wide range of properties. We demonstrate a new type of three terminal resistive switching device where the resistivity of a thin film conductive channel can be controlled by a gate voltage. We demonstrate solid-state ionic gating of the optical properties of metals and oxides and show the versatility of the approach by implementing voltage-controlled transmission, thin film interference, and switchable plasmonic colors. We also show that the approach allows for voltage control of ferrimagnetic order, demonstrating voltage induced 180-degree switching of the Néel vector, as a new way of magnetic bit writing. These findings extend the scope of voltage programmable materials and provide insights into the mechanisms of voltage controlled material properties by solid-state ionic transport and electrochemical reactions.<br>by Mantao Huang.<br>Ph. D.<br>Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Akintunde, Babajide O. "A study on the effect of Fe-Ni variation on the magnetocaloric properties of Mn0.5Fe0.5+xNi1-xSi0.94Al0.06 and Mn0.5Fe0.5-xNi1+xSi0.94Al0.06 systems." Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami16267284137581.
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Esters, Marco. "Experimental and Computational Investigations of Kinetically Stable Selenides Synthesized by the Modulated Elemental Reactants Method." Thesis, University of Oregon, 2018. http://hdl.handle.net/1794/23175.
Full textAbstract:
The controlled and targeted synthesis of new solid materials is still a challenge difficult to overcome. Slow diffusion rates and long diffusion lengths require long reaction times and high synthesis temperatures, resulting in limited control over the reaction pathway. The Modulated Elemental Reactants (MER) method uses compositionally modulated precursors with atomically thin elemental layers that form amorphous alloys upon annealing while maintaining composition modulation. In this amorphous intermediate, nucleation, not diffusion, control the formation of the product, enabling kinetic control of the reaction, and the synthesis of new metastable compounds, heterostructures with designed nanoarchitecture, and thin films with a high degree of texturing.
This dissertation uses experimental and computational methods to investigate compounds synthesized by the MER method. Firth, the MER method is used to synthesize ferromagnetic CuCr2Se4 films that show a large degree of crystallographic alignment and interesting magnetic properties such as temperature-dependent easy axes and negative magnetoresistivity.
The second part investigates ferecrystals, rotationally disordered members of the misfit layer compounds family. The MER method’s ability to control the nanoarchitecture of the products is used to synthesize a new type of structural isomers, allowing for the synthesis of thousands of ternary compounds using the same elements. Experimental methods are also used to monitor the formation of ferecrystalline compounds using [(SnSe)1+δ][VSe2] as a model system.
Despite the vast number of compounds available, however, explaining the properties and stability of ferecrystals is still in its infancy. In the last part of this dissertation, ab initio methods are employed to investigate the components in our ferecrystals. Specifically, isolated layers of VSe2 with its structural distortions due to a charge density wave, SnSe with its thickness-dependent structures, and BiSe with its flexible lattice and anti-phase boundaries are investigated to complement experimental results. Some properties, such as the structural distortion in VSe2 and the different stabilities of BiSe layers, can be explained very well using this simplified model, but others, such as the structure of SnSe layers, are not exclusively determined by their dimensionality, underlining the complex nature of the interactions in ferecrystals.
This dissertation includes previously published and unpublished co-authored material.
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Chaudhary, Praveen, and University of Lethbridge Faculty of Arts and Science. "Lewis-acid and fluoride-ion donor properties of SF₄ and solid-state NMR spectroscopy of Me₃SnF." Thesis, Lethbridge, Alta. : University of Lethbridge, Dept. of Chemistry and Biochemistry, c2011, 2011. http://hdl.handle.net/10133/2621.
Full textAbstract:
Trimethyltin fluoride (Me3SnF) is a useful fluorinating agent in organometallic
chemistry. Its solid-state structure has been investigated by X-ray crystallography
showing a polymeric fluorine-bridged structure. Disorder, however, has precluded the
accurate refinement of all structural parameters. In order to obtain accurate structural
information, trimethyltin fluoride was investigated using high-resolution 13C, 19F, and
119Sn solid-state NMR spectroscopy using a four-channel HFXY capability. The
119Sn{1H} solid-state NMR spectrum agrees with pentacoordination about Sn in this
compound. The high-resolution 119Sn{19F, 1H}, 13C{1H,19F} and 19F{1H} NMR spectra offer unambiguous determination of 1J(119Sn-19F) and 1J(119Sn-13C) coupling constants. Furthermore, the analysis of the 119Sn{19F, 1H}, 119Sn{1H}, and 19F{1H} MAS spectra as a function of spinning speed allowed for the determination of the 119Sn CSA and J anisotropy, as well as the 119Sn-19F dipolar couplings. These were determined via SIMPSON simulations of the 13C, 19F, and 119Sn NMR spectra. Finally the 119Sn{19F, 1H} revealed fine structure as the result of 119Sn-117Sn two bond J-coupling, seen here for the first time. Sulfur tetrafluoride can act as a Lewis acid. Claims had been presented for the formation of an adduct between SF4 and pyridine, but no conclusive characterization had been performed. In the present study, adducts of SF4 with pyridine, lutidine, 4-picoline and triethylamine were prepared and characterized by low-temperature Raman spectroscopy. Sulfur tetrafluoride also acts as a fluoride-ion donor towards strong Lewis acids, such as AsF5 and SbF5, forming SF3
+ salts. Variable-temperature (VT) solid-state 19F NMR spectroscopy showed that SF3
+SbF6 – exists in three phases with phase transitions at ca. –45 and –85°C, while SF3
+AsF6 – exists only as one phase between +20 and –150 °C. The phases of SF3
+AsF6 – were also characterized by VT Raman spectroscopy.<br>xvi, 170 leaves : ill. (some col.) ; 29 cm
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Mastrogiacomo, Giovanni. "Development of Fe-based metallic glasses via destabilization of the solid state and characterization of their magnetic and electrical properties /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17634.
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Schliesser, Jacob M. "Development and Application of New Solid-State Models for Low-Energy Vibrations, Lattice Defects, Entropies of Mixing, and Magnetic Properties." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5841.
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Low-temperature heat capacity data contain information on the physical properties of materials, and new models continue to be developed to aid in the analysis and interpretation of heat capacity data into physically meaningful properties. This work presents the development of two such models and their application to real material systems. Equations describing low-energy vibrational modes with a gap in the density of states (DOS) have been derived and tested on several material systems with known gaps in the DOS, and the origins of such gaps in the DOS are presented. Lattice vacancies have been shown to produce a two-level system that can be modeled with a sum of low-energy Schottky anomalies that produce an overall linear dependence on temperature in the low-temperature heat capacity data. These two models for gaps in the vibrational DOS and the relationship between a linear heat capacity and lattice vacancies and many well-known models have been applied to several systems of materials to test their validity and applicability as well as provide greater information on the systems themselves. A series of bulk and nanoscale Mn-Fe and Co-Fe spinel solid solutions were analyzed using the entropies derived from heat capacity data, and excess entropies of mixing were determined. These entropies show that changes in valence, cation distribution, bonding, and the microstructure between the mixing ions is non-ideal, especially in the nanoparticles. The heat capacity data of ten Al doped TiO2 anatase nanoparticle samples have also been analyzed to show that the Al3+ dopant ions form small regions of short-range order, similar to a glass, within the TiO2 particles, while the overall structure of TiO2 remains unchanged. This has been supported by X-ray diffraction (XRD) and electron energy-loss spectroscopy and provides new insights to the synthesis and characterization of doped materials. The final investigation examines nanocrystalline CuO using heat capacities, magnetization, XRD, and electron microscopy and compares the findings to the known properties of bulk CuO. All of these measurements show transitions between antiferromagnetic and paramagnetic states in the temperature range of about 150-350 K that are greater in number and higher in temperature than the transitions in bulk CuO. These changes are shown to cause an increase in the temperature range of multiferroicity in CuO nanoparticles.
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Drew, Daniel L. Jr. "Investigating the Structure and Dynamic Properties of Bacteriophage S21 Pinholin Using Solid-State Nuclear Magnetic Resonance and Electron Paramagnetic Resonance Spectroscopy." Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami1610187893016095.
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Lafuente, Hernández Mª Pilar. "Computational Study of the Mechanisms that Stabilize Organic Molecule‐Based Magnets." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400864.
Full textAbstract:
The objective of this PhD thesis has been the study of the mechanisms that stabilize high-spin states in organic molecule-based magnetic materials. These materials require organic radicals with permanent magnetic moment as building units. Additionally, these molecules need to interact ferromagnetically, and expand that interaction along all three directions of the space.
We have carried out our studies using computational chemistry techniques, mostly ab- initio methods (MP2, CASSCF and CASMP2), and DFT-based methods (B3LYP or M06L). Besides, we have also used the hybrid Molecular Mechanics Valence Bond method (MMVB) for alternant hydrocarbons with high number of active electrons.
We have demonstrated that in organic radicals the energy gap between two spin states is usually higher when the stabilization of the spin centers occurs by means of through- bond (TB) instead of through-space (TS) interactions. As a result, alternant hydrocarbons (π-delocalized, with TB interactions) are more stable than non-alternant hydrocarbons (π-localized, with TS interactions). Therefore, alternant hydrocarbons would be preferable in the design of permanent molecular magnets.
Polymerization of high-spin radicals leads to high-spin systems. However, our research showed that the gap of energy between the first and second spin states decreases with the number of units bonded when these are alternant hydrocarbons. On the other hand, it has been proved that, when the synthesis of macro-radicals follows the SU-CU- SU methodology (SU=spin-containing unit; CU=coupling unit), the SU and CU units keep their multiplicity once coupled. In that case, the energy gap between the spin states of the system can be described considering the energy gap of the spin states of the constitutive units.
McConnell-I theory is widely applied to describe ferromagnetic intermolecular interactions. Our research has revised systematically this approach. We have explored the existence of a magneto-structural relationship using pairs of well-known radicals (H2NO·, ·CH3 and ·C3H5) at different geometrical orientations. We demonstrated that McConnell-I model predicts correctly the spin preference of the ground state when the interacting spin-containing radical centers are placed in parallel planes and there are mainly TS interactions between them. However, in other cases, the prediction of the spin preference becomes very complex, and more detailed quantum calculations are required. Overall, we have demonstrated that this model must be used carefully when predicting the multiplicity of the through-space interaction between two radicals. Further, we evaluated whether McConnell-I theory could be applied to assess the magnetic character of real crystals on the subset of experimentally FM crystals of the α- nitronyl nitroxide (α-NN) family. We analyzed the closest contacts between two intermolecular ONCNO groups (atoms where the spin densities are mainly located) for
each chosen crystal. We concluded that the ONCNO interactions do not describe entirely the observed macroscopic magnetic property for all the systems. Consequently, TS interactions not considered in the simplistic ONCNO model must play an important role defining the magnetic character. Secondly, we proved there is not a simple magneto-structural relationship, such as the one suggested in McConnell-I model, that can be applied to all through-space interactions in the crystals. This conclusion was reached after a twofold statistical analysis (namely, factor and cluster analyses) of the geometrical parameters as a function of the calculated energy gap ΔES-T.
Charge-transfer salts are successful examples of molecular magnets. However, the formation of diamagnetic dimers of the donor species, [D]22+, or the acceptor species, [A]22-, causes the loss of the magnetic properties. We studied the causes of this dimerization studying the formation of TCNE dimers, [TCNE]22-], as a prototypical example of an organic acceptor. The Eint of two charged molecules has two components: the Coulomb contribution (Ecoul > 0, for molecules with the same charge) and the bonding energy (Ebond < 0). If the repulsion energy is higher than the bonding energy in absolute value (|Ecoul|>|Ebond|) the two molecules will repel and the formation of the dimer will not be stable (Eint > 0). However, if there is any force that counterbalances the repulsion between the two charged molecules, the bonding energy could overcome the repulsion energy in absolute value (|Ecoul|<|Ebond|), and the metastable minima would become stable (Eint < 0). The calculations performed described three metastable minima that agree with those observed experimentally. Besides, the spectroscopic features of each class of these three dimers have been calculated and are in agreement with the
available experimental data. Extended calculations performed in the presence of cations or polar solvents resulted in the stabilization of the dimers, which demonstrates that counterbalance of the repulsive energy is needed for the formation of these long multicenter bonds. The two electrons - four centers (2e-/4c) bond described is unique since it involves 2e- and takes place among four carbon atoms chemically equivalent.<br>El objetivo de esta tesis ha sido estudiar computacionalmente las bases teóricas del magnetismo molecular para poder utilizar el conocimiento adquirido en el diseño de materiales magnéticos moleculares. Hemos analizado los mecanismos a través del enlace (TB: through-bond) y a través del espacio (TS: through-space) que estabilizan moléculas de alto spin (radicales) y sus interaccionan intermoleculares ferromagnéticas. Para llevar a cabo dichos estudios se han utilizado métodos híbridos como el Molecular Mechanics Valence Bond (MMVB), métodos DFT como el B3LYP y métodos ab-initio como MP2, CASSCF, y CASMP2.
Así pues, por un lado, se ha estudiado la estabilidad de moléculas orgánicas de alto spin y su posible polimerización manteniendo su alta multiplicidad de spin. Se ha llegado a la conclusión que el mecanismo TS es de menor coste energético que el TB. Por lo tanto, los radicales cuyos centros de spin se estabilizan a través del enlace TB son más estables. Asimismo, compuestos que presentan ambos mecanismos, los estados de spin de los estados fundamental y primer excitado vendrán determinados por el mecanismo TS.
Por otro lado, se estudiaron las interacciones intermoleculares entre radicales, con el objetivo de establecer las condiciones que favorecen las que son ferromagnéticas. En este contexto, se evaluó la teoría denominada McConnell-I. Tras metódicos estudios de la interacción entre dos radicales (H2NO·, ·CH3 y ·C2H6) en diferentes orientaciones en el espacio, se concluyó que el ámbito de aplicación de esta teoría está limitado a cuando los centros de spin interaccionan en planos paralelos y existe una interacción TS predominante. Estudios adicionales en cristales de la familia α-nitronil nitróxido demostraron que la teoría de McConnell-I no se puede aplicar de forma general a cualquier interacción intermolecular entre radicales. Se observó que esta teoría no predice correctamente el comportamiento magnético de cristales cuando se analiza sólo la interacción entre los átomos que contienen mayoritariamente la densidad de spin (ONCNO). Así pues, el estudio se debe ampliar a otros contactos entre las moléculas para poder describir correctamente el comportamiento magnético observado.
Finalmente hemos establecido que, en sales de transferencia de carga, se dan casos de dimerización de las especies constituyentes, por ejemplo tetracianoetileno (TCNE), cuando la repulsión entre especies de la misma carga se minimiza por la presencia de contra-iones o disolventes polares. De esta manera, se favorece la formación del enlace en el dímero al permitir la interacción de los electrones desapareados.
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Yates, Damian Leonard. "An investigation into the effects of different annealing conditions on the magnetic properties of overload Laâ†2â†-â†xSrâ†xCuOâ†4â†-â†#â†dâ†eâ†lâ†tâ†aâ†#." Thesis, University of Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385683.
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