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Bennie, Simon. "Theoretical calculations of the magnetic properties of inorganic molecules." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/theoretical-calculations-of-the-magnetic-properties-of-inorganic-molecules(3070af2e-6621-4f03-a515-f1113fbcc537).html.
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The zero field splittings (ZFS) of inorganic molecules were studied with a view to understanding the applicability of new methods in Density Functional Theory (DFT). The initial thrust of this work was to benchmark the three methods available: Pederson Kahana, quasirestricted orbitals and the coupled perturbed equations. Simple 3d monometallic systems were studied with a unique focus on the effect of adjusting the basis set size of the metal. We also studied the effect of a range of commonly available functionals. We found that by using a large quadruple zeta basis set that the results of general gradient approximation (GGA) functionals can be improved. Hybrid functionals were found not to be as accurate as the GGAs and are often degraded by going to a larger basis. The degree of accuracy appears to be a function of the covalency of the metal to ligand bond as measured by the Mayer bond orders and Mulliken charges. We also present the results for complete active space self consistent field calculations and ZFS values for restricted open DFT determinants coupled with the multi-reference configuration interaction methods of obtaining the ZFS.Chapter 5 of this work focuses of the characterisation of a more complex di- chromium system called Kremer’s dimer. This system has three magnetically active spin states each of which has well-defined ZFS values. Under the broken symmetry method we found no functional to be able to qualitatively reproduce the ordering of the spin state or the ZFS. Through analysis of the natural orbitals and spin eigenvalues we determined that this is due to a strong amount of multi-configurational character. Simple complete active space self consistent field (CASSCF) calculations were found to reproduce the experimental spin ladder. Multi-reference configuration interaction on the CASSCF solutions were found to accurately calculate the experimental ZFS values, with state optimised calculations being the most accurate choice for the CASSCF.
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Hatter, Nino [Verfasser]. "Fundamental Properties of Molecules on Surfaces : Molecular Switching and Interaction of Magnetic Molecules with Superconductors / Nino Hatter." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1123572216/34.
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Chen, Xing. "Theoretical Studies on Magnetic and Photochemical Properties of Organic Molecules." Doctoral thesis, KTH, Teoretisk kemi och biologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-52818.
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The present thesis is concerned with the theoretical studies on magnetic and photochemical properties of organic molecules. The ab initio and first principles theories were employed to investigate the vibrational effects on the isotropic hyperfine coupling constant (HFCC) known as the critical parameter in electron paramagnetic resonance spectrum, the theoretical simulations of the vibronically resolved molecular spectra, the photo-induced reaction mechanism of α-santonin and the spin-forbidden reaction of triplet-state dioxygen with cofactor-free enzyme. The theoretical predictions shed light on the interpretation of experimental observations, the understanding of reaction mechanism, and importantly the guideline and perspective in respect of the popularized applications. We focused on the vibrational corrections to the isotropic HFCCs of hydrogen and carbon atoms in organic radicals. The calculations indicate that the vibrational contributions induce or enhance the effect of spin polarization. A set of rules were stated to guide experimentalist and theoretician in identification of the contributions from the molecular vibrations to HFCCs. And the coupling of spin density with vibrational modes in the backbone is significant and provides the insight into the spin density transfer mechanism in organic π radicals. The spectral characters of the intermediates in solid-state photoarrangement of α-santonin were investigated in order to well understand the underlying experimental spectra. The molecular spectra simulated with Franck-Condon principle show that the positions of the absorption and emission bands of photosantonic acid well match with the experimental observations and the absorption spectrum has a vibrationally resolved character. α-Santonin is the first found organic molecule that has the photoreaction activities. The photorearrangement mechanism is theoretically predicted that the low-lying excited state 1(nπ*) undergoing an intersystem crossing process decays to 3(ππ*) state in the Franck-Condon region. A pathway which is favored in the solid-state reaction requires less space and dynamic advantage on the excited-state potential energy surface (PES). And the other pathway is predominant in the weak polar solvent due to the thermodynamical and dynamical preferences. Lumisantonin is a critical intermediate derived from α-santonin photoreaction. The 3(ππ*) state plays a key role in lumisantonin photolysis. The photolytic pathway is in advantage of dynamics and thermodynamics on the triplet-state PES. In contrast, the other reaction pathway is facile for pyrolysis ascribed to a stable intermediate formed on the ground-state PES. The mechanism of the oxidation reaction involving cofactor-free enzyme and triplet-state dioxygen were studied. The theoretical calculations show that the charge-transfer mechanism is not a sole way to make a spin-forbidden oxidation allowed. It is more likely to take place in the reactant consisting of a non-conjugated substrate. The other mechanism involving the surface hopping between the triplet- and singlet-state PESs via a minimum energy crossing point (MECP) without a significant charge migration. The electronic state of MECP exhibits a mixed characteristic of the singlet and triplet states. The enhanced conjugation of the substrate slows down the spin-flip rate, and this step can in fact control the rate of the reaction that a dioxygen attaches to a substrate.QC 20111220
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Haque, Md Firoze H. "Single-electron transport spectroscopy studies of magnetic molecules and nanoparticles." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4914.
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Magnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles are found to behave ferromagnetically for diameters below a few nanometers. Some of these manifestations are still intriguing, and novel research approaches are necessary to advance towards a more complete understanding of these exciting nanoscale systems. In particular, the ability to study an isolated individual nanoscale system (i.e just one molecule or nanoparticle) is both challenging technologically and fundamentally essential. It is expected that accessing to the energy landscape of an isolated molecule/nanoparticle will allow unprecedented knowledge of the basic properties that are usually masked by collective phenomena when the systems are found in large ensembles or in their crystal form. Several approaches to this problem are currently under development by a number of research groups. For instance, some groups are developing deposition techniques to create patterned thin films of isolated magnetic nanoparticles and molecular magnets by means of optical lithography, low-energy laser ablation, or pulsed-laser evaporation or specific chemical functionalization of metallic surfaces with special molecular ligands. However, it is still a challenge to access the properties of an individual molecule or nanoparticle within a film or substrate. I have studied molecular nanomagnets and ferromagnetic noble metal nanoparticles by means of a novel experimental approach that mixes the chemical functionalization of nano-systems with the use of single-electron transistors (SETs). I have observed the Coulomb-blockade single-electron transport response through magnetic gold nanoparticles and single-molecule magnet. In particular, Coulomb-blockade response of a Mn[sub4]-based SET device recorded at 240 mK revealed the appearance of two diamonds (two charge states) with a clear switch between one and the other is indicative of a conformational switching of the molecule between two different states. The excitations inside the diamonds move with magnetic field. The curvature of the excitations and the fact of having them not going down to zero energy for zero magnetic field, indicated the presence of magnetic anisotropy (zero-field splitting) in the molecule. In addition, the high magnetic field slope of the excitations indicates that transitions between charge states differ by a net spin value equal to 9 (|ΔS| = 9), as expected from the behavior of Mn4 molecules in their crystalline form. Anticrossings between different excitations are indicative of quantum superpositions of the molecular states, which are observed for the first time in transport measurements through and individual SMM.ID: 029810145; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 92-98).
Ph.D.
Doctorate
Physics
Sciences
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Hu, Jianming, and 胡建明. "Macroscopic quantum phenomenon in molecular magnets." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B26724674.
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Olegário, Raquel Maria. "Theoretical studies of electronic structure and magnetic properties of small molecules." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627171.
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Kahle, Steffen [Verfasser]. "Magnetic Properties of Individual Molecules Studied by Scanning Tunneling Microscopy / Steffen Kahle." Konstanz : Bibliothek der Universität Konstanz, 2013. http://d-nb.info/1045154156/34.
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Fukuda, Ryoichi. "Relativistic quantum chemistry for the magnetic properties of molecules including heavy elements." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/148843.
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Warner, B. "Engineering the properties of magnetic molecules through the interaction with the surface." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1455711/.
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The drive to continue Moore’s Law by shrinking electrical components down to the ultimate limit has led to a great deal of interest in atomic and molecular-scale electronics, in which individual atoms and molecules can be used as circuit elements. More recent proposals also seek to exploit the magnetic properties of these nanoscale objects in new applications in information technology and spintronics. In typical device geometries, the magnetic element is coupled to electrical leads, and these interactions can strongly affect the properties of the quantum system. Using scanning tunneling microscopy and spectroscopy, we study the effects of inter- actions between individual magnetic atoms and molecules that are separated from an underlying metallic surface by a thin insulating layer of copper nitride (Cu2N). By utilising the different growth phases of the Cu2N, we show that the position of magnetic molecules can be controlled, and that the properties of a molecule can be controlled through the binding site. For electrical transport through a junction containing an individual iron phthalocya- nine (FePc) molecule on Cu2N, we observe two novel magnetoresistance behaviours that arise from negative differential resistance (NDR) that shifts by unexpectedly large amounts in a magnetic field. Because voltage is dropped asymmetrically in this double barrier junction, the FePc can become transiently charged when its states are aligned with the Fermi energy of the Cu, resulting in the observed NDR effect. Furthermore, the asymmetric coupling magnifies the observed voltage sensitivity of the magnetic field dependence of the NDR, which inherently is on the scale of the Zeeman energy, by almost two orders of magnitude. These findings represent a new basis for making magnetoresistance devices at the single molecule scale. Fur- thermore, the enhancement of the energy scales created by asymmetric coupling of the junction can be used in conjunction with other multi-step tunnelling processes to allow for the investigation of phenomena that would otherwise be difficult to observe. We also show that it is possible to interact with the f-shell magnetic moment when a bis(phthalocyaninato)Dy(III) complex (DyPc2) is strongly coupled to the Cu(001) surface. DyPc2 is a single molecule magnet, a type of molecule which may have applications in both spintronic and quantum computing applications. A Fano lineshape is observed at the Fermi energy, which is caused by the interference between tunnelling into the continuum and into a resonance created by the Kondo effect. By mapping the variance of the amplitude of the Fano line shape we are able to show that the ligand states create the continuum states and the 4f states create the Kondo resonance.
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Gruber, Manuel. "Electronic and magnetic properties of hybrid interfaces : from single molecules to ultra-thin molecular films on metallic substrates." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE035/document.
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Comprendre les propriétés des interfaces molécules/métaux est d’une importance capitale pour la spintronique organique. La première partie porte sur l’étude des propriétés magnétiques de molécules de phtalocyanine de manganèse. Nous avons montré que les premières couches moléculaires forment des colonnes avec un arrangement antiferromagnétique sur la surface de Co(100). Ces dernières mènent à de l’anisotropie d’échange. La seconde partie porte sur l’étude d’une molécule à transition de spin, la Fe(phen)2(NCS)2, sublimée sur différentes surfaces. Nous avons identifié les états de spin d’une molécule unique sur du Cu(100). De plus, nous avons commuté l’état de spin d’une molécule unique pourvu qu’elle soit suffisamment découplée du substratUnderstanding the properties of molecules at the interface with metals is a fundamental issue for organic spintronics. The first part is devoted to the study of magnetic properties of planar manganese-phthalocyanine molecules and Co films. We evidenced that the first molecular layers form vertical columns with antiferromagnetic ordering on the Co(100) surface. In turn, these molecular columns lead to exchange bias. The second part is focused on the study of a spin-crossover complex, Fe(phen)2(NCS)2 sublimed on different metallic surfaces. We identified the two spin states of a single molecules on Cu(100). By applying voltages pulses, we switched the spin state of a single molecule provided that it is sufficiently decoupled from the substrate
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Ummethum, Jörg [Verfasser]. "Calculation of static and dynamical properties of giant magnetic molecules using DMRG / Jörg Ummethum. Fakultät für Physik." Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2012. http://d-nb.info/1028522843/34.
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Kantola, A. M. (Anu M. ). "Liquid crystal NMR: director dynamics and small solute molecules." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514260704.
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The subjects of this thesis are the dynamics of liquid crystals in external electric and magnetic fields as well as the magnetic properties of small molecules, both studied by liquid crystal nuclear magnetic resonance (LC NMR) spectroscopy. Director dynamics of a liquid crystal 5CB in external magnetic and electric fields was studied by deuterium NMR and spectral simulations. A new theory was developed to explain the peculiar oscillations observed in the experimental spectra collected during fast director rotation. A spectral simulation program based on this new theory was developed and the outcome of the simulations was compared with the experimental results to verify the tenability of the theory.
In the studies on the properties of small solute molecules, LC NMR was utilised to obtain information about anisotropic nuclear magnetic interaction tensors. The nuclear magnetic shielding tensor was studied in methyl halides, the spin-spin coupling tensor in methyl mercury halides and the quadrupolar coupling tensor in deuterated benzenes. The effects of small-amplitude molecular motions and solvent interactions on the obtained parameters were considered in each case. Finally, the experimental results were compared to the corresponding computational NMR parameters calculated in parallel with the experimental work.
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Gruber, Manuel [Verfasser], W. [Akademischer Betreuer] Wulfhekel, and E. [Akademischer Betreuer] Beaurepaire. "Electronic and magnetic properties of hybrid interfaces. From single molecules to ultra-thin molecular films on metallic substrates / Manuel Gruber. Betreuer: W. Wulfhekel ; E. Beaurepaire." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1073936201/34.
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Mishra, Shantanu, Doreen Beyer, Reinhard Berger, Junzhi Liu, Oliver Gröning, José I. Urgel, Klaus Müllen, Pascal Ruffieux, Xinliang Feng, and Roman Fasel. "Topological defect-induced magnetism in a nanographene." American Chemical Society, 2019. https://tud.qucosa.de/id/qucosa%3A73172.
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The on-surface reactions of 10-bromo-10'-(2,6-dimethylphenyl)-9,9'-bianthracene on Au(111) surface have been investigated by a combination of bond-resolved scanning tunneling microscopy, scanning tunneling spectroscopy, and tightbinding and mean-field Hubbard calculations. The reactions afford the synthesis of two open-shell nanographenes (1a and 1b) exhibiting different scenarios of all-carbon magnetism. 1a, an allbenzenoid nanographene with previously unreported triangulenelike termini, contains a high proportion of zigzag edges, which endows it with an exceedingly low frontier gap of 110 meV and edge-localized states. The dominant reaction product (1b) is a non-benzenoid nanographene consisting of a single pentagonal ring in a benzenoid framework. The presence of this nonbenzenoid topological defect, which alters the bond connectivity in the hexagonal lattice, results in a non-Kekulé nanographene with a spin S = ½, which is detected as a Kondo resonance. Our work provides evidence of all-carbon magnetism, and motivates the use of topological defects as structural elements toward engineering agnetism in carbon-based nanomaterials for spintronics.
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Rérat, Michel. "Methode invariante de jauge pour le calcul de proprietes magnetiques : applications a de petites molecules." Paris 6, 1987. http://www.theses.fr/1987PA066024.
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Developpement d'une technique de calcul des proprietes magnetiques qui combine les avantages des methodes classiques tenant compte de la correlation electronique et qui conserve l'invariance de jauge de la methode des polynomes par un systeme de compensation interne. Calcul des corrections rovibroniques, decrites analytiquement par la methode des perturbation, pour des molecules diatomiques (h::(2), co) pour une comparaison des resultats theoriques et experimentaux
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Cruz, Clebson dos Santos. "Propriedades Magnéticas de Magnetos Moleculares." Niterói, 2017. https://app.uff.br/riuff/handle/1/4020.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro
Com o desenvolvimento de novas tecnologias e os avanços nas técnicas de preparação de materiais, uma grande variedade de novos compostos puderam então ser sintetizados, dentre estes compostos estão os Magnetos Moleculares. Neste texto, apresentamos alguns fundamentos do magnetismo molecular, destacando o processo de construção de modelos para a descrição do comportamento magnético destes materiais através do ajuste dos dados da susceptibilidade magnética em função da temperatura. Buscamos compreender a maneira com que os diferentes parâmetros químicos e estruturais e afetam os mecanismos físicos que governam estes sistemas através do estudo de três séries de magnetos moleculares: um polímero bidimesional de Mn(II) sintetizado a partir do ácido 2,6-diclorobenzóico (C7H4Cl2O2), cujos parâmetros otimizados obtidos através do modelo sugerem que este composto possui um caráter global antiferromagnético; uma série de quatro compostos polinucleares de Cu(II) sintetizados com adenina (C5H5N5), cluster hexagonal heptanuclear ferromagnético e três cadeias antiferromagnéticas 2D dinucleares; uma série de quatro estruturas Metal-Orgânicas (Metal organic Frameworks-MOF) de Cu(II)-piperazina, onde foi feito um mapa das possíveis interações magnéticas para cada amostra. Por fim, como perspectiva para este trabalho pretendemos dar continuidade ao estudo de sistemas de magnetos moleculares dando ênfase à aplicação em informação quântica.
From the development of new technologies and advances in materials preparation techniques a wide variety of new compounds could be synthesized, among these compounds are the Molecular Magnets. In this paper, we present some fundamentals of molecular magnetism, highlighting the model-building process for the description of the magnetic behavior of these materials by fitting of the magnetic susceptibility as a function of temperature. Our goal is to understand how different chemical and structural parameters can affect the physical mechanisms that govern these systems . To achieve our aim we study three series of molecular magnets: a two-dimensional polymer Mn(II) synthesized from 2,6-acid dichlorobenzoic (C7H4Cl2O2), the optimized parameters obtained from the model suggest that this compound has an antiferromagnetic global character; a series of four polynuclear compounds of Cu(II) synthesized with adenine (C5H5N5), a ferromagnetic hexagonal cluster and three antiferromagnetic 2 D chains; a series of four Metal-Organic Frameworks (MOF) of Cu(II) -piperazine, where a magnetic interaction map was done for each sample. Finally, the perspective we intend to emphasize the study of molecular magnets systems with applications in quantum information.
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Schelter, Eric John. "Cyanide clusters of ReII with 3d metal ions and their magnetic properties: incorporating anisotropic ions into metal-cyanide clusters with high spin magnetic ground states." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/2205.
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Clusters of metal ions that possess large numbers of magnetically coupled unpaired electrons have attracted much interest in recent years due to their fascinating magnetic behavior. With an appreciable component of magnetic anisotropy, these large-spin paramagnetic molecules can exhibit an energy barrier to inversion of their magnetic dipole, leading to spontaneous magnetization and magnetic hysteresis below a critical temperature. Since this behavior is a property of an individual clusters rather than a collection of molecules, this phenomenon has been dubbed ??Single Molecule Magnetism??. Our approach to the study of new high-spin systems has been to exert a measure of synthetic control in the preparation of clusters. Specifically we are employing highly anisotropic metal ions with the anticipation that these ions would engender large overall magnetic anisotropy in the resulting clusters. The first step in this process was the development of the chemistry of two new d5 ReII (S = ??) complexes, namely [ReII(triphos)(CH3CN)3][PF6]2 and [Et4N][ReII(triphos)(CN)3]. The magnetic, optical and electrochemical properties were studied and theoretical models were developed to describe the origin of the large temperature independent paramagnetism that was observed. Next, we successfully employed transition metal cyanide chemistry using the ReII building blocks to prepare a family of isostructural, cubic clusters of the general formula {[MCl]4[Re(triphos)(CN)3]4} M = Mn, Fe, Co, Ni, Cu, Zn whose 3d ions adopt local tetrahedral geometries. Within the clusters, magnetic exchange is observed between the paramagnetic ions, which has been modeled using an Ising exchange model to account for the dominating anisotropy of the ReII ion. Despite the high pseudo-symmetry of the clusters (Td), this work has yielded a rare example of a metal-cyanide single molecule magnet, {[MCl]4[Re(triphos)(CN)3]4} with an S = 8 ground state, D = -0.39 cm-1 and an effective energy barrier for magnetization reversal of Ueff = 8.8 cm-1. The elucidation of this family of isostructural clusters has also allowed us to pursue fundamental work on the structure/property relationships of the exotic, paramagnetic ReII ion. As the clusters are soluble, stable compounds, the future of this chemistry lies in the development of a true building-block approach to ??super-clusters?? that exhibit very high ground state spin values.
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Krupskaya, Yulia. "Magnetic Properties of Molecular and Nanoscale Magnets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-73289.
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The idea of miniaturizing devices down to the nanoscale where quantum ffeffects become relevant demands a detailed understanding of the interplay between classical and quantum properties. Therefore, characterization of newly produced nanoscale materials is a very important part of the research in this fifield. Studying structural and magnetic properties of nano- and molecular magnets and the interplay between these properties reveals new interesting effects and suggests ways to control and optimize the respective material. The main task of this thesis is investigating the magnetic properties of molecular magnetic clusters and magnetic nanoparticles recently synthesized by several collaborating groups. This thesis contains two main parts focusing on each of these two topics.
In the first part the fundamental studies on novel metal-organic molecular complexes is presented. Several newly synthesized magnetic complexes were investigated by means of different experimental techniques, in particular, by electron spin resonance spectroscopy. Chapter 1 in this part provides the theoretical background which is necessary for the interpretation of the effects observed in single molecular magnetic clusters. Chapter 2 introduces the experimental techniques applied in the studies. Chapter 3 contains the experimental results and their discussion. Firstly, the magnetic properties of two Ni-based complexes are presented. The complexes possess different ligand structures and arrangements of the Ni-ions in the metal cores. This difffference dramatically affffects the magnetic properties of the molecules such as the ground state and the magnetic anisotropy. Secondly, a detailed study of the Mn2Ni3 single molecular magnet is described. The complex has a bistable magnetic ground state with a high spin value of S = 7 and shows slow relaxation and quantum tunnelling of the magnetization. The third section concentrates on a Mn(III)-based single chain magnet showing ferromagnetic ordering of the Mn-spins and a strong magnetic anisotropy which leads to a hysteretic behavior of the magnetization. The last section describes a detailed study of the static and dynamic magnetic properties of three Mn-dimer molecular complexes by means of static magnetization, continuous wave and pulse electron spin resonance measurements. The results indicate a systematic dependence of the magnetic properties on the nearest ligands surrounding of the Mn ions.
The second part of the thesis addresses magnetic properties of nano-scaled magnets such as carbon nanotubes fifilled with magnetic materials and carbon-coated magnetic nanoparticles. These studies are eventually aiming at the possible application of these particles as agents for magnetic hyperthermia. In this respect, their behavior in static and alternating magnetic fifields is investigated and discussed. Moreover, two possible hyperthermia applications of the studied magnetic nanoparticles are presented, which are the combination of a hyperthermia agents with an anticancer drug and the possibility to spatially localize the hyperthermia effffect by applying specially designed static magnetic fifields.
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Selvanathan, Pramila. "Photochromic switches for luminescence, plasmonic resonance, single molecule magnetic properties, and molecular wires for nano junctions." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S145.
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Ce travail est consacré à la synthèse et la caractérisation des commutateurs et des fils moléculaires incorporant l'unité et le ruthénium organométalliques fractions photochromiques. La première partie traite de lanthanides complexe Yb combiné avec l'unité et le ruthénium acétylure fractions photochromiques afin de moduler la luminescence avec l'aide de redox et de stimuli lumineux. Dans la deuxième partie explique la combinaison d'unités DTE photochromiques avec des fragments acétylures de ruthénium pour fixer sur la surface de nanoparticules métalliques afin d'affiner leur résonance plasmonique grâce à la modification de l'environnement de surface en utilisant la lumière et redox stimuli. La troisième partie décrit la préparation de complexes de lanthanides combinés avec une unité photochromique spiropyranne pour commuter les propriétés SMM des complexes via photoisomérisation de l'unité spiropyranne. Dans la dernière partie, nous présentons la synthèse de Oligo (phénylène éthylène) Les fils moléculaires avec différents noyaux centraux afin d'obtenir une variété de fil avec différents niveaux d'énergie HOMO-LUMO pour vérifier l'effet de l'épinglageThis work is devoted to the synthesis and characterization of novel molecular switches and wires incorporating photochromic unit and ruthenium organometallic moieties. The first part deals with lanthanide Yb complex combined with photochromic unit and ruthenium acetylide moieties in order to modulate the luminescence with the help of redox and light stimuli. In the second part explained the combination of photochromic DTE units with ruthenium acetylide moieties to attach on the surface of metal nanoparticles in order to tune their plasmonic resonance through the surface environment modification by using light and redox stimuli. The third part describes the preparation of lanthanide complexes combined with a spiropyran photochromic unit in order to switch the SMM properties of the complexes via photoisomerization of the spiropyran unit. In the last part, we report the synthesis of Oligo(phenylene ethylene) molecular wires with different central cores in order to obtain various wire with different HOMO-LUMO energy levels to check the effect of pinning
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Manninen, P. (Pekka). "Breit-Pauli Hamiltonian and Molecular Magnetic Resonance Properties." Doctoral thesis, University of Oulu, 2004. http://urn.fi/urn:isbn:9514274318.
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In this thesis, the theory of static magnetic resonance spectral parameters of nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy is investigated in terms of the molecular Breit-Pauli Hamiltonian, which is obtained from the relativistic Dirac equation via the Foldy-Wouthuysen transformation. A leading-order perturbational relativistic theory of NMR nuclear shielding and spin-spin coupling tensors, and ESR electronic g-tensor, is presented. In addition, the possibility of external magnetic-field dependency of NMR parameters is discussed.
Various first-principles methods of electronic structure theory and the role of one-electron basis sets and their performance in magnetic resonance properties in terms of their completeness profiles are discussed. The presented leading-order perturbational relativistic theories of NMR nuclear shielding tensors and ESR electronic g-tensors, as well as the theory of the magnetic-field dependent NMR shielding and quadrupole coupling are evaluated using first-principles wave function and density-functional theories.
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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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Martin, Lee. "Structures and properties of magnetic molecular charge transfer salts." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300630.
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Horner, Kate Elizabeth. "An investigation of molecular properties using magnetic shielding calculations." Thesis, University of York, 2014. http://etheses.whiterose.ac.uk/7391/.
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Isotropic shielding calculations were performed across finely spaced two- and three-dimensional grids positioned through and around a wide range of molecules. These magnetic shielding calculations were used to investigate aromaticity, antiaromaticity and a variety of chemical bonding features. This technique was found to be incredibly sensitive and able to distinguish between bonds of different order as well as bonds of the same order but in different environments. The shielding along the whole bonding region, as well as 1 Å above the bond and cross-sections through the bond, can be used to provide detailed information about the nature of the chemical bonding and the conjugation with the rest of the system. Regions of deshielding have been found around unsaturated nuclei and these areas can be used to determine relative aromaticities as well as degrees of conjugation. The same is true of shielding features found at 1 Å above the molecular plane. Unsaturated heavy atoms also display these deshielded surroundings, but they can be harder to observe. Antiaromatic systems exhibit a dumbbell shaped region of deshielding at the ring centre as well as significantly bent bonding regions which have been found to be a result, primarily, of the antiaromaticity rather than ring strain. H-bonding can also be studied with this technique and it has been found that the shielding on the atoms involved is most informative. In the case of substituted malonaldehydes, the oxygen shieldings were used to determine relative aromaticities in the pseudo rings and, therefore, H-bond strength. The sensitivity and information-rich nature of this technique has proven far superior to existing methods, such as the commonly used nucleus-independent chemical shift (NICS) technique, and therefore has great scope for future applications.
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Xu, Xiaoshan. "The magnetism of free cobalt clusters measured in molecular beams." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14649.
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Magnetic properties of cobalt clusters (20 N 200) were studied in molecular beams. The magnetization of cobalt clusters is studied at a broad range of temperatures, magnetic fields and clusters sizes. It is shown that the agnetization of ferromagnetic clusters in a cluster beam can be understood as an adiabatic process using the avoided crossing theory. Besides the ground state that bears magnetic moment of about 2 Bohr magneton per atom, an excited state that has 1 Bohr magneton per atom was discovered for every cobalt cluster observed. The energy separations between the two states was investigated by photo-ionization experiments. The ionization threshold shows that the energy gap between the two states is on the order of 0.1 eV for small clusters (N 100) and vanishes for larger clusters. Experiments also show that the polarizability of the excited state is lower than that of the ground state, which indicates a significant electronic tructure difference between the two states. Two states are also found for iron clusters (20 N 200) for which the magnetic moments per atom are about 3 Bohr magneton for the ground state and 1 Bohr magneton for the excited states. This explains the fractional magnetic moments as well as the local magnetic order observed above the Curie temperatures for iron group ferromagnets. Further experiments show two states for manganese clusters for which the ground state has magnetic moment of 1 Bohr magneton per atom in about the same size range. This suggests that the two states are a universal phenomenon of 3d transition metal clusters, which originate from the interaction between 3d and 4s electrons.
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Wilkins, Caroline Jane Theresa. "Magnetic properties of rare earth superlattices." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368119.
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Allalen, Mohammed. "Magnetic properties and proton spin-lattice relaxation in molecular clusters." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979984777.
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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 spécifiquesThis 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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Inglis, Ross. "Oxime based manganese molecular magnets." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4755.
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The synthesis and characterisation of a large family of hexametallic [MnIII 6] Single-Molecule Magnets with general formula [MnIII 6O2(R-sao)6(X)2(L)4-6] (where sao2- = dianion of salicylaldoxime; R = H, Me, Et, Ph; X = O2CR' (R' = H, Me, Ph etc), Hal , O2PHPh or O2P(Ph)2; L = solvent) are presented. Deliberate structural distortions of the [Mn3O] trinuclear moieties within the complexes are used to tune the observed magnetic properties. These findings highlight a qualitative magnetostructural correlation whereby the type (anti- or ferromagentic) of each Mn2 pairwise magnetic exchange is dominated by the magnitude of each individual Mn-N-O-Mn torsion angle. To shed further light on this intriguing family of nanomagnets, a large family of the analogous “half” molecules has been synthesised and fully characterised. These trimetallic [MnIII 3] complexes can be divided into three categories with general formulae (type 1) [MnIII 3O(R-sao)3(X)(sol)3-4] (where R = H, Me, tBu; X = O2CR (R = H, Me, Ph etc); sol = py and / or H2O), (type 2) [MnIII 3O(R-sao)3(X)(sol)3-5] (where R = Me, Et, Ph, tBu; X = O2CR (R = H, Me, Ph etc); sol = MeOH, EtOH and / or H2O), and (type 3) [MnIII 3O(R-sao)3(sol)3](XO4) (where R = H, Et, Ph, Naphth; sol = py, MeOH, -pic, Et-py, tBu-py; X = Cl, Re). In the crystals the ferromagnetic triangles are involved in extensive inter-molecular H-bonding which is clearly manifested in the magnetic behaviour, producing exchange-biased SMMs. These interactions can be removed by ligand replacement to give “simpler” SMMs. The [MnIII 6] and [MnIII 3] molecular nanomagnets are then exploited as building blocks to construct supramolecular architectures by means of host-guest interactions and coordination driven self-assembly. A number of discrete and infinite architectures based on the molecular triangle [Mn3] and various pyridyl-type ligands were obtained and structurally and magnetically characterised.
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Erler, Philipp [Verfasser]. "Electronic and magnetic properties of single molecule magnets on surfaces / Philipp Erler." Konstanz : Bibliothek der Universität Konstanz, 2016. http://d-nb.info/1114893889/34.
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Ueda, Miki. "Magnetic Properties and Quantum Tunneling of Magnetization in Fe8 Molecular Nanomagnet." Kyoto University, 2002. http://hdl.handle.net/2433/149874.
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Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第9667号
人博第151号
13||136(吉田南総合図書館)
新制||人||36(附属図書館)
UT51-2002-G425
京都大学大学院人間・環境学研究科文化・地域環境学専攻
(主査)教授 前川 覚, 教授 後藤 喬雄, 教授 冨田 博之, 教授 北川 進
学位規則第4条第1項該当
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Wu, Zhenlin. "Magnetic properties of transition metal phthalocyanine molecular thin films and nanostructures." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/10546.
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The unique magnetic properties of transition metal phthalocyanines (MPc) have attracted considerable scientific interest for decades. So far, most of the research was focused on single crystals. In this thesis, MPc materials were grown in thin film form using vacuum-based methods, such as organic vapour phase deposition (OVPD) and organic molecular beam deposition (OMBD). These methods were used to produce a range of molecular film structures and morphologies of MPcs with different spin states. We find that the magnetic properties are superior to single crystals, in terms of Curie-Weiss constant and coercive fields. Understanding the film properties will be essential for future device applications. Firstly, OVPD was used to prepare MnPc thin films that crystallise as the β-polymorph. Superconducting quantum interference device (SQUID) results show that the films behave as canted ferromagnets with a Curie constant of 10.6 K and a coercive field of 9 mT at 2 K. The texture of the MnPc film can be tuned by introducing a molecular layer on to the substrate. Unexpectedly, we find a change of polymorph from β-phase to ε-phase, which was verified by X-ray diffraction (XRD). A strong axial anisotropy of the films was observed from the magnetic measurements. Secondly, α-polymorph FePc films were grown by OMBD with different textures, depending on whether a templating layer was used. Magnetic measurements show that both films behave as canted ferromagnets with strong in-plane anisotropy and have a similar ferromagnetic exchange coupling of 20 K. The coercive fields at 2 K of non-templated and templated film are 85 mT and 35 mT, respectively. Finally, in order to reduce dimensionality and explore a new crystal phase, FePc wires with around 100 nm in width and a few microns in length were prepared by OVPD. XRD indicates that FePc nanowires adopt the η-phase polymorph, identical to what was observed in CuPc nanowires. Both the Curie constant and coercive field are higher than the film form, reaching 40 K and 1 T, respectively.
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Adam, Ahmad Yahia. "Theoretical Prediction of Nuclear Magnetic Shielding Constants of Acetonitrile." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/76769.
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Gauge invariant shielding constants calculations of ?H, ?C, and ??N were calculated for acetonitrile in the gas and liquid phases. Dierent basis sets as well as dierent ab initio and DFT methods were tested to select a time-ecient level of theory with reasonable accuracy. The eect of nuclear motion on the shielding constants was also explored. To investigate solvent eects on the shielding constants of acetonitrile, dierent clusters were extracted from molecular dynamics simulations. Convergence to the experimental values varied for the dierent clusters. The geometry of the central molecule in a cluster played an important factor in reaching convergence.Master of Science
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Yuan, Peng. "Raman and NMR Investigation of Molecular Reorientation and Internal Rotation in Liquids." Thesis, University of North Texas, 1991. https://digital.library.unt.edu/ark:/67531/metadc278558/.
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Molecular rotational motions are known to influence both Raman scattering of light and nuclear spin relaxation. Therefore, the application of Raman bandshape analysis and NMR relaxation time measurements to probe molecular dynamics in liquids will provide us with a deeper understanding of the dynamical behavior and structure of molecules in the liquid phase. Presented here are (i) studies of molecular reorientation of acetonitrile in the neat liquid phase and in solution by Raman bandshape analysis and NMR relaxation; (ii) studies of reorientational dynamics and internal rotation in transition metal clusters by NMR relaxation.
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Zagaynova, Valeria. "Carbon-based magnetic nanomaterials." Doctoral thesis, Umeå universitet, Institutionen för fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-53568.
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Magnetism of carbon-based materials is a challenging area for both fundamental research and possible applications. We present studies of low-dimensional carbon-based magnetic systems (fullerene-diluted molecular magnets, carbon nanotubes, graphite fluoride, and nanoporous carbon) by means of SQUID magnetometer, X-ray diffraction and vibrational spectroscopy, the latter techniques used as complementary instruments to find a correlation between the magnetic behaviour and the structure of the samples.In the first part of the thesis, characteristic features of the magnetization process in aligned films of carbon nanotubes with low concentration of iron are discussed. It is shown that the magnetism of such structures is influenced by quantum effects, and the anisotropy behaviour is opposite to what is observed in heavily doped nanotubes.In the second part, Mn12-based single molecular magnets with various carboxylic ligands and their 1:1 fullerene-diluted complexes are studied. We prove that magnetic properties of such systems strongly depend on the environment, and, in principle, it is possible to design a magnet with desirable properties. One of the studied compounds demonstrated a record blocking temperature for a single molecular magnet. Both fullerene-diluted complexes demonstrated “magnetization training” effect in alternating magnetic fields and the ability to preserve magnetic moment.The third and the fourth parts of the thesis are dedicated to the analysis of various contributions to the magnetic susceptibility of metal-free carbon-based systems – intercalated compounds of graphite fluorides and nanoporous oxygen-eroded graphite. The magnetic properties of these systems are strongly dependent on structure, and can be delicately tuned by altering the π-electron system of graphite, i. e. by degree of fluorination of intercalated compounds and by introduction of boron impurity to the host matrix of nanoporous graphite.Magnetism av kolbaserade material är ett utmanande område för både grundforskning och möjliga tillämpningar. Vi presenterar studier med låg-dimensionella kolbaserade magnetiska system (fulleren-utspädda molekylära magneter, kolnanorör, grafit fluorid och nanoporösa kol) med hjälp av SQUID magnetometer, röntgendiffraktion och vibrerande spektroskopi, de senare tekniker som används som komplement instrument för att finna sambandet mellan den magnetiska uppträdande och strukturen hos proven. I den första delen av avhandlingen är egenheter från magnetisering processen i linje filmer av kolnanorör med låg koncentration av järn diskuteras. Det visas att magnetism av sådana strukturer påverkas av kvantmekaniska effekter och anisotropin beteende är motsatsen till vad som observerats i kraftigt dopade nanorör. I den tvåa delen är Mn12-baserade enda-molekyl magneter med olika karboxylsyror ligander och deras 1:1 fulleren-utspädda komplex studeras. Vi visar att magnetiska egenskaperna hos sådana system beror i hög grad på miljön, och i princip är det möjligt att utforma en magnet med önskvärda egenskaper. En av de studerade föreningarna visade en post blockeringstemperaturen för en enda molekylär magnet. Både fulleren-utspädda komplex visade "magnetisering utbildning" effekt i alternerande magnetfält och möjligheten att bevara magnetiskt moment. Den tredje och fjärde delarna av avhandlingen är avsedda för inneboende magnetism av analys av olika bidrag till magnetisk susceptibilitet av metall-fritt kol-baserade system -inskjutna föreningar grafit fluorider och nanoporösa O2-eroderade grafit. Magnetiska egenskaperna hos dessa system är starkt beroende av strukturen, och kan fint avstämmas genom att man ändrar π-elektronsystem av grafit, i. e. med graden av fluorering av inskjutna föreningar och genom införandet av bor föroreningar till värd matris av nanoporösa grafit.
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Tancharakorn, Somchai. "Instrumentation development for studies of magnetic and structural properties of molecular magnets." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/9781.
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Tetramethyl ammonium manganese trichloride ([CH3)4N][Mn(II)Cl3]) known as TMMC, has been one of the most interesting systems in experimental magnetism due to its highly one-dimensional magnetic Heisenberg behaviour. The focus of this research programme was to study its magnetic and structural properties as a function of pressure. TMMC crystals were prepared by slow evaporation technique at room temperature; however it quickly became apparent that the material is only weakly magnetic and requires a pressure cell with a very low background. This discovery lead to the programme of instrumentation development for studies of weakly magnetic materials and gave a dualistic nature to the project. The first pressure cell developed was a piston-cylinder type cell for magnetic susceptibility measurements in a Magnetic Properties Measurement System (MPMS®) based on Superconducting Quantum Interference Device (SQUID) technology from Quantum Design, USA. It has been carefully designed in order to reduce the magnetic background. One way in which this has been achieved was through making the pressure cell symmetric with respect to the sample in order to provide an integrable response in the SQUID magnetometer. The cell was made of beryllium copper alloy which has a low background even at low temperature. The use of a multi-layered cylinder with the interference fit method has resulted in the increased strength of the cell and allowed larger sample volume. The use of Lamé equation and finite element method to calculate the change of the cell diameter or cell length as a function of internal pressure enables us to eradicate the need of superconductive manometer. The cell has been successfully tested up to a maximum pressure of 10 kbar. Further development of the cell has resulted in development of an electrical plug for in situ pressure measurement inside the pressure cell. This has been achieved by means of a manganin pressure sensor calibrated to provide pressure reading at any given temperature. For structural studies, a diamond anvil cell (DAC) was designed to conduct singlecrystal X-ray diffraction measurements at low temperature. The design was based on the well-known Merrill-Bassett DAC and on the design of the miniature DAC which has been developed for use within He-3 system in the Physical Properties Measurement System (PPMS®), Quantum Design. The cell has been tested down to liquid nitrogen temperatures with a cryostream cooling system and has shown a significant improvement compared to the standard pressure cells. The frost formation on the surface of the cell has slowed down significantly compared to the tests on the Merrill-Bassett cell, which led to a better quality diffraction pattern from the sample inside the cell. This result has been achieved due to the high thermal conductivity of the materials used in the construction and the minimisation of the DAC, which was effectively built around the Boehler-Almax diamond anvils. With the help of some of the high-pressure instruments mentioned above, highpressure properties of TMMC have been studied in this project. The structuremagnetism relationship was established from the results of magnetic and structural measurements under pressure. The magnetic susceptibility data helped to establish the change of the intrachain antiferromagnetic coupling constant as a function of pressure, while X-ray structures of TMMC were refined from ambient pressure to 17 kbar using a synchrotron X-ray diffraction technique. The structure of TMMC at room temperature was confirmed to be hexagonal. However, indirect evidence of the hexagonal-monoclinic structural phase transition was observed at above 17 kbar and room temperature. The combination of the magnetic and structural data has helped to establish that the interaction between high spin d5 metal orbitals (Mn(II)) in facesharing octahedral has a contribution from both direct exchange and superexchange interactions. The power-law relationship developed by Bloch was also observed in this system.
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Feuersenger, Jürgen. "Synthesis and characterisation of 3d-4f-complexes and their magnetic properties." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14195/document.
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Ce travail de thèse décrit (i) la synthèse de complexes hétérométalliques d’ions 3d et 4f à partir de précuseurs de Mn, Fe et Co, de sels de lanthanides et de ligands organiques et (ii) l'étude de leurs structures et propriétés. 41 complexes polynucléaires ont été synthétisés dans le cadre de ce travail. Les structures moléculaires de tous les composés ont été déterminées par diffraction des rayons X. Les propriétés magnétiques de 22 complexes ont été étudiées, dont quatre montrent une relaxation lente de leur aimantation considérée comme la signature d’un comportement de molécule-aimant. L'activité catalytique du complexe {Mn4Dy6Li2} calciné a aussi été étudiée et s'est avérée efficace pour l'oxydation du monoxyde de carbone. L'étude systématique de complexes isostructuraux de lanthanides a montré que l'incorporation d’ions 4f peut introduire de l’anisotropie magnétique et que l’ion DyIII est généralement le meilleur candidat pour le ciblage de molécules-aimants hétérométalliques 3d- 4fThis dissertation describes the syntheses of 3d-4f-metal complexes starting from preformed compounds of Mn, Fe and Co, lanthanide salts and organic ligands and also the investigation of their structures and properties. 41 new polynuclear heterometallic metal complexes were synthesised in the course of this work with different interesting properties. The structures of all obtained compounds have been confirmed using X-ray diffraction. The magnetic properties of 22 complexes were studied, of which four show frequency dependent out-of-phase signals as expected for SMMs. The catalytic activity of calcinated {Mn4Dy6Li2} was investigated and proved effective for the oxidation of CO. It was established, that the use of precursors leads to new families of compounds. Moreover the study of isostructural compounds across the lanthanide series showed 1) that the incorporation of 4f ions introduces magnetic anisotropy and 2) DyIII is usually the best candidate for targeting 3d-4f-SMMs
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Vilela, Ramon Silva. "Caracterização estrutural e magnética de complexos de Cu(II) com ligantes do tipo oxamato." Universidade Federal de Goiás, 2014. http://repositorio.bc.ufg.br/tede/handle/tede/4470.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this work was obtained four new Cu(II) precursors that could be employed as building blocks in the synthesis of new molecular magnets. Using the ligand H2Et2mpyba, was obtained the compounds Na2[Na10Cu2(mpyba)2(Cl)2]·10H2O(2a), {[(CH3)4N]4[Cu2(mpyba)2(H2O)2]•H2O} (2b), {[(CH3)4N]4[K2Na2Cu4(mpyba)4]∙3H2O} (2c). Through the hydrolysis in basic medium of the ligand HEtpmo (2-pirimidil oxamato) was obtained the coordination polymer {[(CH3)4N]2[Cu(C2O4)2]·H2O}n (1a). The crystalline structures was determined by x-ray diffraction, and we could note different structural morphologies as “zig-zag” chains and bidimensional planes (complexes 1a and 2a), metallocycles bounded through potassium atoms (complex 2c) and discrete binuclear unit (complex 2b). The magnetic susceptibilities measurements was carried in the temperature range of 300 – 2 K, and the measures indicates an ferromagnetic coupling between the copper atoms for all the compounds studied, with the values of exchange constant varying between +1,14 and +7,4 cm-1.
Neste trabalho foram obtidos quatro novos precursores de Cu(II) inéditos que podem ser empregados como blocos construtores na síntese de magnetos moleculares. Partindo-se do ligante H2Et2mpyba (meta piridil bis oxamato) obteve-se quatro novos precursores, os complexos Na2[Na4Cu2(mpyba)2(Cl)2]·10H2O (2a), {(CH3)4)][Cu2(mpyba)2(H2O)2]·H2O} (2b), e {[(CH3)4N]4[K2Na2Cu4(mpyba)4]}∙3H2O} (2c). A partir da hidrólise básica do ligante HEtpmo (2-pirimidil oxamato) obteve-se o polímero de coordenação {[(CH3)4N]4[Cu(C2O4)2]·H2O}n (1a). As estruturas cristalinas dos complexos foram determinadas por difração de raios-x de monocristal, e observou-se o desenvolvimento de diferentes morfologias, como cadeias e planos bidimensionais que crescem em “zigue-zague” (complexos 1a e 2a respectivamente), o complexo 2c cristaliza na forma de metalociclos ligados por átomos de potássio e o complexo 2b se apresenta como uma unidade binuclear discreta. Foram realizadas medidas de susceptibilidade magnética em função da temperatura no intervalo de 300 a 2 K para os compostos obtidos, revelando acoplamento ferromagnético entre os átomos de cobre para todos os compostos estudados, com valores de constante de acoplamento J variando entre +1,14 e +7,4 cm-1.
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Spivak, Mariano Alejo. "Electronic structure calculations on extended metal atom chains. Insights on structural, magnetic and transport properties." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/399580.
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En aquest treball, es van utilitzar diferents mètodes computacionals per estudiar les propietats de cadenes esteses de metalls de transició (EMACs en anglès). Es va simular la flexibilitat estructural de cadenes de tres àtoms de crom, amb CASSCF/CASPT2 i es van identificar estructures simètriques i asimètriques en un entorn de baixa energia. Basats en aquests resultats, vam realitzar dinàmiques moleculars de primers principis (AIMD) per entendre l'efecte de l'energia tèrmica i com aquesta modifica la proporció d'estructures. També es van estudiar els enllaços metall-metall en compostos de crom, utilitzant el model d'ordre d'enllaç efectiu (EBO) amb els números d'ocupació naturals de la funció d'ona CASSCF. Es van calcular constants d'acoblament magnètic per a compostos bimetàl·lics i EMACs de níquel mitjançant dues estratègies. MC-PT2 amb espai actiu mínim utilitzant orbitals moleculars millorats a partir d'un càlcul d'estats-mitjanats, i es va utilitzar un mètode nou (MCPDFT) per al magnetisme de EMACs grans, que ha mostrat bons resultats en el compost de cinc níquels. Finalment, estudiem propietats del transport d'electrons per dos EMACs de ruteni. Proposem l'ús d'un elèctrode gate metàl·lic per modular els nivells moleculars dels compostos i obtenir espècies redox actives. També utilitzem un mètode químicament més intuïtiu, que proposa crear parells iònics dins de la cel·la.En este trabajo, se utilizaron diferentes métodos computacionales para estudiar las propiedades de cadenas extendidas de metales de transición (EMACs en inglés). Se simuló la flexibilidad estructural de cadenas de tres átomos de cromo, con CASSCF/CASPT2 y se identificaron estructuras simétricas y asimétricas en un entorno de baja energía. Basados en estos resultados, realizamos dinámicas moleculares de primeros principios (AIMD) para entender el efecto de la energía térmica y como ésta modifica la proporción de estructuras. También se estudiaron los enlaces metal-metal en compuestos de cromo, utilizando el modelo de orden de enlace efectivo (EBO) con los números de ocupación naturales de la función de onda CASSCF. Se calcularon constantes de acoplamiento magnético para compuestos bimetálicos y EMACs de níquel mediante dos estrategias. MC-PT2 con espacio activo mínimo utilizando orbitales moleculares mejorados a partir de un cálculo de estados-promediados, y se utilizó un método nuevo (MCPDFT) para el magnetismo de EMACs grandes, que ha mostrado buenos resultados en el compuesto de cinco níqueles. Finalmente, estudiamos propiedades del transporte de electrones para dos EMACs de rutenio. Proponemos el uso de un electrodo gate metálico para modular los niveles moleculares de los compuestos y obtener especies redox activas. También utilizamos un método químicamente más intuitivo, que propone crear pares iónicos dentro de la celda.
In this work we use different computational methods in the study of the properties of Extended Metal Atom Chains. The structural flexibility of trichromium chains has been simulated with CASSCF/CASPT2 and symmetric and asymmetric structures were identified in an extremely flat energy landscape. Based on these results, Ab initio molecular dynamic simulations were performed to understand how the thermal energy modifies the proportion of cited structures. In addition, the metal-metal bonding of chromium compounds was characterized using the Effective Bond Order (EBO) model with the natural occupation numbers of the CASSCF wave function. Furthermore, magnetic coupling constants were computed for nickel bimetallic and EMACs compounds, using two different approaches. Minimal active space MC-PT2 was performed with improved molecular orbitals based on state-average calculations, and a recently developed method (MCPDFT) used for the magnetism of large EMACs, showing good results in the five-nickel compound. Finally, the electron transport properties were simulated for two ruthenium EMACs. We propose the use of a metallic gate electrode to modulate the molecular levels of the compounds and achieve redox active species. In addition, another more chemically intuitive approach was tested, that consist of forming an ionic pair in-situ.
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Gonidec, Mathieu. "Synthesis and properties of multifunctional single molecule magnets." Doctoral thesis, Universitat Autònoma de Barcelona, 2010. http://hdl.handle.net/10803/3322.
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En aquest treball s'ha dut a terme la síntesi i la caracterització química de varis complexos de doble capa de ftalocianines de terbi amb l'objectiu d'estudiar les seves propietats magnètiques en una varietat de configuracions. Es va obtenir una serie de compostos amb propietats físico-químiques distintes, com les d'autoassemblatje en superfície, d'activitat redox o de propietats mesomòrfiques.
Las propietats magnètiques dels compostos sintetitzats varen ser caracteritzades via SQUID, dicroisme circular magnètic (MCD) y dicroisme circular magnètic de rajos-X (XMCD), en una varietat d'estats sòlids congelats, en submonocapes sobre grafit i en dissolució en varis estats d'oxidació.
En general, es va observar que el comportament d'imant unimolecular (SMM) d'aquests compostos està qualitativament afectat por el estat d'oxidació de la molècula i la superestructura en la que estan integrats,produeixen canvis en la temperatura de bloqueig i en la forma de les histèresis de magnetització. Non obstant, es va constatar que el comportament d'imant unimolecular d'aquest complexos és molt robust ja que ni la substitució química de les ftalocianines, la hibridació amb una superfície de grafit, la oxidació o reducció del sistema o la morfologia del estat sòlid de les mostres va poder destruir aquesta propietat.
En este trabajo se ha llevado a cabo la síntesis y la caracterización química de varios complejos de doble capa de ftalocianinas de terbio con el propósito de estudiar las propiedades magnéticas de estos complejos en una variedad de configuraciones.
Se obtuvo una serie de compuestos con propiedades físico-químicas distintas, como las de autoensamblaje en superficie, de actividad redox o de propiedades mesomórficas.
Las propiedades magnéticas de los compuestos sintetizados fueron entonces caracterizadas vía SQUID, dicroísmo circular magnético (MCD) y dicroísmo circular magnético de rayos-X (XMCD), en una variedad de estados sólidos congelados, en submonocapas sobre grafito y en disolución en varios estados de oxidación.
En general, se observó que el comportamiento de imán unimolecular (SMM) de estos compuestos está cualitativamente afectado por el estado de oxidación de la molécula y la superestructura en la que están integrados, produciendo cambios en la temperatura de bloqueo y en la forma de las hysteresis de magnetización. Non obstante, se constató que el comportamiento de imán unimolecular de estos complejos es muy robusto ya que ni la substitución química de las ftalocianinas, la hibridación con una superficie de grafito, la oxidación o reducción del sistema o la morfología del estado sólido de las muestras pudo destruir está propiedad.
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Goodwin, Jeremy C. "An investigation into the synthesis characterisation and magnetic properties of high nuclearity transition metal arrays." Thesis, University of Sheffield, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369849.
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Mitcov, Dmitri. "Rational functionalization of molecular magnetic materials : towards liquid crystalline phases, improved solubility and modulation of physical properties." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0029/document.
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Ce travail de thèse a été dédié à l’élaboration et l’étude de nouveaux matériaux hybrides obtenus par la fonctionnalisation de molécule-aimants (en anglais single-molecule magnets, SMMs) et de complexes à transfert d’électron. Le premier chapitre fait un état de l’art des deux classes de composés magnétiques utilisées dans ce travail : les molécule-aimants et les systèmes à transfert d’électrons. Une brève description des systèmes magnétiques hybrides présents dans la littérature est ensuite présentée dans le but d’illustrer les motivations qui ont conduit à ce travail. Le chapitre II décrit la fonctionnalisation des molécule-aimants de type [Mn12] dans le but d’obtenir des systèmes cristaux liquides hybrides. Deux approches ont été étudiées : (a) la fonctionnalisation des ligands périphériques avec des groupements fortement lipophiles (longues chaines alkyle) ou (b) le greffage de promoteurs mésogènes par l’intermédiaire d’espaceurs aliphatiques flexibles. Les chapitres III à V présentent les études sur des carrés moléculaires à ponts cyanure {Fe2Co2} qui montrent un transfert d’électron thermo- et photo-induit. Le chapitre III discute de la possibilité de moduler le processus de transfert d’électron de ces carrés moléculaires via le changement du contre anion. La fonctionnalisation du carré moléculaire {Fe2Co2} avec de chaines aliphatiques et son impact induit sur les propriétés physiques à l’état solide et en solutions sont décrits dans le chapitre IV. Le chapitre V discute de l’effet de la fonctionnalisation avec des groupements fortement électrodonneurs, tels que les groupements méthoxy, sur le processus de transfert d’électron des carrés moléculaires {Fe2Co2}The work presented in this thesis was focused on the design and investigation of novel hybrid materials via ligand functionalization of the single-molecule magnets (SMMs) and electron transfer complexes. Chapter I contains general information about these two classes of the magnetic systems. In order to illustrate the motivation behind our work, a brief review on previously reported soft hybrid magnetic systems, is presented. Chapter II is dedicated to the functionalization of [Mn12]-based SMMs towards hybrid liquid crystalline systems via two different approaches: (a) the functionalization of peripheral ligands with strongly lipophilic groups (long alkyl chains), or (b) the grafting of mesogenic promoters through flexible aliphatic spacers. Chapters III – V are focused on cyanido-bridged molecular {Fe2Co2} squares that exhibit thermally or photo-induced electron transfer. Thus, in Chapter III, the possibility to modulate the electron transfer properties in {Fe2Co2} molecular squares via the use of different counter-anion is discussed. The functionalization with long aliphatic chains and its influence over the properties of {Fe2Co2} molecular squares in solid state and solutions are discussed in Chapter IV. Finally, the effect of the ligand functionalization with strongly electron density donating groups (methoxy) over the electron transfer properties of {Fe2Co2} molecular squares is investigated in Chapter V
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Serri, Michele. "Magnetic and structural properties of molecular films, blends and nanostructures based on cobalt phthalocyanines." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/26110.
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Organic semiconductors are a class of materials based on conjugated molecules which has been the subject of intensive research in the past two decades for applications in organic light-emitting diodes (OLEDs), organic thin film transistors (OTFT), photovoltaic cells, sensors and optical amplifiers/lasers. These molecular materials have recently become of interest for spintronic applications, since long spin relaxation times and magnetoresistance have been experimentally measured in these systems. The properties of organic materials can be easily manipulated and combined in novel ways, while their molecular nature paves the way for devices that operate at a single molecule/single spin level and really approach the ultimate limit of the atomic scale. In order to exploit the full potential of organic spintronics, it is essential to increase the temperatures at which the spin effects can be observed. This thesis is concerned with the development of novel organic magnetic materials, which could be of interest for spintronic devices operating above cryogenic temperatures. The work focuses on organic thin films and other nanostructures containing cobalt phthalocyanine and its derivatives. It is shown that some forms of these compounds, in particular alpha-CoPc, exhibit antiferromagnetic spin correlations above the boiling point of liquid nitrogen (77 K), suggesting that phthalocyanine materials may be suitable for high temperature organic spintronic applications.
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Cachia, S. H. "Molecular dynamics simulations of water transport properties and magnetic resonance relaxation in cement nanopores." Thesis, University of Surrey, 2016. http://epubs.surrey.ac.uk/812105/.
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Water transport properties in cement are important for the cement industry. At the nanoscale, a nondestructive experimental method, 1 H nuclear magnetic resonance [NMR] relaxometry, can be used to quantify these properties. However, recent results have proven difficult to reconcile with current understanding of cement. The purpose of this work is to use Molecular Dynamics [MD] simulations to try and better understand water in cement and hence better interpret some of the NMR data. In particular, MD simulations are used to investigate water dynamics in two sizes of nanopores in analogues of calcium-silicate-hydrate [C-S-H], which is the active phase of cement paste. These pores are gel pores (3-5 nm) and interlayer spaces (1 nm). First, a bulk water system is studied and the water diffusion coefficient and NMR relax ation times are calculated. The results are compared to literature values and used to validate the methods. Then, different C-S-H analogues based on SiO 2] α -quartz crystal, tobermorite 11 ̊ A and modified tobermorite 14 ̊ A are presented. Two different sets of interatomic poten tials are used for these model simulations: CLAY FF+SPC/E and Freeman+TIP4P. These simulations are then compared. A model called MD4 which is based on modified tobermorite 14 ̊ A and using CLAY FF+SPC/E potentials is selected for further work. The density profile of water oxygen in MD4 is used to identify four water layers with different properties in the gel pore (L1, L2, TL and B) and one water layer in the interlayer pore (IL). Diffusivity and desorption analyses are performed on water populations related to these layers. The importance of the calcium ions close to the surface is highlighted. The NMR dipolar correlation function is generated for water using data from the MD4. This function underpins relaxation analysis. These outputs are compared to Korb’s single water layer model of surface NMR relaxation. Korb’s model is not supported by the new data. However, a new relaxation model of surface relaxation that takes into account water in two layers is supported by the data. Exchange is possible between these layers and is important for diffusivity as well as relaxation. Simulations are carried out as a function of temperature and used to calculate water trans- port activation energies in bulk and in MD4. Finally, the analysis of water exchange between the interlayer and gel pores is performed. It is shown that the exchange time in simulations is ≈69000 times smaller than measured experimentally. Some possible failings in the model that would account for this are discussed.
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Kettles, Fraser J. "Synthesis, structure and magnetic properties of heterometallic complexes towards single-molecule magnets using flexible aminopolyol ligands." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7488/.
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Krupskaya, Yulia [Verfasser], Bernd [Akademischer Betreuer] Büchner, and Rüdiger [Akademischer Betreuer] Klingeler. "Magnetic properties of molecular and nanoscale magnets / Yulia Krupskaya. Gutachter: Rüdiger Klingeler. Betreuer: Bernd Büchner." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://d-nb.info/1028864981/34.
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Parameswaran, Anupama. "Magnetic properties of Mn, Ni and Fe based metal-organic complexes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-65594.
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This dissertation presents the investigation of magnetic exchange and anisotropy in novel metal-organic complexes containing minimum number of magnetic ions. Such complexes can serve as a model system to understand the exciting magnetic phenomena in such class of materials and also can put forward as candidates for the so called molecular nanomagnets.
A direct assessment of the effective magnetic moment and the effective interaction between the metal ions in the complex can be done using magnetization measurements. Here the magnetization studies are performed as a function of temperature and field using a SQUID magnetometer. Yet another powerful tool to characterize and determine the spin levels, the ESR spectroscopic methods, has also been exploited. The study of the dynamical properties of this class of materials was relevant to understand the relaxation mechanism in the low temperatures. For this a new ac susceptometer has been built in house which was another main objective of this dissertation work. The design, fabrication, calibration and automation done on this device is presented in this thesis. The device has been tested using the known molecular magnet Mn12 acetate, and the antiferromagnet Dy2PdSi3.
The present work is mainly focused on the magnetic properties of Mn, Ni and Fe based organometallic complexes. The studied Mn dimer with different acceptor and donor ligands exhibit the fine tuning of the electron density at the core of molecular complex by variation in ligands. This in turn shows that the change in peripheral ligands can control the magnetism of the molecule. The influence of the change in Ni-S-Ni bond angle in the magnetic exchange interaction is studied in a Ni(2) dimer and a Ni(2) trimer complex. The Ni dimer complex shows a ferromagnetic interaction (J = -42K) whereas trimer shows an antiferromagnetic interaction (J = 140K). Another Ni based complex bridged via phosphorous has been studied which shows the existence of glassy nature at low temperature. Also a polymeric chain compound based on Fe is studied and presented. All these phosphorous or sulphur bridged complexes are novel materials and these are the first data on these complexes.
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Nitin, Nitin. "Optical and MR Molecular Imaging Probes and Peptide-based Cellular Delivery for RNA Detection in Living Cells." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-08102005-120350/.
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Thesis (Ph. D.)--Biomedical Engineering, Georgia Institute of Technology, 2006.Dr. X. Hu, Committee Member ; Dr. Al Merrill, Committee Member ; Dr. Niren Murthy, Committee Member ; Dr. Gang Bao, Committee Chair ; Dr. Nicholas Hud, Committee Member. Includes bibliographical references.
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Jahandar, Kojouri Kimia. "Single Molecule Magnet and Luminescence Properties of Lanthanide and Transition Metal Complexes Using Tetrazine and Naphthalimide Based Ligands." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38384.
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This thesis examined two distinct characteristics of lanthanide and transition metal complexes: Magnetism and Luminescence. In chapter two, synthesis, characterization, magnetic and luminescence investigations of mononuclear lanthanide complexes using Schiff-base tetrazine based ligand were performed. Six novel lanthanide complexes, [LaIIICl3(Htzpy)2], [TbIIICl2(Htzpy)2(MeOH)]Cl, [HoIIICl2(Htzpy)2(MeOH)]Cl, [DyIIICl2(Htzpy)2(MeOH)]Cl, [ErIIICl2(Htzpy)2(MeOH)]Cl and [YbIIICl2(Htzpy)2]Cl have been synthesized successfully and the studies were performed with the application of single crystal X-ray diffractometry, SQUID magnetometry, UV-Vis-NIR spectrometry and custom-built hyperspectral microscope (for luminescence spectroscopy). Chapter three is mainly about the luminescence properties of CoII and CuII complexes using a naphthalimide based ligand. Two complexes, [CoIICl2(Pynap)2] and [CuIIBr2(Pynap)2] were synthesized successfully and characterized using single crystal X-ray diffractometry, UV-Vis spectrometry and hyperspectral microscope (for luminescence spectroscopy). In order to have information about the electrochemical properties of CoII and CuII complexes, their redox activity was monitored by cyclic voltammetry (CV) and compared with the parent ligand. In addition, a rational design to synthesize a new ligand (dipicnap) which consists of both naphthalimide and dipicolinic acid moieties is presented.
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Jiang, Yu Ting. "The Synthesis, Structure and Magnetic Properties of O-Vanillin-Derived Schiff Base Polynuclear Lanthanide Single-Molecule Magnets." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32122.
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This thesis describes the synthesis, characterization and magnetic investigation of homometallic lanthanide complexes based on two different o-vanillin-derived Schiff base ligands: H2ovph and H2ovgrd. The studies were performed using single crystal X-ray diffractometry, Powder XRD and SQUID magnetometry. Chapter 2 focuses on dinuclear systems 1-8 coordinated to the ligand H2ovph and presents their structural and magnetic properties, mainly with respect to their intramolecular interactions. Chapter 3 describes two hexanuclear systems, 9 (DyIII) and 10 (GdIII), with trigonal prism-assembled core structures. A structural comparison to other similar complexes in the literature is performed. A series of dinuclear complexes, 11-15, based on the ligand H2ovgrd are described in Chapter 4, focusing on the synthetic strategy, crystal structures and magnetism. The presence of the lanthanide contraction is evident in this system of complexes and is consistent with the intrinsic lanthanide contraction property.
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Aliabadi, Azar. "ESR and Magnetization Studies of Transition Metal Molecular Compounds." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-195440.
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Molecule-based magnets (molecular magnets) have attracted much interest in recent decades both from an experimental and from a theoretical point of view, not only because of their interesting physical effects, but also because of their potential applications: e.g., molecular spintronics, quantum computing, high density information storage, and nanomedicine. Molecular magnets are at the very bottom of the possible size of nanomagnets. On reducing the size of objects down to the nanoscale, the coexistence of classical properties and quantum properties in these systems may be observed. In additional, molecular magnets exist with structural variability and permit selective substitution of the ligands in order to alter their magnetic properties. Therefore, these characteristics make such molecules suitable candidates for studying molecular magnetism. They can be used as model systems for a detailed understanding of interplay between structural and magnetic properties of them in order to optimize desired magnetic properties.
This thesis considers the investigation of magnetic properties of several new transition metal molecular compounds via different experimental techniques (continuous wave electron spin resonance (CW ESR), pulse ESR, high-field/high-frequency ESR (HF-ESR) and static magnetization techniques).
The first studied compounds were mono- and trinuclear Cu(II)-(oxamato, oxamidato)/bis(oxamidato) type compounds. First, all components of the g-tensor and the tensors of onsite ACu and transferred AN HF interactions of mononuclear Cu(II)- bis(oxamidato) compounds have been determined from CW ESR measurements at 10 GHz and at room temperature and pulse ELDOR detected NMR measurements at 35 GHz and at 20 K. The spin density distributions of the mononuclear compounds have been calculated from the experimentally obtained HF tensors. The magnetic exchange constants J of their corresponding trinuclear compounds were determined from susceptibility measurements versus temperature. Our discussion of the spin density distribution of the mononuclear compounds together with the results of the magnetic characterization of their corresponding trinuclear compounds show that the spin population of the mononuclear compounds is in interplay with the J values of their corresponding trinuclear compounds.
The second studied compounds were polynuclear Cu(II)-(bis)oxamato compounds with ferrocene and ferrocenium ligands. The magnetic properties of these compounds were studied by susceptibility measurements versus temperature to determine J values. In addition, the ESR technique is used to investigate the magnetic properties of the studied compounds because they contain two different magnetic ions and because only the ESR technique can selectively excite different electron spin species. These studies together with geometries of the ferrocenium ligands determined by crystallographic studies indicate that the magnetic interaction between a central Cu(II) and a Fe(III) ions changed from the antiferromagnetic coupling to the ferromagnetic coupling when a stronger distortion of the axial symmetry in the feroccenium cation exists. Therefore, the degree of the distortion of the feroccenium cation is a control parameter for the sign of the interaction between the central Cu(II) ion and the Fe(III) spins of the studied compounds.
The last two studied molecular magnets were a binuclear Ni(II) compound (Ni(II)-dimer) and a cube-like tetranuclear compound with a [Fe4O4]-cube core (Fe4-cube). HF-ESR measurements enabled us to determine the g-factor, the sign, and the absolute value of the magnetic anisotropy parameters. Using this information together with static magnetization measurements, the J value and the magnetic ground state of the studied compounds have been determined. In Ni(II)-dimer, two Ni(II) ions, each having a spin S = 1, are coupled antiferromagnetically that leads to a ground state with total spin Stot = 0. An easy plane magnetic anisotropy with a preferable direction for each Ni(II) ion is found. For Fe4-cube, a ground state with total spin Stot = 8 has been determined. The analysis of the frequency dependence and temperature dependence of HF-ESR lines reveals an easy axis magnetic anisotropy (Dcube = -22 GHz (-1 K)) corresponding to an energy barrier of U = 64 K for the thermal relaxation of the magnetization. These results indicate that Fe4-cube is favorable to show single molecular magnet (SMM) behavior.