No description available.

No description available.

No description available.

Elektronen- und Positronenstrahlen mit niedrigsten Emittanzen und hohen Strömen werden in zukünftigen Linearbeschleunigern, wie zum Beispiel dem Compact Linear Collider (CLIC), benötigt, um die geforderte Leuchtkraft für physikalische Experimente bereit zu stellen. Diese Strahlen können in Dämpfungsringen, ausgestattet mit starken, supraleitenden Dämpfungswigglermagneten, erzeugt werden. In dieser Arbeit sind Designkonzepte verschiedener supraleitender Dämpfungswigglermagnete entwickelt worden. Testspulen sowie Modelle sind gebaut und getestet, elektrische Verbindungstechniken entwickelt worden. Eine Wärmelastrechnung für den Betrieb in Dämpfungsringen und ein Designkonzept für den kryogenen Betrieb bei 4.2 K ist erstellt worden. Es konnte theoretisch und experimentell gezeigt werden, dass supraleitende Dämpfungswigglermagnete mit Nb-Ti und Nb3Sn Niedertemperatursupraleitern die magnetischen, mechanischen, elektrischen und thermischen Anforderungen erfüllen und in Dämpfungsringen betrieben werden können.

Elektronen- und Positronenstrahlen mit niedrigsten Emittanzen und hohen Strömen werden in zukünftigen Linearbeschleunigern, wie zum Beispiel dem Compact Linear Collider (CLIC), benötigt, um die geforderte Leuchtkraft für physikalische Experimente bereit zu stellen. Diese Strahlen können in Dämpfungsringen, ausgestattet mit starken, supraleitenden Dämpfungswigglermagneten, erzeugt werden. In dieser Arbeit sind Designkonzepte verschiedener supraleitender Dämpfungswigglermagnete entwickelt worden. Testspulen sowie Modelle sind gebaut und getestet, elektrische Verbindungstechniken entwickelt worden. Eine Wärmelastrechnung für den Betrieb in Dämpfungsringen und ein Designkonzept für den kryogenen Betrieb bei 4.2 K ist erstellt worden. Es konnte theoretisch und experimentell gezeigt werden, dass supraleitende Dämpfungswigglermagnete mit Nb-Ti und Nb3Sn Niedertemperatursupraleitern die magnetischen, mechanischen, elektrischen und thermischen Anforderungen erfüllen und in Dämpfungsringen betrieben werden können.

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.

No description available.

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.

No description available.

Made available in DSpace on 2016-04-28T14:16:28Z (GMT). No. of bitstreams: 1 Antonio P Magalhaes.pdf: 3251730 bytes, checksum: 0e3e5794c6a8e24e374f425ce2d5079e (MD5) Previous issue date: 2007-03-15 / William Gilbert of Colchester (1544-1603), one of the many personal physicians of Queen Elizabeth the First, was a prominent figure regarding the studies of electric and magnetic phenomena between the end of the XVI century and the beginning of the XVII century. In his attempt to reformulate the approach given to knowledge about the nature of these phenomena in his days, as well as the appropriate way to elaborate such process, William Gilbert would then develop various original and influent works, which would be published in the year of 1600 in his book De Magnete. His declared purpose would be to establish a new philosophy based on arguments and true observations, demonstrated by experiments and experiences. Consequently, he would then create new concepts and conceptions about the nature of electric and magnetic matter. The present work aims to go further in the analysis of this specific book, undertaking initially some aspects of its structure, editions and repercussions, as well as the rare biographical data on the author. Next, we investigate the relationship between De Magnete and some of the sources suggested by the author. Particularly those concerning the experiments regarding the magnetic phenomenon, specially the Epistola attributed to the medieval thinker Petrus Peregrinus, The New attractive (1581), written by the navigation craftsman Robert Norman. We also take into consideration, William Gilbert s criticism of book VII of Magia Naturalis (1558) written by the renaissance magician, Giambattista della Porta. We finally deal with the conceptions of electric matter and magnetic form proposed by William Gilbert. The study of the attractions would force him to separate electric bodies, imperfect for acting through matter, from magnetic bodies, perfect for acting through form. Therefore, form should present similarity with a superior soul and a resemblance with the skies / William Gilbert de Colchester (1544-1603), um dos muitos médicos pessoais da Rainha Elizabeth I, foi uma das mais destacadas figuras no que diz respeito aos estudos sobre os fenômenos elétrico e magnético entre o final do século XVI e início do século XVII. Em sua tentativa de reformular a abordagem dada ao conhecimento sobre a natureza desses fenômenos, em seus dias, bem como a própria maneira de elaborá-lo, William Gilbert desenvolveria trabalhos em muitos pontos originais e influentes, que seriam publicados, no ano de 1600, em seu livro De Magnete. Seu objetivo declarado seria estabelecer uma nova Filosofia baseada em argumentos e observações verdadeiros, demonstrados por experimentos e experiências. Assim, ele criaria novos conceitos e concepções sobre a natureza da matéria elétrica e magnética. O presente trabalho propõe-se a aprofundar a análise dessa obra, retomando inicialmente alguns aspectos de sua estruturação, edições e repercussões, bem como os raros dados biográficos de seu autor. Em seguida, busca-se investigar relações dessa obra com algumas das fontes sugeridas pelo autor, particularmente aquelas concernentes a experimentos relacionados ao fenômeno magnético, em especial a Epistola atribuída ao pensado medieval Petrus Peregrinus, o The New attractiue (1581), escrito pelo artesão náutico Robert Norman e também as críticas que William Gilbert desferiu contra o livro VII do Magia Naturalis (1558) escrito pelo mago renascentista, Giambattista della Porta. Por fim abordam-se as concepções de matéria elétrica e forma magnética propostas por William Gilbert. O estudo das atrações exigia-lhe separar os corpos elétricos, imperfeitos por atuarem através da matéria, dos corpos magnéticos, perfeitos por atuarem através da forma. Dessa maneira, a forma deveria apresentar similaridade com uma alma superior, à semelhança dos céus