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Large electrical current transport in the absence of energy losses is thekey factor in commercial applications of high temperature superconductors. This thesis demonstrates an easy and inexpensive bottom-uptechnique to produce self assembled nanorods, segmented nanorodsas well as nanoparticles in YBa2Cu3O7-δ thin films grown by pulsedlaser deposition. The structural and morphological characteristic ofthe pinning landscapes produced are investigated and correlated totheir effects on the superconducting properties of the thin films. In particular two pinning landscapes are investigated: Ba2YNbO6nanorods are grown in YBa2Cu3O7-δ thin films using a Ba2YNbO6doped YBa2Cu3O7-δ pulsed laser deposition targets andBa2(Y/Gd)(Nb/Ta)O6 segmented nanorods together with (Y/Gd)2O3nanoparticles are grown in (Y/Gd)Ba2Cu3O7-δ thin films using aBa2YNbO6 + Gd3TaO7 doped YBa2Cu3O7-δ pulsed laser depositiontargets. The Ba2YNbO6 + YBa2Cu3O7-δ is deeply characterised and the effectsof the deposition parameters are analysed. Ba2YNbO6 is demonstratedto be an interesting novel pinning addition capable to increasethe critical current and to reduce the YBa2Cu3O7-δ critical currentsangular dependencies anisotropy. The Ba2YNbO6 + Gd3TaO7 + YBa2Cu3O7-δ is found to produce anew complex pinning landscape extremely effective. At high fieldsthe synergetic combination of the different defects typology is shownto generate an interesting new feature in the critical current angulardependencies. Chapter 1 is an introduction to superconductivity, the fundamentals ofthe field are briefly presented. In chapter 2 the discussion in focused onpinning in high temperature superconductors. Cuprates and in particularYBa2Cu3O7-δ are presented. The pinning phenomenon andthe practical pinning engineering in thin films is also discussed in thischapter. Chapter 3 describes the thin films preparation methods andthe characterisation techniques used in the research work. Chapter 4and 5 are focused on the Ba2YNbO6 doped YBa2Cu3O7-δ thin films. Chapter 4 is an introduction to Ba2YNbO6 doped YBa2Cu3O7-δ, thepreliminary results obtained on Ba2YNbO6 doped YBa2Cu3O7-δ thin films are shown in this chapter. The crystalline structure, the morphologyand the superconducting properties of thin films depositedadopting different deposition parameters are analysed and discussedin chapter 5. In chapter 6 the new complex pinning landscape ofBa2(Y/Gd)(Nb/Ta)O6 and (Y/Gd)2O3 in (Y/Gd)Ba2Cu3O7-δ is presented. Concluding remarks on the research described in the workends the thesis in a brief final chapter 7.

In part I, a numerical study of the mixed states in a mesoscopic type-II superconducting cylinder is described. Steady-state configurations and transient behavior of the magnetic vortices for various values of the applied magnetic field H are presented. Transitions between different multi-vortex states as H is changed is demonstrated by abrupt changes in vortex configurations and jumps in the B vs H plot. An efficient scheme to determine the equilibrium vortex configuration in a mesoscopic system at any given applied field, not limited to the symmetry of the system, is devised and demonstrated. In part II, a superconducting thin film is subject to a non-uniform magnetic field from a vertical magnetic dipole, consisting of two magnetic monopoles of opposite charges. For a film with constant thickness and with no pins, it has been found that the film carries two pairs of vortex-antivortex in the steady state in the imposed flux range of 2.15 < (Phi)+ < 2.90 (in units of flux quantum) and no vortex at all for (Phi)+ <= 2.15. Transitions from a superconducting state with 3 pairs of vortex-antivortex to one with 2 pairs, where a pair of vortex-antivortex annihilates, have been observed in the pseudo-time sequence. With a perturbation with antidots (holes), vortexantivortex pair has been created for lower magnetic fluxes down to (Phi)+ = 1.3. In the sample of size 16(Xi) x 16(Xi), the attraction force between the vortex and antivortex always dominates over the pinning force, so that they eventually come out of pins, move toward each other, and annihilate each other. The annihilation rate, measured with time taken for the annihilation, is reduced noticeably by the increase of the distance between pins, or the increase in the pin size. A simulation of the magnetic vortex pinning in the sample of size 32(Xi) x 32(Xi) suggests we are likely to achieve pinning of the vortex-antivortex pair with the sample size around this and vortex-antivortex separation of 22(Xi). Using this sample as a template, the maximum density of pinned vortices achievable is calculates to be about 7.6 x 10^14 vortices/m2 for (Xi) =~ 1.6A°.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 152-160.

Thesis (Ph. D.)--Ohio State University, 2007.

Orientador: Rafael Zadorosny / Resumo: O estudo de materiais supercondutores (SCs) em escalas nanométricas tem se destacado na área da Física de Matéria Condensada nas últimas décadas. O foco tem-se dado aos estudos das propriedades elétricas e magnéticas desses materiais, além da intensificação do desenvolvimento de técnicas para a produção e manipulação em nanoescala. Nos ditos supercondutores mesosocópicos, efeitos de confinamento influenciam na dinâmica de vórtices, ocasionando, inclusive, estados de vórtices múltiplos e de vórtices gigantes. Neste trabalho, usamos a teoria de Ginzburg-Landau para estudar supercondutores mesoscópicos com uma rede de defeitos. Foram analisados o comportamento magnético das amostras para dois tipos diferentes de defeitos, sendo eles, buracos que transpassam o material (antidots, ADs) e buracos com uma fina camada supercondutora (Blind Holes, BHs). As amostras foram expostas a campos externos variáveis e o loop de histerese das mesmas fora levantado. Os sistemas foram simulados com temperatura T=0,9Tc, e possuindo geometria quadrada de tamanho lateral L=54 ξ(0), defeitos também quadrados de lado l=2ξ(0) e espaçados por 2ξ(0). Nestas condições, efeitos de confinamento são muito fortes, inclusive devido ao tamanho dos vórtices, cujo ξ(T=0,9) é aproximadamente 3ξ(0). Com isso, há pouca diferença no comportamento global das diferentes amostras, contudo, a dinâmica de vórtices é alterada devida à natureza distinta entre ADs e BHs. Outro fato interessante é que, sendo os vórtices muito... (Resumo completo, clicar acesso eletrônico abaixo) / Mestre

Graduation date: 1997

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