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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Propriedades est?ticas e din?micas de multicamadas magn?ticas acopladas quasiperiodicamente / Propriedades est?ticas e din?micas de multicamadas magn?ticas acopladas quasiperiodicamente

Machado, Leonardo Dantas 03 August 2009 (has links)
Made available in DSpace on 2015-03-03T15:15:24Z (GMT). No. of bitstreams: 1 LeonardoDM.pdf: 2069021 bytes, checksum: 035347c356e3a06cfd24803d5312e7f8 (MD5) Previous issue date: 2009-08-03 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / In this work we study, for two different growth directions, multilayers of nanometric magnetic metallic lms grown, using Fibonacci sequences, in such a way that the thickness of the non-magnetic spacer may vary from a pair of lms to another. We applied a phenomenological theory that uses the magnetic energy to describe the behavior of the system. After we found numerically the global minimum of the total energy, we used the equilibrium angles to obtain magnetization and magnetoresistance curves. Next, we solved the equation of motion of the multilayers to nd the dispersion relation for the system. The results show that, when spacers are used with thickness so that the biquadratic coupling is strong in comparison to the bilinear one, non usual behaviors for both magnetization and magnetoresistance are observed. For example, a dependence on the parity of the Fibonacci generation utilized for constructing the system, a low magnetoresistance step in low external magnetic fields and regions that show high sensibility to small variations of the applied field. Those behaviors are not present in quasiperiodic magnetic multilayers with constant spacer thickness / Neste trabalho estudamos, para duas dire??es de crescimento distintas, multicamadas de lmes nanom?tricos met?licos magn?ticos crescidas, usando sequ?ncias de Fibonacci, de modo tal que a espessura dos espa?adores n?o-magn?ticos pode variar de um par de lmes para outro. Utilizamos uma teoria fenomenol?gica que usa a energia magn?tica para descrever o comportamento do sistema. Ap?s minimizarmos numericamente a energia total, utilizamos os ?ngulos de equil?brio para obter curvas de magnetiza??o e de magnetoresist?ncia. Em seguida, resolvemos a equa??o de movimento da multicamada para encontrarmos rela??es de dispers?o para o sistema. Os resultados mostram que, quando s?o usados espa?adores com espessura tal que o acoplamento biquadr?tico ? forte em compara??o com o acoplamento bilinear, ocorrem comportamentos distintos dos observados em multicamadas magn?ticas quasiperi?dicas com espa?adores de espessura constante. Dentre estes, podemos citar uma depend?ncia com a paridade da gera??o de Fibonacci utilizada, um patamar de baixa magnetoresist?ncia para campos externos baixos e regi?es que apresentam alta sensibilidade a varia??es pequenas do campo aplicado

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