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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

Ondas de spin em nanofilmes nagn?ticos acoplados quasiperiodicamente

Borges, Filipe Augusto de Souto 06 July 2012 (has links)
Made available in DSpace on 2014-12-17T15:14:58Z (GMT). No. of bitstreams: 1 FilipeASB_DISSERT.pdf: 919582 bytes, checksum: 74ab71c48467a95bd20314187ea48c0d (MD5) Previous issue date: 2012-07-06 / We studied the spin waves modes that can propagate in magnetic multilayers composed of ferromagnetic metallic films in the nanometer scale. The ferromagnetic films (iron) are separated and coupled through the nonmagnetic spacer films (chromium). The films that make up the multilayer are stacked in a quasiperiodic pattern, following the Fibonacci and double period sequences. We used a phenomenological theory taking into account: the Zeeman energy (between the ferromagnetic films and the external magnetic field), the energy of the magneto-crystalline anisotropy (present in the ferromagnetic films), the energy of the bilinear and biquadratic couplings (between the ferromagnetic films) and the energy of the dipole-dipole interaction (between the ferromagnetic films), to describe the system. The total magnetic energy of the system is numerically minimized and the equilibrium angles of the magnetization of each ferromagnetic film are determined. We solved the equation of motion of the multilayer to find the dispersion relation for the system and, as a consequence, the spin waves modes frequencies. Our theoretical results show that, in the case of trilayers (Fe/Cr/Fe), our model reproduces with excellent agreement experimental results of Brillouin light scattering, known from the literature, by adjusting the physical parameters of the nanofilms. Furthermore, we generalize the model to N ferromagnetic layers which allowed us to determine how complex these systems become when we increase the number of components. It is worth noting that our theoretical calculations generalize all the results known from the literature / Neste trabalho, estudamos os modos de ondas de spin que podem se propagar em multicamadas magn?ticas compostas por filmes met?licos ferromagn?ticos em escala nanom?trica. Os filmes ferromagn?ticos (ferro) s?o intercalados e acoplados atrav?s de filmes espa?adores n?o-magn?ticos (cromo). Os filmes que comp?em a multicamada s?o empilhados de uma forma quasiperi?dica, seguindo as sequ?ncias de Fibonacci e per?odo duplo. Utilizamos uma teoria fenomenol?gica levando em conta: a energia Zeeman (entre os filmes ferromagn?ticos e o campo magn?tico externo), a energia de anisotropia magneto-cristalina (presente nos filmes ferromagn?ticos), a energia dos acoplamentos bilinear e biquadr?tico (entre os filmes ferromagn?ticos) e a energia da intera??o tipo dipolo-dipolo (entre os filmes ferromagn?ticos), para descrever o sistema. A energia magn?tica total do sistema ? minimizada numericamente e os ?ngulos de equil?brio das magnetiza??es de cada filme ferromagn?tico s?o determinados. Em seguida, resolvemos a equa??o de movimento da multicamada para encontrarmos a rela??o de dispers?o para o sistema e consequentemente as frequ?ncias dos modos de ondas de spin. Nossos resultados te?ricos mostram que, no caso de tricamadas (Fe/Cr/Fe), nosso modelo consegue reproduzir com excelente concord?ncia resultados experimentais de espalhamento de luz Brillouin, conhecidos da literatura, atrav?s do ajuste dos par?metros f?sicos dos nanofilmes. Al?m disso, generalizamos o modelo para N camadas ferromagn?ticas, o que nos permitiu verificar o qu?o complexo esses sistemas se tornam quando aumentamos o n?mero de componentes. Vale a pena salientar que nossos c?lculos te?ricos generalizam todos os resultados conhecidos da literatura

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