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Previous issue date: 2013-12-12 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / In this paper we investigate the spectra of band structures and transmittance in magnonic quasicrystals
that exhibit the so-called deterministic disorders, specifically, magnetic multilayer
systems, which are built obeying to the generalized Fibonacci (only golden mean (GM), silver
mean (SM), bronze mean (BM), copper mean (CM) and nickel mean (NM) cases) and
k-component Fibonacci substitutional sequences. The theoretical model is based on the Heisenberg
Hamiltonian in the exchange regime, together with the powerful transfer matrix method,
and taking into account the RPA approximation. The magnetic materials considered are simple
cubic ferromagnets. Our main interest in this study is to investigate the effects of quasiperiodicity
on the physical properties of the systems mentioned by analyzing the behavior of spin
wave propagation through the dispersion and transmission spectra of these structures. Among
of these results we detach: (i) the fragmentation of the bulk bands, which in the limit of high
generations, become a Cantor set, and the presence of the mig-gap frequency in the spin waves
transmission, for generalized Fibonacci sequence, and (ii) the strong dependence of the
magnonic band gap with respect to the parameters k, which determines the amount of different
magnetic materials are present in quasicrystal, and n, which is the generation number of the
sequence k-component Fibonacci. In this last case, we have verified that the system presents
a magnonic band gap, whose width and frequency region can be controlled by varying k and
n. In the exchange regime, the spin waves propagate with frequency of the order of a few tens
of terahertz (THz). Therefore, from a experimental and technological point of view, the magnonic
quasicrystals can be used as carriers or processors of informations, and the magnon (the
quantum spin wave) is responsible for this transport and processing / Neste trabalho investigamos espectros de estruturas de banda e de transmit?ncia em quasicristais
magn?nicos que apresentam as chamadas desordens determin?sticas, especificamente,
sistemas de multicamadas magn?ticas que s?o constru?dos obedecendo as sequ?ncias substitutionais
de Fibonacci generalizada (apenas os casos golden mean (GM), silver mean (SM),
bronze mean (BM), copper mean (CM) e nickel mean (NM)) e k-componente de Fibonacci. O
modelo te?rico ? baseado no hamiltoniano de Heisenberg para o regime de troca, juntamente
com o poderoso m?todo da matriz transfer?ncia, e levando em conta a aproxima??o RPA. Os
materiais magn?ticos considerados s?o ferromagnetos c?bicos simples. O principal interesse
deste estudo ? investigar o efeito da quasi-periodicidade nas propriedades f?sicas dos sistemas
citados analisando o comportamento da propaga??o de ondas de spin por meio dos espectros de
dispers?o e de transmiss?o dos magnons nestas estruturas. Entre os resultados destacamos: (i)
a fragmenta??o das bandas de volume que, no limite de altas gera??es, se tornam conjuntos de
Cantor, e a presen?a da frequ?ncia de mid-gap na transmit?ncia das ondas de spin, na sequ?ncia
de Fibonacci generalizada; e (ii) a forte depend?ncia do band gap magn?nico com rela??o
aos par?metros k, que determina a quantidade de materiais magn?ticos diferentes presentes no
quasi-cristal, e n, que ? o n?mero da gera??o da sequ?ncia k-componente de Fibonacci. Neste
?ltimo caso, verificamos que o sistema apresenta uma banda magn?nica proibida, cuja largura
e regi?o de frequ?ncia podem ser controladas variando k e n. No regime de troca, as ondas de
spin propagam-se com frequ?ncia da ordem de algumas dezenas de terahertz (THz). Portanto,
do ponto de vista experimental e tecnol?gico, os quasi-cristais magn?nicos podem ser utilizados
como transportadores ou processadores de informa??es, sendo o magnon (o quantum da
onda de spin) o respons?vel por esse transporte e processamento
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/16625 |
| Date | 12 December 2013 |
| Creators | Costa, Carlos Humberto Oliveira |
| Contributors | CPF:63518163434, http://lattes.cnpq.br/6345339220512423, Albuquerque, Eudenilson Lins de, CPF:05011124487, http://lattes.cnpq.br/3594651355252245, Fulco, Umberto Laino, CPF:67196675487, http://lattes.cnpq.br/9579151361576173, Mauriz, Paulo Wilson, CPF:01080622870, http://lattes.cnpq.br/7636664451155498, Pereira J?nior, Jo?o Milton, CPF:49246763300, http://lattes.cnpq.br/8000258491459487, Vasconcelos, Manoel Silva de |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em F?sica, UFRN, BR, F?sica da Mat?ria Condensada; Astrof?sica e Cosmologia; F?sica da Ionosfera |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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