Propriedades estáticas e dinâmicas de super-redes e multicamadas quasiperiódicas
In this thesis, we investigate the static and dynamic properties of magnetic multilayer and thin film systems, respectively. The propagation of spin waves was investigated in a quasiperiodic superlattice which structure was built according to the so-called Octonacci sequence, composed by two simp...
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| Formato: | doctoralThesis |
| Idioma: | por |
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Brasil
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/26517 |
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| Resumo: | In this thesis, we investigate the static and dynamic properties of magnetic
multilayer and thin film systems, respectively. The propagation of spin waves was investigated
in a quasiperiodic superlattice which structure was built according to the so-called Octonacci
sequence, composed by two simple cubic ferromagnetic materials interacting through bilinear
and biquadratic exchange couplings at their interfaces. The ferromagnetic materials are
described by the Heisenberg model, and a transfer matrix treatment is employed, with the
calculations performed for the exchange-dominated regime, taking into account the random
phase approximation (RPA) to obtain the allowed bands and transmittance spectra. In addition,
the influence of the biquadratic coupling on the band and transmittance spectra is discussed.
We also performed an investigation of the static magnetic properties of nanometric films, with
low symmetry crystallographic growth directions ([211] and [321]), by using two quasiperiodic
models. For the model 1, the magnetic thin films are stacked quasiperiodically, with the nonmagnetic spacers having the same thickness, while for the model 2, the non-magnetic spacers
follows the quasiperiodicity, with different thicknesses. For both models the quasiperiodicity is
according to the Fibonacci and Octonacci quasiperiodic sequences. The theoretical modelling
is based on a realistic magnetic energy taking into account the Zeeman, cubic and uniaxial
anisotropy terms, besides the bilinear and biquadratic couplings. From the equilibrium
configurations, magnetization, magnetoresistance and phase diagrams are obtained. |
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