Magnetorresistência perturbativa e estudo de fenômenos da caloritrônica de Spin em nanoestruturas magnéticas
In this work has been realized studies in thin magnetic films with the purpose of approaching two lines of investigation: (a) the understanding of mechanisms of interaction in coupled ferromagnetic/antiferromagnetic bilayers (FM/AF). In this case the rotatable and unidirectional anisotropy (Excha...
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| Formato: | doctoralThesis |
| Idioma: | pt_BR |
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/27953 |
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| Resumo: | In this work has been realized studies in thin magnetic films with the purpose of
approaching two lines of investigation: (a) the understanding of mechanisms of interaction
in coupled ferromagnetic/antiferromagnetic bilayers (FM/AF). In this case the rotatable and
unidirectional anisotropy (Exchange bias) has been investigated with a new experimental
technique, of magnetic characterization, which allows to test the theoretical models used to
explain the phenomenon, due to this anisotropy. This technique is called perturbative magnetoresistance (PMR) and it has been developed and improved during the doctoral program.
It has also been investigated, with the use of PMR, simple films with uniaxial and cubic
anisotropies [100]. Two types of PMR measurements were used in the magnetic characterization: the measurement of PMR as a function of the modulus of the applied magnetic field in
the sample and the measurement of PMR as a function of the variation of the angle of application of this magnetic field (angular PMR). The other line of investigation, (b) involves the
control and understanding of generation/detection of spin current from the thermal gradient.
In this case, an experimental set-up has been developed to apply a perpendicular thermal
gradient to the magnetic film plane. Therefore, classical and quantum effects are responsible
for generating potential difference in the surface of the film and that can be measured by
nanovoltmeter. The detection of spin current from the electric potential difference requires a
thin film engineering, since the pure spin current does not generate electrical potential difference. Is this work, it will be detailed how it is possible to detect electric potential difference
due to the spin current. The parameter which characterizes the efficiency of spin current
conversion in charge current (electrical potential difference) is of great importance for the
engineering of future devices based on spin current. Particularly in this work, efforts have
been made to measure the efficiency of ferromagnetic materials, since non-magnetic materials
such as platinum (Pt) and tantalum (Ta) are generally used in the literature. In addition,
a study was carried out on the generation and detection of spin current in FM/AF/NM
systems, where the influence of the AF layer (NiO, in this case) on the measured voltage in
NM layer was characterized. In this investigation, it was verified that for some thicknesses
of NiO, there is an amplification of the spin current in the system. |
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