MagnetoresistÃncia em filmes e multicamadas magnÃticas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

In this master dissertation, we have studied, at room temperature, magnetic and transport properties of metallic films and multilayer of different structures such as: single layer thin films, coupled trilayer, ferromagnetic/antiferromagnetic bilayer and spin valve. Phenomenological models, which take in account the most relevant magnetic free energy terms, were proposed to explain the experimental data. It has been shortly reviewed the most important mechanisms responsible for the electric resistance phenomena in magnetic metals, such as: ohmâs law resistance, Hall effects (conventional and anomalous), anisotropic magnetoresistance (AMR), giant agnetoresistance (GMR) and giant magnetoimpedance (GMI). In order to measure the transport properties we have developed an experimental setup that includes DC and AC agnetoresistance techniques. An experimental comparison between the DC and AC techniques was done to highlight the advantages and shortcomings of the two methods. The transport properties of single crystal ilms of iron and polycrystalline films of Ni81Fe19 (permalloy) and cobalt were investigated. The iron films were deposited by DC sputtering onto MgO(001) substrates and the permalloy and cobalt films were deposited onto plates of glass (Corning 7059). In these systems the AMR effect was investigated as a function of the in-plane magnetic field (H0) varying the in-plane angle between the current density and magnetization. For some specific values of angles, the AMR versus H0 curves of the iron films, exhibited anomalies that were interpreted as due to the competition between the Zeeman and magnetocrystalline energy terms. Magnetoresistance effect as a function of the in plane angle were also investigated in coupled trilayer Fe(40Ã)/Cr(31Ã)/Fe(40Ã). The magnetizations of the two iron layers are exchange-coupled via the chromium spacer layer. This couplingcorresponds to the second peak of the ntiferromagnet coupling. This sample exhibits an unexpected biquadratic exchange coupling of the same order as the bilinear coupling. The competition between the Zeeman energy, the magnetocrystalline anisotropy and the bilinear and biquadratic exchanges couplings, originated very remarkable characteristics in the magnetoresistance curves. The AMR contribution from each layer was clearly detached from the GMR effect. The difference of the resistances between the MR curves obtained for the magnetic field applied along the two hard directions were interpreted taking into account the equilibrium positions of the magnetizations of the two layers. Magnetoresistance measurements were also made in exchange-coupled ferromagnetici antiferromagnetic bilayers of permalloy/IrMn, deposited onto glass substrates. The magnetoresistance properties were compared with ferromagnetic resonance (FMR) measurements and phenomenological parameters, such as, exchange bias field and uniaxial anisotropy were obtained. Finally, we have investigated the transport properties of spin valve systems composed by Py(16Ã)/Cu(t)/Py(16Ã)/IrMn(500Ã), for different Cu layer thicknesses. The effect of the GMR phenomena between the free and the pinned layers was investigated as a function of the in-plane angle. In these samples the AMR phenomena was also verified. The MR curves were also interpreted taking into account a phenomenological model

ASSUNTO(S)

fisica efeitos magneto-Ãpticos materiais magnÃticos ressonÃncia ferromagnÃtica magnetoresistÃncia

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