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Transferência de torque por corrente polarizada em spin através de pontas de contato

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Repositório Institucional da UFSC
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Abstract

The possibility of controlling the magnetization from a spin polarized current, was provided by Slonkzewsky and Berger in 1996. Passing a current through a ferromagnetic layer, this current becomes spin polarized. If this current is injected into another ferromagnetic layer, the interaction between this polarized current and the magnetic moments of the material can exert a torque on the magnetization location. Depending on the current density of its polarization and the applied magnetic field, the torque can induce the precession or reorientation of magnetization. Experimentally this can be observed in spin valves through magnetorresistivas measurements where a high density current, flows perpendicular to the plane of the sample. In this study we investigated the production and characterization of spin valves, with the aim of studying the phenomenon of transfer of torque through contact tips. Films IrMn (10nm) / Co (15nm) / Cu (xCu nm) / Co (15nm), where xCu = 2, 5, 8, 11, were produced by sputtering on Si (100) in the presence of magnetic field 130 Oe applied parallel to the plane of the sample. The thickness of copper layer was varied, as it is this which defines the type of coupling and relative orientation between the two ferromagnetic layers. In addition, the IrMn was used in order to "hold" the first ferromagnetic layer magnetically cobalt, which is responsible for polarizing the current that is injected into the second ferromagnetic layer. Contact tips were produced by electropolishing and observed by scanning electron microscopy. This technique showed good reproducibility and allowed to obtain tips with average diameters of 400 nm. Diffraction X-rays reflectivity measure are applied for structural characterization, determination of the thickness and roughness of the layers of the films. Measurements vibrating sample magnetometry and magnetoresistance, were performed for the characterization of magnetic films, which was observed giant magnetoresistance xCu = 8 nm. In order to verify the effect of spin-torque electrical measurements were performed using the tips previously produced. It was possible to observe a variety of effects related to spin-torque and other phenomena. The optimization of the electrical measurements was sought continuously in an attempt to improve the data quality and much has been achieved in this aspect.

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