Navegando por Autor "Costa, R. B."
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Artigo Effects of second order surface anisotropy in YIG sputtered onto GGG (1 0 0) oriented substrate(Elsevier B.V., 2018-08-17) Oliveira, Alexandre Barbosa de; Feitosa, Carlos Chesman de Araújo; Rodríguez-suárez, R. L.; Costa, R. B.; Silva, U. C.; Costa, N. P.; Silva, B. G.; Sommer, R. L.; Bohn, Felipe; Correa, M. A.In this work, we produced Y3Fe5O12 textured films, with thicknesses between 50 nm and 500 nm, onto (1 0 0) Gd3Ga5O12 by magnetron sputtering and post annealing, and investigated the first and second order surface and cubic anisotropy constants using the ferromagnetic resonance technique. The surface anisotropy constants exhibited different behaviors with film thickness, with the first order presenting the usual inverse of ferromagnetic layer thickness. Besides this inverse of thickness behavior, the second order also came up with a constant value. In the frame of spin reorientation transition phenomenon, we evaluated volume and surface contribution to the surface anisotropy. Although the second order cubic anisotropy constant is one order of magnitude stronger than the first order, they did not show any explicit thickness dependence. The second order terms of surface and cubic anisotropy appeared to be essential to allow simultaneous fit of in-plane and out-of-plane angular dependence of resonance field. Moreover, they had to be negative to describe the out-of-plane results correctly. Our results raised critical issues that shall be taken into account when explaining the new and recent spintronics and caloritronics effects in YIG.Artigo Perturbative measurement of magnetoresistance(AIP Publishing, 2018-12-21) Oliveira, Alexandre Barbosa de; Melo, A. C. C.; Costa, R. B.; Costa, N. P.; Azevedo, A.; Feitosa, Carlos Chesman de AraújoIn this paper, we report the development of a novel technique in which the magnetoresistance of nanostructures is perturbatively measured by transversally modulating the DC magnetic field. It measures the electrical transport counterpart of the transverse magnetic AC-susceptibility. The technique was developed in a conventional four-probe configuration in which a small DC current flows through the sample and a small transverse AC-field perturbates the equilibrium position of the sample magnetization. Lock-in detection, in-phase with the AC-perturbation, is used to measure the voltage signal between the two inner electrodes of the four-probe station. We successfully demonstrated that this signal is proportional to the product of the first derivative of sample resistance with respect to the equilibrium position of the magnetization times the second derivative of the energy with respect to the equilibrium position of the magnetization. These dependences add new features to the technique investigated here that were not captured by the investigations previously reported on the same subject. To show the effective use of the technique, we discuss its application in measuring magnetic properties of thin magnetic films in the non-saturated regime.