Navegando por Autor "Azevedo, A."

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Investigation of large enhancement of spin hall angle in heterostructures of Ag nanoparticles randomly grown in Pt
(AIP Advances, 2019) Santos, O. A.; Silva, E. F.; Gamino, M.; Mendes, J. B. S.; Rezende, S. M.; Azevedo, A.
The spin Hall angle (SHA) represents the efficiency of the conversion between spin current into charge current and vice-versa. In this paper, we report the experimental detection of large enhancement of the effective SHA in heterostructures of yttrium iron garnet (YIG)/[Pt-Ag]/Pt and YIG/[Pt-Ag], when compared with measurements in YIG/Pt bilayers. The notation [Pt-Ag] represents the nanoparticles island formation of Ag in the Pt film. In order to investigate the role played by the metallic nanoparticles in the spin-to-charge conversion process, we carried out microwave spin pumping measurements in the following samples: YIG/Ag(3 nm)/Pt(6 nm), YIG/[Pt(3 nm)-Ag(3 nm)]/Pt(3 nm) and YIG/[Pt(6 nm)-Ag(3 nm)]. By means of high-resolution scanning electron microscope (HR-SEM) investigation, we confirmed that layers of Ag exhibit islands nanoparticle structures when grown on the surface of the Pt, which are characterized by the Volmer-Weber mode. The spin pumping results show that the Ag nanoparticles can enhance the charge current created by the inverse spin Hall effect (I ISHE ) up to three times larger than the single Pt layer. Also, by analyzing atomic force microscopy (AFM) images, obtained for samples with different thickness of the Ag layer, we conclude that the roughness plays an important role in the enhancement of the I ISHE . Therefore, taking advantage of poor wetting properties of Ag over Pt layer, it was possible to create nanoscopic particles of Ag randomly grown in the Pt layer. The nanoparticles serve as nanoscopic molds to locally increase the SHA. This feature represents an improvement in searching more efficient methods of the spin-to-charge conversion and opens up the possibility of tuning the SHA by controlling the size and shape of the Ag nanoparticles.
The role of metallic nanoparticles in the enhancement of the spin Hall magnetoresistance in YIG/Pt thin films
(Journal of Magnetism and Magnetic Materials, 2018-11-15) Mendes, J. B. S; Gamino, M.; Silva, E. F.; Santos, O. Alves; Rodríguez-Suárez, R. L.; Machado, F. L. A.; Azevedo, A.; Rezende, S. M.
Enhancements in the spin Hall magnetoresistance (SMR) close to one order of magnitude in bilayers of yttrium iron garnet (YIG) and platinum with embedded metallic nanoparticles of Ag and Cu are reported. The en hancement in the electrical detection of the back reflected spin current in YIG/Pt-MP(t MP )-Pt relative to YIG/Pt is eff attributed to the increase in the effective spin Hall angle ( θ^eff SHA) due to the presence of the metallic nanoparticles. The maximum value observed for the spin Hall magnetoresistance is related to critical thickness of the t MP close to the percolation threshold. The results are also supported by data obtained by means of the spin pumping effect where dc-voltage measurements confirm the enhancement of the spin to charge conversion process.
Spin-current to charge-current conversion and magnetoresistance in a hybrid structure of graphene and yttrium iron garnet
(Physical Review Letters, 2015-11-25) Mendes, J. B. S.; Santos, O. Alves; Meireles, L. M.; Lacerda, R. G.; Vilela-Leão, L. H.; Machado, F. L. A.; Rodríguez-Suárez, R. L.; Azevedo, A.; Rezende, S. M.
The use of graphene in spintronic devices depends, among other things, on its ability to convert a spin excitation into an electric charge signal, a phenomenon that requires a spin-orbit coupling (SOC). Here we report the observation of two effects that show the existence of SOC in large-area CVD grown single-layer graphene deposited on a single crystal film of the ferrimagnetic insulator yttrium iron garnet (YIG). The first is a magnetoresistance of graphene induced by the magnetic proximity effect with YIG. The second is the detection of a dc voltage along the graphene layer resulting from the conversion of the spin current generated by spin pumping from microwave driven ferromagnetic resonance into a charge current, which is attributed to the inverse Rashba-Edelstein effect.