Spin Currents in FePt/Ni80Fe20 bilayers and FePt/Al/Ni80Fe20 trilayers

GASTÓN BLATTER; DANIEL VELÁZQUEZ RODRIGUEZ; AMPUERO TORRES, J.L.; L. AVILÉS-FÉLIX; JAVIER E. GÓMEZ; A. BUTERA

Bariloche

Workshop; International workshop on Spintronics 2022; 2022

Centro Atómico Bariloche

The study of spin currents using the spin pumping mechanism is usually carried out in bilayers in which one film is ferromagnetic (FM) and the other a non-magnetic metal. In the present study we have grown FePt/Ni80Fe20 (Py) bilayers and FePt/Al/Ni80Fe20 trilayers of different thicknesses with the purpose of investigating the injection and detection of spin currents between two ferromagnetic metals.Using dc magnetron sputtering techniques, FePt/Py bilayers and FePt/Al/Py trilayers of variable thickness were grown on Si (100) substrates with native SiO2. In the bilayers, the thickness of one of the FM was kept fixed and the other was varied between 3 nm and 15 nm in steps of 3 nm. In the trilayers, both FM thicknesses were fixed at 6 nm and the thickness of Al was varied between 1.6 nm and 8 nm (every 1.6 nm) in order to reduce the strong magnetic coupling between both FM layers.The samples were characterized with vibrating sample (VSM) and Kerr magnetometry and with ferromagnetic resonance spectroscopy (FMR). In the case of bilayers, both magnetometry and FMR measurements indicate the existence of a strong coupling between FePt and Py. However, in the case of the trilayers with a thicker Al spacer, hysteresis loops with magnetization reversal at two different fields are observed and FMR spectra show two resonance lines, both indicative of decoupling between the FM films.Measurements of the induced voltage between the ends of the samples as a function of the magnetic field when the resonance condition occurs give signals that are a mixture of a symmetric and an antisymmetric contribution in the case of bilayers. For the most decoupled trilayers (thicker Al spacer), two symmetric curves were detected, but of opposite sign, coincident with the resonance of each FM layer. This behavior can be assigned to the effect of spin pumping and the conversion into a charge current by means of the inverse spin Hall Effect. By considering the symmetry of the trilayer, it follows that FePt and Permalloy have a positive spin Hall angle.