Study of spin pumping in Co thin film vis-à-vis seed and capping layers using ferromagnetic resonance spectroscopy

Abstract

We investigated the dependence of the seed (Ta/Pt, Ta/Au) and capping (Pt/Ta, Au/Ta) layers on the spin pumping effect in a 3 nm thick Co thin film using ferromagnetic resonance spectroscopy (FMR). The FMR data were fitted with Kittel’s equation to extract the values of the damping constant and g-factor. A strong dependence of the seed and capping layers on spin pumping has been discussed. The value of the damping constant (α) is found to be relatively large i.e. 0.0326 ± 0.0008 for the Ta(3)/Pt(3)/Co(3)/Pt(3)/Ta(3) (nm) multilayer structure, while it is 0.0104 ± 0.0003 for Ta(3)/Co(3)/Ta(3) (nm). An increase in α is observed, due to the Pt layer that works as a good sink for spins, due to high spin orbit coupling. In addition, we measured the effective spin conductance = 5.82 ± 0.08 × 1018 m−2 for the structure Ta(3)/Pt(3)/Co(3)/Pt(3)/Ta(3) (nm) as a result of the enhancement in α relative to its bulk value. We observed that the evaluated g-factor decreases as effective demagnetizing magnetic field increases in all of the studied samples. The azimuthal dependence of the magnetic resonance field and line width showed relatively high anisotropy in the tri-layer Ta(3)/Co(3)/Ta(3) (nm) structure.