Spin current propagation in metallic heterostructure: Pt, Pt/Au and Ta

Magnetic and structural studies of sputter deposited Py(an alloys, Ni80Fe20) and [Py/Fe] thin films allowed for the characterization of their magnetization dynamics properties relevant for subsequent studies. Spin transport and structural studies of Ta in Py/Ta (single magnetic layer) and Py/Ta/[Py/Fe] (double magnetic layer) structures were performed by spin-pumping. It was found that in order to extract self-consistent spin-pumping parameters it is important to study both the single and double magnetic layer structures. Ferromagnetic resonance studies of Py/Pt/[Py/Fe] multilayers reveal interlayer exchange coupling of ferromagnetic nature. The coupling strength is interpreted by the proximity polarization of the Pt due to the neighboring ferromagnets. The coupled layers exhibit optical and acoustic modes of resonance which provide a very stringent test for the spin-pumping model. The induced magnetic damping of the two modes is found to be very well described by the spin-pumping model suggesting a communication of spin-current between the two magnetic layers. No significant spin memory loss contribution is observed. Lastly, the spin-pumping model is studied in a system in which the coupling is interrupted by a Au spacer layer: Py/Au/Pt/Co. It is found that spin-transport across the Au/Pt interface cannot be modeled by the continuity of chemical potential or the continuity of spin accumulation boundary conditions. A new model is presented which treats Pt as a partial spin-sink and results in good fit to all the data sets. Importantly, both the model and data suggest a large asymmetry in spin transport across the Au/Pt interface.