Spin-flipping in Pt and at Co/Pt interfaces

There has been recent controversy about the magnitude of spin-flipping in the heavy metal Pt, characterized by the spin-diffusion length lsfPt. We propose a resolution of this controversy, and also present evidence for the importance of a phenomenon neglected in prior studies of transport across sputtered Ferromagnet/Pt (F/Pt) interfaces, spin-flipping at the interface. The latter is characterized by an interface spin-flipping parameter, δCo/Pt, that specifies the probability P=[1−exp(−δ)] of a conduction electron flipping its spin direction as it traverses a Co/Pt interface. From studies of the Current-Perpendicular-to-Plane (CPP) Resistances and Magnetoresistances of sputtered ferromagnetically coupled Co/Pt multilayers by themselves, and embedded within Py-based Double Exchange-biased Spin-Valves, we derive values at 4.2 K of δCo/Pt=0.9−0.2+0.5, interface specific resistance, ARCo/Pt⁎=0.74±0.15 fΩ m2, and interface spin-scattering asymmetry, γCo/Pt=0.53±0.12. This value of δCo/Pt is much larger than ones previously found for five other interfaces involving Co but not Pt. To derive δ requires knowledge of lsfPt for our sputtered Pt, which we obtain from separate measurements. Combining our results with those from others, we find that lsfPt for Pt is approximately proportional to the inverse resistivity, 1/ρPt.