Spin-Flipping at Sputtered Co(90)Fe(10)/Cu Interfaces

Knowledge of the spin-flipping probability, P$_{F/N}$ = 1 -- exp[-$\delta $(F/N)], at ferromagnetic/non-magnetic (F/N) interfaces in the Current-Perpendicular-to-Plane (CPP) geometry is minimal [1,2]. We use a new technique [2] to find $\delta $(CoFe/Cu) at 4.2K, where CoFe = Co(90)Fe(10). With thin (3 nm) CoFe layers, the spin-diffusion length of CoFe $\sim $ 12 nm doesn't mask spin-flipping due to $\delta $. Our most important samples, sensitive to $\delta $(CoFe/Cu), have the form FeMn/Py/Cu/X/Cu/Py/FeMn. Here Py = Ni(80)Fe(20), the antiferromagnet FeMn pins the two Py layers to flip at a much higher field than X = [CoFe(3)/Cu(1.4)]$_{n}$CoFe(3), and 1.4 nm of Cu couples the CoFe layers ferromagnetically so X reverses as a unit. We measure, versus the number of repeats $n$, the change in specific resistance, A$\Delta $R = AR(AP) -- AR(P), between states where the X moment is anti-parallel (AP) or parallel (P) to the pinned Py moments. CPP current flows through area A. Our resulting best estimate is $\delta $(CoFe/Cu) $\approx $ 0.2. [1] J. Bass and W.P.Pratt Jr., J. Phys. Cond. Matt. \textbf{19}, 183201 (2007). [2] B. Dassonneville et al., Appl. Phys. Lett. \textbf{96}, 022509 (2010).