Current-Induced Magnetization Switching (CIMS) for `Ballistic' and `Diffusive' Transport Through the Non-Magnetic (N) metal in Permalloy/N/Permalloy Nanopillars*

. Adding 5{\%} Ge to Cu decreases the mean-free-path, $\lambda $, at 4.2K from $\sim $ 130 nm to $\sim $ 3.8 nm, while still leaving the spin-diffusion length $\ge $ 40 nm. Thus, comparing the CIMS switching currents at 4.2K for sputtered Py/N/Py with layer thickness t$_{N}$ = 10nm for N = Cu or Cu(5{\%}Ge), allows testing of the importance of `quasi-ballistic'-- (t$_{Cu}$/$\lambda _{Cu}) \quad \sim $ 0.08, versus `quasi-diffusive'---(t$_{CuGe}$/$\lambda _{CuGe}) \quad \sim $ 2.6, transport, with at most minor correction for spin-flipping in the N-metals. At 4.2K we find a ratio of switching currents, $\Delta $I$_{s}$(CuGe)/$\Delta $I$_{s}$(Cu) = 1.3 $\pm $ 0.2, where $\Delta $I$_{s}$ is the sum of the magnitudes of the critical current for switching from parallel to anti-parallel magnetic order and vice-versa. We will compare this ratio with values calculated using different models.