  We test whether current-induced magnetization switching due to
spin-transfer-torque in ferromagnetic/non-magnetic/ferromagnetic (F/N/F)
trilayers changes significantly when scattering within the N-metal layers is
changed from ballistic to diffusive. Here ballistic corresponds to a ratio r =
lambda/t greater than or equal to 3 for a Cu spacer layer, and diffusive to r =
lambda/t less than or equal to 0.4 for a CuGe alloy spacer layer, where lambda
is the mean-free-path in the N-layer of fixed thickness t = 10 nm. The average
switching currents for the alloy spacer layer are only modestly larger than
those for Cu. The best available model predicts a much greater sensitivity of
the switching currents to diffuse scattering in the spacer layer than we see.
