Ballistic versus diffusive transport in current-induced magnetization switching

We test whether current-induced magnetization switching due to spin-transfer torque in ferromagnetic/nonmagnetic/ferromagnetic (F/N/F) nanopillars changes significantly when scattering within the N metal layers is changed from ballistic to diffusive. Here, ballistic corresponds to a ratio $r=\lambda ∕t⩾3$ for a Cu spacer layer, and diffusive to $r⩽0.4$ for a CuGe alloy spacer layer, where $\lambda$ is the mean free path in the N layer of fixed thickness $t=10\mathrm{nm}$. 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.

Figure 1

$R\left(H\right)$ and $R\left(I\right)$ at 295 (top) and $4.2\mathrm{K}$ (bottom) for one of the six selected CuGe nanopillars (left) and one of the seven selected Cu nanopillars (right). Arrows in the upper left indicate $\Delta R$ and $\Delta I$.