Ballistic vs Diffusive Transport in Current-Induced Magnetization Switching

TL;DR

This study compares current-induced magnetization switching in ferromagnetic trilayers with ballistic and diffusive spacer layers, finding only modest differences in switching currents despite theoretical predictions of higher sensitivity.

Contribution

It provides experimental evidence that switching currents are not significantly affected by the scattering regime in the spacer layer, challenging existing models.

Findings

Switching currents are only modestly larger with diffusive spacer layers.

The experimental results do not match the high sensitivity predicted by models.

Ballistic and diffusive regimes show similar switching behavior.

Abstract

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.