Micromagnetic understanding of current-driven domain wall motion in patterned nanowires

TL;DR

This paper proposes a modified spin transfer torque model in the Landau-Lifshitz-Gilbert equation to better explain current-driven domain wall motion in nanowires, accounting for experimental observations and extrinsic threshold currents.

Contribution

It introduces a new term in the spin transfer torque model that explains domain wall velocities and threshold currents considering wire roughness.

Findings

Modified torque explains experimental DW velocities

Finite threshold current due to wire roughness

Threshold currents are extrinsic, not intrinsic

Abstract

In order to explain recent experiments reporting a motion of magnetic domain walls (DW) in nanowires carrying a current, we propose a modification of the spin transfer torque term in the Landau-Lifchitz-Gilbert equation. We show that it explains, with reasonable parameters, the measured DW velocities as well as the variation of DW propagation field under current. We also introduce coercivity by considering rough wires. This leads to a finite DW propagation field and finite threshold current for DW propagation, hence we conclude that threshold currents are extrinsic. Some possible models that support this new term are discussed.