Mechanism of current-assisted Bloch-point wall stabilization for ultra fast dynamics

TL;DR

This paper investigates how current-induced Oersted fields stabilize Bloch-point domain walls in cylindrical nanowires, enabling ultra-fast magnetic domain wall motion exceeding 600 m/s through micromagnetic simulations and modeling.

Contribution

It reveals the mechanism by which Oersted fields stabilize BPWs and demonstrates the scaling of the threshold current with wire radius, advancing understanding of high-speed magnetic domain wall dynamics.

Findings

Oersted field stabilizes BPW above a current threshold

Threshold current scales with 1/R^3 (wire radius)

Domain wall speed exceeds 600 m/s without Walker breakdown

Abstract

Two types of domain walls exist in magnetically soft cylindrical nanowires: the transverse-vortex wall (TVW) and the Bloch-point wall (BPW). The latter is expected to prevent the usual Walker breakdown, and thus enable high domain wall speed. We showed recently [M. Sch\"obitz \etal, Phys. Rev. Lett. 123, 217201 (2019)] that the previously overlooked OErsted field associated with an electric current is a key in experiments to stabilize the BPW and reach speed above 600 m/s with spin-transfer. Here, we investigate in detail this situation with micromagnetic simulations and modeling. The switching of the azimuthal circulation of the BPW to match that of the OErsted field occurs above a threshold current scaling with $1/R^3$ ($R$ is the wire radius), through mechanisms that may involve the nucleation and/or annihilation of Bloch points. The domain wall dynamics then remains of a below-Walker type, with speed largely determined by spin-transfer torque alone.