Survey of 360$^{\circ}$ domain walls in magnetic heterostructures: topology, chirality and current-driven dynamics

TL;DR

This survey reviews the topology, chirality, and current-driven behavior of 360-degree domain walls in magnetic heterostructures, highlighting how substrate type and spin-orbit torques influence their static and dynamic properties.

Contribution

It systematically characterizes the static and dynamic properties of 360DWs, revealing how substrate-induced interactions and spin-orbit torques affect their behavior, which was less understood before.

Findings

Néel-type 360DWs on normal substrates with no chirality.

iDMI induces specific chirality in 360DWs on heavy-metal substrates.

360DWs do not undergo Walker breakdown and maintain fixed propagation modes under current.

Abstract

Chirality and current-driven dynamics of topologically nontrivial 360$^{\circ}$ domain walls (360DWs) in magnetic heterostructures (MHs) are systematically investigated. For MHs with normal substrates, the static 360DWs are N\'{e}el-type with no chirality. While for those with heavy-metal substrates, the interfacial Dzyaloshinskii-Moriya interaction (iDMI) therein makes 360DWs prefer specific chirality. Under in-plane driving charge currents, as the direct result of "full-circle" topology a certain 360DW does not undergo the "Walker breakdown"-type process like a well-studied 180$^{\circ}$ domain wall as the current density increases. Alternatively, it keeps a fixed propagating mode (either steady-flow or precessional-flow, depending on the effective damping constant of the MH) until it collapses or changes to other types of solition when the current density becomes too high. Similarly, the field-like spin-orbit torque (SOT) has no effects on the dynamics of 360DWs, while the anti-damping SOT has. For both modes, modifications to the mobility of 360DWs by iDMI and anti-damping SOT are provided.