Domain walls within domain walls in wide ferromagnetic strips

TL;DR

This paper uses large-scale micromagnetic simulations to show that internal domain walls within extended domain walls are more robust than those in nanowires, opening new possibilities for spintronics applications.

Contribution

It demonstrates the topological robustness of internal domain walls and their dynamic behavior under various conditions, which was not previously understood.

Findings

Internal domain walls nucleate within domain walls at a threshold force.

Fast dynamics occur without Walker breakdown along pinned domain walls.

Internal domain walls are topologically protected by surrounding out-of-plane domains.

Abstract

We carry out large-scale micromagnetic simulations which demonstrate that due to topological constraints, internal domain walls (Bloch lines) within extended domain walls are more robust than domain walls in nanowires. Thus, the possibility of spintronics applications based on their motion channeled along domain walls emerges. Internal domain walls are nucleated within domain walls in perpendicularly magnetized media concurrent with a Walker breakdown-like abrupt reduction of the domain wall velocity above a threshold driving force, and may also be generated within pinned, localized domain walls. We observe fast field and current driven internal domain wall dynamics without a Walker breakdown along pinned domain walls, originating from topological protection of the internal domain wall structure due to the surrounding out-of-plane domains.