Magnetic domain-wall dynamics in wide permalloy strips

TL;DR

This paper investigates the complex behavior of magnetic domain walls in wide permalloy strips, revealing how their dynamics depend on geometry and external magnetic fields through detailed micromagnetic simulations.

Contribution

It provides a comprehensive analysis of the field-driven dynamics of various equilibrium domain wall structures in wide permalloy strips, highlighting new dynamical behaviors and transitions.

Findings

Complex domain wall dynamics depend on geometry and field strength.

Identification of dynamic transitions between different domain wall structures.

Observation of vortex core behaviors and limitations in supporting compact walls.

Abstract

Domain walls in soft permalloy strips may exhibit various equilibrium micromagnetic structures depending on the width and thickness of the strip, ranging from the well-known transverse and vortex walls in narrow and thin strips to double and triple vortex walls recently reported in wider strips [V. Est\'evez and L. Laurson, Phys. Rev. B {\bf 91}, 054407 (2015)]. Here we analyze the field driven dynamics of such domain walls in permalloy strips of widths from 240 nm up to 6 $\mu$m, using the known equilibrium domain wall structures as initial configurations. Our micromagnetic simulations show that the domain wall dynamics in wide strips is very complex, and depends strongly on the geometry of the system, as well as on the magnitude of the driving field. We discuss in detail the rich variety of the dynamical behaviors found, including dynamic transitions between different domain wall structures, periodic dynamics of a vortex core close to the strip edge, transitions towards simpler domain wall structures of the multi-vortex domain walls controlled by vortex polarity, and the fact that for some combinations of the strip geometry and the driving field the system cannot support a compact domain wall.