Domain wall mobility in nanowires: transverse versus vortex walls

TL;DR

This study numerically investigates the mobility of domain walls in ferromagnetic nanowires, revealing how different wall types and diameters influence mobility, with vortex walls showing a significant increase in mobility at low damping.

Contribution

It provides a detailed comparison of transverse and vortex domain wall mobility in nanowires, highlighting the effects of diameter and damping on their dynamics.

Findings

Transverse walls occur below the exchange length, with mobility matching 1D models.

Vortex walls appear at larger diameters, greatly increasing mobility.

Vortex wall mobility depends strongly on damping, scaling as 1/α^2.

Abstract

The motion of domain walls in ferromagnetic, cylindrical nanowires is investigated numerically by solving the Landau-Lifshitz-Gilbert equation for a classical spin model in which energy contributions from exchange, crystalline anisotropy, dipole-dipole interaction, and a driving magnetic field are considered. Depending on the diameter, either transverse domain walls or vortex walls are found. The transverse domain wall is observed for diameters smaller than the exchange length of the given material. Here, the system behaves effectively one-dimensional and the domain wall mobility agrees with a result derived for a one-dimensional wall by Slonczewski. For low damping the domain wall mobility decreases with decreasing damping constant. With increasing diameter, a crossover to a vortex wall sets in which enhances the domain wall mobility drastically. For a vortex wall the domain wall mobility is described by the Walker-formula, with a domain wall width depending on the diameter of the wire. The main difference is the dependence on damping: for a vortex wall the domain wall mobility can be drastically increased for small values of the damping constant up to a factor of $1/\alpha^2$.