Stability and Nucleation of Dipole Strings in Uniaxial Chiral Magnets

TL;DR

This paper investigates the stability and nucleation of magnetic dipole strings in uniaxial chiral magnets, showing they are stable three-dimensional solitons that can spontaneously form under certain conditions.

Contribution

It demonstrates that isolated dipole strings are stable in uniaxial chiral magnets and can spontaneously nucleate, expanding understanding of topological magnetic textures.

Findings

Dipole strings are stable in unperturbed vacuum.

Energy barriers protect dipole strings from collapse.

Dipole strings can spontaneously nucleate during in-field annealing.

Abstract

We report on the stability of the magnetic dipole string (DS), a three-dimensional magnetic texture formed by two coupled Bloch points with opposite topological charges, separated by an equilibrium distance. Previous studies demonstrated the stability of such configurations through geometric confinement or coupling with local perturbations in the magnetization field, such as skyrmion strings or dislocations in helical modulations. Here, we show that, in uniaxial chiral magnets, an isolated DS remains stable in an unperturbed vacuum, thus representing a true three-dimensional soliton. The phase diagram illustrates the stability of the DS embedded in the conical or helical phases across a broad range of material parameters and external magnetic fields. Using the geodesic nudged elastic band method applied to a regularized micromagnetic model, we demonstrate that isolated DSs are protected from collapse by an energy barrier. Stochastic spin-lattice simulations demonstrate that DSs can spontaneously nucleate during in-field annealing. This work aims to stimulate the experimental observation of DSs and further exploration of uniaxial chiral magnets.