Straight motion of half-integer topological defects in thin Fe-N magnetic films with stripe domains

S Fin,D Bisero,S Tacchi,F Fortuna,M Eddrief,M Marangolo,L.-C Garnier,C Hepburn,A Rettori,M G Pini,R Silvani

doi:10.1038/s41598-018-27283-7

Abstract

In thin magnetic films with perpendicular magnetic anisotropy, a periodic “up-down” stripe-domain structure can be originated at remanence, on a mesoscopic scale (~100 nm) comparable with film thickness, by the competition between short-range exchange coupling and long-range dipolar interaction. However, translational order is perturbed because magnetic edge dislocations are spontaneously nucleated. Such topological defects play an important role in magnetic films since they promote the in-plane magnetization reversal of stripes and, in superconductor/ferromagnet hybrids, the creation of superconducting vortex clusters. Combining magnetic force microscopy experiments and micromagnetic simulations, we investigated the motion of two classes of magnetic edge dislocations, randomly distributed in an {{rm{N}}}_{2}^{+}-implanted Fe film. They were found to move in opposite directions along straight trajectories parallel to the stripes axis, when driven by a moderate dc magnetic field. Using the approximate Thiele equation, analytical expressions for the forces acting on such magnetic defects and a microscopic explanation for the direction of their motion could be obtained. Straight trajectories are related to the presence of a periodic stripe domain pattern, which imposes the gyrotropic force to vanish even if a nonzero, half-integer topological charge is carried by the defects in some layers across the film thickness.

Highlights

The formation of domain patterns[1] in the stripe morphology has been observed in a variety of physical systems, such as high-Tc superconductors[2], mixtures of lipids in monolayers at the air-water interface[3], self-assemblies of lamellar diblock copolymers[4], and two-dimensional electron systems[5]
We study the motion of topological defects that develop, in the form of magnetic edge dislocations, in the stripe domain structure of nitrogen-implanted iron (Fe-N) thin films with a moderate PMA22
The analysis of the field-driven motion of magnetic edge dislocations is somewhat complicated by the presence of other types of structures which perturb the periodicity of the stripe pattern, such as ripples and phase jumps

Summary

Introduction

The formation of domain patterns[1] in the stripe morphology has been observed in a variety of physical systems, such as high-Tc superconductors[2], mixtures of lipids in monolayers at the air-water interface[3], self-assemblies of lamellar diblock copolymers[4], and two-dimensional electron systems[5] In all these cases, spontaneous phase separation on a mesoscopic scale takes place as the result of competing interactions acting on different spatial scales[1,6,7,8]. We study the motion of topological defects that develop, in the form of magnetic edge dislocations, in the stripe domain structure of nitrogen-implanted iron (Fe-N) thin films with a moderate PMA22. The gyrotropic force is shown to vanish owing to the presence of the periodic stripe domain pattern even if a nonzero, half-integer topological charge is carried by the dislocation in some layers across the film thickness

Methods

Results

Conclusion