Creation and annihilation of topological meron pairs in in-plane magnetized films

N Gao,M -Y Im,H -S Han,J Li,J W Choi,M Yang,W Chao,S -G Je,T Y Wang,Z Q Qiu,C Hwang,Q Li,K -S Lee,S Lee

doi:10.1038/s41467-019-13642-z

Abstract

Merons which are topologically equivalent to one-half of skyrmions can exist only in pairs or groups in two-dimensional (2D) ferromagnetic (FM) systems. The recent discovery of meron lattice in chiral magnet Co8Zn9Mn3 raises the immediate challenging question that whether a single meron pair, which is the most fundamental topological structure in any 2D meron systems, can be created and stabilized in a continuous FM film? Utilizing winding number conservation, we develop a new method to create and stabilize a single pair of merons in a continuous Py film by local vortex imprinting from a Co disk. By observing the created meron pair directly within a magnetic field, we determine its topological structure unambiguously and explore the topological effect in its creation and annihilation processes. Our work opens a pathway towards developing and controlling topological structures in general magnetic systems without the restriction of perpendicular anisotropy and Dzyaloshinskii–Moriya interaction.

Highlights

Merons which are topologically equivalent to one-half of skyrmions can exist only in pairs or groups in two-dimensional (2D) ferromagnetic (FM) systems
Since the discovery of stable skyrmions (N = ±1)[6,7,8] in perpendicularly magnetized ferromagnetic (FM) films consisting of the Dzyaloshinskii–Moriya interaction (DMI)[9,10] due to inversion symmetry breaking, intensive studies[11,12,13,14,15,16,17,18,19] have been carried out over the last decade on the creation, manipulation, and detection of skyrmions toward future spintronic technologies[20]
One promising structure is the so-called meron, which was originally described in the context of quark confinement[22] and later identified in condensed matter physics, as a magnetic vortex and topologically equivalent to one-half of a skyrmion. (Note that an important difference between merons and skyrmions is their peripheral spin textures: those of merons align in the in-plane while those of skyrmions point toward out-of-plane directions.)

Summary

Introduction

Merons which are topologically equivalent to one-half of skyrmions can exist only in pairs or groups in two-dimensional (2D) ferromagnetic (FM) systems. The recent discovery of meron lattice in chiral magnet Co8Zn9Mn3 raises the immediate challenging question that whether a single meron pair, which is the most fundamental topological structure in any 2D meron systems, can be created and stabilized in a continuous FM film? We develop a new method to create and stabilize a single pair of merons in a continuous Py film by local vortex imprinting from a Co disk. One promising structure is the so-called meron, which was originally described in the context of quark confinement[22] and later identified in condensed matter physics, as a magnetic vortex and topologically equivalent to one-half of a skyrmion. It was only recently that topologically nontrivial meron lattice was observed in chiral magnet Co8Zn9Mn341 in the form of square lattices

Methods

Results

Conclusion