Mechanisms of skyrmion and skyrmion crystal formation from the conical phase

TL;DR

This paper uncovers the microscopic mechanisms behind skyrmion and skyrmion crystal formation from the conical phase, revealing processes like nucleation, growth, and mitosis-like division using advanced microscopy and simulations.

Contribution

It introduces the concept of skyrmion mitosis and adapts crystal growth theory to magnetic topological states, providing new insights into their manipulation.

Findings

Skyrmion crystals nucleate and grow from the conical phase.

Skyrmions can divide mitosis-like, unlike traditional crystals.

Growth is governed by competition between attractive and repulsive interactions.

Abstract

Real-space topological magnetic structures such as skyrmions and merons are promising candidates for information storage and transport. However, the microscopic mechanisms that control their formation and evolution are still not clear. Here, using in-situ Lorentz transmission electron microscopy, we demonstrate that skyrmion crystals (SkXs) can nucleate, grow, and evolve from the conical phase in the same ways that real nanocrystals form from vapors or solutions. More intriguingly, individual skyrmions can also "reproduce" by division in a mitosis-like process that allows them to annihilate SkX lattice imperfections, which is not available to crystals made of mass-conserving particles. Combined string method and micromagnetic calculations show that competition between repulsive and attractive interactions between skyrmions governs particle-like SkX growth, but non-conservative SkX growth appears to be defect-mediated. Our results provide insights towards manipulating magnetic topological states by applying established crystal growth theory, adapted to account for the new process of skyrmion mitosis.