Spontaneous Topological Locking and Symmetry Restoration of Meron Lattices in Synthetic Antiferromagnets

TL;DR

This study uses large-scale simulations to explore how weak interlayer coupling in synthetic antiferromagnets stabilizes topological textures and restores symmetry in meron lattices under anisotropic conditions.

Contribution

It reveals how ultra-weak interlayer exchange enforces vertical synchronization and symmetry restoration, advancing understanding of topological texture stabilization in spintronic systems.

Findings

Interlayer coupling enforces vertical synchronization of meron structures.

Anomalous lattice compression maximizes exchange energy at high anisotropy.

Local topological locking persists even when global order collapses.

Abstract

Synthetic antiferromagnets offer a robust platform for stabilizing fractional topological textures, effectively circumventing the limitations of ferromagnetic systems. In this study, we utilize large-scale Monte Carlo simulations to investigate the spontaneous topological locking and structural symmetry restoration of meron-antimeron crystals within SAF bilayers subjected to easy-plane magnetic anisotropy. In the uncoupled monolayer limit, increasing anisotropy induces an extreme core-shrinking effect that physically expands the inter-core distance and triggers a $C_4 \rightarrow C_2$ symmetry breaking. However, the introduction of an ultra-weak interlayer antiferromagnetic exchange acts as an active structural scaffold. For rigid crystals, this coupling strictly enforces vertical synchronization, forming robust antiferromagnetic bimeron dipoles and fully restoring the macroscopic $C_4$ rotational symmetry. Furthermore, in highly expanded, pre-collapse crystals, we observe an anomalous interlayer-induced lattice compression that actively maximizes the exchange energy. At extreme anisotropy limits where macroscopic crystalline order irrecoverably collapses, the bilayer coupling continues to enforce a strict local topological locking of surviving isolated defects. These findings reveal a fundamental decoupling between local vertical synchronization and global structural order, providing a comprehensive theoretical roadmap for stabilizing and manipulating fractional topological textures in beyond-skyrmion spintronic architectures.