Imaging topological defects in a non-collinear antiferromagnet

TL;DR

This study visualizes topological defects in the cycloidal antiferromagnetic order of BiFeO$_3$ at room temperature, revealing complex domain structures and defect types with potential spintronics applications.

Contribution

It demonstrates the formation and imaging of topological defects in a non-collinear antiferromagnet, highlighting their coexistence and continuous rotation of magnetic wavevectors.

Findings

Coexistence of multiple antiferromagnetic domains within a single ferroelectric domain.

Wavevector directions are not strictly locked to crystallographic axes.

Presence of topological line defects at domain junctions.

Abstract

We report on the formation of topological defects emerging from the cycloidal antiferromagnetic order at the surface of bulk BiFeO$_3$ crystals. Combining reciprocal and real-space magnetic imaging techniques, we first observe, in a single ferroelectric domain, the coexistence of antiferromagnetic domains in which the antiferromagnetic cycloid propagates along different wavevectors. We then show that the direction of these wavevectors is not strictly locked to the preferred crystallographic axes as continuous rotations bridge different wavevectors. At the junctions between the magnetic domains, we observe topological line defects identical to those found in a broad variety of lamellar physical systems with rotational symmetries. Our work establishes the presence of these magnetic objects at room temperature in the multiferroic antiferromagnet BiFeO$_3$, offering new possibilities for their use in spintronics.