Résumé
We report on the formation of topological defects emerging from the cycloidal order at the surface of bulk BiFeO3 crystals [1]. Combining reciprocal and real-space magnetic imaging techniques, we first observe, in a single ferroelectric domain, the coexistence of regions in which the antiferromagnetic cycloid propagates along different wave vectors. We then show that the direction of these wave vectors is not strictly locked to the preferred crystallographic axes but rather rotates continuously. 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 BiFeO3 , offering new opportunities in terms of robustness and electrical control towards their use in spintronic devices.[1] Finco et al, Phys. Rev. Lett. 128, 187201 (2022)