Résumé
Bismuth ferrite is a room-temperature multiferroic material hosting an antiferromagnetic order which exhibits a cycloidal modulation. In this work, we combine real-space and reciprocal space measurements to show the coexistence of several propagation directions of the cycloid inside a single ferroelectric domain in a bulk BiFeO3 single crystal [1].Our results also demonstrate that the direction of the cycloid wavevectors are not strictly locked to the preferred crystallographic axes as continuous rotation of the propagation direction bridge different wavevectors.Using the high magnetic sensibility and the nanoscale spatial resolution of scanning-NV center magnetometry, we observe the formation of topological defects at the junction between the magnetic rotational domains. These line defects, ±π-disclinations and edge dislocations, are identical to those found in a broad variety of lamellar phys-ical systems with rotational symmetries, illustrating the universality of such patterns.With this work, we establish that these topological defects, previously observed in a chiral ferromagnet [2], can be transposed in a multiferroic antiferromagnet, offering new opportunities in terms of robustness and electrical control towards their use in spintronic devices.[1] A. Finco et al, Phys. Rev. Lett. 128, 187201 (2022).[2] P. Schönherr et al, Nat. Phys. 14, 465 (2018).