Controlling Topological Polar and Antiferromagnetic Textures in Multiferroic BiFeO₃

Antiferromagnetic materials are currently emerging as a new paradigm for spintronics as they offer key advantages over ferromagnets: insensitivity to external magnetic fields, much faster spin dynamics (THz range), and higher density packing because of the absence of stray fields. Moreover, tailoring topological spin textures in antiferromagnetic materials as it was done for ferromagnetic skyrmions is generating a lot of attention in the spintronics community. As antiferromagnets are insensitive to external magnetic fields, one must find alternative ways to control them. An optimal writing mechanism would demand low current densities (or ideally no current) to generate a complete reversal of antiferromagnetic domains or textures.<br/><br/>Here we take advantage of the room-temperature magnetoelectric coupling in epitaxial thin films of multiferroic BiFeO₃ to deterministically control antiferromagnetic spin textures via the ferroelectric domains. In as-grown single ferroelectric domains, while the surface of single crystals shows an unexpected continuous rotation of the antiferromagnetic cycloid propagation vector with the presence of antiferromagnetic topological defects [1], we are able to design a single antiferromagnetic domain by imposing an anisotropic strain in (111) epitaxial thin films. This model system, containing both a single ferroelectric and cycloidal domains, opens further opportunities for investigations of the interplay between non-collinear antiferromagnetic orders and spin transport. In striped ferroelectric domains of (001) BiFeO₃ thin films, we use epitaxial strain to finely tune the as-grown spin textures [2]. The anisotropy induced by epitaxial strain leads to a single antiferromagnetic cycloid within each ferroelectric domain [3]. The modification of the ferroelectric landscape allows us to control the propagation vector of the spin cycloid, to switch from one type of spin cycloid to another, or to convert from a collinear antiferromagnetic texture to a spin cycloid [1]. Furthermore, using resonant elastic X-ray scattering, we reveal the existence of chiral antiferromagnetic and ferroelectric objects at the domain walls of these periodic arrays [4, 5]. Finally, in BiFeO₃ nanostructures, we stabilize topological centre polar states using a radial electric field with antiferromagnetic objects embedded. These results open the way for electrically-reconfigurable antiferromagnetic topological objects.<br/><br/>[1] Finco et al., Phys. Rev. Lett. 128, 187201 (2022)<br/>[2] Haykal et al., Nature Commun. 11, 1704 (2020)<br/>[3] Gross et al., Nature 549, 252 (2017)<br/>[4] Chauleau et al., Nature Mater. 19, 386 (2020)<br/>[5] Fusil et al., Adv. Elec. Mater. 8, 2101155 (2022)