Vincent Garcia
Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
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. Both reading and writing the antiferromagnetic textures are pending challenges.
For reading, we use a highly sensitive scanning magnetometer based on a single nitrogen-vacancy (NV) defect in diamond, to visualize the non-collinear antiferromagnetic order of multiferroic BiFeO3, at room temperature. At the surface of BiFeO3 single crystals, we show an unexpected continuous rotation of the antiferromagnetic cycloid propagation vector with the presence of antiferromagnetic topological defects [1]. In 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]. We also manage to stabilize an as-grown single-domain ferroelectric and cycloidal state, opening further opportunities for investigations of the interplay between non-collinear antiferromagnetic orders and spin transport.
For writing, 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. Taking advantage of the room-temperature magnetoelectric coupling of BiFeO3, we deterministically control these textures using an electric field [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 [2]. 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]. In addition, in BiFeO3 nanostructures, we stabilize topological polar states using a radial electric field with antiferromagnetic objects embedded. These results open the way for electrically-reconfigurable antiferromagnetic topological objects.
References
[1] Finco et al., Phys. Rev. Lett. 128, 187201 (2022)[2] Haykal et al., Nature Commun. 11, 1704 (2020)
[3] Gross et al., Nature 549, 252 (2017)
[4] Chauleau et al., Nature Mater. 19, 386 (2020)
[5] Fusil et al., Adv. Elec. Mater. 8, 2101155 (2022)