Résumé
The high versatility and nanoscale spatial resolution of scanning NV center microscopy makes it a very attractive technique for the investigation of skyrmions and complex magnetic textures in a broad range of materials, in particular antiferromagnets. In this talk, I will present recent results about multiferroic solitons in bismuth ferrite and show that we are able to estimate the sign and strength of DMI in magnetic thin films through the measurement of thermal spin wave noise. Bismuth ferrite is the most studied multiferroic material, and scanning NV magnetometry is among the very few techniques allowing the imaging of its very complex antiferromagnetic state, which is strongly coupled to the ferroelectric order. Here, we look at nanodisks in which we electrically write centre-convergent or divergent ferroelectric states, and probe the resulting magnetic whirl forming at the center. We observe flux closures of antiferromagnetic spin cycloids, with distinct antiferromagnetic entities at their cores depending on the electric field polarity, thus forming multiferroic solitons [1].In a second part, I will report on the detection of DMI-induced spin wave non-reciprocity in synthetic antiferromagnets using scanning NV center relaxometry. We probe the thermal spin wave noise produced by thermal spin waves confined in domain walls and skyrmions [2] and find that the intensity of this noise is strongly dependent on the magnetic chirality of the texture, and thus the DMI sign, by measuring it from both sides of a stack grown on a membrane. We explain this effect by the filtering in frequency and wavevector intrinsic to the NV-based noise detection, which is thus sensitive to the spin wave non-reciprocity.[1] A. Chaudron et al, Nature Materials (2024)[2] A. Finco et al, Nature Communications 12, 767 (2021)