  Antiferromagnetic materials are promising platforms for next-generation
spintronics owing to their fast dynamics and high robustness against parasitic
magnetic fields. However, nanoscale imaging of the magnetic order in such
materials with zero net magnetization remains a major experimental challenge.
Here we show that non-collinear antiferromagnetic spin textures can be imaged
by probing the magnetic noise they locally produce via thermal populations of
magnons. To this end, we perform nanoscale, all-optical relaxometry with a
scanning quantum sensor based on a single nitrogen-vacancy (NV) defect in
diamond. Magnetic noise is detected through an increase of the spin relaxation
rate of the NV defect, which results in an overall reduction of its
photoluminescence signal under continuous laser illumination. As a
proof-of-concept, the efficiency of the method is demonstrated by imaging
various spin textures in synthetic antiferromagnets, including domain walls,
spin spirals and antiferromagnetic skyrmions. This imaging procedure could be
extended to a large class of intrinsic antiferromagnets and opens up new
opportunities for studying the physics of localized spin wave modes for
magnonics.
