&Bullet; physics 14, p31
Researchers record the previously hidden rotations of spins in the domain wall of a “real” antiferromagnetic material, chromium oxide.
“Interesting, but useless,” is how Louis Néel described antiferromagnets, materials for whose discovery he received the 1970 Nobel Prize in Physics. If you jump 50 years forward, these materials are trending among condensed matter physicists investigating their use in next generation information processing and storage devices. But to take the step from useless to useful, there are still many unknowns to be revealed. Now Martin Wörnle and his colleagues from the Swiss Federal Institute of Technology (ETH) in Zurich are solving one of these puzzles: How to twist the spins in a “real” antiferromagnetic material – one in which the spins can only point up or down – between domains  .
The team used a technique called nanoscale scanning diamond magnetometry, which can measure magnetic fields as small as a few microtesla with a spatial resolution of less than 50 nm, to map the stray magnetic field for various chromium oxide samples. The stray magnetic field is the field that protrudes from a material and it can be used to infer the orientation of the spins within the domain walls.
Wörnle and his colleagues observed two types of domain walls. In Bloch-type walls, the spin direction rotates smoothly in the plane of the domain wall and passes the center point in the center of the wall. In Néel-type walls, the pointing direction is perpendicular to the wall and the spins have a chiral rotation. Most of the samples contained the energetically favored Bloch-type walls, which have a smaller stray magnetic field. Other researchers have captured similar images for antiferromagnets, where the spins can point in more than two directions, but the team notes that these are the first images for a bulk sample of a proper antiferromagnet.
Katherine Wright is assistant editor of physics.
- M. Woernle et al., “Coexistence of Bloch and Néel Walls in a Collinear Antiferromagnet”, Phys. Rev. B103, 094426 (2021).