Shining Light on Antiferromagnets
Antiferromagnets (AFMs) are materials in which the spins of neighboring magnetic atoms cancel each other, resulting in zero total magnetization in the absence of a magnetic field. The canceling spins make AFMs resistant to stray magnetic fields but also hard to probe or control using conventional magnetic techniques. Now Scott Crooker at Los Alamos National Laboratory in New Mexico and his colleagues have demonstrated that light provides a powerful alternative technique, allowing magnetic domains in certain AFMs to be imaged and even magnetically manipulated [1].
Crooker and his colleagues studied cobalt niobium sulfide, a van der Waals AFM in which the magnetic cobalt atoms are arranged in stacked 2D sheets. This material has a “tetrahedral” AFM order, meaning that the spins point toward or away from the centers of the tetrahedral network defined by the cobalt atoms. Such a structure creates a chiral spin texture that affects how strongly the material couples to circularly polarized light. The absorption and reflection coefficients depend not only on the light’s frequency and polarization but also on the chirality of the local magnetic domain.
Exploiting these magneto-optical properties, the researchers probed the AFM’s domains with micrometer resolution using a scanning magnetic circular dichroism microscope, which measures the difference in reflectivity between left- and right-circularly-polarized light. They also showed that the same microscope can be used to switch the magnetization of chiral domains by locally heating the material above its ordering temperature while an external magnetic field is applied to the whole sample.
The researchers say that the ability to probe and manipulate chiral AFM domains using light opens new opportunities for developing magnetic information-storage technologies based on the fast dynamics and stability of AFMs.
–Tianhan Liu
Tianhan Liu is an Associate Editor of Physical Review Letters and Physical Review Materials.
References
- E. Kirstein et al., “Topological magneto-optics in the noncoplanar antiferromagnet Co1/3NbS2: Imaging and writing chiral magnetic domains,” Phys. Rev. Lett. 135, 196702 (2025).