Using X-ray beams with orbital angular momentum to probe an antiferromagnetic ground state*

Artificial spin ice systems present an interesting platform to study magnetic interactions and dynamics. A square array of permalloy nanomagnets can be used to create an artificial antiferromagnetic lattice. Furthermore, topological defects such as edge dislocations can be introduced into the lattice. Resonant X-ray scattering from such an artificial spin ice with a defect of topological charge Z = 2 imparts an orbital angular momentum onto the scattered beam [1]. Here, we show how circular dichroism in the scattered diffraction pattern can be used to determine the ground state of the antiferromagnet and the magnetization configuration around the defect. By thermal cycling, two different degenerate ground states can be reached, and these can be differentiated using circular dichroism.

[1] J. S. Woods, X. M. Chen, et al. Phys. Rev. Lett. 126, 117201 (2021).