Antiferromagnetic real-space configuration probed by dichroism in scattered x-ray beams with orbital angular momentum

TL;DR

This paper demonstrates a novel x-ray dichroic effect using orbital angular momentum beams to probe antiferromagnetic configurations, revealing real-space magnetic structures and their reversibility with thermal cycling.

Contribution

It introduces a new soft x-ray spectroscopy method utilizing OAM beams to characterize antiferromagnetic states and topological defects.

Findings

Circular dichroism at the antiferromagnetic Bragg peak depends on OAM helicity.

Reversal of dichroism sign indicates change in antiferromagnetic ground state.

First demonstration of OAM-based soft x-ray spectroscopy for magnetic materials.

Abstract

X-ray beams with orbital angular momentum (OAM) are a promising tool for x-ray characterization techniques. Beams with OAM have a helicity--an azimuthally varying phase--which leads to a gradient of the light field. New material properties can be probed by utilizing the helicity of an OAM beam. Here, we demonstrate a novel dichroic effect in resonant diffraction from an artificial antiferromagnet with a topological defect. We found that the scattered OAM beam has circular dichroism at the antiferromagnetic Bragg peak whose sign is coupled to its helicity, which reveals the real-space configuration of the antiferromagnetic ground state. Thermal cycling of the artificial antiferromagnet can change the ground state, as indicated by reversal of the sign of circular dichroism. This result is one of the first demonstrations of a soft x-ray spectroscopy characterization technique utilizing the OAM of x-rays. This helicity-dependent circular dichroism exemplifies the potential to utilize OAM beams to probe matter in a way that is inaccessible using currently available x-ray techniques.