X-ray beams with orbital angular momentum (OAM) are an up-and-coming tool for
x-ray characterization techniques. Beams with OAM have an azimuthally varying
phase that leads to a gradient of the light field. New material properties can
be probed by utilizing the unique phase structure of an OAM beam. Here, we
demonstrate a novel type of phase dichroism in resonant diffraction from an
artificial antiferromagnet with a topological defect. The scattered OAM beam
has circular dichroism whose sign is coupled to the phase of the beam, 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 the changing phase dichroism. These results exemplify the
potential of OAM beams to probe matter in a way that is inaccessible using
typical x-ray techniques