  Compulsory Dirac multipoles in the bilayer perovskite Ca3Ru2O7 are absent in
published analyses of experimental data. In a first step at correcting
knowledge of the magnetic structure, we have analysed existing Bragg
diffraction patterns gathered on samples held well below the N\'eel temperature
at which A-type antiferromagnetic order of axial dipoles spontaneously
develops. Patterns were gathered with neutrons, and linearly polarized x-rays
tuned in energy to a ruthenium atomic resonance. Neutron diffraction data
contains solid evidence of Dirac dipoles (anapoles or toroidal moments). No
such conclusion is reached with existing x-ray diffraction data, which instead
is ambiguous on the question. To address this shortcoming by future
experiments, we calculated additional diffraction patterns. Chiral order of
Dirac multipoles is allowed by magnetic space-group PCna21, and it can be
exposed in Bragg diffraction using circularly polarized x-rays. Likewise, a
similar experiment can expose a chiral order of axial dipoles. A magnetic field
applied parallel to the b-axis creates a ferrimagnetic structure in which bulk
magnetization arises from field-induced nonequivalent Ru sites (magnetic
space-group Pm'c'21).
