  Newly published diffraction data on hexagonal YMnO3 at a temperature of 10 K
are shown to be consistent with a trusted expression of the magnetic symmetry,
although the data alone are not definitive [M. Ramakrishnan et al., Phys. Rev.
Research 5, 013203 (2023)]. Howard et al. conclude from an exhaustive review of
experimental data that the symmetry of the antiferromagnetic motif of Mn ions
is most likely P63'cm' [C. J. Howard et al., Acta Crystallogr. B 69, 534
(2013)]. The data reported by Ramakrishnan et al. does not eliminate symmetry
P63' from our calculated diffraction patterns, because the studied reflection
vector is parallel to the common chiral vector associated with each triangle of
Mn axial dipole moments. Proposed diffraction patterns will give decisive
statements about the magnetic symmetry in future investigations using resonant
x-ray and magnetic neutron diffraction. To this end, both axial and polar
magnetism in the multiferroic are essential in the analysis of diffraction
patterns. The account by Ramakrishnan et al. of polar magnetism in resonant
x-ray diffraction uses a magnetic symmetry of hexagonal YMnO3 not yet
justified, e.g., ferromagnetism and a linear magnetoelectric effect allowed by
their chosen symmetry have not been observed. We study polar magnetism in
symmetry P63'cm' using Dirac multipoles, including Mn anapoles. They also
feature in amplitudes for magnetic neutron diffraction together with Dirac
quadrupoles, previously shown to account for diffraction by pseudo-gap phases
of cuprate superconductors.
