A case for resonant x-ray Bragg diffraction by a collinear antiferromagnet Li2Ni3P4O14

TL;DR

This paper analyzes how magnetic multipoles contribute to resonant x-ray Bragg diffraction in the antiferromagnetic compound Li2Ni3P4O14, highlighting the role of symmetry and polarization effects in diffraction experiments.

Contribution

It introduces a symmetry-informed analysis of magnetic multipoles in Li2Ni3P4O14, emphasizing the potential for resonant x-ray diffraction to detect Dirac multipoles in this material.

Findings

Magnetic multipoles contribute to resonant x-ray Bragg amplitudes.

The magnetic space group is P21/c, supporting coupling to circular polarization.

Neutron diffraction confirms the space group without Dirac multipoles.

Abstract

Magnetic axial and polar (Dirac) nickel multipoles contribute to resonant x-ray Bragg amplitudes in a symmetry informed analysis of monoclinic Li2Ni3P4O14 presented for future diffraction experiments. Magnetic long-range order below a temperature 14.5 K can be viewed as a two-dimensional trimerized antiferromagnet with Ni ions in two Wyckoff positions in the centrosymmetric magnetic space group P21/c. It permits the coupling to circular polarization in the primary x-ray beam, unlike the corresponding diffraction by an antiferromagnet characterized by anti-inversion and a linear magnetoelectric effect, e.g., historically significant chromium sesquioxide (Cr2O3) and Cu2(MoO4)(SeO3) (Lovesey & van der Laan, 2024). The space group is inferred from neutron Bragg diffraction patterns, without an allowance for permitted Dirac dipoles (anapoles) and quadrupoles (Chikara et al., 2025).