Anapoles and other magneto-electric multipoles in BaFe2Se3

TL;DR

This paper identifies the magnetic space group of BaFe2Se3, revealing it supports magneto-electric multipoles like anapoles and magnetic charges, and demonstrates how neutron and x-ray diffraction can detect these complex magnetic structures.

Contribution

It provides a detailed symmetry analysis and simulation framework for detecting magneto-electric multipoles in BaFe2Se3 using neutron and x-ray diffraction.

Findings

BaFe2Se3 supports magneto-electric multipoles including anapoles.

Neutron and x-ray diffraction can detect these multipoles.

The symmetry analysis constrains the magnetic structure.

Abstract

We submit that the magnetic space-group Cac (#9.41) is consistent with the established magnetic structure of BaFe2Se3, with magnetic dipole moments in a motif that uses two ladders [Caron J M et al 2011 Phys. Rev. B 84 180409(R)]. The corresponding crystal class m1' allows axial and polar dipoles and forbids bulk ferromagnetism. The compound supports magneto-electric multipoles, including a magnetic charge (monopole) and an anapole (magnetic toroidal dipole) visible in the Bragg diffraction of x-rays and neutrons. Our comprehensive simulation of neutron Bragg diffraction by BaFe2Se3 exploits expressions of a general nature that can be of use with other magnetic materials. Electric toroidal moments are also allowed in BaFe2Se3. A discussion of our findings for resonant x-ray Bragg diffraction illustrates the benefit of a common platform for neutron and x-ray diffraction.