Local structural distortion induced by antiferromagnetic ordering in Bi$_2$Fe$_4$O$_9$ studied using neutron total scattering analysis

TL;DR

This study investigates how local atomic arrangements in Bi$_2$Fe$_4$O$_9$ change at the antiferromagnetic transition using neutron scattering, revealing local distortions without altering overall crystal symmetry.

Contribution

It demonstrates the presence of local structural distortions associated with magnetic ordering, using combined neutron diffraction and pair distribution function analysis.

Findings

Local atomic arrangements vary below $T_N$

No change in long-range symmetry observed

Local distortions linked to magnetic ordering

Abstract

To unravel the origin of the dielectric anomaly at the antiferromagnetic ordering of magnetoelectric Bi$_2$Fe$_4$O$_9$ we performed neutron powder diffraction measurements across the N$\acute{\rm e}$el temperature, $T_{\rm N}$. Both local structures and long-range symmetry are studied using the complementary analyses of atomic pair distribution function (PDF) and Rietveld methods at temperatures 300~K, 250~K, and 200~K. We present that PDF peaks which reflect local atomic arrangements exhibit a noticeable variation below $T_{\rm N}$ without long-range symmetry change. The implication of the PDF evolution is discussed in view of a local structural distortion at the onset of the antiferromagnetic ordering.