Low-energy, planar magnetic defects in BaFe2As2: nanotwins, twins, antiphase and domain boundaries

TL;DR

This study uses density-functional theory to analyze low-energy planar magnetic defects in BaFe2As2, revealing nanoscale defects' stability, magnetic properties, and their impact on magnetic order and scattering data interpretation.

Contribution

It provides a detailed theoretical analysis of various planar defects in BaFe2As2, highlighting their low energy, magnetic behavior, and significance in understanding experimental observations.

Findings

Nano defects have very low surface energy, favoring mesoscale structures.

Defects exhibit reduced magnetic moments near boundaries, affecting magnetic order.

Nano twins can explain features in scattering data and influence magnetic properties.

Abstract

In BaFe2As2, structural and magnetic planar defects begin to proliferate below the structural phase transition, affecting descriptions of magnetism and superconductivity. We study using density-functional theory the stability and magnetic properties of competing antiphase and domain boundaries, twins and isolated $nano$twins (twin nuclei) - spin excitations proposed and/or observed. These nanoscale defects have very low surface energy ($22$-$210$~$m$Jm$^{-2}$), with twins favorable to the mesoscale. Defects exhibit smaller moments confined near their boundaries -- making a uniform-moment picture inappropriate for long-range magnetic order in real samples. {\it{Nano}}twins explain features in measured pair distribution functions, so should be considered when analyzing scattering data. All these defects can be weakly mobile and/or have fluctuations that lower assessed "ordered" moments from longer spatial and/or time averaging, and should be considered directly.