Study of the hyperfine fields in the BaFe$_2$As$_2$ family and its relation to the magnetic moment

TL;DR

This study investigates hyperfine fields and magnetic properties in various doped BaFe$_2$As$_2$ compounds using relativistic calculations, revealing dopant-dependent hyperfine fields and challenging previous assumptions linking hyperfine fields directly to magnetic moments.

Contribution

It provides a comprehensive relativistic analysis of hyperfine fields across multiple doped BaFe$_2$As$_2$ compounds, highlighting the dopant dependence and questioning the direct correlation with magnetic moments.

Findings

Hyperfine fields strongly depend on dopant type and concentration.

Relativistic effects are more significant in iron pnictides than in bulk Fe.

Hyperfine field $B_{hf}$ should not be directly related to the average magnetic moment $$.

Abstract

The hyperfine field $B_\text{hf}$ and the magnetic properties of the BaFe$_2$As$_2$ family are studied using the fully relativistic Dirac formalism for different types of substitution. The study covers electron doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$, hole doped (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ and also isovalently doped Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ and BaFe$_2$(As$_{1-x}$P$_x$)$_2$ for a wide range of the concentration $x$. For the substituted compounds the hyperfine fields show a very strong dependence on the dopant type and its concentration $x$. Relativistic contributions were found to have a significantly stronger impact for the iron pnictides when compared to bulk Fe. As an important finding, we demonstrate that it is not sensible to relate the hyperfine field $B_\text{hf}$ to the average magnetic moment $\mu$ of the compound, as it was done in earlier literature.