# Stoner factors of doped 122 Fe-based superconductors: First principles results

## TL;DR

This study uses first principles calculations to analyze how doping affects the Stoner factor and magnetic fluctuations in 122 Fe-based superconductors, revealing correlations with structural parameters and Fermi surface nesting.

## Contribution

It provides a comprehensive first-principles analysis of doping effects on the Stoner factor in 122 Fe-based superconductors, linking electronic structure, doping type, and magnetic properties.

## Key findings

- Co/Ru and P doping reduce the Stoner factor with increased doping.
- Na/K doping enhances the Stoner factor at higher doping levels.
- The Stoner factor correlates with pnictide height and Fermi surface nesting.

## Abstract

A comprehensive study on the evolution of Stoner factor with doping concentration for various doped 122 systems (like BaFe$_2$As$_2$, SrFe$_2$As$_2$) of Fe-based superconductors is presented. Our first principles electronic structure calculations reveal that for Co/Ru (electron or iso-electronic) doping at Fe sites or P doping at As sites result in a reduction of Stoner factor with increasing doping concentration. On the contrary, in case of Na/K (hole) doping at the Ba sites, Stoner factor is enhanced for higher doping concentrations. This may be considered as an indicator of elevation of "magnetic fluctuation" in these systems. We find that the Stoner factor uniquely follows the variation of the pnictide height z$_{As}$/Fe-As bond length with various kinds of doping. Our calculated Fermi surfaces explicate the diversities in the behaviour of Stoner factors for various doped 122 systems ; larger degree of Fermi surface nesting, larger the value of Stoner factor and vice versa.