# Impact of the first order antiferromagnetic phase transition on the paramagnetic spin excitations and nematic phase of SrFe$_2$As$_2$

## TL;DR

This study investigates how the first order antiferromagnetic phase transition affects spin excitations and nematic phases in SrFe$_2$As$_2$, revealing that a strongly first-order transition weakens nematicity and resistivity anisotropy.

## Contribution

It provides new insights into the impact of the first order magnetic transition on nematic phases in iron pnictides, contrasting SrFe$_2$As$_2$ with BaFe$_2$As$_2$.

## Key findings

- Nematic signatures persist above the transition in SrFe$_2$As$_2$ but are weaker in BaFe$_2$As$_2$.
- Strongly first-order magnetic transitions weaken nematicity and resistivity anisotropy.
- Differences in transition order influence electronic nematic behavior in parent compounds.

## Abstract

Understanding the nature of the electronic nematic phase in iron pnictide superconductors is important for elucidating its impact on high-temperature superconductivity. Here we use transport and inelastic neutron scattering to study spin excitations and in-plane resistivity anisotropy in uniaxial pressure detwinned BaFe$_2$As$_2$ and SrFe$_2$As$_2$, the parent compounds of iron pnictide superconductors. While BaFe$_2$As$_2$ exhibits weakly first order tetragonal-to-orthorhombic structural and antiferromagnetic (AF) phase transitions below $T_s > T_N\approx 138$ K, SrFe$_2$As$_2$ has strongly coupled first order structural and AF transitions below $T_s= T_N\approx 210$ K. We find that the direct signatures of the nematic phase persist to lower temperatures above the phase transition in the case of SrFe$_2$As$_2$ compared to BaFe$_2$As$_2$. Our findings support the conclusion that the strongly first-order nature of the magnetic transition in SrFe$_2$As$_2$ weakens the nematic phase and resistivity anisotropy in the system.