Uniaxial pressure effect on structural and magnetic phase transitions in NaFeAs and its comparison with as-grown and annealed BaFe$_2$As$_2$

TL;DR

This study investigates how uniaxial pressure affects structural and magnetic phase transitions in NaFeAs and compares it with BaFe$_2$As$_2$, revealing that pressure-induced shifts are minimal and intrinsic electronic anisotropy causes resistivity differences.

Contribution

The paper demonstrates that uniaxial pressure has a negligible effect on transition temperatures in NaFeAs and annealed BaFe$_2$As$_2$, highlighting intrinsic electronic anisotropy as the source of resistivity anisotropy.

Findings

Uniaxial pressure causes minimal shifts in $T_N$ and $T_s$ in NaFeAs and annealed BaFe$_2$As$_2$.

Resistivity anisotropy above $T_N$ and $T_s$ is intrinsic, not strain-induced.

Previous effects observed in as-grown BaFe$_2$As$_2$ are not universal across related materials.

Abstract

We use neutron scattering to study the effect of uniaxial pressure on the tetragonal-to-orthorhombic structural ($T_s$) and paramagnetic-to-antiferromagnetic ($T_N$) phase transitions in NaFeAs and compare the outcome with similar measurements on as-grown and annealed BaFe$_2$As$_2$. In previous work on as-grown BaFe$_2$As$_2$, uniaxial pressure necessary to detwin the sample was found to induce a significant increase in zero pressure $T_N$ and $T_s$. However, we find that similar uniaxial pressure used to detwin NaFeAs and annealed BaFe$_2$As$_2$ has a very small effect on their $T_N$ and $T_s$.Since transport measurements on these samples still reveal resistivity anisotropy above $T_N$ and $T_s$, we conclude that such anisotropy cannot be due to uniaxial strain induced $T_N$ and $T_s$ shifts, but must arise from intrinsic electronic anisotropy in these materials.