Impact of Uniaxial Pressure on Structural and Magnetic Phase Transitions in Electron-Doped Iron Pnictides

TL;DR

This study investigates how uniaxial pressure influences structural and magnetic phase transitions in electron-doped iron pnictides, revealing a strong coupling between lattice distortion and electronic nematicity affecting resistivity anisotropy.

Contribution

It provides new insights into the effects of uniaxial pressure on phase transitions and nematic susceptibility in iron pnictides, using advanced neutron and diffraction techniques.

Findings

Uniaxial pressure increases $T_N$ and induces orthorhombic distortion.

Pressure effects depend on magnetic phase transition nature.

Resistivity anisotropy is sensitive to lattice distortion and nematic susceptibility.

Abstract

We use neutron resonance spin echo and Larmor diffraction to study the effect of uniaxial pressure on the tetragonal-to-orthorhombic structural ($T_s$) and antiferromagnetic (AF) phase transitions in iron pnictides BaFe$_{2-x}$Ni$_{x}$As$_{2}$ ($x=0,0.03,0.12$), SrFe$_{1.97}$Ni$_{0.03}$As$_2$, and BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$. In antiferromagnetically ordered BaFe$_{2-x}$Ni$_{x}$As$_{2}$ and SrFe$_{1.97}$Ni$_{0.03}$As$_2$ with $T_N$ and $T_s$ ($T_N\leq T_s$), a uniaxial pressure necessary to detwin the sample also increases $T_N$, smears out the structural transition, and induces an orthorhombic lattice distortion at all temperatures. By comparing temperature and doping dependence of the pressure induced lattice parameter changes with the elastoresistance and nematic susceptibility obtained from transport and ultrasonic measurements, we conclude that the in-plane resistivity anisotropy found in the paramagnetic state of electron underdoped iron pnictides depends sensitively on the nature of the magnetic phase transition and a strong coupling between the uniaxial pressure induced lattice distortion and electronic nematic susceptibility.