Anisotropic thermal expansion of AEFe2As2 (AE = Ba, Sr, Ca) single crystals

TL;DR

This study investigates the anisotropic thermal expansion of AEFe2As2 (AE = Ba, Sr, Ca) single crystals, revealing anisotropy above phase transitions and lattice parameter changes across the transitions, consistent with diffraction data.

Contribution

It provides detailed measurements of anisotropic thermal expansion in AEFe2As2 compounds, highlighting differences among Ba, Sr, and Ca variants and their behavior near phase transitions.

Findings

Anisotropic thermal expansion coefficients observed above phase transition.

Sharp anomalies at structural/antiferromagnetic transitions.

Lattice parameter changes consistent with diffraction data.

Abstract

We report anisotropic thermal expansion of the parent, AEFe2As2 (AE = Ba, Sr, and Ca), compounds. Above the structural/antiferromagnetic phase transition anisotropy of the thermal expansion coefficients is observed, with the coefficient along the a-axis being significantly smaller than the coefficient for the c-axis. The high temperature (200 K < T < 300 K) coefficients themselves have similar values for the compounds studied. The sharp anomalies associated with the structural/antiferromagnetic phase transitions are clearly seen in the thermal expansion measurements. For all three pure compounds the "average" a-value increases and the c-lattice parameter decreases on warming through the transition with the smallest change in the lattice parameters observed for SrFe2As2. The data are in general agreement with the literature data from X-ray and neutron diffraction experiments.