Evidence of Magnetically Driven Structural Phase Transition in Parent Compounds RFeAsO (R = La, Sm, Gd, Tb): study of low-temperature X-ray diffraction

TL;DR

This study investigates the structural phase transition in RFeAsO compounds using low-temperature X-ray diffraction, revealing magnetically driven transitions influenced by the interlayer distance and dimensionality.

Contribution

It provides experimental evidence linking magnetic ordering and structural transitions in RFeAsO compounds, highlighting the role of interlayer spacing in these phenomena.

Findings

Both lattice constants decrease with different R elements.

Structural transition temperature decreases with R element change.

The temperature gap between structural and magnetic transitions narrows with shorter FeAs layer distance.

Abstract

We report measurements of structural phase transition of four parent compounds $R$FeAsO ($R$ = La, Sm, Gd, and Tb) by means of low-temperature X-ray diffraction (XRD). Magnetic transition temperatures associated with Fe ions ($T_{N1}$) are also determined from the temperature dependence of resistivity. As $R$ is changed from La, through Sm and Gd, to Tb, both the c-axis and a-axis lattice constants decrease significantly. Meanwhile both the structural phase transition temperature ($T_S$) and $T_{N1}$ decrease monotonously. It is also found that the temperature gap between $T_S$ and $T_{N1}$ becomes smaller when the distance between FeAs layer becomes shorter. This result is consistent with magnetically driven structural phase transition and suggests that the dimensionality have an important effect on the AFM ordering.