Magneto-structural coupling and harmonic lattice dynamics in CaFe$_2$As$_2$ probed by M\"ossbauer spectroscopy

TL;DR

This study uses Mössbauer spectroscopy to analyze the magneto-structural phase transition and lattice dynamics in CaFe$_2$As$_2$, revealing a first-order transition and strong magneto-structural coupling.

Contribution

It provides detailed insights into the first-order nature of the phase transition and the magneto-structural coupling in CaFe$_2$As$_2$ using Mössbauer spectroscopy.

Findings

The phase transition is first-order.

The compressibility is $1.67\times10^{-2}\,GPa^{-1}$.

Lattice dynamics are similar in paramagnetic and antiferromagnetic phases.

Abstract

In this paper we present detailed M\"ossbauer spectroscopy study of structural and magnetic properties of the undoped parent compound CaFe$_2$As$_2$ single crystal. By fitting the temperature dependence of the hyperfine magnetic field we show that the magneto-structural phase transition is clearly first-order in nature and we also deduced the compressibility of our sample to be $1.67\times10^{-2}\,GPa^{-1}$. Within the Landau's theory of phase transition, we further argue that the observed phase transition may stem from the strong magneto-structural coupling effect. Temperature dependence of the Lamb-M\"ossbauer factor show that the paramagnetic phase and the antiferromagnetic phase exhibit similar lattice dynamics in high frequency modes with very close Debye temperatures, $\Theta_D \sim$270\,K.