Magnetic and lattice coupling in single-crystal SrFe$_2$As$_2$: A neutron scattering study

TL;DR

This neutron scattering study of SrFe$_2$As$_2$ reveals that its structural and magnetic phase transitions are first order, coinciding at around 201.5 K, and are strongly coupled with evidence of phase coexistence and possible order-disorder transition.

Contribution

The study provides detailed insights into the coupled magnetic and structural transitions in SrFe$_2$As$_2$, highlighting the first order nature and phase coexistence at the transition.

Findings

Structural transition is first order.

Magnetic and structural transitions are coincident and coupled.

Evidence of phase coexistence and possible order-disorder transition.

Abstract

A detailed elastic neutron scattering study of the structural and magnetic phase transitions in single-crystal SrFe$_2$As$_2$ reveals that the orthorhombic (O)-tetragonal (T) and the antiferromagnetic transitions coincide at $T_\texttt{O}$ = $T_\texttt{N}$ = (201.5 $\pm$ 0.25) K. The observation of coexisting O-T phases over a finite temperature range at the transition and the sudden onset of the O distortion provide strong evidences that the structural transition is first order. The simultaneous appearance and disappearance within 0.5 K upon cooling and within 0.25 K upon warming, respectively, indicate that the magnetic and structural transitions are intimately coupled. We find that the hysteresis in the transition temperature extends over a 1-2 K range. Based on the observation of a remnant orthorhombic phase at temperatures higher than \emph{T}$_\texttt{O}$, we suggest that the T-O transition may be an order-disorder transition.