Elastic Instability of the Orthorhombic Antiferromagnetic Phase of 122-Pnictides Under Pressure

TL;DR

This paper investigates the pressure-induced phase transition and elastic instability in 122-pnictides, revealing a metastable orthorhombic phase and anomalies in magnetism and structure near critical pressures.

Contribution

The study provides first-principles calculations showing the pressure-driven transition from orthorhombic to tetragonal phases and identifies elastic instability and magnetic anomalies.

Findings

Transition pressure $P_H$ where tetragonal phase becomes energetically favorable

Metastability of orthorhombic phase up to higher pressure $P_M$

Anomalies in magnetism and orthorhombicity near $P_M$

Abstract

A-122 pnictides (A an alkaline earth element) possess striped antiferromagnetic states of orthorhombic (OR) symmetry and nonmagnetic states of tetragonal (T) symmetry. Based on total energy calculations, we show that the T = 0K pressure-driven transition from OR to T states occurs at a pressure, $P_H$, where the tetragonal enthalpy drops below the orthorhombic. The OR state remains metastable up to a higher pressure, $P_M$ > $P_H$. We find anomalies in magnetism and orthorhombicity as $P \rightarrow P_M$, and a trend towards elastic instability.