Uniaxial stress effects on the structural and electronic properties of BaFe2As2 and CaFe2As2

TL;DR

This study uses ab initio DFT and Ginzburg-Landau modeling to explore how uniaxial stress influences the structural and magnetic properties of BaFe2As2 and CaFe2As2, revealing stress-induced phase and magnetic state transitions.

Contribution

It provides a detailed theoretical analysis of uniaxial stress effects on iron-pnictide compounds, highlighting the role of magneto-elastic coupling in phase and magnetic state changes.

Findings

Sign-changing jump in orthorhombicity at critical stress

Reversal of orbital occupancy and magnetic order

Insights into detwinning mechanisms under uniaxial stress

Abstract

Starting from the orthorhombic magnetically ordered phase, we investigate the effects of uniaxial tensile and compressive stresses along a, b, and the diagonal a+b directions in BaFe2As2 and CaFe2As2 in the framework of ab initio density functional theory (DFT) and a phenomonological Ginzburg-Landau model. While -contrary to the application of hydrostatic or c-axis uniaxial pressure- both systems remain in the orthorhombic phase with a pressure-dependent nonzero magnetic moment, we observe a sign-changing jump in the orthorhombicity at a critical uniaxial pressure, accompanied by a reversal of the orbital occupancy and a switch between the ferromagnetic and antiferromagnetic directions. Our Ginzburg-Landau analysis reveals that this behavior is a direct consequence of the competition between the intrinsic magneto-elastic coupling of the system and the applied compressive stress, which helps the system to overcome the energy barrier between the two possible magneto-elastic ground states. Our results shed light on the mechanisms involved in the detwinning process of an orthorhombic iron-pnictide crystal and on the changes in the magnetic properties of a system under uniaxial stress.