High-resolution diffraction reveals magnetoelastic coupling and coherent phase separation in tetragonal CuMnAs

TL;DR

This study uses high-resolution diffraction to uncover magnetoelastic coupling and phase separation in tetragonal CuMnAs, revealing inhomogeneity, multiple magnetic transitions, and potential implications for electrical switching.

Contribution

It demonstrates that subtle diffraction differences indicate pervasive inhomogeneity and phase separation in CuMnAs, and links these to magnetic transitions and possible high-temperature decomposition.

Findings

Inhomogeneity and phase separation detected in Cu-rich CuMnAs.

Two magnetic transitions identified: Néel temperature and ferromagnetic transition.

Crystallographic signatures of magnetic transitions observed during in-situ heating and cooling.

Abstract

Tetragonal CuMnAs was the first antiferromagnet where reorientation of the N\'eel vector was reported to occur by an inverse spin galvanic effect. A complicating factor in the formation of phase-pure tetragonal CuMnAs is the formation of an orthorhombic phase with nearly the same stoichiometry. Pure-phase tetragonal CuMnAs has been reported to require an excess of Cu to maintain a single phase in traditional solid state synthesis reactions. Here we show that subtle differences in diffraction patterns signal pervasive inhomogeneity and phase separation, even in Cu-rich Cu$_{1.18}$Mn$_{0.82}$As. From calorimetry and magnetometry measurements, we identify two transitions corresponding to the N\'eel temperature (T$_N$) and an antiferromagnet to weak ferromagnet transition in Cu$_{1.18}$Mn$_{0.82}$As and CuMn$_{0.964}$As$_{1.036}$. These transitions have clear crystallographic signatures, directly observable in the lattice parameters upon in-situ heating and cooling. The immiscibility and phase separation could arise from a spinoidal decomposition that occurs at high temperatures, and the presence of a ferromagnetic transition near room temperature warrants further investigation of its effect on the electrical switching behavior.