Mechanism of magnetostructural transformation in multifunctional Mn$_3$GaC

TL;DR

This study reveals that the magnetostructural transition in Mn$_3$GaC is driven primarily by distortions in the Mn sub-lattice, affecting magnetic interactions and causing a volume-discontinuous phase change.

Contribution

It demonstrates that Mn-C interactions play a minimal role, highlighting the importance of Mn sub-lattice distortions in the magnetic transition of Mn$_3$GaC.

Findings

Mn sub-lattice distortions cause magnetic phase change.

Shorter Mn-Mn bonds favor antiferromagnetism.

Transition involves abrupt shortening of Mn-Mn bonds.

Abstract

Mn$_3$GaC undergoes a ferromagnetic to antiferromagnetic, volume discontinuous cubic-cubic phase transition as a function of temperature, pressure and magnetic field. Through a series of temperature dependent x-ray absorption fine structure spectroscopy experiments at the Mn K and Ga K edge, it is shown that the first order magnetic transformation in Mn$_3$GaC is entirely due to distortions in Mn sub-lattice and with a very little role for Mn-C interactions. The distortion in Mn sub-lattice results in long and short Mn-Mn bonds with the longer Mn-Mn bonds favoring ferromagnetic interactions and the shorter Mn-Mn bonds favoring antiferromagnetic interactions. At the first order transition, the shorter Mn-Mn bonds exhibit an abrupt decrease in their length resulting in an antiferromagnetic ground state and a strained lattice.