# Absence of first order magnetic transition, a curious case of Mn3InC

## TL;DR

This study investigates why Mn3InC does not exhibit a first-order magnetostructural transition, unlike similar compounds, revealing that larger In atoms constrain octahedral distortion and favor ferromagnetic interactions.

## Contribution

The paper uncovers that the larger In atom size prevents octahedral distortion in Mn3InC, maintaining ferromagnetic interactions and preventing a first-order transition, unlike Mn3GaC and Mn3SnC.

## Key findings

- Mn3InC has distorted Mn6C octahedra with long and short Mn--Mn bonds.
- Despite distortion, Mn3InC remains ferromagnetic without a first-order transition.
- Larger In atom size constrains octahedral deformation, favoring ferromagnetism.

## Abstract

The volume expanding magnetostructural transition in Mn$_3$GaC and Mn$_3$SnC has been identified to be due to distortion of Mn$_6$C octahedra. Despite a similar lattice volume as Mn$_3$SnC and similar valence electron contribution to the density of states as in Mn$_3$GaC, Mn$_3$InC does not undergo a first order magnetostructural transformation like the Ga and Sn antiperovskite counterparts. A systematic investigation of its structure and magnetic properties using probes like x-ray diffraction, magnetization measurements, neutron diffraction and extended x-ray absorption fine structure (EXAFS) reveal that though the octahedra are distorted resulting in long and short Mn -- Mn bonds and different magnetic moments on Mn atoms, the interaction between them remains ferromagnetic. This has been attributed to the strain on the Mn$_6$C octahedra produced due to the relatively larger size of In atom compared to Sn and Ga. The size of In atom constricts the deformation of Mn$_6$C octahedra giving rise to Mn -- Mn distances that favor only ferromagnetic interactions in the compound.