# Theory of Magnetism-Driven Negative Thermal Expansion in Inverse Perovskite Antiferromagnets

## TL;DR

This paper presents a theoretical study of magnetism-driven negative thermal expansion in inverse perovskite antiferromagnets, revealing a mechanism where magnetic ordering causes crystal expansion upon cooling.

## Contribution

It introduces a classical spin model explaining NTE in inverse perovskite antiferromagnets and suggests this mechanism could apply to other crystal structures.

## Key findings

- Reproduced crystal-volume expansion upon cooling in simulations.
- Expansion driven by maximizing energy gain of antiferromagnetic interactions.
- Proposed other crystal structures that may exhibit NTE through this mechanism.

## Abstract

Magnetism-induced negative thermal expansion (NTE) observed in inverse perovskite antiferromagnets Mn3AN (A=Zn, Ga, etc.) is theoretically studied by a classical spin model with competing bond-length-dependent exchange interactions. We numerically reproduce the crystal-volume expansion upon cooling triggered by a non-coplanar antiferromagnetic order and show that the expansion occurs so as to maximize an energy gain of the nearest-neighbor antiferromagnetic interactions. This mechanism is not specific to inverse perovskite magnets and might also be expected in magnets with other crystal structures. We propose other candidate crystal structures that might exhibit NTE through this mechanism.