# Negative thermal expansion in the plateau state of a magnetically-frustrated spinel

## TL;DR

This study reveals negative thermal expansion in a frustrated magnetic insulator's high-field plateau phase, linking it to spin excitations and magnetization changes, with implications for discovering new NTE materials.

## Contribution

It provides the first detailed phase diagram of CdCr2O4 under high magnetic fields and explains the origin of NTE through spin-lattice coupling and localized spin excitations.

## Key findings

- NTE observed in the half-magnetization plateau phase above 27T
- Phase diagram mapped up to 30T using dilatometry
- NTE linked to large negative magnetization change with temperature

## Abstract

We report on negative thermal expansion (NTE) in the high-field, half-magnetization plateau phase of the frustrated magnetic insulator CdCr2O4. Using dilatometry, we precisely map the phase diagram at fields of up to 30T, and identify a strong NTE associated with the collinear half-magnetization plateau for B > 27T. The resulting phase diagram is compared with a microscopic theory for spin-lattice coupling, and the origin of the NTE is identified as a large negative change in magnetization with temperature, coming from a nearly-localised band of spin excitations in the plateau phase. These results provide useful guidelines for the discovery of new NTE materials.