# A molecular diamond lattice antiferromagnet as a Dirac semimetal candidate

## TL;DR

This study investigates a molecular diamond-lattice compound, revealing antiferromagnetic order at high temperature and potential as a Dirac semimetal, with implications for topological materials.

## Contribution

It demonstrates that (ET)Ag$_4$(CN)$_5$ exhibits high-temperature antiferromagnetic order and is a candidate for a three-dimensional topological Dirac semimetal.

## Key findings

- Antiferromagnetic order at 102 K with weak ferromagnetism.
- Transition temperature increases to ~195 K under 2 GPa pressure.
- First-principles calculations suggest Dirac semimetal potential.

## Abstract

The ground state of a molecular diamond-lattice compound (ET)Ag$_4$(CN)$_5$ is investigated by the magnetization and nuclear magnetic resonance spectroscopy. We found that the system exhibits antiferromagnetic long-range ordering with weak ferromagnetism at a high temperature of 102 K owing to the strong electron correlation. The spin susceptibility is well fitted into the diamond-lattice Heisenberg model with a nearest neighbor exchange coupling of 230 K, indicating the less frustrated interactions. The transition temperature elevates up to $\sim$195 K by applying pressure of 2 GPa, which records the highest temperature among organic molecular magnets. The first-principles band calculation suggests that the system is accessible to a three-dimensional topological semimetal with nodal Dirac lines, which has been extensively searched for a half-filling diamond lattice.