# Quantum Paramagnet and Frustrated Quantum Criticality in a Spin-One Diamond Lattice Antiferromagnet

## TL;DR

This paper models a spin-one diamond lattice antiferromagnet, revealing a quantum phase transition from a trivial quantum paramagnet to magnetic order, with unique critical properties due to frustration and degeneracy.

## Contribution

It introduces a minimal model incorporating Heisenberg interactions and single-ion anisotropy, elucidating the phase diagram and critical behavior of spin-one diamond lattice systems.

## Key findings

- Existence of a quantum phase transition driven by anisotropy and exchange interactions.
- Degenerate bosonic modes become critical near the transition.
- Phase diagram and experimental predictions for NiRh$_2$O$_4$ ground states.

## Abstract

Motivated by the proposal of topological quantum paramagnet in the diamond lattice antiferromagnet NiRh$_2$O$_4$, we propose a minimal model to describe the magnetic interaction and properties of the diamond material with the spin-one local moments. Our model includes the first and second neighbor Heisenberg interactions as well as a local single-ion spin anisotropy that is allowed by the spin-one nature of the local moment and the tetragonal symmetry of the system. We point out that there exists a quantum phase transition from a trivial quantum paramagnet when the single-ion spin anisotropy is dominant to the magnetic ordered states when the exchange is dominant. Due to the frustrated spin interaction, the magnetic excitation in the quantum paramagnetic state supports extensively degenerate band minima in the spectra. As the system approaches the transition, extensively degenerate bosonic modes become critical at the criticality, giving rise to unusual magnetic properties. Our phase diagram and experimental predictions for different phases provide a guildeline for the identification of the ground state for NiRh$_2$O$_4$. Although our results are fundamentally different from the proposal of topological quantum paramagnet, it represents interesting possibilities for spin-one diamond lattice antiferromagnets.