# Chemical composition induced quantum phase transition in Cs$_{1-x}$Rb$_{x}$FeCl$_{3}$

## TL;DR

This study explores how changing chemical composition in Cs$_{1-x}$Rb$_{x}$FeCl$_{3}$ induces a quantum phase transition from a gapped state to magnetic order, with disorder effects prominent at intermediate Rb levels.

## Contribution

It provides experimental evidence of a composition-driven quantum phase transition in an $S=1$ quantum magnet using thermodynamic and neutron scattering techniques.

## Key findings

- Quantum phase transition at x~0.35
- Magnetic excitations broaden at intermediate x
- Disorder influences magnetic excitations

## Abstract

The isostructural series of $S=1$ quantum magnets Cs$_{1-x}$Rb$_{x}$FeCl$_{3}$ is investigated, using both thermodynamic measurements and inelastic neutron scattering experiments. It is found that increasing Rb content the system evolves from the gapped state at $x=0$, through a quantum phase transition at $x\sim 0.35$, and to the magnetically ordered state at larger $x$. Inelastic neutron experiments for $x=0$, $x=0.3$, and $x=1$ demonstrate that the magnetic anisotropy and spin interactions are continuously tuned by the chemical composition. For the intermediate concentration all magnetic excitations are substantial broadened suggesting that disorder plays a key role in this species. For the two end-compounds, excitations remain sharp.