Chemical composition induced quantum phase transition in Cs1−xRbxFeCl3...

The isostructural series of S=1 quantum magnets Cs1−xRbxFeCl3 is investigated, using both thermodynamic measurements and inelastic neutron scattering experiments. It is found that with increasing Rb content the system evolves from the gapped state at x=0, through a quantum phase transition at x∼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 substantially broadened suggesting that disorder plays a key role in this species. For the two end compounds, excitations remain sharp.