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

Abstract

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 increasing with 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.