Impact of structural transitions on the local spin environment and lattice dynamics in K₂IrBr₆

K₂IrBr₆ is a transition metal compound with 5d Ir ions in an ideal local octahedral environment with J_eff = ½ Mott insulating state. It undergoes structural phase transitions from cubic to tetragonal to monoclinic phases towards low temperatures. We have studied the impact of such transitions on the local spin environment and lattice dynamics using temperature-dependent electron paramagnetic resonance (EPR) and Raman scattering, respectively. At room temperature in the cubic phase, EPR revealed anisotropic -factor that suggests the entangled spin and lattice due to strong spin-orbit interaction of Ir-ions. EPR further reveals that the local spin structure and dynamics are strongly interlinked to the structural transitions. Our Raman scattering experiments did not obtain any new phonon modes as the structural transitions happen. However, a soft phonon anomaly has been observed across the cubic-to-tetragonal phase transition. In summary, our study obtains how the structural transitions affect the local spin structure and lattice dynamics in K₂IrBr₆.