Pressure-induced dimerization and collapse of antiferromagnetism in the Kitaev material α−Li2IrO3

Abstract

We present magnetization measurements carried out on polycrystalline and single-crystalline samples of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ under hydrostatic pressures up to 2 GPa and establish the temperature-pressure phase diagram of this material. The N\'eel temperature (${T}_{\mathrm{N}}$) of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ is slightly enhanced upon compression with $d{T}_{\mathrm{N}}/dp$ = 1.5 K/GPa. Above 1.2 GPa, $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ undergoes a first-order phase transition toward a nonmagnetic dimerized phase, with no traces of the magnetic phase observed above 1.8 GPa at low temperatures. The critical pressure of the structural dimerization is strongly temperature dependent. This temperature dependence is well reproduced on the ab initio level by taking into account lower phonon entropy in the nonmagnetic phase. We further show that the initial increase in ${T}_{\mathrm{N}}$ of the magnetic phase is due to a weakening of the Kitaev interaction $K$ along with the enhancement of the Heisenberg term $J$ and off-diagonal anisotropy $\mathrm{\ensuremath{\Gamma}}$. Our study reveals a common thread in the interplay of magnetism and dimerization in pressured Kitaev materials.