Interplay of magnetism and dimerization in pressurized Kitaev material $\beta$-Li$_2$IrO$_3$

TL;DR

This study investigates how pressure influences magnetism and structural dimerization in $eta$-Li$_2$IrO$_3$, revealing a first-order magnetic collapse, a dimerized phase, and the absence of a pressure-induced spin-liquid state.

Contribution

It provides the first detailed phase diagram of $eta$-Li$_2$IrO$_3$ under pressure, combining experimental magnetization data with ab initio calculations to elucidate the interplay of magnetism and dimerization.

Findings

Magnetic order breaks down at ~1.4 GPa in a first-order transition.

A dimerized phase with mixed magnetic and non-magnetic Ir sites develops above critical pressure.

No evidence of a pressure-induced spin-liquid phase in the studied pressure range.

Abstract

We present magnetization measurements on polycrystalline $\beta$-Li$_2$IrO$_3$ under hydrostatic pressures up to 3~GPa and construct the temperature-pressure phase diagram of this material. Our data confirm that magnetic order breaks down in a first-order phase transition at $p_{\rm{c}}$ $\approx$ 1.4~GPa and additionally reveal a step-like feature -- magnetic signature of structural dimerization -- that appears at $p_{\rm{c}}$ and shifts to higher temperatures upon further compression. Following the structural study by L. S. I. Veiga et al. [Phys. Rev. B 100, 064104 (2019)], we suggest that a partially dimerized phase with a mixture of magnetic and non-magnetic Ir$^{4+}$ sites develops above $p_{\rm{c}}$. This phase is thermodynamically stable between 1.7 and 2.7~GPa according to our ab initio calculations. It confines the magnetic Ir$^{4+}$ sites to weakly coupled tetramers with a singlet ground state and no long-range magnetic order. Our results rule out the formation of a pressure-induced spin-liquid phase in $\beta$-Li$_2$IrO$_3$ and reveal peculiarities of the magnetism collapse transition in a Kitaev material. We also show that a compressive strain imposed by the pressure treatment of $\beta$-Li$_2$IrO$_3$ enhances signatures of the 100~K magnetic anomaly at ambient pressure.