Chemical- and hydrostatic-pressure effects on the Kitaev honeycomb material Na${}_2$IrO${}_3$

Abstract

The low-temperature magnetic properties of \tcr{polycrystalline} Na${}_2$IrO${}_3$, a candidate material for the realization of a quantum spin-liquid state, were investigated by means of muon-spin relaxation and nuclear magnetic resonance methods under chemical and hydrostatic pressure. The Li-for-Na chemical substitution promotes an inhomogeneous magnetic order, whereas hydrostatic pressure (up to 3.9\,GPa) results in an enhancement of the ordering temperature $T_{\mathrm{N}}$. In the first case, the inhomogeneous magnetic order suggests either short- or long-range correlations of broadly distributed $j=$\textonehalf\ Ir${}^{4+}$ magnetic moments, reflecting local disorder. The increase of $T_{\mathrm{N}}$ under applied pressure points at an increased strength of three dimensional interactions arising from interlayer compression.