Chemical and hydrostatic-pressure effects on the Kitaev honeycomb material Na2IrO3

The low-temperature magnetic properties of polycrystalline Na2IrO3, 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-N. In the first case, the inhomogeneous magnetic order suggests either short- or long-range correlations of broadly distributed j =1/2 Ir4+ magnetic moments, reflecting local disorder. The increase of T-N under applied pressure points at an increased strength of three-dimensional interactions arising from interlayer compression.