Deviation from nonmagnetic <i>J </i>= 0 state in a pentavalent columnar iridate Sr₃NaIrO₆

Strong spin-orbit coupling (SOC) leads to the exotic properties in otherwise banal pool of 'paramagnetic' heavy ion oxides. The 5d⁴ iridates eventually stirred up a controversy about the origin of magnetism in them. A nonmagnetic J=0 ground state should be realized ideally for a pentavalent d⁴ iridate in the jj coupling limit, which has never been achieved in any of the reported d⁴ Ir oxides to date. Briefly introducing the previously handled (by our group) such 5d⁴ cases with different Ir environments, we here pay serious focus on Sr₃NaIrO₆, a 5dt_2g⁴ columnar iridate having well separated Ir⁵⁺ centers, which is expected to have a singlet J=0 ground state with no net magnetic moment under strong SOC. However, stabilization of such state at moderate SOC is exceptionally fragile to minute external perturbation and enhanced magnetic responses appear. Moreover, the magnetic interaction between these developed magnetic moments becomes another important point. We, in this work, using detailed magnetic and thermodynamic measurements, refute any chance of nonmagnetic ground state in Sr₃NaIrO₆ compound. Instead, our experimental observations reveal the existence of quantum spin-orbital liquid state down to 40 mK atleast with sufficiently large magnetic moments on individual Ir⁵⁺.