Disordered magnetic ground state in a quasi-1-D d 4 columnar iridate Sr3LiIrO6

Abstract

Abstract Spin–orbit coupling offers a large variety of novel and extraordinary magnetic and electronic properties in otherwise ‘ordinary pool’ of heavy ion oxides. Here we present a detailed study on an apparently isolated hexagonal 2H spin-chain d 4 iridate Sr3LiIrO6 with geometric frustration. Our structural studies reveal Li–Ir chemical order with desired stoichiometry in this compound, while x-ray absorption together with x-ray photoemission spectroscopic characterizations establish pure 5+ valence of Ir. We have established a magnetic ground state with finite Ir5+ magnetic moments in this compound, contrary to the anticipated nonmagnetic J eff = 0 state, through combined dc susceptibility, 7 Li nuclear magnetic resonance (NMR), muon spin relaxation (µSR) and ab-initio electronic structure studies. These investigations together with ac magnetic susceptibility and specific heat measurements reveal that despite having noticeable antiferromagnetic correlation among the Ir5+ local moments, this system does not magnetically order down to at least 0.05 K, possibly due to geometrical exchange frustration, arising from the comparable nearest- and next-nearest-neighbor interchain Ir–O–O–Ir superexchange interaction strengths with opposite signs. However, the zero-field µSR analysis shows emergence of a considerable proportion of spin-freezing on top of a spin-fluctuating dynamic magnetic background down to the lowest measured temperature of 1.7 K, possibly due to some inhomogeneity and/or the much stronger intra-column Ir–Ir magnetic exchange interaction strength relative to the inter-column Ir–Ir ones. The linear temperature dependence of the magnetic specific heat ( C m ) in both zero and applied magnetic fields, plus the power-law behavior of the NMR spin-lattice relaxation rate suggest a gapless spinon density of states in this charge gapped disordered magnetic ground state of Sr3LiIrO6.