Probing the Magnetic Ground State of Ba2YIrO6: Impact of Nonmagnetic Dopants and Spin–Orbit Coupling

Strong spin-orbit coupling (SOC) in iridates has long been predicted to lead to exotic electronic and magnetic ground states. Ba2YIrO6 (BYIO) has attracted particular attention due to the expectation of a J(eff) = 0 state for Ir5+ ions under the jj-coupling scheme. However, controversies surround the actual realization of this state, as finite magnetic moments are consistently observed experimentally. We present a multi-physics study of this system by progressively introducing nonmagnetic Sb5+ ions in place of Ir5+ (Ba2YIr1-ySbyO6, BYISO). Despite similar charge and ionic radii, Sb5+ doping appears highly inhomogeneous, coexisting with a fraction of nearly pure BYIO regions, as confirmed by X-ray diffraction (XRD). This aligns with observations in related compounds. While inhomogeneity creates uncertainty, the doped majority phases offer valuable insights. It is relevant that the inclusion of even small amounts of Sb5+ (10-20%) leads to a rise in magnetization. This strengthens our previous suggestion that magnetic Ir ions form dynamic singlets in BYIO, resulting in a near-nonmagnetic background. The observed moment enhancement with nonmagnetic doping supports the breakdown of these singlets. Furthermore, the magnetization steadily increases with an increasing Sb5+ content, contradicting the anticipated approach towards the J(eff) = 0 state with increased SOC due to reduced hopping between Ir5+ ions. This reinforces the presence of individual Ir5+ moments. Overall, our findings suggest that Ba2YIrO6 might not possess sufficiently strong SOC to be solely described within the jj-coupling picture, paving the way for further investigation.