Iridates with the $5d^4$ electronic configuration have attracted recent interest due to reports of magnetically ordered ground states despite longstanding expectations that their strong spin-orbit coupling would generate a $J=0$ electronic ground state for each ${\mathrm{Ir}}^{5+}$ ion. The major focus of prior research has been on the double perovskite iridates ${\mathrm{Ba}}_2{\mathrm{YIrO}}_6$ and ${\mathrm{Sr}}_2{\mathrm{YIrO}}_6$, where the nature of the ground states (i.e., ordered vs nonmagnetic) is still controversial. Here, we present neutron powder diffraction, high-energy-resolution fluorescence-detected x-ray absorption spectroscopy (HERFD-XAS), resonant inelastic x-ray scattering (RIXS), magnetic susceptibility, and muon spin relaxation data on the related double perovskite iridates ${\mathrm{Ba}}_2{\mathrm{LuIrO}}_6, {\mathrm{Sr}}_2{\mathrm{LuIrO}}_6, {\mathrm{Ba}}_2{\mathrm{ScIrO}}_6$, and ${\mathrm{Sr}}_2{\mathrm{ScIrO}}_6$ that enable us to gain a general understanding of the electronic and magnetic properties for this family of materials. Our HERFD-XAS and RIXS measurements establish $J=0$ electronic ground states for the ${\mathrm{Ir}}^{5+}$ ions in all cases, with similar values for Hund's coupling $J_{\mathrm{H}}$ and the spin-orbit coupling constant ${\lambda }_{\mathrm{SOC}}$. Our bulk susceptibility and muon spin relaxation data find no evidence for long-range magnetic order or spin freezing, but they do exhibit weak magnetic signals that are consistent with extrinsic local moments. Our results indicate that the large ${\lambda }_{\mathrm{SOC}}$ is the key driving force behind the electronic and magnetic ground states realized in the $5d^4$ double perovskite iridates, which agrees well with conventional wisdom.

• Received 11 March 2022
• Revised 26 August 2022
• Accepted 30 August 2022

DOI:https://doi.org/10.1103/PhysRevMaterials.6.094409