Effect of charge doping in Os-based double perovskites with strong spin-orbit coupling

The combined effects of strong electronic correlations and spin-orbit coupling (SOC) leads to a plethora of emergent novel quantum states. However, predicting such emergent properties is complicated by the fact that spin is not a good quantum number in the presence of SOC. Therefore, experimental studies by local probes are highly sought to guide theoretical descriptions of this new physics. Double perovskite structures are particularly interesting cases of materials with such novel quantum states. Here, we investigate the effects of charge doping via the Na⁺/Ca⁺⁺ partial substitution on the magnetic ground state of Ba₂NaOsO₆, a double perovskite with strong SOC. Ba₂NaOsO₆ is a 5d¹ Mott insulator that displays an exotic canted two-sublattice ferromagnetic state believed to be driven by the staggered quadrupolar order [L. Lu et al. Nature Comm. 2017], while Ba₂CaOsO₆ is a 5d² compound which displays an antiferromagnetic phase [C.M. Thompson et al. J. Phys. Cond. Matter 2014]. We present zero field μSR measurements on powder samples of the compound Ba₂Na_1-xCa_xOsO₆ for 0 < x < 1 to investigate the interplay between spin, orbital, and charge degrees of freedom, which are believed to govern novel quantum states of compounds with strong SOC.