Hybridization effects on the magnetic ground state of ruthenium in double perovskite La2ZnRu1−xTixO6

An exotic quantum mechanical ground state, i.e. the non-magnetic Jeff = 0 state, has been predicted for higher transition metal t 2 g 4 systems, due to the influence of strong spin-orbit coupling (SOC) or in other words, due to unquenched orbital moment contribution. However, previous attempts to experimentally realize such a state in 5d4 systems had mostly been clouded by solid-state effects or the reduced strength of the renormalized SOC that might allow significant triplon condensation. Interestingly, a recent study on vacancy ordered double perovskite compound K2RuCl6 by Takahashi et al (2021 Phys. Rev. Lett. 127 227201) concluded that even within LS coupling regime the Ru4+ 4d4 ions, within isolated RuCl6 octahedra, strongly accommodate J multiplets having Jeff = 0 as the ground state with weakly interacting Jeff = 1 excitation, due to large unquenced Ru orbital angular momentum in the system. In the present report, we show results from the double perovskite La2ZnRuO6, where Ru4+ ions form isolated RuO6 octahedra but unlike K2RuCl6, they remain chemically connected via corner-sharing with nonmagnetic ZnO6 octahedra. Next, we move on to separate out the RuO6 octahedra further by doping the Ru-site with Ti4+, in order to probe the character of the Ru4+ ions within a different structural background. We find that the system stabilizes in P2 1 / n space group with tilted octahedra without distortion as has been confirmed by the x-ray powder diffraction and x-ray absorption spectroscopic studies. Interestingly, the x-ray photoelectron spectroscopic valance band spectra indicated certain inhomogeneity around the half-doping region, while confirming insulating ground state for all. Moreover, unlike the vacancy ordered double perovskite cases, it is observed that here the Ru orbital angular momentum gets substantially quenched and only the Ru spin magnetic moments are realized.