Hybridization effects on the magnetic ground state of ruthenium in double perovskite La₂ZnRu_{1- x}Ti_xO₆

An exotic quantum mechanical ground state, i.e. the nonmagneticJ_eff= 0 state, has been predicted for higher transition metal t⁴_2gsystems, 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 5d⁴systems had mostly been clouded by solid-state effects or the reduced strength of the renormalized SOC that might
allow significant triplon condensation. Surprisingly, a recent study on vacancy ordered double perovskite compound K₂RuCl₆by Takahashiet.al.[1] concluded that even withinLScoupling regime the Ru⁴⁺4d⁴ions, within isolated RuCl₆octahedra, strongly accommodate
Jmultiplets having Jeff = 0 as the ground state with weakly interactingJ_eff= 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 RuO₆octahedra but unlike K₂RuCl₆, they remain chemically connected via corner-sharing with nonmagnetic ZnO₆octahedra. Next, we move on to separate out the RuO₆octahedra 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 P2₁/n space group with tilted octahedra without distortion as has been confirmed by the x-ray power diffraction (XRPD) and x-ray absorption spectroscopic (XAS) studies. Interestingly, the XPS VB 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.