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

An exotic quantum mechanical ground state, i.e. the non-magneticJ_eff= 0 state, has been predicted for higher transition metalt2g4systems, 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. Interestingly, a recent study on vacancy ordered double perovskite compound K₂RuCl₆by Takahashiet al(2021Phys. Rev. Lett.127227201) concluded that even withinLScoupling regime the Ru⁴⁺4d⁴ions, within isolated RuCl₆octahedra, strongly accommodateJmultiplets havingJ_eff= 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 inP21/nspace 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.