Spin-glass transition in the spin–orbit-entangled J(eff) = 0 Mott insulating double-perovskite ruthenate

We have successfully synthesized new Ru(4+) double perovskite oxides SrLaInRuO(6) and SrLaGaRuO(6), which are expected to be a spin–orbit coupled J(eff) = 0 Mott insulating ground state. Their magnetic susceptibility is much significant than that expected for a single Ru(4+) ion for which exchange coupling with other ions is negligible. Their isothermal magnetization process suggests that there are about 20 percent isolated spins. These origins would be the Ru(3+)/Ru(5+) magnetic defects, while the regular Ru(4+) sites remain nonmagnetic. Moreover, SrLaGaRuO(6) shows a spin-glass-like magnetic transition at low temperatures, probably caused by isolated spins. The observed spin-glass can be interpreted by the analogy of a dilute magnetic alloy, which can be seen as a precursor to the mobile J(eff) = 1 exciton as a dispersive mode as predicted.