Investigation of novel quantum magnetic ground state in a spin-orbit driven 4d ruthenate antiferromagnet La2MgRuO6

An intricate interplay between spin-orbit interaction and electronic correlation can lead to collective quantum phenomena with exotic excitations in 4d and 5d transition metal oxides. According to recent theoretical work, the d4 electronic configuration is quite interesting as super-exchange competes with spin-orbit coupling, yielding a phase transition from nonmagnetic atomic singlets to novel and unconventional magnetic phases. A promising candidate to test this physics is La2MgRuO6, a double perovskite with an ordered B-site where the Ru4+ is in the 4d4 configuration. Our preliminary characterizations suggests this material to be at the border between those phases. The dc magnetic susceptibility and specific heat show neither any signature of magnetic long-range ordering nor spin-freezing down to 50 mK despite a strong antiferromagnetic interaction between Ru4+ (4d4) moments. In addition, the power law behavior of low-T magnetic specific heat suggests a gapless excitation spectrum. We therefore plan to perform microscopic muon-spin-relaxation experiments down to sub-Kelvin temperatures on EMU instrument to shed insights into the correlated quantum magnetic ground state of this spin-orbit driven novel quantum magnet.