Evolution of magnetism in Ruddlesden-Popper bilayer nickelate revealed by muon spin relaxation

Here we report the positive muon spin relaxation study on Pr-doped La$_{1.9}$Pr$_{1.1}$Ni$_2$O$_{6.97}$ and oxygen-deficient La$_3$Ni$_2$O$_{6.63}$ polycrystalline under ambient pressure. Zero-field $\mu^+$SR experiments reveal the existence of bulk long-range magnetic order in La$_{1.9}$Pr$_{1.1}$Ni$_2$O$_{6.97}$ with $T_{N}=161\ \rm{K}$, while La$_3$Ni$_2$O$_{6.63}$ exhibits a short-range magnetic ground state with $T_N=30\ \rm{K}$. The magnetic transition width of La$_{1.9}$Pr$_{1.1}$Ni$_2$O$_{6.97}$ revealed by weak-transverse-field $\mu^+$SR is narrower compared to La$_3$Ni$_2$O$_{6.92}$. Our $\mu^+$SR experiment results provide a comprehensive view on the correlation between magnetism and structure perfection in Ruddlesden-Popper bilayer nickelates under ambient pressure.