Antiferromagnetic metallic state in doped manganites

Electronic and magnetic properties are systematically investigated for doped manganites ${R}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ $(R={\mathrm{La}}_{1\ensuremath{-}z}{\mathrm{Nd}}_{z})$ by changing the nominal hole concentration $x$ and the averaged ionic radius of the perovskite $A$ site $(z),$ or the one-electron bandwidth $W.$ In the heavily doped region $(x>~0.50),$ we observed a layered-type ($A$-type) antiferromagnetic state with metallic conductivity ($\ensuremath{\rho}\ensuremath{\approx}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\ensuremath{\Omega}\mathrm{cm}$ at 5 K for ${\mathrm{La}}_{0.46}{\mathrm{Sr}}_{0.54}{\mathrm{MnO}}_{3}$). This observation suggests that the antiferromagnetic metallic (AFM) state is the alternative ground state for doped manganites, besides the ferromagnetic metallic (FM) state.