The nuclear and magnetic structures and properties of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ with $0.45<~x<~1$ and ${\mathrm{Pr}}_{1-y}{\mathrm{Sr}}_y{\mathrm{MnO}}_3$ $(0.58\mathrm{}<~y<~1)$ were investigated using neutron powder diffraction, resistivity and magnetic measurements. In this paper, we present the full magnetic and structural phase diagram for ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ and a partial phase diagram for ${\mathrm{Pr}}_{1-y}{\mathrm{Sr}}_y{\mathrm{MnO}}_3.$ At low temperatures, we observe a series of structural phase transitions evolving as a function of increasing x as follows: orthorhombic $\mathrm{Pbn}\overrightarrow{m}\mathrm{rhombohedral}$ $R3\mathrm{}¯\overrightarrow{c}\mathrm{orthorhombic}$ $\mathrm{Fmm}\overrightarrow{m}\mathrm{tetragonal}$ $I4/mc\overrightarrow{m}\mathrm{cubic}$ $\mathrm{Pm}3\mathrm{}¯m.\mathrm{}$ At higher temperatures, the orthorhombic Fmmm structural region disappears. We also identify four magnetic states (FM, A, C, and G type) evolving as a function of increasing x. The magnetic and nuclear structural transitions coincide for samples with $0.8<~x<~\mathrm{0.95.}$ In the $0.5<~x<~0.9$ region, resistivity and magnetic measurements show a substantial hysteresis near $T_N.$ This hysteresis of a few K is indicative of a first order antiferromagnetic transition in good agreement with the neutron diffraction results. Our data also suggest the existence of a strong competition between the ferromagnetic and A-type states for $x\sim 0.5,$ and between the C- and G-type states for $x\sim \mathrm{0.95.}$ A similar behavior is observed for ${\mathrm{Pr}}_{1-y}{\mathrm{Sr}}_y{\mathrm{MnO}}_3.$

• Received 30 September 2002

DOI:https://doi.org/10.1103/PhysRevB.67.094431