Structural study of the electron-doped manganites Sm0.1Ca0.9MnO3 and Pr0.1Sr0.9MnO3: Evidence of phase separation

The investigation of two perovskite manganites with the same carrier concentration of 0.1 electron per Mn has been performed using neutron powder diffraction and electron microscopy, and completed with transport and magnetic measurements. For ${\mathrm{Sm}}_{0.1}{\mathrm{Ca}}_{0.9}{\mathrm{MnO}}_{3},$ whatever the temperature (from 2 to 300 K), a unique crystalline structure (Pnma space group) is observed. The magnetic state below ${T}_{N}{=T}_{C}=110\mathrm{K}$ is phase separated, consisting of ferromagnetic domains of different sizes ranging from small clusters to macroscopic regions, which are embedded in an antiferromagnetic G-type matrix. The high conductivity observed in ${\mathrm{Sm}}_{0.1}{\mathrm{Ca}}_{0.9}{\mathrm{MnO}}_{3}$ at low temperature is established through a percolation of the ferromagnetic domains. At room temperature, the structure of the analogous compound ${\mathrm{Pr}}_{0.1}{\mathrm{Sr}}_{0.9}{\mathrm{MnO}}_{3}$ is cubic $(Pm3m$ space group). At low temperature $(Tl200\mathrm{K}),$ this manganite exhibits a complex microstructure, consisting of an intergrowth of G and C-type antiferromagnetically ordered layers, both from tetragonal $I4/mcm$ structure, with appreciable lattice distortion. In agreement with the insulating behavior of ${\mathrm{Pr}}_{0.1}{\mathrm{Sr}}_{0.9}{\mathrm{MnO}}_{3}$ at low temperature, no ferromagnetism is observed.