Critical control of competition between metallic ferromagnetism and charge/orbital correlation in single crystals of perovskite manganites

Abstract

The transition between a ferromagnetic metal and an insulator with short-range charge/orbital correlation has been investigated for the manganites $R_{0.55}{\mathrm{Sr}}_{0.45}{\mathrm{MnO}}_3$ $[R=\mathrm{Sm},$ Eu, Gd, and ${\mathrm{Sm}}_{1-y}{\mathrm{Gd}}_y$ $(0\mathrm{}<~y<~1)]$. The phase diagram as a function of the averaged radius of perovskite A-site cations is entirely modified from the prototypical bicritical phase diagram, e.g., for ${\mathrm{Pr}}_{0.55}({\mathrm{Ca}}_{1-y}{\mathrm{Sr}}_y{)}_{0.45}{\mathrm{MnO}}_3$ with the competition between the ferromagnetic metal and charge/orbital-ordered insulator. Larger randomness via the local lattice distortion in $R_{0.55}{\mathrm{Sr}}_{0.45}{\mathrm{MnO}}_3$ enhances the phase fluctuation between ferromagnetic metal and charge/orbital-ordered insulator and suppresses their long-range orders.