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

The transition between a ferromagnetic metal and an insulator with short-range charge/orbital correlation has been investigated for the manganites R_0.55Sr_0.45MnO₃ [R=Sm, Eu, Gd, and Sm_1-yGd_y (0<~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 Pr_0.55(Ca_1-ySr_y)_0.45MnO₃ with the competition between the ferromagnetic metal and charge/orbital-ordered insulator. Larger randomness via the local lattice distortion in R_0.55Sr_0.45MnO₃ enhances the phase fluctuation between ferromagnetic metal and charge/orbital-ordered insulator and suppresses their long-range orders.