Global phase diagram of perovskite manganites in the plane of quenched disorder versus one-electron bandwidth

A competition between a ferromagnetic metallic phase and a charge/orbital-ordered insulating one has been investigated for manganese oxides with perovskite structure, RE_1−xAE_xMnO₃ (x=0.45) with RE and AE being rare earth elements (more than 50 specimens mostly in forms of single crystal), ranging from La to Gd, and alkaline earth elements, Ca, Sr, and Ba, respectively. The global phase diagram is deduced in the plane of the effective one-electron bandwidth versus the magnitude of quenched disorder, which can be controlled by the averaged value and the variance of the RE∕AE ionic radii, respectively. As the disorder increases, the long range orders of both phases tend to be suppressed, and the bicritical feature of the ferromagnetic metal versus the charge/orbital-ordered insulator is changed to such a complex one as intervened by a spin glasslike insulator that is viewed as the frozen state of charge/orbital correlation. The ferromagnetic transition temperature is critically suppressed near the phase boundary with the spin-glass, where the colossal magnetoresistance is most enhanced.