Bicritical features of the metal-insulator transition in bandwidth-controlled manganites: Single crystals of Pr1−x(Ca1−ySry)xMnO3

Abstract

The phase change from a charge- and orbital-ordered insulator to a ferromagnetic metal has been investigated for single crystals of ${\mathrm{Pr}}_{0.55}({\mathrm{Ca}}_{1-y}{\mathrm{Sr}}_y{)}_{0.45}{\mathrm{MnO}}_3$ with controlled one-electron bandwidth. At $0<~y<~0.2,$ the ground state is the charge- and orbital-ordered insulator, while for $y>~0.25$ it changes to a ferromagnetic metal. At around $y=0.25,$ the critical temperatures for the charge-orbital ordering and the ferromagnetic transition coincide with each other (≈200 K), forming the bicritical point in the electronic phase diagram. Around this insulator-metal phase boundary, prototypical colossal magnetoresistance emerges in the metallic regime, while the charge-orbital ordering is melted by a relatively low magnetic field of a few tesla in the charge- and orbital-ordered insulating regime. The phase diagrams of ${\mathrm{Pr}}_{1-x}({\mathrm{Ca}}_{1-y}{\mathrm{Sr}}_y{)}_x{\mathrm{MnO}}_3$ $(0\mathrm{}<~y<~1)$ with various doping levels of $x=0.35,$ 0.45, and 0.5 indicate that such a competition between the charge-orbital ordering and the ferromagnetic metal is critically dependent on the doping level. In particular, the commensurate doping level $\mathrm{}(x=0.5\mathrm{})\mathrm{}$ tends to stabilize the charge- and orbital-ordered state even beyond the bicritical point in the lower-temperature side of the ferromagnetic phase.