Pressure effects on charge, spin, and metal-insulator transitions in the narrow bandwidth manganite Pr_1-xCa_xMnO₃

Pressure effects on the charge and spin states and the relation between the ferromagnetic and metallic states were explored on the small bandwidth manganite Pr_1-xCa_xMnO₃ (x=0.25, 0.3, 0.35). Under pressure, the charge ordering state is suppressed and a ferromagnetic metallic state is induced in all three samples. The metal-insulator transition temperature (T_MI) increases with pressure below a critical point P*, above which (T_MI) decreases and the material becomes insulating as at the ambient pressure. The e_g electron bandwidth and/or band filling mediate the pressure effects on the metal-insulator transition and the magnetic transition. In the small bandwidth and low doping concentration compound (x=0.25), the T_MI and the Curie temperature (T_C) change with pressure in a reverse way and do not couple under pressure. In the x=0.3 compound, the relation of T_MI and T _C shows a critical behavior: They are coupled in the range of ∼0.8-5 GPa and decoupled-outside of this range. In the x=0.35 compound, T_MI and T_C are coupled in the measured pressure range where a ferromagnetic state is present.