Pressure effects on the charge and spin states and the relation between the ferromagnetic and metallic states were explored on the small bandwidth manganite ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x\mathrm{Mn}{\mathrm{O}}_3$ ($x=0.25$, 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 $\left(T_{\mathit{MI}}\right)$ increases with pressure below a critical point $P*$, above which $\left(T_{\mathit{MI}}\right)$ 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 $T_{\mathit{MI}}$ and the Curie temperature $\left(T_C\right)$ change with pressure in a reverse way and do not couple under pressure. In the $x=0.3$ compound, the relation of $T_{\mathit{MI}}$ and $T_C$ shows a critical behavior: They are coupled in the range of $\sim 0.8–5\mathrm{GPa}$ and decoupledoutside of this range. In the $x=0.35$ compound, $T_{\mathit{MI}}$ and $T_C$ are coupled in the measured pressure range where a ferromagnetic state is present.

• Received 3 December 2003

DOI:https://doi.org/10.1103/PhysRevB.70.094409