Pressure effects on charge, spin, and metal-insulator transitions in the narrow bandwidth manganitePr1−xCaxMnO3

Abstract

Pressure effects on the charge and spin states and the relation between the ferromagnetic and metallic states were explored on the small bandwidth manganite ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ ($x=0.25$, 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 $({T}_{\mathit{MI}})$ increases with pressure below a critical point $P*$, above which $({T}_{\mathit{MI}})$ 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 ${T}_{\mathit{MI}}$ 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 ${T}_{\mathit{MI}}$ and ${T}_{C}$ shows a critical behavior: They are coupled in the range of $\ensuremath{\sim}0.8--5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ 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.