Magnetic-field-induced metal-insulator phenomena in ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x\mathrm{Mn}{\mathrm{O}}_3$ with controlled charge-ordering instability

Field-induced insulator-to-metal transitions have been found in ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x\mathrm{Mn}{\mathrm{O}}_3(0.3\mathrm{}<~x<~0.5)$ single crystals, which are accompanied by a melting of the insulating charge-ordered (i.e., ${\mathrm{Mn}}^{3+}$/${\mathrm{Mn}}^{4+}$ ordered) state. The transition is of the first order with a hysteresis and is even irreversible at low temperatures. The $x$-dependent metal-insulator phase diagrams in the $H-T$ plane indicate that a deviation of $x$ from 0.5 modifies the robustness of the charge-ordering state, which is argued in terms of the effect of discommensuration of the charge concentration on the charge-ordered state.