Abstract
Magnetization, resistivity, thermal expansion, thermopower, and neutron powder diffraction data are presented for the perovskite manganite ${\mathrm{Pr}}_{0.7}{\mathrm{Ba}}_{0.3}{\mathrm{MnO}}_{3}.$ A distinct ferromagnetic insulating state, similar to that observed in the ${\mathrm{La}}_{0.88}{\mathrm{Sr}}_{0.12}{\mathrm{MnO}}_{3}$ system, is observed in the temperature range between the paramagnetic-ferromagnetic transition at ${T}_{\mathrm{FM}}\ensuremath{\approx}180 \mathrm{K}$ and the broad metal-insulator transition near ${T}_{p}=120 \mathrm{K}.$ The large A-site cation-size mismatch appears to suppress the ferromagnetic double-exchange interactions relative to the competing ferromagnetic superexchange interactions, thereby giving rise to the ferromagnetic insulating state.
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