A ferromagnetic insulating (FM-I) state in ${\mathrm{Pr}}_{0.75}{\mathrm{Ca}}_{0.25}{\mathrm{MnO}}_3$ has been studied by neutron scattering experiment and theoretical calculation. The insulating behavior is robust against an external magnetic field, and is ascribed to neither the phase separation between a ferromagnetic metallic (FM-M) phase and a nonferromagnetic insulating one, nor the charge ordering. We found that the Jahn-Teller type lattice distortion is much weaker than ${\mathrm{PrMnO}}_3$ and the magnetic interaction is almost isotropic. These features resemble the ferromagnetic metallic state of manganites, but the spin exchange interaction J is much reduced compared to the FM-M state. The theoretical calculation based on the staggered type orbital order well reproduces several features of the spin and orbital state in the FM-I phase.

• Received 24 June 2003

DOI:https://doi.org/10.1103/PhysRevB.69.054433