Magnetic and Magnetoresistive Properties of Pr$_{1 - {\rm x}}$ Ca$_{\rm x}$ CoO$_{3}$ $({\rm x} =0.3, 0.5)$ Cobaltites

Polycrystalline perovskite Pr
_0.7
Ca
_0.3
CoO
₃
and Pr
_0.5
Ca
_0.5
CoO
₃
have been investigated by electrical resistivity, magnetization, ac susceptibility, and mu SR measurements. The magnetic measurements data indicate that the samples have, at low temperatures, similar properties to the frustrated magnets. The muSR measurements, suggest the presence of magnetic clusters at low temperatures. The electrical behavior has the main features of conduction in a phase separated system: it shows negative magnetoresistance and it is controlled by grain-boundary effects.