The structural, magnetic and electrical properties of the hole-doped cobaltites La0.7(Ca1-xBax)0.3CoO3 (x=0.0, 0.5 and 1.0)

We have studied the structural, magnetic and electrical properties of hole-doped cobaltites with compositions, La-0.7 (Ca1-xBax)(0.3) CoO3 (x = 0.0, 0.5 and 1.0). Due to the large difference in size between the Ca and Ba ions (size mismatch), these compounds show interesting changes in the magnetic and transport behaviours with an increase in the concentration of Ba. The distortion in the perovskite structure decreases with the substitution of Ba for Ca. Magnetic studies indicate that the anisotropy in their ferromagnetic characters, which contribute to the observations of large thermomagnetic irreversibilities and large coercive fields in these compounds, change significantly with the substitution of Ba for Ca. The unusual magnetic behaviour of the La0.7Ba0.3CoO3 compound, as reflected in its M-H behaviour, has been explained on the basis of a possible coexistence of different magnetic phases. Observations of the low-temperature resistivity minimum, and negative magnetoresistance up to 26% in the low-temperature insulating regions of these polycrystalline compounds, have been ascribed to grain boundary effects.