Doping effects of rare-earth ions in La0.5-xRxBa0.5CoO3 (R=Y, Ce, Pr, Nd)

La0.5-xRxBa0.5CoO3 (R=Y, Ce, Pr and Nd) compounds were synthesized. The effects of doping another kind of rare-earth ions on the magnetic and transport properties were studied systematically. With increasing R dopant the magnetic moments of the compounds decrease. This is caused by the charge transfer (for Y- or Ce-doped samples) or the spin state transition (for Pr- or Nd-doped samples). The increasing antiferromagnetic interaction between the Co ions with increasing Y dopant results in the magnetic moment to decrease more quickly. The Curie temperature decreases with increasing R doping. This can be explained in terms of the size effect of the rare-earth ions. The charge transfer causes the resistivity of the Y- or Ce-doped samples to increase dramatically with increasing doping amount. The conductive mechanism for the Y- or Ce-doped samples at the temperature ranging from 77 to 300 K belongs to the variable range hopping conduction. Different conductive mechanisms in the different temperature range are found for the Pr- or Nd-doped samples