Charge order and magnetoresistivity in a perovskite family of bismuth based manganites

We exemplify some of the problems in designing novel functional materials with the substitution effects on colossal magnetoresistive (CMR) series CaCu₃(Mn_4-xFe_x)O₁₂ (x = 0, 0.5, 1.0) and on the charge order phenomenon in half hole-doped manganites Bi_0.25RE_0.25Ca_0.5MnO₃ (RE = La, Nd, Ho, Er, Tm) and Bi_0.5Ca_0.5MnO₃ (RE = La, Nd, Ho, Er, Tm) Bi_0.5Ca_0.5MnO₃. All the CaCu₃(Mn_4-xFe_x)O₁₂ samples are ferromagnetic and show a progressive decrease of Tc, saturation magnetization and Weiss temperatures, as the Fe contents increases, which suggests an increment of the antiferromagnetic interactions at the (Mn,Fe) octahedral sublattice and to a considerable canting of the Fe vs Mn spins. The magnetoresistance also decreases upon Fe-doping. In contrast, the Bi-RE samples remain semiconducting by entering antiferromagnetic state at low temperature and similarly to end members Bi_0.5Sr_0.5MnO₃ and Bi_0.5Ca_0.5MnO₃ are remarkable for their particularly stable charge order of the e_g electrons. Although giving rise to important modifications in the resulting magnetic properties and leading at rather low Fe substitution level to full suppression of charge order in Bi_0.5Ca_0.5(Mn_1-xFe_x)O₃ the Fe substitution does not induce magnetoresistive effect.