Factors Governing the Magnetoresistance Properties of the Electron-Doped Manganites Ca_1-xA_xMnO₃ (A = Ln, Th)

Magnetotransport properties of the Mn(IV)-rich perovskites Ca1-xLnxMnO3 and Ca1-xThxMnO3 (0 ≤ x ≤ 0.20) have been systematically investigated. Among the different factors governing their colossal magnetoresistance (CMR), we demonstrate that the electron concentration is the predominant one by comparing the effects of Ln3+ and Th4+, the optimal x value giving the highest magnetoresistance being twice for the former compared to the latter, in accordance with their respective oxidation states. CMR is linked to the ferromagnetism−antiferromagnetism competition that is maximum for xopt = 0.08 in the case of Th, whereas xopt increases from x = 0.135 for Pr to x = 0.16 for Ho.