Induced ferromagnetism and colossal magnetoresistance by Ir-doping in Pr_(1-x)Ca_xMnO_3

摘要

The doping of the manganese site by iridium (up to 15%) in the small A cation manganites Pr_(1-x)Ca_xMnO_3 (0.4 ≤ x ≤ 0.8), has been investigated as a new method to suppress charge-ordering and induce CMR effects. Ir doping leads to ferromagnetism and to insulator to metal transitions, with high transition temperatures reaching 180 K and CMR ratio in 7 T as large as 10~4. The efficiency with which iridium induces ferromagnetism and CMR is compared to previous results obtained with other substitutions (Ru, Rh, Ni, Cr...). The ionic radius of the foreign cations and their mixed-valencies are found to be the main parameters governing the ability to collapse the charge-ordered state.