  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 180K and CMR ratio in 7T 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.
