Competing interactions and the isotope effect in colossal magnetoresistance materials

The experimentally observed large isotope effect on the ferromagnetic trans ition temperature in doped manganites R(1-x)A(x)MnO(3) is shown to be in ag reement with a local Jahn-Teller coupling mechanism. With increasing doping towards the insulating antiferromagnetic state the Mn-O-Mn bond substantia lly distorts, which is taken into account through intersite (Mn-O) interban d electron-phonon interactions. It is shown that there is a competition bet ween the local Jahn Teller and intersite interband couplings; depending on the bond angle distortion, the isotope effect can be suppressed substantial ly and even reverse sign, consistent with recent experimental results.