On O-16-O-18 isotope effects in manganese perovskites

Large isotope effects which have been found by others [1,2] in some colossa l magneto resistance manganite perovskites, AMnO(3), are evidence of unusua lly strong interactions between the lattice and magnetism. We offer a model which is based upon the approximate degeneracy of two Mn+3 states: one wit h high spin S = 2, and the other with low spin S = 1. These states have dif ferent radii and different electron form factors. They thus have different fold constants governing the interaction with neighboring oxygen ions which provide the sought for link between magnetism and oxygen mass. The experim ents can be understood with the reasonable assumption that the LS has great er force constants than HS. The dependence of changes in T-c with isotopic substitution as a function of the A-ion radius. the metal insulator transit ions and the Mossbauer effect changes, are discussed in terms of this model .