EPR EVIDENCE FOR JAHN-TELLER POLARONS IN LA1-XCAXMNO3+Y

We present the results of the electron paramagnetic resonance (EPR) st udy in the mixed valence perovskite La1-xCaxMnO3+y for O-16 and O-18 i sotope substituted compounds. The characteristic differences observed in EPR intensity and linewidth for the two isotope samples can be expl ained by a model in which a bottlenecked spin relaxation takes place f rom the exchange-coupled constituent Mn4+ ions via the Mn3+ Jahn-Telle r ions to the lattice. For x=0.2 the ferromagnetic exchange energy J e xhibits a O-16/O-18 oxygen isotope effect of similar to-10%. The obser ved isotope effects provide the microscopic evidence for the formation of Jahn-Teller polarons in doped manganese perovskites.