Disorder-induced polaron formation in the magnetoresistive perovskite La_0.54Ba_0.46MnO₃

The effect of A-site chemical disorder on the ferromagnetic transition and spin dynamics for the magnetoresistive perovskite La_0.54 Ba _0.46 MnO₃ were discussed. It was found that the disorder reduced exchange interactions by only 9% that were revealed by low temperature spin waves. It was also found that the transition was discontinuous in the disordered sample with the development of a quasielastic peak in the spectrum below T_C and long time relaxation of the order parameter. The results show that the chemical disorder lowered the energy for polaron formation in manganese perovskites and was the origin of 50 K reduction in T_C.