Comparative Mossbauer and magnetization study of 1% 119Sn-doped La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3

A detailed comparative Mossbauer study of La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 samples doped with 1% Sn is presented. The spectra at 5 K can be analyzed by a single ferromagnetic component. However, at higher temperatures two separate ferromagnetic components and a paramagnetic one are required to fit the spectra. The ferromagnetic component with the lower hyperfine field is attributed to clusters of weakened double-exchange interactions due to competition by localization mechanisms. Clear differences between the two samples in regard to the critical behavior arise: (i) The hyperfine field of La0.67Ca0.33Mn0.99Sn0.01O3 disappears abruptly at T-c in contrast to that of La0.67Sr0.33Mn0.99Sn0.01O3 which varies continuously and goes to zero smoothly at the critical temperature. (ii) The second ferromagnetic phase appears above 0.35T(c) in the Ca sample but only above 0.83T(c) in the Sr sample. The paramagnetic component appears for T > 0.67T(c) in the former compared to T > 0.9T(c) in the latter. The results support recent studies that show differences in the polaronic character, and critical behavior thereof, between the two materials.