57Fe Mõssbauer Experiments of Doped (La0¢67Ba0¢33)(Mn0¢9Fe0¢1)O3⁄

We report on Mõssbauer efiect (ME) experiments on the compound (La0 ¢67 Ba0 ¢33)(Mn0 ¢9 Fe0 ¢1)O3 with the simple perovskite-like structure in the range from 4 ¢2 to 300 K. From 190 to 300 K the spectra are described by a single quadrupole split doublet with a total splitting of e2qQ=2 = 0 ¢38 mm s¡1. This indicates that the local environment of the Fe3+ ions is not cubic, in contrast to the X-ray difiraction result on the same sample. At 4 ¢2 and 25 K complex hyperflne (hf) split spectra are obtained. At least eight magnetically split subspectra with difierent hf flelds must be used for describing these spectra adequately. From about 50 K up to 150 K the ME spectra re°ect a relaxation process, indicating that the Fe moments °uctuate with frequencies in the range of the Larmor frequency in this temperature range. By describing the latter ME spectra by a magnetically split six-line spectrum with average hf flelds and strongly broadened linewidths, the Fe moments are found to order below about 110 K. This value is much lower than the Curie temperature of Tc = 190 K obtained from our magnetisation measurements. The °uctuations of the Fe moments observed down to low temperatures might be responsible for the fact that the metal{semiconducting transition, which usually occurs at T c according to the double exchange model, is shifted from Tc = 190 K down to 140 K. 1