Moessbauer studies of La-Ca-Mn-Fe-O compounds

Magnetic and structural properties of La0.67Ca0.33Mn1-xFexO3 (x = 0.0 to 0.05) powders have been studied with Moessbauer spectroscopy, vibrating sample magnetometer (VSM), and X-ray diffraction. A single phase of the polycrystalline perovskite powder has been prepared using the metal salt routed sol-gel method. The results of X-ray measurements show that there was no appreciable change in the value of the lattice parameter when a small amount of iron was added. However, the results of Moessbauer and VSM measurements demonstrate that the Curie temperature of the perovskite powder (x = 0.05) has decreased from 282 K to 180 K and that the large decrease of the saturation magnetization from 84 emu/g at 77 K has been observed as 57Fe (x = 0.05) was introduced into the compound. Moessbauer spectra of La0.67Ca0.33Mn1-xFexO3 powders have been taken at various temperatures ranging from 4.2 K to room temperature. It is observed that the patterns of the spectra were changed from a doublet line to a 6-line as the temperature decreased. Four experimental magnetic hyperfine fields at 4.2 K are found to be 465, 514, 489 and 417 kOe and isomer shifts at 4,2 K are 0.37, 0.38, 0.35 and 0.29 mm/s. These isomer shifts indicate that the valence state of Fe ions is ferric (Fe3+), which are relative to α-Fe at room temperature. It should be noted that superparamagnetic relaxation begins at 37 K. (author)