Moessbauer Studies of Perovskite La_(0.67)Ca_(0.33)Mn_(1-x)Fe_xO_3

摘要

The perovskite of La_(0.67)Ca_(0.33)Mn_(1-x)~(57)Fe_xO_3 (x = 0, 0.01, 0.03, and 0.05) compounds have been studied with Moessbauer spectroscopy, vibrating sample magnetometer (VSM), and x-ray diffractometer. The La_(0.67)Ca_(0.33)Mn_(1-x) ~(57)Fe_xO_3 powders have been prepared by sol-gel processing method. Moessbauer spectra of La_(0.67)Ca_(0.33)Mn_(1-x) Fe_xO_3 powders have been taken at various temperatures ranging from 4.2 K to room temperature. The line width of each Lorentzian 6-line at 4.2 K was broaden in proportion as doped ~(57)Fe increased. Analysis of ~(57)Fe Moessbauer spectrum data has considered nearest-neighbor interactions and anisotropic hyperfine field fluctuation. Analysis of ~(57)Fe Mossbauer data in terms of the local configurations of Mn atoms has permitted the influence of the magnetic hyperfine interaction to be monitored. The values of the isomer shifts show that all the iron ions are in the ferric (Fe~(3+)) state. The temperature dependence of the resistance under zero and 10 kOe applied magnetic field shown that a semiconductor-metal transition temperature, T_(SC-M), decreased from 274 to 155 K in proportion as doped ~(57)Fe increased. The relative magnetoresistance (MR) of the La_(0.67)Ca_(0.33)Mn_(0.97)~(57)Fe_(0.03)O_3 is about 45 % at the T_(SC-M)= 210 K.