Neutron Diffraction and Mossbauer Studies of the La{sub}0.67Ba{sub}0.33Mn{sub}(0.99)57{sup left}Fe{sub}0.01O{sub}3

摘要

The pcrovskitc La{sub}0.67Ba{sub}0.33Mn{sub}(0.99)57{sup left}Fe{sub}{sub}0.01O{sub}3 compound was prepared by wet chemical solution process at 1200 ℃ for 3 h. Magnetic properties of La{sub}0.67Ba{sub}0.33Mn{sub}(0.99)57{sup left}Fe{sub}0.01O{sub}3 were studied using X-ray diffraction, Rutherford backscattcring speetroscopy (RBS), neutron diffraction, Mossbauer spectroscopy, vibrating sample magnetometry, and magnetoresistancc measurements. The polycrystalline La{sub}0.67Ba{sub}0.33Mn{sub}(0.99)57{sup left}Fe{sub}0.01O{sub}3 had a space group Pnma of orthorhombic perovskite structure with lattice constants a{sub}0 = 5.526 A, b{sub}0 = 7.830 A, and c{sub}0 = 5.540 A, respectively. A chemical composition was confirmed to be stoichiometric by RBS. The maximum magnetoresistance ratio (△p/p(0)) was observed at 281 K, with a magnitude of 9.5 in 1 Tesla. The Curie temperature (T{sub}C) was determined to be 345 K. MOssbaucr spectra of La{sub}0.67Ba{sub}0.33Mn{sub}(0.09)57{sup left}Fe{sub}0.01O{sub}3 were taken at various temperatures ranging from 15 to 400 K. Below 77 K, two magnetic phases were increased and showed two sharp sextets of spectra. The magnetic hyperfine fields of outer (51) and inner (49) subspectrum were H{sub}(hf) = 530 and 480 kOe, respectively. These unusual phenomena provide direct evidence of the two-magnetic phase character of the metallic state in the mixed valence of La{sub}0.67Ba{sub}0.33Mn{sub}(0.99)57{sup left}Fe{sub}0.01O{sub}3 powder. The outer sextet of Mossbauer spectra rapidly collapsed to paramagnetic phase with increasing temperature.