Neutron diffraction and Mossbauer studies of the La/sub 0_67/Ba/sub 0_33/Mn/sub 0_99/ /sup 57/Fe/sub 0_01/O/sub 3/

Abstract

The perovskite La/sub 0.67/Ba/sub 0.33/Mn/sub 0.99//sup 57/Fe/sub 0.01/O/sub 3/ compound was prepared by wet chemical solution process at 1200/spl deg/C for 3 h. Magnetic properties of La/sub 0.67/Ba/sub 0.33/Mn/sub 0.99//sup 57/Fe/sub 0.01/O/sub 3/ were studied using X-ray diffraction, Rutherford backscattering spectroscopy (RBS), neutron diffraction, Mossbauer spectroscopy, vibrating sample magnetometry, and magnetoresistance measurements. The polycrystalline La/sub 0.67/Ba/sub 0.33/Mn/sub 0.99//sup 57/Fe/sub 0.01/O/sub 3/ had a space group Pnma of orthorhombic perovskite structure with lattice constants a/sub 0/=5.526 /spl Aring/, b/sub 0/=7.830 /spl Aring/, and c/sub 0/=5.540 /spl Aring/, respectively. A chemical composition was confirmed to be stoichiometric by RBS. The maximum magnetoresistance ratio (/spl Delta//spl rho///spl rho/(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. Mossbauer spectra of La/sub 0.67/Ba/sub 0.33/Mn/sub 0.99//sup 57/Fe/sub 0.01/O/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 0.67/Ba/sub 0.33/Mn/sub 0.99//sup 57/Fe/sub 0.01/O/sub 3/ powder. The outer sextet of Mossbauer spectra rapidly collapsed to paramagnetic phase with increasing temperature.