Crystallization and Mössbauer Studies of Y_3-xLa_xFe₅O₁₂ (x=0.0, 0.25, 0.5, 0.75, 1.0)

Abstract

Magnetic and structural properties of garnet Y_3-xLa_xFe₅O₁₂(x= 0.0, 0.25, 0.5, 0.75, 1.0) have been studied by using X-ray diffraction, Mössbauer spectroscopy, and vibrating sample magnetometer. Polycrystalline cubic powders have been prepared by a metal-salt routed sol-gel method. Mössbauer spectra of Y_3-xLa_xFe₅O₁₂ have been taken at various temperatures ranging from 12 to 700 K. The lattice parameter increases linearly with increasing La concentration and follows Vegard's law approximately. Magnetic hyperfine fields of Y_2.5La_0.5Fe₅O₁₂ at 12 K are found to be 543 kOe (octahedral site) and 469 kOe (tetrahedral site). The values of the isomer shifts show that all of iron ions are in the ferric (Fe⁺³). The Curie temperature. T_c, is found to depend strongly upon La concentration. i.e., 578 K for x=0 and 625 K for x=0.5. The dependence of the Curie temperature suggests that the strengthen of superexchange interaction by La-O-Fe link is stronger than that by Y-O-Fe link.