Neutron and Mossbauer studies of the double perovskite A2FeMoO6 (A = Sr and Ba)

The double perovskite oxide Ba2FeMoO6 has a cubic structure with a(0) = 8.0747 Angstrom, whereas Sr2FeMoO6 has a tetragonal symmetry with a(0) = 5.5729 Angstrom and c(0) = 7.9077 Angstrom. The unit-cell parameters of the strontium compound increase linearly on increasing the temperature, and the crystal symmetry changes into cubic in the paramagnetic phase (above the Curie temperature T-C). Magnetization measurements show a ferrimagnetic behavior for both materials, with T-C = 345 K for Ba2FeMoO6 and T-C = 425 K for Sr2FeMoO6, respectively. As the temperature increases toward T-C, Mossbauer spectra show line broadening and 1, 6 and 3, 4 linewidth difference because of anisotropic hyperfine field fluctuation. Temperature dependence of anisotropy energy is calculated from the relaxation rate. (C) 2002 Elsevier Science B.V. All rights reserved.