Temperature Dependence of Magnetization, Anisotropy, and Hyperfine Fields of NiFe2–xYbxO4 ( $x = 0$ , 0.05, 0.075)
Temperature dependence of magnetization, anisotropy, and hyperfine interaction parameters of NiFe2-xYbxO4 (x = 0 , 0.05, and 0.075) was investigated, and the results are presented. All the compounds were prepared by solid-state reaction formed in cubic inverse spinel phase with the space group Fd3̅m . Increments in the lattice constant were observed upon partial substitution of Fe3+ by Yb3+. Decreased magnetic moment and increased magnetic anisotropy with Yb3+ substitution were observed through magnetization measurements, carried out at 5, 100, 200 and 300 K. Analyses of Mössbauer spectra recorded at 5 K and 300 K, revealed decreased hyperfine fields and magnetic moments at the B-site (and hence net moment) with increasing Yb3+ content. In addition all the compounds exhibited Neel-type, collinear ferrimagnetic structure.
Combustion synthesis and characterization of Sn4+ substituted nanocrystalline NiFe2O4
Abstract A series of Sn4+ substituted NiFe2O4 with general formula Ni1−xSnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, and 0.8) has been prepared by novel combustion synthetic method. The prepared compounds have been sintered at 1000 °C and evaluated for their structural and electrical properties. XRD studies reveal the synthesized compounds are nanocrystalline size with cubic structure. The Fourier transform infrared (FT-IR) spectra show the characteristic features of the synthesized ferrite compounds. The UV–vis spectra reveal the optical band gap of the synthesized compounds. The dc electrical conductivity of the compounds found to increase with increasing measuring temperature. A maximum dc electrical conductivity of 6.0 S cm−1 was obtained at a measuring temperature of 1000 °C in the composition of x = 0.8, for which the activation energy for conduction is found to be minimum.
Methanol Decomposition on Fe2O3 /MCM-48 Silica Catalyst
Fe2O3/MCM-48 silica samples are characterized by high catalytic activity and methane selectivity in methanol decomposition. The catalytically active phase is substantially changed by the reaction medium and/or hydrogen pretreatment.