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.
Structural, chemical and low-temperature magnetic properties of lead-Free 0.6NiFe2O4-0.4Na0.5Bi0.5TiO3 magnetoelectric composite
We report on structural, chemical and low-temperature magnetic properties of lead-free 0.6NiFe2O4-0.4Na0.5Bi0.5TiO3 composite. NiFe2O4 (NFO) and Na0.5Bi0.5TiO3 (NBTO) are seen to crystallize in inverse spinel and perovskite structure, respectively. 0.6NiFe2 O4-0.4Na0.5Bi0.5TiO3 composite exhibits both NFO and NBTO phases in appropriate composition. Zero field-cooled (ZFC) and field-cooled (FC) magnetization measurements carried out from 15 to 300 K shows a large bifurcation at room temperature. ZFC and FC magnetization measurement exhibit a hump at Tm ∼\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim$$\end{document}259.5 K, indicates the possible existence of competing magnetic interactions in 0.6NiFe2 O4-0.4Na0.5Bi0.5TiO3 composite. Saturation magnetization, remnant magnetization and coercivity values are observed to increase with decreasing the temperature. Temperature-dependent saturation magnetization is fit to the Bloch’s law. Magnetocrystalline anisotropy (K1) value at various temperatures are estimated and is seen to increase from 0.23 × 104 erg/cc (at 300 K) to 0.34 × 104 erg/cc (at 15 K).
Phase characterisation of simulated high burn-up UO2 fuel
Abstract To determine the lattice constant variation with burn-up and the oxidation behaviour at high temperatures, simulated UO2-spent fuels with burn-ups up to 200 GWd tM−1 were prepared by cold pressing and sintering and characterised by X-ray diffraction analysis and thermogravimetry. The fcc-lattice parameter of the sintered samples determined at room temperature, showed a continuous decrease with the simulated burn-up. During oxidation the conversion of the simulated fuels to the (U,FP)4O9 and (U,FP)3O8-type phases was strongly delayed when the simulated burn-up exceeded 80 GWd tM−1. Also, at high burn-ups (>100 GWd tM−1), large fractions of the (U,FP)4O9-type phase remained untransformed to (U,FP)3O8 after prolonged exposure to air at 950–1000°C. This suggests a marked widening of the (U,FP)4O9-phase field when the amount of substituted uranium atoms exceeds values of about 8%.