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.
Structure-Property Correlations of Carbon and Nitrogen Incorporated NiFe2O4
In this paper, carbon (C) and nitrogen (N) were incorporated into the interstitial sites of nickel (Ni) ferrite lattice. Structural studies of the incorporated NiFe<sub>2</sub>O<sub>4</sub> (NFO) samples (C-NFO and N-NFO) using X-ray diffraction revealed changes in the values of the lattice parameter, bond angle, and bond length. Raman spectroscopic studies revealed shifts in peak positions of <inline-formula> <tex-math notation="LaTeX">${\text{E}}_{g}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$\text{T}_{2g}$ </tex-math></inline-formula> (3) vibrational modes of the spectra. Magnetization measurements at 20 and 300 K using vibrating sample magnetometer showed decrease in the values of <inline-formula> <tex-math notation="LaTeX">$M_{s}$ </tex-math></inline-formula> upon incorporation of C/N (<inline-formula> <tex-math notation="LaTeX">$2.3~\mu _{B}$ </tex-math></inline-formula>/f.u. of C-NFO and <inline-formula> <tex-math notation="LaTeX">$2.4~\mu _{B}$ </tex-math></inline-formula>/f.u. of N-NFO from <inline-formula> <tex-math notation="LaTeX">$2.9~\mu _{B}$ </tex-math></inline-formula>/f.u. of NFO, at 20 K). An increase in intrinsic coercive field (<inline-formula> <tex-math notation="LaTeX">$H_{c}$ </tex-math></inline-formula>) value (18.2 Oe of C-NFO and 14.2 Oe of N-NFO from 5.2 Oe of NFO, at 20 K) was also observed. However, a reduction in the value of first-order cubic magnetocrystalline anisotropy constant (<inline-formula> <tex-math notation="LaTeX">$K_{1}$ </tex-math></inline-formula>) was observed upon incorporation of C/N. Microstructural analysis using scanning electron microscopic images revealed modifications in the shape and the size of the grains. The average grain size was found to be reduced upon C/N incorporation (~600 nm of NFO, while ~550 nm of C-NFO and ~400 nm of N-NFO).
Mechanochemically synthesized nano-dimensional iron–cobalt spinel oxides as catalysts for methanol decomposition
Abstract Iron–cobalt spinel oxide nanoparticles with different Fe/Co ratios have been prepared by the combination of chemical precipitation with simultaneous ultrasonic treatment and subsequent mechanical milling. For comparison, their analogues obtained by thermal synthesis were also studied. Phase composition and structural properties of iron–cobalt oxides are investigated by X-ray diffraction and Moessbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. A well-defined effect of the preparation method and Fe/Co ratio on the reduction and catalytic properties of iron–cobalt samples is established.