A. D. Al-Rawas

Structural and magnetic analysis of the transformation of Sn-doped magnetite to Sn-doped hematite by mechanical milling

Spinel-related Sn-doped Fe3O4 has been ball milled for different times up to 35h. Milling was found to transform the material to corundum-related Sn-doped α-Fe2O3. The influence of the milling time, the crystallite size, and the cationic distribution on transformation process is being analyzed with x-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. The relatively fast spinel-to-corundum structural transformation observed is associated with more Fe3+ ions being reduced to Fe2+ due to doping with Sn4+ ions.

Structural and magnetic characterization of Ti-substituted Li0.5Fe2.5O4 prepared using hydrothermal and solid-state routes

Single-phased spinel-related Ti4+-substituted Li0.5Fe2.5O4 has been synthesized by heating a mixture of hydrothermally prepared Ti4+-substituted α-Fe2O3 and Li2CO3 at 850°C (12 h). This temperature is ca. 250-350°C lower than those at which the material is conventionally prepared by the ceramic techniques. X-ray diffraction was used to analyze the evolution of the formation process and, in conjunction with Mossbauer and magnetization measurements, to determine the cation distribution of the resulting ferrite. The results imply that the Ti4+ ions substitute for Fe3+ ones at the octahedral (B) sites whilst the excess Li+ ions, required for balancing the charge in the spinel-related structure, replace Fe3+ ions at the tetrahedral (A) sites.

The influence of mechanical milling and subsequent calcination on the formation of nanocrystalline CuFe2O4

The influence of mechanical milling and subsequent calcination of a 1:1 molar mixture of CuO and α‐Fe2O3 on the formation of CuFe2O4 has been investigated with X‐ray powder diffraction (XRD) and Mossbauer spectroscopy. Pre‐milling the mixture for 160h leads to the formation of CuFe2O4 nanocrystallites at 750°C. This temperature is ca. 400–450°C lower than the temperatures at which the material is conventionally prepared using the ceramic technique that involves no pre‐milling of the reactants. Rietveld refinement of the XRD reveals the presence of both cubic and tetragonal crystal structures in the CuFe2O4 obtained.

Effect of iron on vanadium (001) strained surface magnetism

The magnetism of the vanadium (001) surface has been a controversial subject on both theoretical and experiment fronts. Both strongly ferromagnetic and paramagnetic phases were reported. We have used the first principle full-potential linearized-augmented plane waves (FP-LAPW) as implemented in WIEN2k package to study the magnetic properties of strained surfaces of vanadium films as a function of film thickness. We found that for films thicker than about 11 monolayers, the magnetism of the strained surfaces converge to a constant value of about 0.15μB. Introduction of Fe monolayers and impurities at the centre of the films affects the magnetic structure of thin films but has no influence on the surface magnetism of thicker films. For Fe monolayers positioned at the centre of thick films, the Fe atoms maintain magnetic moment of order 0.86μB, a quadruple splitting of order -0.3 mm/s and a small negative isomer shift, while an Fe impurity has vanishing hyperfine fields and magnetic moment. In addition we have varied the location of the Fe monolayer and impurity within the V films and found that their position affects the surface magnetism.

Magnetic properties of Cu/sub 1+x/M/sub x/Fe/sub 2-2x/O/sub 4/ mixed ferrites (M=Ti, Ge, 0/spl les/x/spl les/0.4)

In this paper, we investigate the magnetic properties of Cu/sub 1+x/M/sub x/Fe/sub 2-2x/O/sub 4/ mixed ferrites (M=Ti, Ge, 0/spl les/x/spl les/0.4) using X-ray diffraction, Mossbauer spectroscopy and magnetic susceptibility measurements.

The Magnetic Structure of Doped Gamma Iron Oxide

Microcrystals of doped gamma iron oxide samples with copper, magnesium, aluminium, chromium, titanium and tin have been prepared and studied by electron microscopy, x-ray powder diffraction and Mossbauer spectra recorded between 80 and 300K. The Mossbauer spectra at room temperature reveal different degrees of superparamagnetism. The hyperfme interaction parameters have been calculated using a distribution of hyperfme fields and the magnetic anisotropy constant for each sample has been deduce using either superparamagnetic relaxation or collective magnetic excitations models. The influence of the dopant on the magnetic structure of the iron oxide has been investigated.

Mössbauer Studies of the tetravalent doped Magnetite

Hydro-thermally prepared Sn4+ and Ti4+ doped -magnetite samples are characterized through scanning electron microscopy and X-ray diffraction (XRD). The samples are studied using 57Fe Mossbauer spectroscopy in the temperature range from liquid nitrogen to room temperature. The XRD pattern shows that the samples are in pure spinel structure. The room temperature Mossbauer spectrum of Sn4+ -Fe3O4 exhibits a broadened magnetic sextet superimposed on a paramagnetic doublet while the spectrum of Ti4+ -Fe3O4 is very broad with a larger paramagnetic component. However, at liquid nitrogen temperature the two spectra are similar. The influence of the doping of each cation on the iron sites is discussed.