H. M. Widatallah

On the Generalized Continuity Equation

A generalized continuity equation extending the ordinary continuity equation is found using quanternions to show it is compatible with Dirac, Schrodinger, Klein–Gordon and diffusion equations. This generalized equation is Lorentz invariant. The transport properties of electrons are found to be governed by the Schrodinger-like equation and not by the diffusion equation.

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.

Mössbauer Studies of Fe0.7−xSi0.3Mnx Alloys

In this work we present Fe57 Mössbauer study for the alloy system Fe0.7−xSi0.3Mnx, where 0≤x≤0.3. Mössbauer spectroscopic results show that all the samples studied are magnetically ordered at 77 K, and at room temperature, except for x=0.3 at 300 K where it shows paramagnetic behavior. The average magnetic hyperfine field is found to decrease with increasing the manganese concentration at 77 K and 300 K. The average magnetic hyperfine field is found to increase with decreasing the temperature from 300 K to 77 K for all samples under investigation. The average isomer shift is found to decrease with increasing the manganese concentration.

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.

Mössbauer Studies of Fe 0.7− x Si 0.3 Mn x Alloys

In this work we present Fe57 Mossbauer study for the alloy system Fe0.7− x Si0.3Mn x , where 0 ≤ x ≤ 0.3. Mossbauer spectroscopic results show that all the samples studied are magnetically ordered at 77 K, and at room temperature, except for x = 0.3 at 300 K where it shows paramagnetic behavior. The average magnetic hyperfine field is found to decrease with increasing the manganese concentration at 77 K and 300 K. The average magnetic hyperfine field is found to increase with decreasing the temperature from 300 K to 77 K for all samples under investigation. The average isomer shift is found to decrease with increasing the manganese concentration.