A. Rais

Studies on Al Kidirate and Kapoeta meteorites

Mössbauer spectroscopy (20–300 K), magnetic susceptibility measurements (77–350 K), scanning electron microscopy and X-ray diffraction experiments have been performed on two meteorite samples: one from an old fall (Kapoeta) and another from a very recent fall (Al Kidirate). The two specimens differ in their mineralogy. Chondrules appear to be absent in Kapoeta and it is probably a pyroxene-plagioclase achondrite with ferrohypersthene as the most abundant mineral. On the other hand, the Al Kidirate meteorite is an ordinary chondrite and the specimen consists of olivine, orthopyroxene, troilite and kamacite. The Mössbauer measurements confirm the above characterization, showing a paramagnetic doublet for the Kapoeta sample and at least two paramagnetic doublets and magnetic sextets for the Al Kidirate specimens. The former were assigned to Fe in pyroxene sites, while the latter was assigned to Fe in pyroxene, olivine, Fe-S and Fe-Ni alloys. The difference in the mineralogy of the two meteorites has also been reflected in the temperature-dependent magnetic susceptibility. The magnetization and the hyperfine interaction parameters will be discussed in relation to the mineralogy.

Identification of Corrosion Products Due to Seawater and Fresh Water

Mossbauer and X-ray diffraction (XRD) measurements were performed on corrosion products extracted from the inner surface of two different metal tubes used in a desalination plant in Oman. One of the tubes corroded due to the seawater while the second was corroded due to fresh water. The corrosion products thus resulted due to seawater were scrapped off in to two layers, the easily removable rust from the top is termed outer surface corrosion product and the strongly adhered rust as internal corrosion product. The Mossbauer spectra together with the XRD pattern of the outer surface showed the presence of magnetite (Fe3O4), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), goethite (α-FeOOH) and hematite (Fe2O3). The inner surface however showed the presence of akaganite, goethite, and magnetite. On the other hand, the corrosion products due to the fresh water showed only the presence of goethite and magnetite. The mechanism of the corrosion process will be discussed based on the significant differences between the formation of the iron components of the corrosion products due to seawater and the fresh water.

Mössbauer and magnetic investigation of Fe-Mn alloy

Mössbauer, X-ray, magnetization and susceptibility measurements were performed to study Fe100−xMnx,x=5, 15, 39, 50. The different phases of Fe-Mn were identified, and hyperfine interaction parameters and average magnetic moments of some samples were determined. The average hyperfine field and average magnetic moment decrease asx increases. The influence of the Mn neighbourhood on the derived parameters is discussed in the light of calculations using the first principle discrete variational method in the local density approximation.

Lattice parameters and magnetic properties of F-Sb-Te alloys with nickel arsenide structure

Abstract Single phase Fe-Sb-Te alloys with NiAs-type structure have been prepared in the composition range from Fe 1.173 Sb to Fe 1.105 Te and characterized by X-ray diffraction. Magnetic susceptibility measurements have been taken on these alloys in the temperature range from 77 up to 500 K. The lattice parameters show a linear variation with the alloy composition in the Sb-rich side but an anomalous change for the binary Fe 1.105 Te. The effective magnetic moments extracted from the susceptibility variations with temperature show a similar anomaly at approximately the same composition. These are discussed in terms of a model of additive magnetic moments of different atomic species.

Magnetic susceptibilities of chromites from Oman

MINERALOGICAL and physical characteristics of natural chromites from Oman ophiolites have been recently investigated using M6ssbauer spectrocopy (MS), X-ray diffraction (XRD) and Scanning electron microscopy (SEM) by Al-Alawi et al. (1996). From the MS analysis together with the SEM data, they derived the chemical formula for specimens collected from two separate chromite deposits named Tawiyah (15 km NNW of Nakhal) and Khobar (on the Luzugh-Semail road) and proposed respectively as follows:

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.

Modeling of optical and geometrical data of Al thin films on GaAs

In this paper, we show how optical excitation of surface plasmons (SPs) can be used to obtain optical and geometrical parameters of specific layers in multilayered thin film systems. The optimum coupling phenomenon between incoming p-polarized light and SPs appears as a minimum in the reflectance that is calculated using a standard matrix formalism. The sensitive dependence of the reflectance minimum on optical and geometrical parameters suggests that they can be determined accurately by fitting the measured attenuated total reflectance (ATR) to the matrix-calculated reflectance using the Simplex minimization method. The procedure is applied to the multilayered system: Prism/Air gap/Al-oxide/Al/GaAs. At fixed incident light wavelength, the fitting parameters are the Al-oxide optical constant and the thickness of the air gap, Al-oxide and Al layers. Fortran codes are implemented for the reflectance calculations and the fitting procedures. The results show that the theoretical reflectance fits well the measured ATR at 633-nm wavelength. Moreover, the modeled Al-oxide optical constant at this wavelength agrees well with the literature. However, the reflectance fits are less good at 590- and 458-nm wavelengths and their modeled Al-oxide optical constants show a dispersion effect in disagreement with the literature. The modeled geometrical parameters are consistent with the nominal values.

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.

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.