Mohamed Elzain - Academia.edu (original) (raw)

Papers by Mohamed Elzain

Physica E: Low-dimensional Systems and Nanostructures, 2008

... [12] SA Maier. Opt. Commun., 258 (2006), p. 295. [13] A. Boltasseva, T. Nikolajsen, K. Leosso... more ... [12] SA Maier. Opt. Commun., 258 (2006), p. 295. [13] A. Boltasseva, T. Nikolajsen, K. Leosson, K. Kjaer, MS Larsen and SI Bozhevolnyl. J. Lightwave Technol., 23 (2005), p. 413. ... [16] MC Marco de Lucas, B. Jacquier, E. Lebrasseur, JY Rivoire and B. Varrel. Rev. Sci. ...

Journal of Physics: Conference Series, 2010

Journal of Physics: …, 2010

Single-phased spinel-related Ti 4+-substituted Li 0.5 Fe 2.5 O 4 has been synthesized by the heat... more Single-phased spinel-related Ti 4+-substituted Li 0.5 Fe 2.5 O 4 has been synthesized by the heating mixture of hydrothermally prepared Ti 4+-substituted α-Fe 2 O 3 and Li 2 CO 3 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 Mössbauer and magnetization measurements, to determine the cation distribution of the resulting ferrite. The results imply that the Ti 4+ ions substitute for Fe 3+ ones at the octahedral (B) sites whilst the excess Li + ions, required for balancing the charge in the spinel-related structure, replace Fe 3+ ions at the tetrahedral (A) sites.

... Proceedings Editors: Michael Thomas Terry Gibb John Williams ICAME2001 ... and AF Pasquevich ... more ... Proceedings Editors: Michael Thomas Terry Gibb John Williams ICAME2001 ... and AF Pasquevich p. 153 57Fe MOSSBAUER STUDY OF NOVEL SERIES OF INTERMETALLIC COMPOUNDS R3(Fe,^Cox)29_yTy (R = Nd, Tb, Dy; T = Ti, V) O. Kalogirou, C. Sarafidis, T. Bakas and ...

Physica E-low-dimensional Systems & Nanostructures, 2008

Temperature dependent Mössbauer studies together with X-ray diffraction (XRD) and scanning electr... more Temperature dependent Mössbauer studies together with X-ray diffraction (XRD) and scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray microanalysis have been performed on an old fall achondrite meteorite named Kapoeta. Pyroxene with a variable composition ranging from bronzite through ferrohypersthene with intermediate pigeonite has been identified as the only iron bearing mineral. The Mössbauer spectra show Fe2+ present in two different crystallographic sites M1 and M2. The population ratio Fe2+(M1)/Fe2+(M2) derived from the relative area of the subspectra reveals the degree of cation disorder.

Hyperfine Interactions

In this work we present Fe57 Mössbauer study for the alloy system Fe0.7−xSi0.3Mnx, where 0x0.3.... more 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.

Nanoscale Research Letters, 2015

We report investigation on properties of multiwall carbon nanotubes (mCNTs) containing Ni residua... more We report investigation on properties of multiwall carbon nanotubes (mCNTs) containing Ni residuals before and after encapsulation of zinc ferrite nanoparticles. The pristine tubes exhibit metallic character with a 0.3 eV reduction in the work function along with ferromagnetic behavior which is attributed to the Ni residuals incorporated during the preparation of tubes. Upon encapsulation of zinc ferrite nanoparticles, 0.5 eV shift in Fermi level position and a reduction in both the π band density of state along with a change in the hybridized sp(2)/sp(3) ratio of the tubes from 2.04 to 1.39 are observed. As a result of the encapsulation, enhancement in the σ bands density of state and coating of the zinc ferrite nanoparticles by the internal layers of the CNTs in the direction along the tube axis is observed. Furthermore, Ni impurities inside the tubes are attracted to the encapsulated zinc ferrite nanoparticles, suggesting the possibility of using these particles as purifying agents for CNTs upon being synthesized using magnetic catalyst particles. Charge transfer from Ni/mCNTs to the ZnFe2O4 nanoparticles is evident via reduction of the density of states near the Fermi level and a 0.3 eV shift in the binding energy of C 1 s core level ionization. Furthermore, it is demonstrated that encapsulated zinc ferrite nanoparticles in mCNTs resulted in two interacting sub-systems featured by distinct blocking temperatures and enhanced magnetic properties; i.e., large coercivity of 501 Oe and saturation magnetization of 2.5 emu/g at 4 K.

$Research paper thumbnail of Mn fraction substitutional site and defects induced magnetism in Mn-implanted 6H-SiC$

Journal of Alloys and Compounds, 2015

a b s t r a c t n-type 6H-SiC (0 0 0 1) single crystal substrates were implanted with three fluen... more a b s t r a c t n-type 6H-SiC (0 0 0 1) single crystal substrates were implanted with three fluences of manganese (Mn + ) ions: 5 Â 10 15 , 1 Â 10 16 and 5 Â 10 16 cm À2 with implantation energy of 80 keV at 365°C to stimulate dynamic annealing. The samples were characterized using Rutherford backscattering channeling spectroscopy (RBS/C), high-resolution X-ray diffraction technique (HRXRD), and Superconducting Quantum Interference Device (SQUID) techniques. Two main defect regions have been identified using RBS/C spectra fitted with the McChasy code combined to SRIM simulations. Intermediate defects depth region is associated with vacancies (D V ) and deeper defect (D N ) essentially related to the Si and C interstitial defects. The defect concentration and the maximum perpendicular strain exhibit similar increasing trend with the Mn + fluence. Furthermore, the amount of Mn atoms at Si substitutional sites and the corresponding magnetic moment per Mn atom were found to increase with increasing Mn fluence from 0.7 l B to 1.7 l B and then collapsing to 0.2 l B . Moreover, a strong correlation has been found between the magnetic moment and the combination of both large D V /D N ratio and high Mn at Si sites. These results are corroborated by our ab initio calculations considering the most stable configurations showing that besides the amount of Mn substituting Si sites, local vacancy-rich environment is playing a crucial role in enhancing the magnetism.

Journal of Physics: Conference Series, 2015

ABSTRACT We investigated the local magnetic properties of Mn-doped 6H-SiC using ab-initio calcula... more ABSTRACT We investigated the local magnetic properties of Mn-doped 6H-SiC using ab-initio calculations. The calculation addresses various configurations of Mn single impurity and Mn dimers at substitutional/interstitial sites with and without neighboring Si and C vacancies. The calculations showed that a substitutional Mn atom at either Si or C sites possesses a magnetic moment. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. Our calculations show that antiferromagnetically coupled pair of Mn atoms at Si sites with neighboring C vacancy is magnetically more stable. The calculation also showed that the interstitial sites with C neighbors are more favorable than those with Si and the magnetic moment for Mn at interstitial sites is less compared to that at substitutional sites. The results are used to understand the experimental data obtained on Mn- 6H-SiC for various Mn concentrations.

Materials Research Bulletin, 2015

ABSTRACT The influence of ball milling and subsequent sintering of a 3: 1 molar mixture of SrCO3 ... more ABSTRACT The influence of ball milling and subsequent sintering of a 3: 1 molar mixture of SrCO3 and α-Fe2O3 on the formation of Sr3Fe2O7-δ double perovskite is investigated with different analytical techniques. Milling the mixture for 110 h leads to the formation of SrCO3-α-Fe2O3 nanocomposites and the structural deformation of α-Fe2O3 via the incorporation of Sr2+ ions. Subsequent sintering of the pre-milled reactants’ mixture has led to the partial formation of an SrFeO3 perovskite-related phase in the temperature range 400ºC-600ºC. This was followed by the progressive development of an Sr3Fe2O7-δ phase that continued to increase with increasing sintering temperature until of a single-phased nanocrystalline Sr3Fe2O7-δ phase was attained at 950ºC (12 h). This temperature is ~ 350 ºC lower than the temperature at which the material is prepared conventionally using the ceramic method. The evolution of different structural phases during the reaction process is discussed. ietveld refinement of the X-ray diffraction data shows a value of 0.60 for the oxygen deficiency δ, in consistency with the Fe3+/Fe4+ ratio derived from the 57Fe Mössbauer data recorded at both 300 K and 78 K. The Mössbauer data suggests that the Sr3Fe2O6.4 nanoparticles are superparamagnetic with blocking temperatures below 78 K. The surfaces of the Sr3Fe2O6.4 nanoparticles were shown to have a complex structure and composition relative to those of their cores with traces of SrCO3, SrO and SrFeO3-δ being detected.

We have studied the Fe-X (X = B, C and N) systems, represented by clusters of atoms, using the di... more We have studied the Fe-X (X = B, C and N) systems, represented by clusters of atoms, using the discrete variational method. The calculated properties at the cluster's central site are compared with experimental and other theoretical results. The local magnetic, contact magnetic hyperfine field and contact charge density at the central site were calculated for different locations of impurities in bct, fcc and for intermediate structures. The calculated properties for N impurities are somehow different from those obtained for B and C impurities. The reasons behind the large average magnetic moment at Fe site in Fe-N systems were not convincingly clarified, however, distinctive features related to these systems are pointed out.

We report on real time fluctuations and chain-like assemblies of copper oxide (CuO) nanorods at t... more We report on real time fluctuations and chain-like assemblies of copper oxide (CuO) nanorods at the liquid-liquid interface. The rods were found to transform into whiskers and 3D structures upon spincasting on silicon substrates. The results of atmospheric scanning electron microscope (ASEM) and atomic force microscopy (AFM) provide compelling evidence that both the transformation and the assembly are driven by interaction between the π electrons of toluene and CuO nanorods, and to a smaller extent by breath figure dynamics rather than the solution-liquid-solid mechanism that was previously believed to account for whisker formation. These results open up a way for studying and understanding the dynamics of nanoparticles at liquid-liquid interfaces.

The spin polarized discmte variational method in the local density a p proximation is used to cal... more The spin polarized discmte variational method in the local density a p proximation is used to calculate the electronic structure of 15-atom dusters repre senting Fe-Cr alloys. The Fe local moment at the central site is found to depend on the orientation (relative to that of Fe) of the Cr moment in the neighbouring shell. For parallel orientation, the Fe moment decreases with increasing number of Cr atoms while it increases slightly in the antiparallel case. The Cr moment dependence on Cr in the N N shell is also determined. These results are incorporated in an approximate relation leading to computation of average moments, and comparison to experimental data is made. It is concluded that there is ferromagnetic coupling hetween Fe and Cr in the Cr-rich region.