Papers by DR. Mahmoud Abdelrazek Ahmida
المجلة الليبية العالمية, Sep 12, 2022
ChemInform, Jun 1, 2010
The new intermetallic title compound is synthesized from the elements by high-frequency induction... more The new intermetallic title compound is synthesized from the elements by high-frequency induction heating at 1250 K (10 min), followed by annealing at 1000 K (30 min). The samples are characterized by single crystal XRD, magnetic measurements, XANES, and 151 Eu Moessbauer spectroscopy. Eu2AgGe3 crystallizes in the orthorhombic space group Fddd with Z = 16 (Ba 2 LiSi 3-type structure). The structure contains stacked arrays of hexagonal [Ag3Ge3] units with Eu sandwiched between these networks. The compound exhibits a structural phase transition from orthorhombic to hexagonal (space group P6/mmm) above 477 K and an unusual reversible transition to the original orthorhombic phase at around 718 K. Eu2AgGe3 shows paramagnetic behavior above 100 K and weak ferromagnetic interactions below 80 K.
The intermetallic series EuCu 2 (Ge 1−x Si x) 2 crystallizing in the tetragonal ThCr 2 Si 2type s... more The intermetallic series EuCu 2 (Ge 1−x Si x) 2 crystallizing in the tetragonal ThCr 2 Si 2type structure combines the antiferromagnetic (AF) compound EuCu 2 Ge 2 (T N = 14 K) with the homogeneous intermediate valent (IV) compound EuCu 2 Si 2. Thus, the system offers the opportunity to investigate charge fluctuations across a quantum phase transition (QPT) at x ≈ 0.7. Such a study is of fundamental interest in view of the observation of pressure-induced superconductivity in CeCu 2 Si 2 and Eu metal, where superconductivity could be mediated by critical charge fluctuations. To gain a microscopic insight into the change of the magnetic and valence state and their interplay across the QPT, we have performed systematic 151 Eu Mössbauer effect and x-ray diffraction measurements on EuCu 2 (Ge 1−x Si x) 2 as a function of concentration (0 ≤ x ≤ 1) as well as external pressure at different temperatures (4.2 to 300 K). The analysis of the results shows that the collapse of AF ordering for x > 0.5 is associated with a simultaneous sharp increase of the valence state of Eu towards a homogeneous intermediate valence state. Both values of the Eu mean valence (ν) at/near the QCP induced by doping or external pressure are found to be enhanced (ν ≈ 2.45), indicating enhanced charge fluctuations. The nature of valence fluctuations at/near the QCP and its coupling to the lattice is discussed.
Journal of Applied Mathematics and Physics, 2019
In this paper, an overview of the theory of Mössbauer effect is covered, and the main hyperfine i... more In this paper, an overview of the theory of Mössbauer effect is covered, and the main hyperfine interactions parameters which affect the shape of the resultant Mössbauer spectrum are explained and illustrated as well. In principle, Mössbauer effect applies to any and all nuclides, but in practice, certain ideal properties are desirable; that is, the conditions for recoil-free emission and absorption of gamma rays must be optimized. Therefore, briefly discussed in this review, one of the most commonly used for practical and fundamental studies the 151 Eu Mössbauer isotope. Also, the intermediate valence phenomena and their theoretical treatments are briefly discussed.
Zeitschrift für anorganische und allgemeine Chemie, Sep 1, 2006
Journal of Physics: Condensed Matter, Feb 19, 2016
We synthesized a high-quality sample of the boride Eu4Pd29+x B8 (x = 0.76) and studied its stru... more We synthesized a high-quality sample of the boride Eu4Pd29+x B8 (x = 0.76) and studied its structural and physical properties. Its tetragonal structure was solved by direct methods and confirmed to belong to the Eu4Pd29B8 type. All studied physical properties indicate a valence fluctuating Eu state, with a valence decreasing continuously from about 2.9 at 5 K to 2.7 at 300 K. Maxima in the T dependence of the susceptibility and thermopower at around 135 K and 120 K, respectively, indicate a valence fluctuation energy scale on the order of 300 K. Analysis of the magnetic susceptibility evidences some inconsistencies when using the ionic interconfigurational fluctuation (ICF) model, thus suggesting a stronger relevance of hybridization between 4f and valence electrons compared to standard valence-fluctuating Eu systems.
Inorganic Chemistry, Feb 10, 2011
Inorganic Chemistry, Dec 9, 2009
Pure EuC(2), free of EuO impurities, was obtained by the reaction of elemental europium with grap... more Pure EuC(2), free of EuO impurities, was obtained by the reaction of elemental europium with graphite at 1673 K. By means of synchrotron powder diffraction experiments, the structural behavior was investigated in the temperature range from 10 to 1073 K. In contrast to former results, EuC(2) crystallizes in the ThC(2) type structure (C2/c, Z = 4) at room temperature. A tetragonal modification (I4/mmm, Z = 2) is only observed in a very small temperature range just below the transition to a cubic high-temperature modification (Fm3m, Z = 4) at 648 K. DTA/TG investigations confirm these results. According to Raman spectroscopy, EuC(2) contains C(2)(2-) ions (nu(C[triple bond]C) = 1837 cm(-1)). The divalent character of Eu is confirmed by the results of magnetic susceptibility measurements and (151)Eu Mossbauer spectroscopy. In these measurements a transition to a ferromagnetic state with T(C) = 15 K is observed, which is in reasonable agreement with literature data. Above T(C) EuC(2) is a semiconductor according to measurements of the electric resistivity vs temperature, again in contrast to former results. Around T(C) a sharp maximum of the electric resistivity vs temperature curve was observed, which collapses on applying external magnetic fields. The observed CMR effect (colossal magnetoresistance) is much stronger than that reported for other EuC(2) samples in the literature. These investigations explicitly show the influence of sample purity on the physical and even structural properties of EuC(2).
Instrumentation Mesure Métrologie
A preliminary investigation of some factors which can affect the reflected light intensity from g... more A preliminary investigation of some factors which can affect the reflected light intensity from granular and icing sugar has been carried out using an end viewing hemispherical tip probe. It is found that the reflectance is strongly dependent on the size range of the sugar particles, with the finer particles being more reflective. This property could be very useful in monitoring segregation in mixtures of mono-colored powders having different size distributions. Force applied to the probe will also affect the intensity readings. A layered mixture of sugar and slag powder was used to compare the sampling performance of the above probe with a side viewing wedge tip probe. Calibration curves for reflected light intensity versus percent slag concentration are obtained for two types of slag.
European Journal of Engineering and Technology Research, Nov 21, 2022
International Science Review, 2021
In the steam boiler industrial sector, pressure and temperature of the water tube are the two mai... more In the steam boiler industrial sector, pressure and temperature of the water tube are the two main factors that affect the safety and efficiency of a steam boiler. Explosions may be occurring because of a sudden drop in pressure without a corresponding drop in temperature. Therefore, understanding the temperature distribution of the water tube boiler is essential to control the failure and explosion of the boiler. Once the temperature distribution is known than the limiting factors that affect the water tube life such as the maximum allowable pressure can be determined. ANSYS software will be used to determine the temperature distribution in the water tube of a utility boiler during operation at elevated inlet water and furnace temperature. The theory of axisymmetric has been utilized since the water- tube is cylindrical in shape. In axisymmetric theory, a three-dimensional cylindrical problem like a water tube can be reduced to two-dimensional by ignoring the circumferential ...
Physical Review B, 2020
Iṣlâḥ ibâḍite et intégration nationale : vers une communauté mozabite ? (1925-1964) Résumé. Const... more Iṣlâḥ ibâḍite et intégration nationale : vers une communauté mozabite ? (1925-1964) Résumé. Constitué en mouvement social au cours des années 1930, principalement sous la direction du cheikh Bayyûḍ, l'iṣlâḥ constitue un élément majeur de l'histoire et de la mémoire du Mzab à l'époque contemporaine. Si les oulémas réformistes ont principalement affirmé leur action dans le domaine éducatif, ils se sont aussi engagés dans une action politique, à la fois à l'échelle locale, par la conquête des institutions « traditionnelles » du Mzab et, à l'échelle algérienne, en entrant ouvertement dans le jeu institutionnel colonial à partir de 1947. Ce mouvement religieux et les actions politiques qu'il a générées se sont accompagnés d'une réflexion sur le rapport de l'ibadisme aux autres madhâhib et sur la place des berbères dans l'histoire du Maghreb arabe et de l'Algérie. Ainsi par leur action politique, les oulémas réformistes se sont affirmés comme les leaders d'une communauté qu'ils construisaient en réinterprétant les institutions traditionnelles. Au même moment, par leur réflexion dans le domaine de l'historiographie, ils ont oeuvré à articuler les identités ibâḍite et mozabite à celle, en construction, de la nation algérienne. Dans cet article, je me propose d'interroger le rôle que les oulémas réformistes ont joué dans ce processus double, politique et intellectuel, de construction de la population ibâḍite et mozabite en communauté politique, processus qui a accompagné son entrée dans l'ensemble algérien. Pour cela je m'appuierai sur certains textes des oulémas de l'iṣlâḥ et de l'historiographie du mouvement, ainsi que sur les archives coloniales (ANOM) et celles des Missionnaires d'Afrique (Pères Blancs, Rome).
Journal of Applied Mathematics and Physics, 2019
In this paper, an overview of the theory of Mössbauer effect is covered, and the main hyperfine i... more In this paper, an overview of the theory of Mössbauer effect is covered, and the main hyperfine interactions parameters which affect the shape of the resultant Mössbauer spectrum are explained and illustrated as well. In principle, Mössbauer effect applies to any and all nuclides, but in practice, certain ideal properties are desirable; that is, the conditions for recoil-free emission and absorption of gamma rays must be optimized. Therefore, briefly discussed in this review, one of the most commonly used for practical and fundamental studies the 151 Eu Mössbauer isotope. Also, the intermediate valence phenomena and their theoretical treatments are briefly discussed.
The intermetallic series EuCu 2 (Ge 1−x Si x) 2 crystallizing in the tetragonal ThCr 2 Si 2type s... more The intermetallic series EuCu 2 (Ge 1−x Si x) 2 crystallizing in the tetragonal ThCr 2 Si 2type structure combines the antiferromagnetic (AF) compound EuCu 2 Ge 2 (T N = 14 K) with the homogeneous intermediate valent (IV) compound EuCu 2 Si 2. Thus, the system offers the opportunity to investigate charge fluctuations across a quantum phase transition (QPT) at x ≈ 0.7. Such a study is of fundamental interest in view of the observation of pressure-induced superconductivity in CeCu 2 Si 2 and Eu metal, where superconductivity could be mediated by critical charge fluctuations. To gain a microscopic insight into the change of the magnetic and valence state and their interplay across the QPT, we have performed systematic 151 Eu Mössbauer effect and x-ray diffraction measurements on EuCu 2 (Ge 1−x Si x) 2 as a function of concentration (0 ≤ x ≤ 1) as well as external pressure at different temperatures (4.2 to 300 K). The analysis of the results shows that the collapse of AF ordering for x > 0.5 is associated with a simultaneous sharp increase of the valence state of Eu towards a homogeneous intermediate valence state. Both values of the Eu mean valence (ν) at/near the QCP induced by doping or external pressure are found to be enhanced (ν ≈ 2.45), indicating enhanced charge fluctuations. The nature of valence fluctuations at/near the QCP and its coupling to the lattice is discussed.
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Papers by DR. Mahmoud Abdelrazek Ahmida