Research Center for Computing

Sfax, Tunisia

Research Center for Computing

Sfax, Tunisia

Time filter

Source Type

Messaoui I.,University of Sfax | Messaoui I.,Research Center for Computing | Kumaresavanji M.,University of Porto | Riahi K.,University of Sfax | And 5 more authors.
Journal of Alloys and Compounds | Year: 2017

We present an investigation on structural, magnetic and magnetocaloric properties of La0.78Ca0.22−xPbxMnO3 (x = 0, 0.05 and 0.1) polycrystalline compounds prepared by conventional solid-state reaction method. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that all samples crystallize in the orthorhombic structure, with the Pnma space group. Magnetization as a function of temperature shows that all samples exhibit a paramagnetic (PM) – ferromagnetic (FM) phase transition at the Curie temperature TC which increases from 202 K to 242 K for x = 0–0.1, respectively. The magnetic-entropy changes,ΔSM, were calculated from the field dependence of magnetization data using the Maxwell's thermodynamic relation. The magnetic entropy change |ΔSM max| decreases from 6.9 J kg−1 K−1 for x = 0 to 5.53 J kg−1 K−1 for x = 0.1, while the relative cooling power (RCP) also decreases from 274 to 241 J kg−1, respectively, under an applied magnetic field of 5 T. All of the investigated manganites exhibit a second-order magnetic phase transition at TC, which is also confirmed by Arrot plot and Landau's theory. Also, by normalizing the ΔSM(T,H) curves to their respective ΔS'(=ΔSM(T)/ΔSM max) value we indicate that all these curves of the samples are collapsed onto a universal master curve. In addition, field dependence of the magnetic entropy change showing the power law dependenceΔSM max∝(μ0H)n, at the TC is also analyzed. The obtained ‘n’ values are 0.64, 0.75 and 0.97 for x = 0, 0.05 and 0.1 respectively, which confirms that our samples does not follow the mean field model. The deviation from the mean field behavior for all the samples demonstrates an existence of short-range ferromagnetic order in the samples. © 2016 Elsevier B.V.


Rejeb M.B.,University of Sfax | Rejeb M.B.,University Paris Diderot | Cheikhrouhou-Koubaa W.,University of Sfax | Koubaa M.,University of Sfax | And 5 more authors.
Journal of Superconductivity and Novel Magnetism | Year: 2015

Structural, magnetic and magnetocaloric properties of La0.65Ca0.2K0.15MnO3 powder sample elaborated by sol-gel method and annealed at several temperatures (600–1000 °C) were studied. The X-ray diffraction patterns at room temperature show that all our synthesized samples are single phase and crystallize in the distorted orthorhombic system with Pbnm space group. The scanning electron microscopy images evidence a progressive grain growth and consolidation when the annealing temperature increases. The magnetic entropy change ΔSM(T), deduced from M(H) isotherms, exhibits a maximum of 4.6 J/kg/K at 310 K under a magnetic applied field change of 5 T for the sample annealed at 1000 °C. The corresponding relative cooling power (RCP) is found to be 260 J/kg which is about 63 % of that obtained in pure gadolinium known as prototype refrigerant at room temperature. © 2014, Springer Science+Business Media New York.


Ben Rejeb M.,University of Sfax | Ben Rejeb M.,University Paris Diderot | Cheikhrouhou-Koubaa W.,University of Sfax | Koubaa M.,University of Sfax | And 2 more authors.
Journal of Superconductivity and Novel Magnetism | Year: 2015

A comparative study of the structural, magnetic, and magnetocaloric properties of La0.65Ca0.35−xKxMn03 powder samples elaborated by solid-solid and sol-gel methods is given. The X-ray diffraction patterns at room temperature show that all our synthesized samples elaborated by both methods are single phase. Samples elaborated by solid-solid method crystallize in the orthorhombic structure (Pbnm space group) for x ≤ 0.1 and in the rhombohedral one (R-3C space group) for x= 0.2, while for x = 0.15, the system begins to exhibit both phases with different proportions. The structural transition from Pbnm space group to R-3C one occurs for x > 0.15 for samples elaborated by sol-gel method. Magnetization measurements versus temperature in a magnetic applied field of 50 mT indicate that all our studied samples display a paramagnetic ferromagnetic transition with decreasing temperature. Curie temperature TC increases with increasing K content. It increases from 248 K for x = 0 to 310 K for x = 0.2 for samples elaborated by solid-solid method and from 275 K for x = 0 to 320 K for x = 0.2 for samples elaborated by sol-gel route. The maximum of the magnetic entropy change (Formula Presented.) under Δμ0H= 5 T is obtained for x = 0.2 sample elaborated by both methods. (Formula Presented.) is found to be 5.78 J/kg/K at 305 K and 7.5 J/kg/K at 325 K for sample elaborated by solid-solid and sol gel, respectively. The relative cooling power RCP exhibits a maximum value of 313 J/kg at Δμ0H= 5 T for x = 0.05 elaborated by solid-solid method and 300 J/kg at Δμ0H= 5 T for x = 0.2 elaborated by sol-gel method. © 2014, Springer Science+Business Media New York.


Bouderbala A.,University of Sfax | Makni-Chakroun J.,University of Sfax | Cheikhrouhou-Koubaa W.,University of Sfax | Koubaa M.,University of Sfax | And 4 more authors.
Ceramics International | Year: 2015

This paper reports the structural, magnetic and magnetocaloric properties of La0.7-xEuxSr0.3MnO3 (x=0.1, 0.2 and 0.3) polycrystalline manganites elaborated using the solid-state reaction at high temperatures. The X-ray powder diffraction shows that all the prepared compounds are single phase. La0.6Eu0.1Sr0.3MnO3 is crystallized in the rhombohedral symmetry, whereas a structural transition towards orthorhombic system is observed for x'0.2. Eu doping was found to induce a decrease of the Curie temperature TC from 343 K (x=0.1) to 272 K (x=0.3). All compounds undergo a large magnetocaloric effect and have consequently potential applications in magnetic refrigeration domain around room temperature. © 2015 Elsevier Ltd. and Techna Group S.r.l. All rights reserved.


Sellami-Jmal E.,University of Sfax | Marzouki A.,University of Sfax | Cheikhrouhou-Koubaa W.,University of Sfax | Cheikhrouhou A.,University of Sfax | And 2 more authors.
Journal of Superconductivity and Novel Magnetism | Year: 2015

Magnetic and magnetocaloric properties of La0.65−xxCa0.35MnO3 (≤ x ≤ 0.15) perovskite manganites were investigated. Our polycrystalline samples were elaborated using sol–gel method. The Rietveld refinement shows that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Lanthanum deficiency leads to a decrease of the unit cell volume. The surface morphology was carried out using scanning electron microscopy (SEM). Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our deficient samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. With increasing lanthanum deficiency, the Curie temperature Tc decreases from 275 K for x = 0 to 257 K and for x = 0.15. A large magnetic entropy change |ΔSM|, deduced from isothermal magnetization curves, has been observed in our samples with a peak centred around their respective transition temperature. The maximum of the magnetic entropy change |Δ(Formula Presented.) under a magnetic field change of 5 T is found to decrease from 5.11 J/kg/ K for x = 0 to 3.98 J/kg K and for x = 0.15. The relative cooling power decreases from 237.5J/kg for x = 0 to 217.4 J/kg −1 and for x = 0.15. © 2014, Springer Science+Business Media New York.


Makni-Chakroun J.,University of Sfax | Cheikhrouhou-Koubaa W.,University of Sfax | Cheikhrouhou-Koubaa W.,Research Center for Computing | Koubaa M.,University of Sfax | Cheikhrouhou A.,University of Sfax
Journal of Alloys and Compounds | Year: 2015

Abstract In this paper, we report the effect of both lanthanum and calcium (1%) on the structural and magnetic properties of nanocrystalline La0.7Ca0.3MnO3 manganite. Our powder specimens were synthesized using the sol-gel method with an annealing temperature of 850 °C. The X-ray diffraction patterns refined using Rietveld method confirms that our compounds are single phase and crystallize in the orthorhombic perovskite structure (Pbnm space group). The morphology of the samples, observed using a scanning electron microscope (SEM), reveals a spherical shape with an average grain size lower than 100 nm. Magnetization measurements versus temperature under low magnetic applied field (0.05T) show a paramagnetic-ferromagnetic transition for all compounds. The Curie temperature TC is found to increase with lacuna in both cases. In addition, the inverse of the susceptibility (1/χ) as a function of temperature indicates a deviation from the Curie Weiss lawn, signature of Griffiths phase occurrence. Experimental results for the critical β and γ exponents are typical of a behavior governed by the tricritical mean-field theory model. Using magnetization measurements as a function of magnetic applied field at several temperatures, we have deduced the magnetic entropy change, which undergoes an enlargement for both lacuna sites. The obtained results are compared to calculated ones based on the Landau theory and a good concordance is observed. © 2015 Elsevier B.V.

Loading Research Center for Computing collaborators
Loading Research Center for Computing collaborators