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Kairouan, Tunisia

M'Nassri R.,Kairouan University | M'Nassri R.,University of Monastir | Chniba-Boudjada N.,CNRS Neel Institute | Cheikhrouhou A.,University of Sfax
Journal of Alloys and Compounds | Year: 2015

The structure, critical exponents and magnetocaloric effect (MCE) of Pr0.4Eu0.2Sr0.4MnO3 were investigated in detail. A solid state reaction method was used in the preparation phase. Phase purity, structure, size, and crystallinity were investigated using XRD and SEM. The Reitveld refinement of XRD pattern shows that the sample adopts an orthorhombic structure with Pnma space group. Analyzing temperature and field dependences of magnetization around the ferromagnetic-paramagnetic transition reveals the sample undergoing the second-order magnetic phase transition with the critical parameters TC ∼ 238 K, β = 0.310(3), γ = 1.264(1) and δ = 4.761(9).The exponents are close to 3D-Ising values. This reflects an existence of ferromagnetic short-range order in our sample. With these values one can scale the magnetization below and above TC following a single equation of state. However, it is noteworthy that the scaling relations are obeyed indicating renormalization of interactions around the TC. Temperature variation in effective exponents βeff and γeff resemble with those for disordered ferromagnet. In the vicinity of TC, the magnetic entropy change ΔS reached maximum values of 2.80 and 5.32 J/kg K under magnetic field variations of 2 and 5 T, respectively. The field dependence of the magnetic entropy changes are also analyzed, which show power law dependence ΔSMmax≈aμ0Hn at transition temperature. The critical exponent analysis related to magnetocaloric effect is described. Moreover, the temperature dependence of the exponent n for a different magnetic field is also studied. The values of n obey to the Curie Weiss law above the transition temperature. In particularly, n can be related to the critical exponents β, γ and δ at the magnetic transition. We used the scaling hypotheses to scale the magnetic entropy change and heat capacity changes to a single universal curve respectively for Pr0.4Eu0.2Sr0.4MnO3 sample. © 2015 Elsevier B.V. All rights reserved. Source


M'Nassri R.,Kairouan University | Chniba Boudjada N.,CNRS Neel Institute | Cheikhrouhou A.,University of Sfax
Journal of Alloys and Compounds | Year: 2014

This article covers the detailed study on the magnetic and magnetocaloric properties of Pr0.5Eu0.1Sr0.4MnO3 samples. The materials were synthesized through the sol-gel using nitrate-citrate route method by sintering at four different temperatures starting from 600 to 1000 °C. Phase purity, structure, size, and crystallinity were investigated using XRD and SEM. The structure, magnetic properties and magnetocaloric effect of Pr0.5Eu0.1Sr0.4MnO3 ceramics with different particle sizes have been investigated. Regardless of the sintering temperature, the orthorhombic crystal structure with the Pnma space group is stable. XRD analysis showed that the particle size increases with the increase in sintering temperature. The Curie temperature shifted from 90 K to 270 K. Magnetization, magnetic entropy change (ΔS), and relative cooling power (RCP) also increased with size in the nanocrystalline samples. The magnetic entropy changes were about 0.89 J/kg K, 2.75 J/kg K, 3.34 J/kg K, and 3.82 J/kg K for the samples sintered at 600 °C, 800 °C, 900 °C and 1000 °C, respectively when a magnetic field of 5 T was applied. It is shown that for Pr0.5Eu0.1Sr0.4MnO3 the magnetic entropy change follows a master curve behavior. © 2014 Elsevier B.V. Source


M'nassri R.,University of Sfax | M'nassri R.,Kairouan University | Cheikhrouhou A.,University of Sfax | Cheikhrouhou A.,CNRS Neel Institute
Journal of the Korean Physical Society | Year: 2014

The magnetocaloric proprieties of Ba2Fe1-xCrxMoO6 (cubic, Fm3m) have been investigated. With the help of the phenomenological model, the temperature dependences of the magnetization for Ba2Fe1-xCrxMoO6 (0 ≤ x ≤ 1) in a 1 T magnetic field were simulated. The behavior of the temperature-dependent magnetocaloric effect was investigated in the vicinity of magnetic phase transitions. The magnetic entropy change and the specific heat were obtained. The values of the maximum magnetic entropy change, the full width at half maximum, and the relative cooling power for a change in the magnetic field of 1 T were calculated. The values and the shapes of -ΔSM and -ΔCp strongly depended on the Cr concentration. As x was increased, the maximum values of -ΔSM and -ΔCp decreased and the peaks of -ΔSM and -ΔCp became broader. The magnetocaloric effect of this material is large and tunable, suggesting a possible technical application of the material at moderate magnetic fields at temperatures near room temperature. For Ba2Fe1-xCrxMoO6, the magnetic entropy change was shown to follow a master curve behavior. © 2014 The Korean Physical Society. Source


Selmi A.,University of Sfax | M'Nassri R.,Kairouan University | Cheikhrouhou-Koubaa W.,University of Sfax | Chniba Boudjada N.,CNRS Neel Institute | Cheikhrouhou A.,University of Sfax
Journal of Alloys and Compounds | Year: 2014

Structural, magnetic and magnetocaloric properties of Pr0.7Ca0.3Mn0.95X0.05O3(X = Cr, Ni, Co and Fe) ceramics have been investigated by X-ray diffraction (XRD) and magnetic measurements. Powder samples have been elaborated using the solid state reaction method at high temperature. The Rietveld analysis of the powder X-ray diffraction shows that the samples crystallize in the orthorhombic structure with Pnma space group. Magnetic measurements show that all our materials exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Arrott plots of ours materials reveal the occurrence of a second-order phase transition. The maximum values of magnetic entropy change |ΔSMmax| are 2.92, 2.96, 3.1, and 2.38 J kg-1K-1and the relative cooling power (RCP) values are 405.8, 378.2, 352.2 and 337.4 J kg-1for a magnetic-field change from 0 to 5 T for Cr, Ni, Co and Fe respectively. The large RCP found in our substituted samples will be interesting for magnetic refrigeration over a wide temperature range ∼130 K around its paramagnetic to ferromagnetic transition temperature. With the scaling laws of ΔSM, the experimental ΔSMcollapse onto a universal curve for several ceramics, where an average curve is obtained. With the phenomenological universal curve, the experimental ΔSMare well predicted for all materials. © 2014 Published by Elsevier B.V. Source


M'Nassri R.,University of Sfax | M'Nassri R.,Kairouan University | Cheikhrouhou A.,University of Sfax | Cheikhrouhou A.,CNRS Neel Institute
Journal of Superconductivity and Novel Magnetism | Year: 2014

Effects of oxygen deficiency on the thermomagnetic properties of La 2/3Ba1/3MnO3-δ polycrystalline perovskites have been predicted. By the help of the phenomenological model, the temperature dependences of the magnetization for La2/3Ba 1/3MnO3-δ with δ=0.0, 0.02, 0.05, 0.08, and 0.1 upon 1 T magnetic field were simulated. The behavior of the temperature dependent magnetocaloric effect, in the vicinity of magnetic phase transitions, was investigated. The magnetic entropy change, specific heat, and adiabatic temperature change for several δ were obtained. The values of maximum magnetic entropy change, full-width at half-maximum, and relative cooling power, in 1 T magnetic field variation, were calculated. As the oxygen content increases, the magnetocaloric effect of La2/3Ba1/3MnO 3-δ, decreases and shifts to room temperature. The results obtained show a strong dependence on the oxygen deficiency of the materials. The magnetocaloric effect of these materials is large and tunable, suggesting a possible technical application of the materials at moderate magnetic fields near room temperature. It is shown that for La2/3Ba1/3MnO 3-δ, the magnetic entropy change and adiabatic temperature change follows a master curve behavior. © 2013 Springer Science+Business Media New York. Source

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