-
[show abstract]
[hide abstract]
ABSTRACT: La(0.8)Ca(0.2 - x)□(x)MnO(3) (x = 0.00, 0.10, and 0.20) perovskite was prepared by the conventional solid-state reaction and annealed at 1473 K. X-ray diffraction and scanning electron microscopy shown the existence of a secondary phase attributed to the unreacted Mn(3)O(4) oxide. The magneto transport properties have been investigated based on the temperature dependence of the resistivity ρ(T) measurements under several applied magnetic fields. We note that the La(0.8)Ca(0.2)MnO(3) (x = 0.00) sample has a classical metal-insulator transition at T(ρ). But we have observed that the lacunars samples (x = 0.10 and 0.20) include a metallic and insulator behavior simultaneously below T(ρ) and the resistivity is dominated by tunneling through the barriers associated with the insulating phase. In other words, the calcium deficiency favors the enhancement of the insulator behavior. The electrical resistivity is fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. Furthermore, we found that the estimated results are in good agreement with experimental data. Above all, the resistivity dependence on the temperature and magnetic field data is used to deduce the magnetic entropy change. We have found that these magnetic entropy change values are similar to those calculated in our previous work from the magnetic measurements. Finally, we have found an excellent estimation of the magnetic entropy change based on the Landau theory.
Journal of Applied Physics 05/2012; 111(10):103909-1039096. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, a new complex magnetic materials La0.70Ca0.15Sr0.15Mn1−xFexO3 (x= 0.000, 0.025, 0.050, 0.075 and 0.100), suitable for the Ericsson cycle, has been investigated. For these materials, the effect of Fe doping can be attributed to a combination of doping disorder, Fe–Mn super exchange interactions and a site-percolation mechanism, which suppress the metallic conduction and ferromagnetism. We have found that these compounds crystallize in the rhombohedral structure with the space group. We have also verified that the substitution of the manganese with iron leads to an important decrease of the Curie temperature TC from 335 to 225 K for 0%–10% of Fe. The magnetocaloric study exposes a quite large value of the magnetic entropy change, which decreases when increasing Fe concentration. For an applied magnetic field of 2 T, the Relative Cooling Power (RCP) values are found to vary between 80 and 125 J/kg. As a result, the studied compounds could be considered as potential material for magnetic Ericsson refrigeration by using complex magnetocaloric compounds.
Solid State Communications 149:969-972. · 1.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Polycrystalline perovskite samples of La0.7Ca0.3−xKxMnO3 (0.05 ≤ x ≤ 0.10) have been prepared using the solid-state reaction. Detailed measurements of the magnetization as function of temperature and magnetic field for these samples were carried out. Significant magnetic-entropy changes (ΔSMmax) near the Curie temperature are obtanied from the magnetization data. The increase of the K concentration x is accompanied by a decrease of ΔSMmax from 3.95 to 3.49 J/kg K for x = 0.05 and 0.10, respectively, with μ0H = 2 T. For all samples, we find quite large values of ΔSMmax, which are very close to that provided by Gd the prototypical magnetocaloric material. In view of theses results, the La0.7Ca0.3−xKxMnO3 compounds are strongly recommended to use as an active magnetic refrigerant for magnetic refrigerators.
Journal of Alloys and Compounds 442:136-138. · 2.29 Impact Factor
