Effect of A-site deficiency on investigation of structural, magnetic and magnetocaloric behaviors for (LaSr)-lacunar manganites (original) (raw)
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Journal of Superconductivity and Novel Magnetism, 2015
We present in this paper the effect of calcium deficiency on the structural, magnetic and magnetocaloric in La 0.65 Ca 0.35−x x MnO 3 (x= −0.15) powder samples. Our compounds were prepared using the solid-state reaction at high temperatures. Rietveld analysis show that all our synthesized samples are single phase without any detectable impurity and crystallize in the orthorhombic system with Pbnm space group. The Mn atom is coordinated by six oxygen atoms forming an irregular octahedron. The scanning electron microscopy (SEM) micrographs reveal that all the structure is characterized by various shapes and a uniform grain size which clearly increase from 1.528 μm for x= 0 to 3.36 μm for x= 0.1. Magnetic measurements as a function of temperature show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature exhibits a minimum of 228 K for x= 0.10. The maximum value of the relative cooling power RCP is obtained for x= 0.15 and is found to be W. Cheikhrouhou-Koubaa
Magnetocaloric effect in La0.75Sr0.25MnO3 manganite
Journal of Magnetism and Magnetic Materials, 2010
The polycrystalline manganite La 0.75 Sr 0.25 MnO 3 prepared by an alternative carbonate precipitation route reveals the rhombohedral perovskite structure. Magnetization isotherms measured up to 2 T are used to determine Curie temperature of 332 K by means of Arrott plot. Maximum of magnetic entropy change is found at Curie temperature. The relative cooling power equal to 64 J/kg for 1.5 T magnetic field, is superior as compared to the manganite with the same chemical composition from the sol-gel method.
Materials Science and Engineering: B, 2007
We have investigated the effect of nominal strontium deficiency on the structure and the magnetic properties of La 0.6 Sr 0.4−δ MnO 3 (0 ≤ δ ≤ 0.3) manganese perovskites. The polycrystalline samples have been elaborated by the conventional ceramic method at 1573 K. The morphology, grain sizes and chemical analysis were analyzed by scanning electron microscope (SEM) and energy dispersive X-ray (EDX) techniques. The refinement of the structure by the Rietveld method revealed that most of these compounds crystallize in a rhombohedral (R3c) perovskite structure. Magnetization as a function of temperature, M(T), shows that these compounds exhibit a paramagnetic (PM) to ferromagnetic (FM) phase transition with decreasing temperature. The Curie temperature (T C ) decreases from 361 K to nearly the room temperature (292 K) with decreasing nominal strontium content. In the paramagnetic region the inverse of the magnetic susceptibility was fitted by a Curie-Weiss law. Magnetization as a function of magnetic field, M(H), measured at 50 K shows that all compounds are FM with a maximum in the magnetic saturation moment for the nominal value δ = 0.12. A comparative analysis shows that nominal vacancies, δ, cannot generally be achieved by our conventional ceramic method and results in a shift of the perovskite manganite composition compensated by the formation of an additional Mn 3 O 4 phase.
Physics Procedia, 2009
Structural, magnetic and magnetocaloric effects of powder perovskite manganites La 0.7 M 0.2 M' 0.1 MnO 3 (M=Sr, Ba and M'=Na, Ag and K) have been investigated. Our samples have been elaborated using the conventional solid state reaction at high temperature. X-Ray diffraction characterizations showed that all our synthesized samples crystallize in the distorted rhombohedral system with c R3 space group. Magnetization measurements versus temperature in a magnetic applied field of 50mT showed that all our samples are ferromagnetic above room temperature. From the measured magnetization data of our synthesized samples as a function of magnetic applied field, the associated magnetic entropy change close to their respective Curie temperature T C and the relative cooling power RCP have been determined. A maximum magnetic entropy change, Max M S Δ , of 4.07Jkg-1 K-1 around 345K was obtained in La 0.7 Sr 0.2 Na 0.1 MnO 3 sample upon a magnetic field change of 5T. The Max M S Δ values of La 0.7 Ba 0.2 M' 0.1 MnO 3 are smaller in magnitude compared to La 0.7 Sr 0.2 M' 0.1 MnO 3 samples and occur at lower temperatures.
Journal of Physics and Chemistry of Solids, 2009
The effects of K doping in the A-site on the structural, magnetic and magnetocaloric properties in La 0.65 Ca 0.35Àx K x MnO 3 (0pxp0.2) powder samples have been investigated. Our samples have been synthesized using the solid-state reaction method at high temperature. The parent compound La 0.65 Ca 0.35 MnO 3 is an orthorhombic (Pbnm space group) ferromagnet with a Curie temperature T C of 248 K. X-ray diffraction analysis using the Rietveld refinement show that all our synthesized samples are single phase and crystallize in the orthorhombic structure with Pbnm space group for xp0.1 and in the rhombohedral system with R3 c space group for x ¼ 0.2 while La 0.65 Ca 0.2 K 0.15 MnO 3 sample exhibits both phases with different proportions. Magnetization measurements versus temperature in a magnetic applied field of 50 mT indicate that all our investigated samples display a paramagnetic-ferromagnetic transition with decreasing temperature. Potassium doping leads to an enhancement in the strength of the ferromagnetic double-exchange interaction between Mn ions, and makes the system ferromagnetic at room temperature. Arrott plots show that all our samples exhibit a second-order magnetic-phase transition. The value of the critical exponent, associated with the spontaneous magnetization, decreases from 0.37 for x ¼ 0.05 to 0.3 for x ¼ 0.2. A large magnetocaloric effect (MCE) has been observed in all samples, the value of the maximum entropy change, |DS m | max , increases from 1.8 J/kg K for x ¼ 0.05 to 3.18 J/kg K for x ¼ 0.2 under a magnetic field change of 2 T. For x ¼ 0.15, the temperature dependence of |DS m | presents two maxima which may arise from structural inhomogeneity.
Applied Physics A, 2014
The effect of Cr doping on the structural, magnetic and magnetocaloric properties of perovskite manganites La 0.75 Sr 0.25 Mn 1-x Cr x O 3 (x = 0.15, 0.20, and 0.25) has been investigated. Crystalline structure and magnetic properties are investigated by using X-ray powder diffraction and magnetization measurements, respectively. All samples show a single phase and are found to crystallize in the distorted rhombohedral system with R3 c space group. A monotonous change of Curie temperature (T C ), from 314 to 253 K, is observed when content doping increases. Substantial magnetic entropy change reaching 4.20 J/kg K is revealed. Relative cooling power was estimated as well. It was found to reach 289, 323, and 386 J/kg for x = 0.15, 0.20, and 0.25, respectively. Field dependence of the magnetic entropy change showing the power law dependence DS M / l 0 H ðÞ n is also analyzed and discussed.
Journal of Physics: Conference Series, 2009
The effects of monovalent doping in the A-site on the structural, magnetic and magnetocaloric properties in La 0.65 Ca 0.3 M 0.05 MnO 3 (M=Na, Ag, K) powder perovskite manganites have been investigated. Our samples have been synthesized using the conventional solid state reaction at high temperature. Rietveld refinements of the X-ray diffraction patterns at room temperature show that all our powder samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Magnetization measurements versus temperature in a magnetic applied field of 50mT indicate that our investigated samples display a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature T C is found to be 295K, 254K and 285K for M=Na, Ag and K respectively. From the measured magnetization data of La 0.65 Ca 0.3 M 0.05 MnO 3 (M=Na, Ag, K) samples as a function of magnetic applied field, the associated magnetic entropy change close to their respective Curie temperature T C and the relative cooling power RCP have been determined. The maximum magnetic entropy change, max m S ∆ , in a magnetic field change of 5T is found to be 3, 5.16 and 3.54 Jkg/K for M=Na, Ag and K respectively. The La 0.65 Ca 0.3 K 0.05 MnO 3 sample exhibits the largest RCP value of 295J/kg.