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Highlights • La 0.8 Ca 0.2 MnO 3 compounds show a magnetic transition from ferromagnetic to paramagnetic state. • Magnetic order phase transition are confirmed using the Bean-Rodbell model. • Magnetic measurement are simulated in bases of the mean-field theory. • We found a good medialization of the magnetic entropy change. Abstract Magnetic and magnetocaloric properties of La 0.8 Ca 0.2 MnO 3 manganese oxides has been analyzed based on the mean-field theory. The Bean-Rodbell equation of state shows a second and first order magnetic phase transition for the sample annealed at 1200 °C (S 1) and 800 °C (S 2) with a η factor of η = 0.6 and η = 1.4 respectively. Using the experimental data of magnetization M (H,T), the molecular mean-field parameter are found to be λ 1 = 0.6564 T g eum−1 and λ 1 = 0.8876 T g eum−1 for S 1 et S 2 respectively. Brillouin function allows us to determine the total angular moment J, the saturation magnetization M S and the Lande factor g for all samples. Knowing all these parameters, and by applying the mean-field theory, we simulated the magnetization as a function of the magnetic field and the temperature, as well as the variation of the magnetic entropy change ΔS M (T). We can see that the simulated results are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

La0.8Ca0.2MnO3 manganese oxides have been prepared by the conventional solid-state reaction. The samples crystallize in the orthorhombic structure with Pnma space group. A first-order magnetic phase transition from ferromagnetic to paramagnetic state is observed at the Curie temperature that is found to be around 241 K. The magnetic and magnetocaloric properties have been simulated using a phenomenological model. The maximum of magnetic entropy change is of order 8.2 J/kg K for an applied magnetic field of 5 T, and the adiabatic temperature change is found to be of 4 K under a same magnetic field; this high value gives the sample the possibility of technologic application in the magnetic refrigeration area. The simulated results of magnetization and magnetic entropy change are compared with the experimental measurements. Finely, we found a good agreement between experimental and theoretical results. [ABSTRACT FROM AUTHOR]

La0.8Ca0.2MnO3 manganese oxides have been prepared by the conventional solid-state reaction. The samples crystallize in the orthorhombic structure with Pnma space group. A first-order magnetic phase transition from ferromagnetic to paramagnetic state is observed at the Curie temperature that is found to be around 241 K. The magnetic and magnetocaloric properties have been simulated using a phenomenological model. The maximum of magnetic entropy change is of order 8.2 J/kg K for an applied magnetic field of 5 T, and the adiabatic temperature change is found to be of 4 K under a same magnetic field; this high value gives the sample the possibility of technologic application in the magnetic refrigeration area. The simulated results of magnetization and magnetic entropy change are compared with the experimental measurements. Finely, we found a good agreement between experimental and theoretical results. [ABSTRACT FROM AUTHOR]

The critical behavior associated with the magnetic phase transition has been investigated by in La 0.8 Na 0.2− x □ x MnO 3 (0.00 ≤ x ≤ 0.15) (□ is the sodium deficiency). The critical exponents are estimated by various techniques such as the modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. Compared to standard models, the critical exponent values determined in our work are close to those expected by the tricritical model (β = 0.25, γ = 1, and δ = 5) for x = 0.00 and 0.05 samples and by mean field theory (β = 0.5, γ = 1, and δ = 3) for x = 0.10 and 0.15 samples. We conclude that the Na deficiency rate affect the critical exponents. [ABSTRACT FROM AUTHOR]

This investigation is interested in studying the relation between magnetocaloric effect and transport properties i LaCaMnO manganite compound. The value of the magnetocaloric effect has been determined from the calculation of magnetization as a function of temperature under different external magnetic fields. This study also provides an alternative method to determine the magnetocaloric properties such as magnetic entropy change and heat capacity change on the basis of M( T, H) measurements. On the other hand, based on magnetic and resistivity measurements, the magnetocaloric properties of this compound were investigated using an equation of the form ${\Delta } S \,=\, - \alpha {\int \limits _{0}^{H}} {\left [ {\frac {\delta Ln\left (\rho \right )}{\delta T}} \right ]}_{H} dH$ , which relates magnetic order to transport behavior of the compounds. As an important result, the values of MCE and the results of calculation are in good agreement with the experimental ones, which indicates the strong correlation between the electric and magnetic properties in manganites. [ABSTRACT FROM AUTHOR]

The magnetocaloric properties of the polycrystalline manganites La 0.7 □ 0.1 Ca 0.2 MnO 3 based on magnetic and resistivity measurements were investigated. Firstly, the equation Δ S = - α ∫ 0 H δ Ln ( ρ ) δ T H dH relates magnetic order to the transport behavior of the compounds. The relation between ρ and M was found to maintain the form of ρ = ρ 0 exp ( - M / α ) for temperatures near and slightly below T C . This result reveals the important effect of magnetic polarons on the transport properties. It is obvious that magnetic disorder, characterized by Δ S M , affects the magnetic polarons, while the latter influence the electronic transport properties, which may be the underlying reason for the salient Δ S M – ρ relation. On the other hand, based on a phenomenological model, the value of the magnetocaloric effect has been determined from the calculation of magnetization as a function of temperature under different magnetic fields M ( T , H ). This study also provides an alternative method to determine magnetic entropy change on the basis of magnetic and resistivity measurements. [ABSTRACT FROM AUTHOR]

Polycrystalline compounds La0.8Na0.2-x...xMnO3 were prepared by the solid-state reaction with 0.00=x=0.15. Structural, magnetic and electrical measurements were investigated. The XRD data have been analyzed by Rietveld refinement technique which reveals that all samples are crystallized in a rhombohedral structure with R...c space group. Magnetic measurement versus temperature shows that all samples exhibit a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase when increasing temperature. The Curie temperature (TC) decrease from 340K for x=0.00 samples to 260K for x=0.15 one. Hysteresis cycles confirm the ferromagnetic character at low temperature with a decrease of the remanent magnetization and the coercive field when the vacancy rate increases. Moreover, the temperature dependence of electrical resistivity shows a metal-insulator transition at Tρ for all samples. In addition, Tρ decreases with vacancy content in accordance with TC. Thus, the conduction mechanism was explained by the adiabatic small polaron hopping (ASPH) in the insulating region and by the competition between the small-polaron and spin-wave scattering and the electron-magnon scattering mechanisms. Finally, the minimum of resistivity at very low temperature range is explained by the Kondo-like scattering model. [ABSTRACT FROM AUTHOR]

The magnetic entropy change (Δ S) of polycrystalline samples LaCa□MnO ( x=0.00; x=0.10 and x=0.20) with a second-order phase transition has been investigated. The field dependence of the magnetic entropy change expressed as Δ S∝ H follows the phenomenological curves and at the temperature of the peak corresponds to a large field independent exponent of n=0.581; 0.642 and 0.671 for x=0.00; x=0.10 and x=0.20 samples, respectively. Then, we have constructed the phenomenological universal curve by normalizing the magnetic entropy change curves with respect to their maximum values, $\Delta S_{M_{\mathrm{max}}}$, and rescaling the temperature axis. These universal curves collapse onto a single curve for any applied magnetic field for all samples. Moreover, we note that the universal curve for x=0.10 and x=0.20 samples collapses with a small deviation compared with x=0.00 sample. This is consistent with our previous work where we demonstrated that the magnetic phase transition relative to the samples x=0.00 belongs to the 3D-Ising universal class and to the 3D-Heisinberg class for x=0.10 and x=0.20 samples. This universal curve can be used to predict the response of materials in different conditions not available in the laboratory by extrapolations in field or temperature. [ABSTRACT FROM AUTHOR]

The La□CaMnO compounds were prepared by the solid-state reaction with 0.00≤ x≤ 0.20. Morphologic, X-ray diffraction (XRD), magnetic, and electrical measurements were performed to examine the effect of the lanthanum deficiency on the physical properties of these materials. The scanning electron microscopy shown the existence of a secondary phase attributed to the MnO oxide. The XRD data have been analyzed by the Rietveld refinement technique. We have found that all samples crystallize in an orthorhombic symmetry with Pnma space group and the unit cell volume decreases with lanthanum deficiency. A magnetization versus temperature study has shown that all samples exhibit a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase with increasing temperature. The Curie temperature T increases with the lanthanum deficiency from 236 K to 247 K for the samples x=0.00 and x=0.20, respectively. Moreover, the temperature dependence of electrical resistivity shows a metal-insulator transition at T for all samples which increase with vacancy rate. 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. Thus, show that the conduction mechanist was explained by the electron-electron and electron-phonon scattering process at low temperature and by small polaron hopping at high temperature. Furthermore, we found that the estimated results are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

We have investigated the effect of iron substitution on the magnetocaloric properties of manganites with LaCaSrMnFeO ( x=0, 0.075, 0.15, 0.175, and 0.2) nominal composition. The magnetocaloric effect (MCE) was estimated, in terms of isothermal magnetic entropy change (−Δ S), using the M( T, μ H) data and employing the thermodynamic Maxwell equation. The large magnetic entropy in AMnFeO is attributed to the field-induced suppression of short-range charge-orbital ordering and antiferromagnetic fluctuations present above T. The increase of the Fe concentration x is accompanied by a decrease of (−Δ S), from 5.205 to 0.95 J/kg K for x=0 and 0.20, respectively, with μ H=5 T. For all samples, we find quite large values of (−Δ S), which are very close to that provided for Gd, the prototypical magnetocaloric material. [ABSTRACT FROM AUTHOR]

Abstract: The critical behavior associated with the magnetic phase transition has been investigated by magnetization isotherms in La0.8Ca0.2MnO3 and La0.8Ca0.1□0.1MnO3 (□ is the calcium deficiency). The critical exponents are estimated by various techniques such as the Modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. The critical exponents values for La0.8Ca0.2MnO3 are very close to those found out by the 3D-Ising model (β=0.328, γ=1.180, and δ=4.826 at an average T C =181.676K). Moreover, the estimated critical exponents of La0.8Ca0.1□0.1MnO3 are consistent with the prediction of the 3D-Heisenberg model (β=0.357, γ=1.167, and δ=4.802 at an average T C =178.182K). We noted that the critical exponents γ are almost similar to the value of the mean-field theory which can be explained by the existence of a long-range dipole–dipole interaction. Following the Harris criterion, we deduced that the disorder in our case is relevant, which can be the cause of the change in the universality class. [Copyright &y& Elsevier]

Abstract: The La0.8Ca0.2−x □ x MnO3, (x =0–0.20) compounds were prepared by the solid-state reaction. X-ray diffraction (XRD) and magnetic measurements were used to investigate the calcium-vacancy effect on the physical properties. The XRD data have been analyzed by Rietveld refinement technique. Samples with x =0, 0.05 and 0.10 are found to be single phase and crystallize in orthorhombic symmetry with Pnma space group. Moreover, for x =0.15 and 0.20 samples, the refinement has revealed the coexistence of both Pnma orthorhombic and rhombohedral phases. The magnetic study has showed that the magnetization exhibits maximum at x =0.15 and minimum at x =0.2. Such behavior was interpreted in terms of orthorhombic distortion contribution, which is related to the orthorhombic structure, leading to magnetization decrease. In addition, maximum magnetic entropy change (ΔS M) for x =0 sample was found to reach ∼4.1J/kgK under an applied magnetic field of 5T, which is very sufficient for potential application in magnetic refrigeration. For the same applied magnetic field (μ 0 H =5T), the Relative Cooling Power (RCP) values are found to vary between 270 and 300J/kg. As consequence, the La0.8Ca0.2−x □ x MnO3compounds can be used as a composite for magnetic refrigeration in the [175–183] K temperature range. [Copyright &y& Elsevier]

• La 0.67 Ca 0.33 Mn 0.98 Ni 0.02 O 3 sample was prepared by sol-gel method. • La 0.67 Ca 0.33 Mn 0.98 Ni 0.02 O 3 crystallizes in a rhombohedral R 3 - c structure. • The samples exhibit PM-FM phase transition at T c. • The Δ S M max and RCP are determined and a large magnetocaloric effect is observed. In this article, we provide a detailed study of structural, magnetic properties and magnetocaloric effects of the perovskite manganite compound. The preparation of the sample made according to the sol-gel method. The compound stabilizes in the rhombohedral structure with a R 3 - c space group. The discussion of magnetic properties of this sample is made, depending on the magnetization and the inverse of the susceptibility. Phase transition from a paramagnetic (PM) to a ferromagnetic (FM) was presented by the magnetization measurements as a function of temperature at a Curie temperature T c = 244 K, under an applied magnetic field of 0.05 T. The associated magnetic entropy change resolution Δ S M as well as the relative cooling power (RCP) are made from the measured magnetization data of La 0.67 Ca 0.33 Mn 0.98 Ni 0.02 O 3 sample depending on the applied magnetic field. The maximum entropy change reaches a significant value of 8 J· k g - 1 Â · K - 1 and RCP = 217 J Â · k g - 1 observed at 5 T magnetic field, Then, 4 J. k g - 1 Â · K - 1 and RCP = 43 J Â · k g - 1 reached when a magnetic field of 1 T was applied. [ABSTRACT FROM AUTHOR]

The corresponding author would like to indicate his correction to his affiliation. [ABSTRACT FROM AUTHOR]

This paper presents the effects of oxygen deficiency on the structural, magnetic and magnetocaloric properties of La 0.8 Na 0.2 MnO 3 − δ where δ =0 and 0.05. The Polycrystalline La 0.8 Na 0.2 MnO 3 − δ samples were synthesized by a new method. The introduction of the oxygen deficiency in our samples leads to an increase of Mn 3+ content according to the electronic formula La 0 . 3 + N a 0.2 + M n 0.6 + 2 δ 3 + M n 0.4 − 2 δ 4 + O 3 − δ . The X-ray diffraction analysis shows a phase transition from a rhombohedral system with R 3 ¯ c space group for δ =0.00 to an orthorhombic with P n m a space group for δ =0.05. It also induces a great variation in the magnetic properties. The magnetization versus temperature study has shown that all samples exhibit a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase with the increase in temperature. However, it can be clearly seen that the oxygen deficiency induces an increase in the magnetization and a decrease in the Curie temperature T C . Besides, the magnetocaloric effect (MCE) as well as the Relative Cooling Power (RCP) has been estimated. As an important result, the values of MCE and RCP in our oxygen deficiency manganites are reported to be close to those found in gadolinium that is considered as magnetocaloric reference material. [ABSTRACT FROM AUTHOR]

Abstract: Lanthanum-deficiency effect on the magnetic and magnetocaloric properties of La0.8−x □ x Ca0.2MnO3 (0.00≤x≤0.20) polycrystalline samples has been investigated using X-ray diffraction and magnetization measurements. The structural characterization has revealed that all samples are crystallized in the orthorhombic structure with Pnma space group. From magnetic measurement a first-order magnetic phase transition from ferromagnetic to paramagnetic state is observed at the Curie temperature (T C) which is found to increase from 236.5 to 247K when lanthanum-deficiency rate increases. Besides, both magnetocaloric effect (MCE) and relative cooling power (RCP) has been estimated. As important result, the values of MCE and RCP in our managanite with Lanthanum-deficiency are reported to be near to those found in the gadolinium considered as magnetocaloric material reference. Finally, the first-order magnetic phase transition has been confirmed by the construction of the universal curve of the magnetic entropy change. [Copyright &y& Elsevier]

The effect of strontium doping on the structural, magnetic and magnetocaloric properties of La 0.67 Ca 0.33- x Sr x Mn 0.98 Fe 0.02 O 3 samples for (x = 0.15; 0.2.and 0.3) has been investigated. Analysis using X-ray diffraction shows there is an orthorhombic structure with Pnma space group symmetry for x = 0.15 compound, whereas there is a rhombohedral structure exhibiting R 3 ‾ c space group symmetry found for x = 0.2, and x = 0.3 compounds. A second-order magnetic phase transition from ferromagnetic to paramagnetic state transition is evidenced for all samples, with Curie temperature (T C) values equal to 329 K, 330 K and 350 K and that respectively for x = 0.15, 0.2 and 0.3. Based on isothermal magnetization measurements versus applied magnetic field at several temperatures around T C , the magnetic entropy change was calculated, which is very close to that approximated by the Landau theory for. x = 0.15. Under an applied magnetic field of 5 T, one can see the maximum magnetic entropy change (− Δ S M m a x) values, which are around 4.89, 4.71 and 3.35 J.kg− 1.K−1 for x = 0.15, 0.2, and 0.3 respectively. It confirms that close to room temperature, these manganites are admirably potential functional materials, which can be applied as solid state magnetic refrigerants. [Display omitted] • Structural and magnetic properties have been studied in detail. • A large magnetocaloric effect is observed just above room temperature. • High values of Δ S M and relative cooling power are reported. • Second-order of ferromagnetic phase transition is confirmed. [ABSTRACT FROM AUTHOR]