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A systematic study of the magnetocaloric effect in La0.7Ca0.15Sr0.15MnO3 perovskite has been performed by both direct and indirect measurement techniques. In particular, the adiabatic temperature change has been measured by a purpose-built probe suitable for laboratory-scale samples, while magnetic measurements were carried out by standard magnetometric techniques. The observation of the effective behavior of the studied systems in adiabatic conditions and the significant value of the isothermal entropy variation indicate that La0.7Ca0.15Sr0.15MnO3 could be considered as a potential candidate for application in magnetic refrigeration around room temperature. Moreover, the critical exponents (γ, β and δ) determined using the Kouvel–Fisher method, the modified Arrott plot and the critical isotherm analysis are in good agreement with the theoretical prediction of the 3D-Ising model, indicating that the magnetic interactions are of short-range nature.

In this paper, we investigate the field dependence of the magnetocaloric properties of La0.7Ca0.2Sr0.1MnO3 powder sample using a phenomenological model. Our compound was elaborated by the conventional solid state reaction. The model parameters were determined from the magnetization data and were used to give better fits to magnetic transition and to calculate the magnetocaloric quantities. The magnetocaloric parameters such as the maximum of the magnetic entropy change $$\Delta S_M^{max}$$ and the relative cooling power RCP, have been determined from the calculation of the magnetization as a function of temperature under several magnetic applied field. Thus, from the magnetocaloric results, such as RCP ≈ b(μ0H)1+1/δ and Tpeak − TC ≈ b (µ0H)1/Δ, the critical exponents values related to the magnetic transition have been determined. The estimated results are close to those expected by the tricritical mean-field model. Furthermore, the values of the ferromagnetic transition temperature TC, as well as the critical exponents β, γ and δ obtained by the theoretical model, are compared with those obtained by other various techniques (such as the modified Arrott plots, the Kouvel–Fisher method and the critical isotherm analysis). A good agreement has been found in the vicinity of the Curie temperature.

In this paper, we studied in detail the critical behavior of La0.7Ca0.2Ba0.1MnO3 manganite sample synthesized by the solid state reaction. The critical properties near the ferromagnetic–paramagnetic phase transition have been analyzed from the magnetic data, using various techniques such as the modified Arrott plots, the Kouvel fisher method, critical isotherm analysis and the field dependence of magnetocaloric results. Moreover, the validity of the critical exponents using the various methods has been confirmed by the scaling equation of state and all data fall on two distinct branches, one for T TC, indicating that the critical exponents obtained in this work are accurate. The exponents determined in this study have revealed that the β value is in between the theoretically expected values for 3D-Ising and tricritical mean field model. While, the γ value is close to the mean field theory. The third exponent δ was determined independly from the critical isotherms satisfying the Widom scaling relation. Our systematic result reflects the coexistence of a long range and short range ferromagnetic order in our sample. The temperature variation in the effective exponents βeff and γeff resemble with those for disordered ferromagnet around Curie temperature.

In this paper, a profound study has been conducted on magnetocaloric effect in (1-x)La0.7Ca0.25Sr0.05MnO3/xLa0.7Ca0.2Sr0.1MnO3 composite system. The present research work reveals an especial agreement between the experimental results and the continuous curves investigated by the numerical calculations in a two phases composite system (1-x)La0.7Ca0.25Sr0.05MnO3/xLa0.7Ca0.2Sr0.1MnO3. This approach can be used to elaborate magnetic material with enhanced magnetocaloric properties. In addition, the ability to adjust the temperature transition near room temperature is revealed to be possible by the mixture of both individual phases La0.7Ca0.25Sr0.05MnO3 and La0.7Ca0.2Sr0.1MnO3. Our samples have been synthesized using the solid state reaction. Rietveld refinement of the X-ray diffraction patterns reveals the same orthorhombic structure with Pnma space group for both component manganites. Magnetization measurements versus temperature in a magnetic applied field of 0.05T show that all our samples exhibit a paramagnetic ferromagnetic transition with decreasing temperature. The Curie temperature TC is found to be 282 K and 308 K for La0.7Ca0.25Sr0.05MnO3 and La0.7Ca0.2Sr0.1MnO3, respectively. Moreover, the magnetic entropy change and the Relative Cooling Power (RCP) values were estimated for the biphasic system (1-x)La0.7Ca0.25Sr0.05MnO3/xLa0.7Ca0.2Sr0.1MnO3 with 0

This paper presents a theoretical work on magnetic and magnetocaloric properties of La0.7Ca0.2Ba0.1MnO3 powder sample elaborated by high energy ball milling. Using the phenomenological model, the magnetocaloric parameters such as the magnetic entropy change ΔSM and the relative cooling power RCP, have been determined from the magnetization data as a function of temperature at several magnetic applied fields. In addition, from the magnetocaloric results, such as ΔSmax ≈ a (μ0H) n and Tpeak-TC ≈ b (μ0H)1/Δ, the critical exponents values related to the magnetic transition have been determined. The estimated results are close to those expected by the tricritical mean-field model. Furthermore, using other various techniques (such as the modified Arrott plots, the Kouvel-Fisher method and the critical isotherm analysis), the values of the ferromagnetic transition temperature TC, as well as the critical exponents β, γ and δ are simulated and compared with those obtained by the theoretical model. A good agreement has been found in the vicinity of the Curie temperature. The field and temperature dependent magnetization follow the scaling theory, and all data fall on two distinct branches, one for T TC, indicating that the critical exponents obtained in this work are accurate.

Magnetic, magnetocaloric and critical behavior properties of La0.69Dy0.01Ca0.3MnO3 are studied. The Rietveld refinements of the X-ray diffraction patterns show that our sample crystallizes in the orthorhombic structure with Pnma space group. The Curie temperature is found to be 245 K. In the vicinity of TC, |-ΔSM| reached, in a magnetic applied field of 5T, maximum value of 14.94 J kg−1 K−1. The critical exponents β, γ and δ have been determined using various techniques such as the modified Arrott plot, Kouvel–Fisher methods as well as the critical isotherm, and are found to be β = 0.25 at TC = 246.74 K and γ = 0.87 at TC = 246.2 K for La0.69Dy0.01Ca0.3MnO3. The values of critical exponents are close to the tri-critical mean-field model.

We have synthesized La0.7Ca0.2Sr0.1MnO3 sample using two different methods: the solid-state reaction (S1) and the sol–gel process (S2). Structural, morphological, infrared and magnetic properties were investigated by X-ray diffraction, scanning electron microscopy, Spectrum Two FT-IR Spectrometer and vibrating sample magnetometer. Despite the various conditions employed in the elaboration, the crystallographic study shows that our samples are single phase and crystallize in orthorhombic system with Pnma space group. A small difference appears in the microstructural and magnetic properties. The Curie temperature TC is found to be 308–256 K for S1 and S2 respectively. A large magnetocaloric effect has been observed in both samples, besides; the relative cooling power for S2 is bigger than S1. It attains exactly 250.75 J kg−1 under a magnetic applied field of 5 T. These results show that the elaboration process has an important impact on the magnetic and magnetocaloric properties. Furthermore, the importance of the magnetoelastic coupling and electron interaction in the magnetocaloric properties of manganite was confirmed by the analysis of Landau theory.

In this paper, we investigate the effect of elaborating method on the magnetocaloric properties of La0.7Ca0.2 Ba0.1Mn03 manganite powder. Our samples have been synthesised using the solid state reaction (sample 1) and high energy ball milling method (sample 2). X-ray diffraction and magnetization measurements were performed to investigate the crystallographic structure and magnetocaloric properties. An orthorhombic structure with Pbnm space group is deduced from the refinement of the XRD patterns for both samples. A second-order magnetic phase transition from ferromagnetic to paramagnetic state is observed and confirmed in terms of Landau theory and universal theory. The Curie temperature TC is found to be 297 K for sample 1 and 230 K for sample 2. The maximum of the magnetic entropy change Δ S M M a x at μ0H = 3 T decreases from 2.5 J/kg K−1 for sample 1–2.25 J/kg K−1 for sample 2, while, the relative cooling power RCP increases from 132.5 J/Kg for sample 1–142.8 J/Kg for sample 2. The comparison of the values reported in the reference Gd material underlines that the proposed manganite material has substantial advantages for magnetic refrigeration. Field dependences of Δ S M M a x and RCP can be expressed by the power laws, Δ S M M a x ≈ a ( μ 0 H ) n and RCP ≈ b (μ0H) m, where a and b are coefficients, n and m are the field exponents, respectively.