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The lanthanum deficient La0.65−x□xCa0.35MnO3 (0 ≤ x ≤ 0.12) have been elaborated by the solid-state reaction at high temperatures. All samples have been studied by several techniques including X-ray diffraction, scanning electron microscopy (SEM), spectrum two FT-IR Spectrometer and vibrating sample magnetometer. Rietveld refinement shows that all samples crystallize in the orthorhombic structure with Pbnm space group and that lanthanum deficiency leads to a decrease of the unit cell volume. Magnetization measurements versus temperature exhibit a large ferromagnetic-paramagnetic transition with decreasing temperature. The TC decreases from 270 K for x = 0 to 254 K for x = 0.12. A large magnetic entropy change associated with the ferromagnetic-paramagnetic transition has been observed. The maximum of the magnetic entropy change Δ S M Max decreases from 5 Jkg−1K−1 for x = 0 2.1 Jkg−1K−1 for x = 0.12. Moreover, the maximum magnetic entropy change exhibits a linear dependence with applied magnetic field. The relative cooling power (RCP) decreases from 214 J/Kg for x = 0 to 106 J/Kg for x = 0.12 under an applied magnetic field of 5 T.

An exhaustive study of structural, magnetic and magnetocaloric properties on La1.95Sr0.05BMnO6 (B = Ni and Co) double perovskite were performed. The samples were prepared by the sol–gel method. The crystallographic structure was studied by the X-ray diffraction patterns and Rietveld refinement which revealed that all samples crystallize in a monoclinic structure with P21/n space group. The magnetic behaviors of these double perovskite have been studied in detail. For La1.95Sr0.05NiMnO6, the M(T) curves exhibit double magnetization transition temperature at 68 K and 266 K which can be ascribed to Ni3+–O–Mn3+ and Ni2+–O–Mn4+ superexchange interaction, respectively. However, unique magnetic transition has been observed for the La1.95Sr0.05CoMnO6 double perovskite at 210 K due to Co2+–O–Mn4+ superexchange interaction. A deep investigation based on the Landau Theory and Arrot analysis confirmed a second order ferromagnetic phase transition for both samples. Besides, the magnetocaloric behaviors of these new samples have been studied by analysis the magnetic entropy change. This latter reached maximum values of 1.01 and 1.35 J/kg/K for La1.95Sr0.05NiMnO6 and La1.95Sr0.05CoMnO6, respectively, under µ0H = 5 T. Moreover, the relative cooling power values for La1.95Sr0.05NiMnO6 and La1.95Sr0.05CoMnO6 are found to be 94 J/kg and 116 J/kg, respectively, under µ0H = 5 T. Based on the obtained ΔSM data, we have also described the universal master curve for (ΔSM/ $$\Delta S_{M}^{{\hbox{max} }}$$ ) versus rescaled temperature to confirm the order magnetic phase transition. Interestingly, all the ΔSM(T, H) data points are collapsed into a universal curve in the whole temperature range. The significant values of relative cooling power for both samples suggest that they might be an interesting candidate for exploring a new kind of magnetic refrigerants.

We have synthesized La1.95Ca0.05BMnO6 (B = Ni and Co) double perovskite using sol–gel method. The structural properties were investigated by X-ray diffraction. Ritveld analysis show that ours samples crystallize in the monoclinic system with P21/n space group. Refinement of X-ray results reveal that the cell parameters, the unit cell volume and the crystallite size increase with the ionic radius of B-site. In addition, a paramagnetic to ferromagnetic (PM–FM) phase transition is observed at 275 and 201 K for La1.95Ca0.05NiMnO6 and La1.95Ca0.05CoMnO6, respectively. The magnetization measurements, Arrott analysis and Landau theory suggest ferromagnetic phase transition with second order for all the synthesized samples. The magnetic entropy change was evaluated from the measurement of isothermal magnetization. The maximum values of magnetic entropy change are found to be $${-\varDelta S}_{M}^{max}$$ = 1.18 and 0.91 J/Kg K for La1.95Ca0.05NiMnO6 and La1.95Ca0.05CoMnO6, respectively, under µ0H = 5 T. We have also described the universal master curve for ΔSM, which is the evolution of (ΔSM/ $${\varDelta S}_{M}^{max}$$ ) versus rescaled temperature θ = (T − TC)/(Tr − TC), where Tr is the reference temperature. Interestingly, all the ΔSM (T, H) data points are collapsed into a universal curve in the whole temperature range.

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 report the magnetic properties of Ca vacancies in La0.65Ca0.35−x□xMnO3 (0 ≤ x ≤ 0.15) powder samples synthesized using the sol–gel reaction. Rietveld refinement of powder X-ray diffraction data reveals that all samples crystallize in the orthorhombic structure with Pbnm space group. Then, the magnetic properties of these compounds are discussed in detail, building on the magnetization and the susceptibility. The temperature dependence of magnetization reveals a magnetic transition from ferromagnetic to paramagnetic phase when increasing temperature. The inverse of magnetic susceptibility shows a downturn with decreasing temperature before the Curie temperature TC indicating the existence of Griffiths phase for the temperature range TC ≤ T ≤ TG, where TG is the Griffiths temperature, which proves the existence of ferromagnetic clusters in the paramagnetic domain. Furthermore, by investigating the magnetocaloric parameters, the field dependences of $${{{\Delta}}}S_{M}^{{Max}}$$ and RCP can be expressed by the power laws, $$\Delta S_{M}^{{max}}$$ ≈ a (µ0H)n and RCP ≈ b (µ0H)m, where a and b are coefficients, n and m are the field exponents, respectively.

In the present research work, we investigate the magnetocaloric properties of a composite system by experiments and numerical calculations. The ability to adjust the magnetic entropy change in a large temperature range revealed to be possible by the mixture of both phases La0.7Ca0.2Sr0.1MnO3 and La0.7Ca0.15Sr0.15MnO3. Our composite 0.5La0.7Ca0.2Sr0.1MnO3/0.5La0.7Ca0.15Sr0.15MnO3 was synthesized using the solid–state reaction. Crystallographic structure and magnetocaloric properties were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). Rietveld refinements of the X-ray diffraction patterns show that both samples are single phase and we have noticed a structural transition from orthorhombic structure with Pnma space group for La0.7Ca0.2Sr0.1MnO3 to rhombohedral structure with R-3C space group for La0.7Ca0.15Sr0.15MnO3. A second-order magnetic phase transition from ferromagnetic to paramagnetic state is observed and confirmed in terms of Landau theory. Therefore, two successive magnetic transitions in La0.7Ca0.2Sr0.1MnO3 and La0.7Ca0.15Sr0.15MnO3 resulting a nearly constant “table-like” magnetic-entropy change. Both peaks are partially overlapped with each other and induced an enhancement of the RCP in the composite when comparing with that of individual components. These results make that the proposed composite has substantial advantages for magnetic refrigeration.

The present work reveals an especial agreement between the experimental results and the continuous curves investigated by the numerical calculations in (1 − x)La0.7Ca0.2Sr0.1MnO3/xLa0.7Ca0.15Sr0.15MnO3 composite system. Moreover, the ability to adjust the magnetic entropy change in a large temperature range is revealed to be possible by the mixture of both individual phases La0.7Ca0.2Sr0.1MnO3 and La0.7Ca0.15Sr0.15MnO3. Our samples have been synthesised using the solid state method. Rietveld refinements of the X-ray diffraction patterns show that both samples are single phase. The Curie temperature TC is found to be 308 K and 338 K for La0.7Ca0.2Sr0.1MnO3 and La0.7Ca0.15Sr0.15MnO3, respectively. Moreover, the magnetic entropy change and the Relative Cooling Power (RCP) values were estimated. We have shown that the optimum magnetocaloric effect at μ0H = 2T has been found for the composition with x = 0.45, which exhibits a table-like ΔS curve with a peak value slightly lowered and strongly expanded when comparing with the parent compounds.

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.

Structural, magnetic and magnetocaloric properties of La 0.7-x Dy x Sr 0.3 MnO 3 (x = 0.00, 0.01 and 0.03) powder samples have been investigated by X-ray diffraction (XRD) and magnetic measurements. Our samples have been synthesized using the sol-gel method. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and we have noticed that the Dy doping causes a structural transition from a rhombohedral structure with R-3c space group to an orthorhombic one with Pnma space group and a decrease in the unit cell volume. In fact, the substitution of La 3+ by Dy 3 induces a distortion of the unit cell, an elongation along the a- and c-axes and therefore a decrease of the unit cell volume. Magnetization measurements versus temperature in a magnetic applied field of 0.05 T show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature T C is found to be 319 K, 315 K and 264 K for x = 0.00, 0.01 and 0.03, respectively. Arrott plots show that all our samples exhibit a second order magnetic phase transition. From the measured magnetization data of La 0.7-x Dy x Sr 0.3 MnO 3 (x = 0.00, 0.01 and 0.03) samples as a function of the magnetic applied field, the associated magnetic entropy change |−ΔS M | and the relative cooling power RCP have been determined. In the vicinity of T C , |−ΔS M | reached, in a magnetic applied field of 5 T, a maximum value of 1.63 J/KgK, 1.21 J/kg K and 1.05 J/kg K for x = 0.00, 0.01 and 0.03, respectively.

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.

The critical properties of La0.7Ca0.2Sr0.1MnO3 manganite elaborated using two different methods have been investigated around the ferromagnetic-paramagnetic phase transition. Our sample was successfully synthesized by solid-state reaction (S1) and sol-gel route (S2). The X-ray diffraction characterizations show that (S1) crystallized in orthorhombic structure with Pnma space group without any detectable impurity. Though, (S2) crystallized in rhombohedra structure with R-3C space group. Various techniques such as modified Arrott plots, Kouvel-Fisher method and critical isotherm analysis were used to determine the values of the Curie temperature TC, as well as the critical exponents β (corresponding to the spontaneous magnetization), γ (corresponding to the initial susceptibility) and δ (corresponding to the critical magnetization isotherm). The estimated results are close to those expected by the mean-field model for sample S2; while for sample S1, the exponents values are close to those expected using the tricritical model. The obtained values from critical isotherm M (TC, μ0H) are close to those determined using the Widom scaling relation, and also there are found to follow scaling equation with the magnetization data scaled into two different curves below and above TC, which implies the reliability and accuracy of the exponents. The change of the universality class can be explained by the reduction of the grain size. These results show that the critical behavior of our sample depend havely on the synthesis technique.

In this work, we studied in detail the magnetic and magnetocaloric properties of the La0.7Ca0.2Ba0.1MnO3 compound according to the phenomenological model. Based on this model, the magnetocaloric parameters such as the maximum of the magnetic entropy change ΔS M and the relative cooling power (RCP) have been determined from the magnetization data as a function of temperature at several magnetic fields. The theoretical predictions are found to closely agree with the experimental measurements, which make our sample a suitable candidate for refrigeration near room temperature. In addition, field dependences of ${{\Delta } S}_{\mathrm {M}}^{\max }$ and RCP can be expressed by the power laws ${\Delta S}_{\mathrm {M}}^{\max }\approx a$ (μ 0 H) n and RCP ≈b(μ 0 H) m , where a and b are coefficients and n and m are the field exponents, respectively. Moreover, phenomenological universal curves of entropy change confirm the second-order phase transition.

In this paper, a profound theoretical work has been conducted on magnetic and magnetocaloric properties of La0.65−x x Ca0.35MnO3 (0 ≤ x ≤ 0.15) perovskite manganites. Our work is based on a phenomenological model. The magnetization data as a function of temperature at several magnetic fields allows to determine the magnetocaloric parameters such as the maximum of the magnetic entropy change (ΔS M), the relative cooling power (RCP), and the magnetic specific heat change (ΔC P). The theoretical predictions nearly match with the experimental measurements. These materials present large magnetocaloric effect, suggesting their possible application in moderate magnetic fields.

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.

La 0.7 (Ca,Sr) 0.3 Mn 1−x Gd x O 3 (with x = 0; x = 2% and x = 6%) manganites samples have been studied by several techniques including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), 55 Mn and 139 La nuclear magnetic resonance (NMR) spectroscopy and magnetometric measurements. The X-ray powder diffraction shows that all the prepared samples are single phase. La 0.7 Ca 0.15 Sr 0.15 MnO 3 manganite is crystallized in the rhombohedral structure, whereas a structural transition towards orthorhombic system is observed for x ≥ 2%. Magnetization as a function of temperature shows that all samples exhibit a ferromagnetic (FM)-paramagnetic (PM) phase transition. Gadolinium doping in Manganese site was found to induce a strong initial decrease of the Curie temperature T C . The single double-exchange-narowed 55 Mn NMR line, though broadened by Gd, demonstrates a metallic state in all samples. The current manganites exhibit a second-order magnetic phase transition at T C , which is also confirmed by the criterion of Banerjee. In addition, the normalized entropy change curves of all the compounds collapse onto a universal master curve, a further signature of a second-order transition. The Gd-doped compounds undergo a large magnetocaloric effect, with an enhanced width T FWHM of the entropy change peak as compared to the Gd-free materials, and have consequently potential applications in magnetic refrigeration.

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.