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In this study, the magneto-caloric and magneto-transport properties of the perovskites manganites composites (x = 0.00, 0.07, and 0.18) synthesized by the solid-state reaction method are reported. X-ray diffraction (XRD) study to confirm the formation of two phases in composites. The Arrott plot analysis and master curve behavior reveal a second-order magnetic phase transition in the composite samples. Indeed, the value of the magnetic entropy (ΔSM) correlates with that predicted by Landau and Hamad models. On the other hand, the resistivity of the composite samples was measured at the applied magnetic fields of 0 T, 2 T, and 5 T. All the specimens undergo a metallic–semiconductor transition at the temperature Tρ. The temperature dependence of resistivity shows that the transport behavior is governed by the grain boundaries. It is suggested that the CuO addition acts as a separation layer between grains. Therefore, around room temperature, the magnetoresistance (MR) enhancement of the composite is caused by the magnetic disorder. The enhanced MR and ∆SM of these composites make them attractive for potential applications. [ABSTRACT FROM AUTHOR]

The La0.7Sr0.3Mn0.95Fe0.05O3 sample has been prepared by solid-state method. The crystallographic analysis demonstrates that the sample crystallizes with the P n m a space group in the orthorhombic structure. For the morphologic study, the size counting garnered from SEM images, the value of the average grain size is DSEM = 140 nm. A phenomenological model is used in present research work to explain the magnetocaloric effect. Using the measurements of magnetization, the magnetocaloric properties are estimated under different external magnetic fields based on this model. Additionally, based on the modified Bean–Rodbell model, we theoretically studied the magnetocaloric properties of the elaborated material with consideration of the magnetic disorder effect. [ABSTRACT FROM AUTHOR]

In this research paper, we have carried out an in-depth study of the critical phenomena at the FM–PM phase transition for Nd0.5Ba0.5CoO3 (NBCO). The FM–PM phase transition is identified as second order for our material. Moreover, the critical exponents of NBCO compound were estimated based on multiple techniques such as Kouvel–Fisher, modified Arrott plot method, and critical isotherm analysis. Therefore, the average values of the critical exponent and the critical temperature obtained by the various methods are (βmoy = 0.506; γmoy = 1.011; δmoy = 3.042; TC = 125.543). The obtained critical exponents are in agreement with the mean-field model. Furthermore, the exponent n as a function of temperature reveals the non-homogeneous nature of NBCO compound. According to the mean field theory, the magnetic entropy change (ΔSM vs. M2) was invested to determine the spontaneous magnetization (Mspont) values. Results match reasonably well with those obtained from the classical extrapolation of Arrott plots (μ0H/M vs. M2). [ABSTRACT FROM AUTHOR]

We discussed the binary rare-earth-based intermetallic Er1-xCo2 systems structurally, magnetically and in the field of the magnetic cooling with the effect of Er deficiency on all these properties. Four series of Er1–xCo2 (x = 0.00; 0.04, 0.06, 0.08 and 0.15) samples were prepared via arc-melting method and investigated as magnetic refrigerants. A high magnetocaloric effect was detected in these systems that follow a first-order magnetic transition. Magnetic entropy changes were most important compared to those of other Laves phase compounds. Structures of x = 0.00–0.06 compounds were indexed as a cubic state of space group Fd-3m with MgCu2 structure-type, e.g. as Laves phase. Whereas compounds of x = 0.08 and x = 0.15, due to the presence of some peaks, were attributed to rhombohedral as a second phase symmetry of space group R-3m with PuNi3 structure type. All systems were characterized by ferrimagnetic to paramagnetic transition upon temperature increase. Er1–xCo2 compounds exhibited significant relative cooling power values, i.e. at x = 0.06 sample, achieving approximately 585.52 J/kg at 7 T, making them appropriate candidates for the magnetic refrigeration technique. [ABSTRACT FROM AUTHOR]

In this research paper, a detailed investigation is conducted on the magnetocaloric effect (MCE) properties of the two phases (1−x) La0.6Ca0.4MnO3/(x) La0.6Sr0.4MnO3 composite system by experiments and numerical calculations. The polycrystalline manganites La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3 are synthesized by the citric-gel method. Rietveld refinements of the X-ray diffraction patterns show that both samples are single phase. The Curie temperature Tc is found to be 255 and 365 K for La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3, respectively. The study of the temperature dependence of the magnetic entropy change of (1−x)La0.6Ca0.4MnO3/(x)La0.6Sr0.4MnO3 composite indicates that the optimum composition stands for x = 0.6. Indeed, it gives comparable contributions of two parent compounds, leading to a practically uniform variation of entropy over a wide temperature range. The theoretical modeling of the MCE using Landau theory reveals an acceptable concordance with experimental data indicating the importance of magnetoelastic coupling and electron interaction in the MCE properties of manganite systems. [ABSTRACT FROM AUTHOR]

In the present work, we aim to analyze the magnetocaloric and electrical properties of (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 manganite prepared by solid-state method at high temperature. The experimental results of the magnetization show that the (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 compound exhibits a paramagnetic–ferromagnetic transition at TC = 240 K. In addition to the experimental study, theoretical approaches are adopted to investigate the magnetocaloric behavior of this sample. The important parameters such as maximum entropy change, full width at half maximum (δTFWHM) and relative cooling power are explained qualitatively. The electrical properties of the studied sample have been investigated by using a complex impedance spectroscopy technique. These electrical measurements reveal that (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 sample exhibits a metallic behavior at low temperature and insulator one at high temperature. The temperature (TMI) of the metal–insulator transition is found to be about 240 K. The effects of frequency, temperature and composition on permittivity ε′, ε″ and dielectric loss (tanδ) have been also discussed in terms of hopping of charge carriers between Mn3+ and Mn4+ ions. [ABSTRACT FROM AUTHOR]

In this paper, we study the structural, magnetic, and magnetocaloric properties of the polycrystalline peroviskite manganites La0.5Pr0.3Ba0.2Mn1-xTixO3 with x = 0 and 0.1. Our samples were prepared by solid-state reaction method. The XRD study has been analyzed by Rietveld refinement technique. Both samples crystallize in the rhombohedral symmetry with R 3 ¯ c space group. The second order of magnetic phase transition in all samples is confirmed by the Arrott analysis and the behavior of the master curve. Moreover, the magnetic entropy change ∆SM has been determined by the Maxwell relation, using phenomenological model and Landau theory. The relative cooling power (RCP) value under a magnetic field of 5 T is 236.29 J kg−1 for La0.5Pr0.3Ba0.2Mn0.9Ti0.1O3 sample which will be an interesting compound for application materials. Also, an agreement was found between the magnetic entropy change values calculated by Landau theory and those obtained using Maxwell relation above TC and a difference below it, for a magnetic field of 2 T. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the influence of substitution of Nd by Sr on the structural, magnetic, and magnetocaloric properties of Nd1 − xSrxMnO3 (x = 0.3 and x = 0.4). These compounds were prepared using the solid state method. The structural, morphological, and magnetic properties of our system were characterized by XRD, MEB techniques, and a magnetometer for magnetic characterization. The Rietveld refinement has revealed the coexistence of both Pnma orthorhombic and R-3c rhombohedral phases. The magnetic data indicate that the compounds exhibit a continuous paramagnetic (PM) to ferromagnetic (FM) phase transition. In addition, the critical behavior in both compounds associated with the magnetic phase transition has been studied by the magnetization isotherms. The critical exponents are deduced using various techniques such as the modified Arrott plot, Kouvel–Fisher plot, and critical isotherm technique. Finally, the results obtained of the magnetocaloric effect are in agreement with the reported values of previous researches. These results show that our samples can be used as a magnet refrigerant at room temperature. [ABSTRACT FROM AUTHOR]

Polycrystalline perovskite AMn1−xTiO3 with A = La0.5Pr0.2Sr0.3 (x = 0.0 and 0.1) have been prepared using solid-state reaction method. X-ray powder diffraction and Rietveld refinement revealed that all samples crystallize in a rhombohedral structure with space group R 3 ̄ c From M–T curve, we determined the Curie temperature, where the magnetization value decreases abruptly. The Curie temperature (TC) decreases from 280 to 123 K when the percentage of Ti increases to 10%. The values of the magnetization M(H) decrease when increasing the Ti content. Moreover, the magnetocaloric effect (MCE) was estimated in terms of isothermal entropy change (−ΔSM) using the M(T, μ0H) data and employing the thermodynamic Maxwell equation. In addition, using a phenomenological model, we determine magnetocaloric effect from the calculation of magnetization as a function of temperature under different external magnetic fields. Also, we can determine the relative cooling power (RCP) and the specific heat which varies from 2.803 to 7.354 J/(kg/K) for the undoped sample from M(T, μ0H) data at different magnetic fields theoretically. [ABSTRACT FROM AUTHOR]

The structure, magnetic and magnetocaloric properties of arc-melted Gd2Fe17-xCux (x= 0, 0.5, 1 and 1.5) solid solution have been studied. The Rietveld refinement shows that these compounds crystallize in the rhombohedral Th2Zn17-type structure with the R3¯m space group, and the substitution of iron by copper leads to a decrease in the unit cell volume. The Curie temperature (TC) of the prepared samples depends on the copper content. The reduction of the ferromagnetic phase transition temperature from 475 K (for x=0) to 460 K (for x=1.5) is due to the substitution of the magnetic element (Fe) by non-magnetic atoms (Cu). The magnetocaloric effect was determined in the vicinity of the Curie temperature TC. By increasing the Cu content, an increase in the values of magnetic entropy (ΔSM) in a low applied field is observed. The preferred inequivalent crystallographic site of Cu atoms was determined by Mössbauer spectrometry analysis based on the isomer shift parameter correlation with the Wigner-Seitz cell volumes. [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]

Structural, magnetic, magnetocaloric, electrical properties, and spin-polarized tunneling effect in La0.5Ca0.3Te0.2MnO3 polycrystalline were studied in details. The temperature dependence of the inverse of the magnetic susceptibility indicates the presence of ferromagnetic exchange interaction between the nearest neighbors at the Weiss temperature θp = 265.32 ± 0.109. Based on the magnetic field dependence of magnetization, M(H), and employing the thermodynamic Maxwell equation, the magnetic entropy change |ΔSM| of the studied sample was determined. The maximum entropy change value of the system was around 4.99 J kg−1 K−1 under a magnetic field of 5 T. Electrically, the upturned region of resistivity was observed at low temperature. The recovery of the resistivity was found to be strongly affected by the external magnetic field. The electrical data were analyzed considering various models. Interestingly, the exception of the spin-polarized tunneling (SPT) model is in good agreement with the experimental data among other models. In the current work, the SPT is the dominant mechanism leading to the rise of resistivity, while decreasing the temperature values. Magnetotransport analysis was successfully carried out using percolation model in the temperature range between around 50 K to nearly 300 K under different magnetic fields up to 8 T. The isothermal field dependence of magnetoresistance was recorded fairly well via a phenomenological model based on the spin-polarized tunneling model. [ABSTRACT FROM AUTHOR]

The composite $$(\hbox {La}_{0.67}\hbox {Ca}_{0.33}\hbox {MnO}_{3})/\hbox {La}_{0.7}\hbox {Ba}_{0.3}\hbox {MnO}_{3})$$ sample was prepared using the conventional solid-state reaction method, and their crystallographic structure was achieved by X-ray diffraction pattern analysis. The magnetic and magnetocaloric effect has been studied by magnetization measurements. Based on the relation: $$\chi ^{-1}(T)\propto (T-T_\mathrm{C}^\mathrm{Rand} )^{1-\lambda }$$ , the inverse of susceptibility shows a downturn before $$T_\mathrm{C }$$ indicating the existence of Griffiths phase for the temperature range $$T_\mathrm{C}^\mathrm{Rand}

We report an interesting structural and nanostructural correlation to the Curie temperature and coercivity, respectively. The effect of Ni substitution and magnetocaloric effect (MCE) response for the uniaxial nanocrystalline SmNi2Fe compound was demonstrated. The nanocrystalline SmNi2Fe(SmNi2Fe) powder has been synthesized by mechanical milling for the first time. The nanocrystalline SmNi2Fe powder has been synthesized by mechanical milling. The structural properties have been studied by x-ray diffraction and have been refined with the Rietveld method. This analysis reveals that the samples crystallize in the rhombohedral PuNi3-type structure (R3m-space group). The Curie temperature of SmNi2Fe material is about 450 K. It is a direct measure of the exchange interaction, which is the origin of ferromagnetic phase transition. This interaction depends markedly on the interatomic distance. The magnetic entropy change Δ SM, as well as the relative cooling power around the second-order magnetic transition and the Arrott plots for the compound have been reported. It was estimated from isothermal magnetization curves, and it decreases with the increase of Fe content from 2.3 J/kg K (x = 0) to 0.6 J/kg K (x = 0.8) at 50 kOe. The compound presents high coercivity exceeding 12 kOe at room temperature, obtained based on the optimization of SmNi2Fe nanostructure. The objective of this optimization is to obtain a homogeneous nanostructure developed by the mechanical milling process, subsequent annealing and to the high uniaxial magnetocrystalline anisotropy. [ABSTRACT FROM AUTHOR]

The SmNiFe ( x = 0; 0.3 and 0.8) were synthesized by arc melting and annealed at 1073 K for 1 week. The Rietveld refinement showed that these compounds crystallize in the PuNi-type structure ( $R\bar 3m$ -Space group) and the substitution of nickel by iron leads to an increase of the unit cell volume. The Curie temperature (T) of the SmNiFe ( x = 0; 0.3 and 0.8) samples increases from 60 K for SmNi to 230 K for SmNiFe, the enhancement of T is ruled by electronic and magnetovolumic effects. All the samples exhibit a second-order magnetic phase transition at Curie temperature T. The magnetic entropy change Δ S was estimated from isothermal magnetization curves and it decreases with the increase of Fe content from 2.3 J/kg.K ( x = 0) to 0.6 J/kg.K ( x = 0.8) at 50 kOe. The critical properties of SmNiFe (as an example) intermetallic compound at the ferromagnetic-paramagnetic (FM-PM) transition have been analyzed. The estimated critical exponents derived from the magnetic data using various methods such as modified Arrott plot, Kouvel-Fisher method and critical magnetization isotherms M( T , H). The critical exponent values for the material are in a close agreement with those predicted for the mean-field theory. The reason for this behavior may be long-range interactions between spins in this system. [ABSTRACT FROM AUTHOR]

The structural, magnetic, and magnetocaloric properties of Er6Fe23-xAlx (x = 0 and 3) intermetallic compounds have been studied systematically. Samples were prepared using the arc furnace by annealing at 1073 K for one week. Rietveld analysis of XRD shows the formation of pure crystalline phase with cubic Fm-3m structure. Refinement results show that the unit cell volume decreases with increasing Al content. The Curie temperature Tc of the prepared samples was found to be strongly dependent on the aluminum content. This reduces magnetization and the ferrimagnetic phase transition temperature (Tc) from 481 K (for x = 0) to 380 K (for x = 3), is due to the substitution of magnetic element (Fe) by non-magnetic atoms (Al). With the increase of the Al content, a decrease in the values of magnetic entropy is observed. The magnitude of the isothermal magnetic entropy (|DSM|) at the Tc decreases from 1.8 J/kg·K for x = 0 to 0.58 J/kg.K for x = 3 for a field change 14 kOe. Respectively, the relative cooling power (RCP) decreases with increasing Al content reaching 42 Jkg-1 for x = 0 to 28 Jkg-1 for x = 3. [ABSTRACT FROM AUTHOR]

An investigation of the critical behavior and magnetic entropy from resistivity of (La 0.75 Nd 0.25 ) 2/3 (Ca 0.8 Sr 0.2 ) 1/3 MnO 3 is presented. The magnetocaloric properties of the polycrystalline manganite (La 0.75 Nd 0.25 ) 2/3 (Ca 0.8 Sr 0.2 ) 1/3 MnO 3 based on resistivity measurements were investigated. Using, the equation Δ S = − α ∫ 0 H ∂ L n ( ρ ) ∂ T ) H d H relates magnetic order to the transport behavior of the compound, we measure the magnetic entropy change Δ S M from the resistivity which is similar to that calculated from the magnetic measurement. Moreover, we have found an excellent estimation of critical behavior from resistivity and magnetic analysis. [ABSTRACT FROM AUTHOR]

We report magnetic properties of (LaCaMnO)/ x(CuO) compounds in terms of isothermal magnetization analysis and scaling behavior with various critical exponents in the vicinity of the PM to FM transition region. According to the Banerjee criterion, we found that the FM-PM phase transition is the type of SOMT. Moreover, the critical exponents β, γ, and δ are determined using the modified Arrott-plot (MAP), the Kouvel-Fisher method (KF), as well as the critical isotherm (CI) analysis. The estimated results are close to those expected for three-dimensional Heisenberg class with short-range interaction. From the field dependence of RCP and Δ S , it was possible to evaluate the critical exponents of the magnetic phase transition. These values are in good agreement with those obtained from the critical exponents using the Kouvel-Fisher plot (KF). Finally, we used the scaling hypotheses to scale the heat capacity changes to a single universal curve for (LaCaMnO)/ x(CuO) composites. [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]

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: In the present work we analyze the magnetic entropy change ΔS M of La0.8Pb0.1MnO3 (LPMO) and La0.8Pb0.1Na0.1MnO3 (LPNMO). Using Arrott plots, it was found that the phase transition for both samples is of second-order. The presence of short-range magnetic order (SRMO) in the paramagnetic phase of these samples greatly depresses the magnetic entropy: the values are well below the values expected without considering the effect of SRMO. Moreover, the analysis of the MCE using Landau theory of phase transition shows that the contributions to the free energy from the presence of ferromagnetic clusters are strongly influencing the MCE by coupling with the order parameter around the Curie temperature. [ABSTRACT FROM AUTHOR]

Abstract: The structural and magnetic properties of perovskite oxides La0.7Ca0.3−x K x MnO3 (0≤ x ≤0.15) have been investigated to explore the influence of the A-site cation size-disorder (σ 2). The materials were prepared by the solid-state method and then characterized by X-ray diffraction (XRD). The XRD data have been analyzed by Rietveld refinement technique. For K doping concentration x ≤0.075, the samples crystallize in the orthorhombic structure, while for x ≥0.1, the structure becomes rhombohedral. The variation of the magnetization M as a function of the applied magnetic field μ 0 H reveals the presence of a structural distortion leading to a reduction of the magnetization at low μ 0 H values. When increasing μ 0 H, the structural distortion decreases and for a high applied magnetic field, the M (μ 0 H) curves saturate indicating the disappearance of the structural distortion. The influence of K doping concentration and the applied magnetic field on the magnetocaloric properties has been considered. A large magnetic-entropy change (|ΔS M|∼5J/kgK) is obtained in all samples at Curie temperatures between 270 and 280K for an applied magnetic field of 3T. These results show that these materials can be used as candidates for magnetic refrigerants near room temperature. [Copyright &y& Elsevier]

The lanthanum deficiency manganites La0.8-x□xCa0.2MnO3 (x = 0, 0.1 and 0.2), where □ is a lanthanum vacancy, were prepared using the classic ceramic methods with different thermal treatments (1373 K and 973 K). The structural, magnetic, and magnetocaloric properties of these compounds were studied as a function of annealing temperature. It was noted that the annealing temperature did not affect the crystal structure of our samples (orthorhombic structure with Pnma space group). Nevertheless, a change in the variation of the unit cell volume V, the average bond length dMn–O, and the average bond angles θMn–O–Mn were observed. Magnetization versus temperature study has shown that all samples exhibited a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase with increasing temperature. However, it can be clearly seen that the annealing at 973 K induced an increase of the magnetization. In addition, the magnetocaloric effect (MCE) as well as the relative cooling power (RCP) were estimated. As an important result, the values of MCE and RCP in our Lanthanum-deficiency manganites are reported to be near to those found in gadolinium, considered as magnetocaloric reference material.

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]

Abstract The critical behavior of manganite perovskite type La 0.8-x·x Na 0.2-x·x MnO 3 (with x = 0 and 0.1) was studied based on the experimental magnetic measurements in the paramagnetic ferromagnetic transition region using different techniques such as the modified Arrott plot, the Kouvel-Fisher method and critical isothermal analysis. Experimental results revealed that the two samples show a second-order magnetic phase transition. The deduced critical exponents are close to a 3D Ising model for La 0.8 Na 0.2 MnO 3 and a 3D tricritical mean field model for La 0.7·0.1 Na 0.1·0.1 MnO 3. The reliability of these critical exponents was confirmed by the Widom scaling relation and the universal scaling hypothesis. Moreover, an excellent agreement was found between the spontaneous magnetization determined from the entropy change and from the extrapolation of the modified Arrott plots, confirming the universal behavior of the magnetocaloric effect in these systems. Highlights • The β, γ and δ critical exponents are determined with various techniques. • We deduce from (RS) that the ising mean-field model is the most adequate model for La 0·8 Na 0.2 MnO 3 and the tricritical mean-field model for La 0.7·0.1 Na 0.1·0.1 MnO 3. • Correlation between the critical behavior and the magnetocaloric properties to be determined. [ABSTRACT FROM AUTHOR]

The structural, critical behavior and magnetocaloric properties of Pr 2 Fe 16.9 Ni 0.1 alloy have been studied. Rietveld's refinement of the X-ray powder diffraction patterns shows that the sample crystallizes in the rhombohedral structure with an R 3 ¯ m space group. Based on thermomagnetic measurements, critical behavior was investigated using the modified Arrott plot, Kouvel-Fisher methods, and critical isotherm analysis. The critical exponents (β , γ , and δ) were found to be similar to the 3D-Ising type indicating that the magnetic interactions extend beyond the nearest neighbors. Furthermore, Pr 2 Fe 16.9 Ni 0.1 exhibits a direct magnetocaloric effect around room temperature with moderate magnetic entropy change (− Δ S M max = 6.2 J.kg−1.K−1 at μ 0 Δ H = 5 T) and a wide working temperature range. Additionally, the Relative Cooling Power (RCP) is about 89% of the well-known gadolinium (Gd) for μ 0 Δ H = 2 T. The good magnetocaloric response of this compound is comparable or even better than that of many other intermetallic alloys. • Iron-Rich intermetallic Pr 2 Fe 16 Ni 0.1 alloy was prepared by arc melting. • High-resolution X-ray diffraction reveals that the Th 2 Zn 17 -type rhombohedral crystal structure is maintained. • Magnetic analysis revealed that our sample exhibited a PM - FM transition near room temperatures. • The determined critical exponents are close to those predicted 3D-Ising model. • A ramarkable magnetocaloric effect in the Pr 2 Fe 16.9 Ni 0.1 alloy is observed around room temperature. [ABSTRACT FROM AUTHOR]

Structural, magnetic and magnetocaloric properties of La 0.5 □ 0.1 Ca 0.4 MnO 3 manganite prepared by conventional solid state reaction route have been carried out. The X-ray diffraction characterization has revealed that this sample crystallized in the orthorhombic symmetry, with Pnma space group. In order to check if this sample can be good candidate for magnetic refrigeration, relative cooling power was determined depicting that the sample can be useful for magnetic refrigeration at with about 232.20 J/kg under a magnetic field of 5 T. The magnetocaloric data has been well analyzed by using the Landau theory. The theoretical and experimental plots seem nearly similar. Based on these amazing properties, our compound is suggested as an effective candidate for various potential applications such as refrigeration application. [ABSTRACT FROM AUTHOR]

With a view to investigate the influence of nanosize on the magnetocaloric properties of the La 0.67 Sr 0.33 MnO 3 nanoparticles, a systematic investigation of their temperature-dependant magnetic entropy change has been undertaken. The maximum of magnetic entropy change - Δ S M max and the relative cooling power ( RCP ) decrease with decreasing particle size. As a result the magnetocaloric effect was greatly changed by the particle size. Indeed, the relative cooling power can be tuned dramatically by particle size. Moreover, the nature of phase transition has been determined using Banerjee’s criterion plots and confirmed by the construction of the universal curve of the magnetic entropy change. [ABSTRACT FROM AUTHOR]