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The La0.9·0.1MnO2.9 compound were prepared by sol–gel method with the aim of obtaining a material with interesting magnetocaloric and thermoelectric properties. The prepared material crystallized in rhombohedric system with R-3c space group. In the magnetization vs. temperature graph, it is observed a paramagnetic (PM)-ferromagnetic (FM) transition with a Curie temperature TC of 209 K. From the fit of hysteresis cycle at 5 K, it is observed that the dominant contribution is ferromagnetic. A magnetic entropy change, calculated from the isothermal magnetization curves, was observed for the sample with a peak centered on TC. The total electronic density states (TDOS) show the coexistence of metallic behavior for spin-up states and semiconductor characteristic, with a Eg = 1.3 eV, for spin-down states. Thermoelectric properties analysis revealed promising behavior with ZT that assesses the efficacy of a compound in a thermoelectric field, reaching 1.1 at 420 K. [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]

The critical behavior of La0.6Sr0.4MnO3/x(Sb2O3) (x = 0.07 and x = 0.18) compounds has been studied based on the data of static magnetic measurements in the vicinity of its critical temperature TC. Using various techniques such as modified Arrott plot, Kouvel–Fisher method and critical isotherm analysis, the estimated critical exponents are found to be (β = 0.323, γ = 1.238, δ = 4.862 at TC = 350.719) and (β = 0.321, γ = 1.243, δ = 4.37at TC = 365.054), for x = 0.07 and 0.18, respectively; both close to Ising model values. The reliability of critical exponents values was confirmed by the Widom scaling relation and the universal scaling hypothesis. Based on 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. To study the influence of critical exponents on magneto-caloric effect, the local exponent n was studied in terms of the field dependence of the magnetic entropy change. From the field dependence of RCP and ΔSM, 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 (K-F). [ABSTRACT FROM AUTHOR]

A detailed study of structural, magnetic, magnetocaloric and magneto-transport properties of Nd0.6Sr0.4−xKxMnO3 (x = 0.0, 0.1 and 0.2) manganite, prepared using the sol–gel process, has been performed. All compounds are pure single phase crystallized in the orthorhombic system with Pnma space group. Rietveld analysis reveals the dependence of structural properties upon the monovalent substitution rate. The nanometric size determined through Debye–Scherrer formula is validated by SEM micrographs. Magnetization curves as a function of temperature exhibit a clear ferromagnetic to paramagnetic (FM-PM) phase transition at Curie temperature (Tc) which is found to decrease with increasing K fraction x. Large relative cooling power (RCP) value standing for about 50% of that noticed in pure Gd under magnetic field of 5 T is achieved for x = 0.0 compound, indicating its potential application in the cooling fields. Electrical resistivity curves as a function of temperature exhibit a metal–semiconductor (M-Sc) transition for all samples. The magnetoresistance (MR) ratio reaches its highest value for x = 0.2 sample under an external magnetic field of 2 T making this material a promising magnetoresistive sensor used in a wide range of industrial applications. Significant values of thermal coefficient of resistivity (TCR) are noted under zero external magnetic field giving these materials a potential application for the infrared (IR) and bolometric detectors. [ABSTRACT FROM AUTHOR]

In this work, we study the structural and dielectric properties of La0.5Pr0.3Ba0.2Mn1-xTixO3 (x = 0.0 and 0.1) samples prepared using the solid-state reaction technique. The X-ray structural analysis using Rietveld refinement method exhibits that both compounds are single phase and crystallize in the rhombohedral structure with R 3 ¯ C space group. In addition, a scanning electron microscopy (SEM) study proved an increase in the grain size with substitution of Mn by Ti in the B site. The dielectric properties of these compounds have been studied by complex impedance spectroscopy in the frequency range from 40 Hz to 1000 kHz and temperatures from 100 K to 200 K. The DC conductivity decreases with the substitution of Ti, and the experimental data were fitted by Jonscher's universal power law. The impedance plot exhibits semicircle arcs at different temperatures. Similarly, the variations of imaginary parts of modulus and impedance show an electrical relaxation phenomenon with non-Debye nature for both samples. The values of the activation energy are determined from the conductivity data analysis and imaginary impedance. [ABSTRACT FROM AUTHOR]

In the current research work, a phenomenological model is applied to describe the magnetocaloric effect (MCE) of the two phases 0.75 La0.6Ca0.4MnO3/0.25 La0.6Sr0.4MnO3 composite system. Based on this model, the values of the magnetocaloric properties are predicted from the calculation of magnetization as a function of temperature under different external magnetic fields. A significant MCE is obtained over a large range of temperature compared to those observed in the mother compounds, La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3, making of this material considered as a promising candidate for magnetic refrigeration applications in moderate magnetic fields near room temperature. The results are then compared to those obtained experimentally in our previous work. The excellent agreement observed between both data proves the validity of the adopted model in the estimation of the MCE properties of material under investigation. [ABSTRACT FROM AUTHOR]

This report presents the structural, magnetoresistance (MR) and magneto-electrical properties of Ag substituted La0.57Nd0.1Sr0.13Ag0.2MnO3 compound synthesized by solid state reaction method. To obtain crystallographic parameters, the X-ray diffraction patterns are fitted in R-3c space group with Rietveld refinement method. The resistivity and magneto-transport measurements are performed using standard four-probe assembly with and without magnetic fields. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic isolant regions. So, we found that the estimated results are in adequate accordance with experimental data. The obtained values of the temperature coefficient of resistance (TCR) for La0.57Nd0.1Sr0.13Ag0.2MnO3 sample are comparable with some systems used for infrared sensors. The Large MR of La0.57Nd0.1Sr0.13 Ag0.2MnO3 is suitable for utilization in electronic instruments such as computer hard discs, high field magnetic sensors, and memory devices. [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]

Abstract We report on the structural, magnetic and transport properties of the Pr-doped manganite (La 1- x Pr x) 0.7 Ba 0.3 MnO 3 (x = 0.05 and 0.15). X-ray diffraction data demonstrate that both samples possess dual crystallographic phases: rhombohedral R 3 ¯ c and orthorhombic Pnma. This is due to the martensitic phase transition inherent to the pristine La 0.7 Ba 0.3 MnO 3 sample, whose impact is seen as a second metal-insulator (MI) transition below the ordered temperature in electric measurements. Griffiths phase (GP)-like behavior in the inverse magnetic susceptibility (χ−1(T)) was observed only for Pr -15%. The origin of the Griffiths singularity could be understood in terms of the competing accommodation strain arising from martensite-like phase transition and quenched disorder. Interestingly, GP cannot be considered as a precursor for the magnetoresistance (MR), but can be essential for improving the temperature coefficient of resistance (TCR). At low temperature, the magnetization follows the Bloch's T 3/2 law, while the resistivity shows a shallow minimum in both samples. Our work reveals that, at low temperature, the influence of the magnetic contribution of Pr3+ becomes relevant against the quenched disorder (σ 2). These findings suggest that quenched disorder, strain field, and the coupling between rare-earth and Mn3+/Mn4+ sublattice are important factors in determining the structural and magneto-transport properties in manganite systems. Graphical abstract Image 1 Highlights • Quenched disorder destroys the martensitic transition. • Two metal–insulator transitions are detected in the electrical resistivity. • Griffiths singularity improve the temperature coefficient of resistance. • A shallow minimum has been observed at low temperature resistivity. [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 electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic isolant regions. So, we found that the estimated results are in adequate accordance with experimental data. The relationship between electrical and magnetic properties of manganites has been traced through the analysis of temperature dependence of the La0.6Sr0.4Mn0.9V0.1O3 resistivity. The estimated critical exponents are (β = 0.326 ± 0.01; γ=1.237 ± 0.02 and α = 0.112). The values of these exponents obtained from resistivity are very close to them predicted by the 3D-Ising model. These results are in good agreement with the analysis of critical exponents from magnetization measurements. The obtained values of the temperature coefficient of resistance (TCR) for La0.6Sr0.4Mn0.9V0.1O3 sample is comparable with some systems used for infrared sensors. [ABSTRACT FROM AUTHOR]

Based on the modified Arrott plots and the critical isotherm analysis, the critical exponents of both LaCaMnO and LaCaAgMnO systems have been comprehensively studied and investigated near the paramagnetic-ferromagnetic (PM-FM) phase transition. Critical exponents, β, γ, and δ, which are corresponding to the thermal variation of the spontaneous magnetization, initial susceptibility, and the isothermal magnetization, respectively, obeyed the Widom scaling law δ = 1 + γ/β. It indicates thus the validity the obtained results. We performed then another analysis of the critical behavior via the magnetocaloric effect presenting an accord with the analysis of magnetization measurements. Relative cooling power (RCP) follows the evolution of the magnetic field as RCP ∼ H . The acquired critical exponents were in conformity with those gotten from the modified Arrott plots and Widom scaling law. [ABSTRACT FROM AUTHOR]

We investigated the influence of silicone (Si) doping on the structural, magnetic and electrical properties of polycrystalline sample La 0.6 Gd 0.1 Sr 0.3 Mn 0.8 Si 0.2 O 3 (LGSMSiO), prepared by sol–gel method. The crystallographic study showed that the sample crystallizes in orthorhombic system with Pnma space group. The relationship between the electrical and magnetic properties of manganites was traced through analyzing the dependence of LGSMSiO resistivity on temperature. The measurement of resistivity versus the temperature ρ(T) showed a transition change from ferromagnetic (FM) to paramagnetic (PM) at Curie temperature (T C ), this usually accompanied by a simultaneous metal-semiconductor (M-semiconductor) transition. Resistivity decreased with increasing the applied magnetic field. The values of T M-semiconductor were found to move towards a high temperature side with increasing the magnetic field. The critical properties of electron doped manganite LGSMSiO were investigated on the data of static magnetization measurements around the second order ferromagnetic-paramagnetic transition region T C . The magnetic data analyzed in the critical region using Kouvel-Fisher method yield the critical exponents of γ = 1.013 ± 0.02 with T C = 270.69 ± 0.22 K (from the temperature dependence of inverse initial susceptibility above T C ) and β = 0.2535 ± 0.0032 with T C = 269.89 ± 0.12 K (from the temperature dependence of spontaneous magnetization below T C ). The critical magnetization isotherm M(T C , μ 0 H) gives δ = 5.01 ± 0.03. The critical exponents found in this study obeyed the Widom scaling relation: δ = 1+γ/β, implying that the obtained values of γ and β are reliable. The exponents values obtained from resistivity were quite close to those predicted by the tricritical mean-field model. These results were in good agreement with the analysis of the critical exponents from magnetization measurements. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of the ferromagnetic metallic regions and the paramagnetic semiconductor regions. So, we found that the estimated results were in accordance with the experimental data. The magnetocaloric value is 5.35 J/kgK, extracted from the M(μ 0 H) curves. [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 influence of partial substitution of Mn by Si on the structural, magnetic and electrical properties of La 0.6 Gd 0.1 Sr 0.3 Mn 1-x Si x O 3 (0 ≤ x ≤ 0.15) is studied. All compositions were synthesized using the sol-gel technique. X-ray diffraction and structure refinement show that they crystallize in the rhombohedra structure with the R 3 ¯ c space group. The magnetization and electrical measurements versus temperature proved that all samples exhibit a paramagnetic to a ferromagnetic transition and a semi-conductor to a metallic one when the temperature decreases. The substitution of Mn by silicon (Si) leads to a continuous decrease of both the Curie temperature T C (from 350 K for x = 0.0–278 K for x = 0.15) and the resistivity transition temperature T M-Sc (from 325 K for x = 0.0–263 K for x = 0.15). The magnetoresistance (MR) as well as the resistivity are found to increase. [ABSTRACT FROM AUTHOR]

The critical properties of the electron-doped manganite LaSrMn V O were investigated based on the data of static magnetization in the vicinity of the ferromagnetic-paramagnetic phase transition. According to the modified Arrott plot, Kouvel-Fisher method, and critical isotherm analysis, we have determined the critical parameters ( T , β, γ, and δ) in the two characteristic regions of low and high magnetic fields. The estimated critical exponents are close with a 3D Ising model. The reliability of the critical exponent values was confirmed by the Widom scaling relation and the universal scaling hypothesis. Using the field dependence of RCP and Δ S , it was possible to evaluate the critical exponents of the magnetic transitions. These values are in good agreement with those obtained from the critical exponents using modified Arrott plot. [ABSTRACT FROM AUTHOR]

The magnetic properties and the critical behavior in SrNdMnO have been investigated by magnetization measurements. The magnetic data indicate that the compound exhibits a second-order phase transition. The estimated critical exponents derived from the magnetic data using various techniques such as modified Arrott plot, Kouvel-Fisher method, and critical magnetization isotherms M ( T, H). The critical exponent values for this compound was found to match well with those predicted for the mean-field model ( δ = 2.212 ± 0.124, γ = 0.975 ± 0.018, and β = 0.502 ± 0.012) at T = 228.59 ± 0.17. The critical exponent γ is slightly inferior than predicted from the mean-field model. Such a difference may be due, within the context of the quenched disorder and essentially the presence of the Griffiths phase. The temperature variation in the effective exponent ( γ) is similar to those for disordered ferromagnets. [ABSTRACT FROM AUTHOR]

This paper reports the magnetic and magnetocaloric properties of LaSrMnVO polycrystalline manganite elaborated using the solid-state reaction method. The X-ray powder diffraction shows that the prepared compound has a single phase. Magnetocaloric effect is calculated from the measurement of initial isothermal magnetization versus magnetic field at various temperatures. The enhanced relative cooling power (RCP) and ${\Delta } S_{\mathrm {M}}^{\max }$ values show that this sample has potentials for future technological application. Moreover, we have studied the universal behavior used as a further criterion to distinguish the order of the phase transition in LaSrMnVO. [ABSTRACT FROM AUTHOR]

We present the effect of vacancy in Pr0.6Sr0.4MnO3via dc magnetisation measurements. Using various techniques such as modified Arrott plots, the Kouvel–Fisher method, and Widom scaling relationship the values of TC (ferromagnetic transition temperature), as well as the β, γ and δ (critical exponents) are estimated. Critical exponents for the stoichiometric sample and the strontium deficient sample match well with those predicted for the tricritical mean field model. The vacancy in Pr0.5□0.1Sr0.4MnO3 changes the universal class. The estimated critical exponents of the praseodymium deficient sample are close to those found out by the 3D-Ising model. [ABSTRACT FROM AUTHOR]

This study presents the electrical properties, complex impedance analysis and dielectrical behavior of La0.5Ca0.5−xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤x≤ 0.2). Transport measurements indicate that all the samples have a semiconductor-like behavior. The metal-semiconductor transition is not observed across the whole temperature range explored [80 K–700 K]. At a specific temperature, a saturation region was marked in the σ (T) curves. We obtained a maximum σdc value at ambient temperature with the introduction of 20% Ag content. Two hopping models were applied to study the conduction mechanism. We found that activation energy (Ea) related to ac-conductivity is lower than the Ea implicated in dc-conductivity. Complex impedance analysis confirms the contribution of grain boundary to conductivity and permits the attribution of grain boundary capacitance evolution to the temperature dependence of the barrier layer width. From the temperature dependence of the average normalized change (ANC), we deduce the temperature at which the available density of trapped charge states vanishes. Such a temperature is close to the temperature at which the saturation region appears in σ(T) curves. Moreover, complex impedance analysis (CIA) indicates the presence of electrical relaxation in materials. It is noteworthy that relaxation species such as defects may be responsible for electrical conduction. The dielectric behavior of La0.5Ca0.5−xAgxMnO3 manganites has a Debye-like relaxation with a sharp decrease in the real part of permittivity at a frequency where the imaginary part of permittivity (ε′′) and tg δ plots versus frequency demonstrate a relaxation peak. The Debye-like relaxation is explained by Maxwell–Wagner (MW) polarization. Experimental results are found to be in good agreement with the Smit and Wijn theory. [ABSTRACT FROM AUTHOR]

Magnetocaloric effect and order of transition in (LaNd)(CaSr)MnO, prepared by conventional solid-state reaction, have been investigated. Using Banerjee criterion, we demonstrate first-order transition for ( J1) and ( J2 ) as well as second-order transition for ( J3 ), ( J4 ), and ( J5 ) samples. The Δ S is ranging between 9.18 Jkg K and 4.87 when Nd and Sr content changes leading to relative cooling power (RCP) varying between 330 and 229.35 J/kg. Both Δ S and the RCP are found sensitive to the disorder σ. The universal behavior obtained from Δ S variation curves confirmed the first-order transition for ( J1) and ( J2 ) samples and second-order transition for ( J3), ( J4), and ( J5 ) samples obtained by Banerjee criterion. All samples with second-order phase transition exhibit inhomogeneous character estimated from local exponent n. [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]

In this paper, we have studied the magnetic and magnetocaloric properties of the perovskite manganites LaPbAgMnO (0≤ x≤0.15), which show a sharp paramagnetic-ferromagnetic phase transition over a wide temperature range ( T=250-401 K). The Curie temperature has been analyzed by two methods: using the numerical derivative dM/ dT and the thermodynamic model. The experimental results indicate that T decreases from 368 to 288 K with increasing Ag substitution independently of the method used to obtain T. Upon 10 KOe applied magnetic field, the large magnetic-entropy change (|Δ S|) reaches values of 2.75, 3, 3.25 and 3.5 J/kg K for x=0, 0.05, 0.10 and 0.15 compositions, respectively, which are comparable to that of Gd. The relative cooling power (RCP) increases with increasing Ag content from 68.75 ( x=0) to 156.27 J/kg ( x=0.15) for Δ H=10 KOe. Through these results, LaPbAgMnO materials are strongly suggested for the use of active refrigerants for magnetic refrigeration technology near room 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: We present the effect of vacancy and Na doping on the critical behavior in La0.8Pb0.2MnO3 via dc magnetization measurements. Critical exponents values for La0.8Pb0.2MnO3 match well with those predicted for the three-dimensional Heisenberg model. The vacancy in La0.8Pb0.1□ 0.1 MnO3 does not alter the Heisenberg universality class. However, the critical isotherm exponent is slightly larger than predicted consistent with the presence of a Griffiths phase. For La0.8Pb0.1Na0.1MnO3, we found that the critical exponents values 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. [Copyright &y& Elsevier]

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]

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

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]

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]

The present work undertakes an investigation of magnetic memory effect in Dy 0.5 (Sr 1−x Ca x ) 0.5 MnO 3 (x = 0 and x = 0.3) nanoparticles heated at 700 °C and 1350 °C. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements displayed the existence of magnetic memory effect in only samples with a Ca concentration x = 0.3. However, there is no sign of magnetic memory in samples with x = 0 of Ca amount. This confirms that the effect of substituting the Sr by Ca on the appearance of magnetic memory is of great importance, admitting that magnetic memory is mainly due to the powerful inter-particle interactions. [ABSTRACT FROM AUTHOR]

Magnetic entropy change of Dy 0.5 (Sr 1−x Ca x ) 0.5 MnO 3 nanoparticles (0 ≤ x ≤ 0.3) was analyzed at low temperatures to investigate the magnetic refrigeration as a promising tool for hydrogen liquefaction. These samples depict interesting values of maximum magnetic entropy change and large relative cooling power, especially for x = 0.3 sample (about 169 J/Kg). It could be a promising candidate for magnetic refrigeration at cryogenic temperatures. Landau theory presents a discord between the experimental magnetic entropy change and the theoretical one. This disagreement is tending to be in accordance as Ca substitution is increasing and also with augmenting the applied magnetic field. [ABSTRACT FROM AUTHOR]

The effect of smaller and heavy rare-earth cation Gd 3+ ( r Gd 3+ =1.107 Å and S G d 3 + = 7 / 2 ) on the magnetic and structural properties of Nd 0.55 Sr 0.45 MnO 3 has been investigated. The orthorhombic structure (space group, Pnma ) evolves from orbital distorted- O ” type symmetry ( c > a ) for x =0 to orbital ordered- O ’ type ( a > c ) for x ≥ 0.1 . Diffraction data shows the crucial role of the shear strains involved in the structure. The magnetization measurement shows two magnetic transitions occurring in compounds x ≥0.1. Spectacular feature was observed in the heavily Gd-doped sample ( x =0.5) such as: the continuous increase of M with high magnetic field, the low value of saturation magnetization at low temperature, the metamagnetic transition, and the presence of exchange bias. These findings are interpreted as the fingerprints of the phase separation. Our result indicates that the martensitic accommodation strain, in addition to quenched disorders, may be an alternative approach to understand the physical phase separation. The interesting feature for x =0.5 sample is the negative magnetization observed at low field. Result is interpreted in terms of two interacting networks, with negative exchange interaction between the (Gd+Nd) and the ferromagnetic Mn lattices. The disappearance of the negative magnetization for magnetic field well below the coercive field (~0.047 T) suggest that the magnetic properties of x =0.5 behaves as an inhomogeneous ferrimagnet at low field. [ABSTRACT FROM AUTHOR]

The La 0.75 Sr 0.1 Ca 0.15 MnO 3 sample have been prepared by sol–gel method. The crystallographic study shows that the sample crystallize in the rhombohedral structure with R 3 ¯ c space group. The field dependence of magnetocaloric properties of manganite La 0.75 Sr 0.1 Ca 0.15 MnO 3 with second order phase transition material is investigated using a phenomenological model. The model parameters were determined from the magnetization data adjustment and were used to give better fits to magnetic transition and to calculate the magnetocaloric thermodynamic quantities. The magnetic entropy change reaches a peak of about 5.8 J/kg K and the relative cooling power (RCP) value of 195 J/kg at 305 K upon 5 T applied magnetic field. The critical exponents associated with ferromagnetic transition have been determined from magnetocaloric effect methods. [ABSTRACT FROM AUTHOR]

We have investigated the effect of the isovalent substitutions of the larger La 3+ by the smaller Pr 3+ in polycrystalline La 0.7− x Pr x Ba 0.3 MnO 3 ( x = 0, 0.1 and 0.2) on ferromagnetic (FM) phase transition and magnetocaloric properties. Using Banerjee's criterion plots, it was found that the phase transition for all samples is of second-order. The magnetic transition temperature is tuned to room temperature by the substitution of Pr in La 0.7 Ba 0.3 MnO 3 , but the maximum magnetic entropy change remains nearly constant about 4 J/kg K. According to magnetocaloric investigations, x = 0.2 sample has a quite high relative cooling power with 371.45 J/kg for Δ H = 5 T, which makes it an interesting cooling material. A local exponent n ( T C , H ) was calculated to determine the field dependence of the experimental −Δ S M . Recently, a master curve behavior for the magnetic entropy change is also followed by these specimens. [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]

Abstract: The La0.7−x Pr x Ba0.3MnO3 (x=0.00, 0.1, 0.2) polycrystalline samples were prepared by solid-state reaction and their crystallographic structure was achieved by XRD patterns analysis. Magnetization measurements were performed versus temperature and applied magnetic field to investigate magnetic properties such as critical behavior near T c . Analysis in the vicinity of the ferromagnetic (FM)–paramagnetic phase-transition temperature evidences a second-order phase transition. Saturation magnetization and the initial susceptibility versus temperature are found to obey asymptotic relations. Using modified Arrott plot, Kouvel–Fisher method and critical isotherm analysis, the critical parameters (T C , β, γ, and δ) are determined in the two characteristic regions of low- and high-magnetic fields. The estimated critical exponents are close to both 3D-Heisenberg and mean field model values. The reliability of the critical exponent values was confirmed by the Widom scaling relation and the universal scaling hypothesis. The change in the universality class should be due to the increase of Pr content. [Copyright &y& Elsevier]

Abstract: The critical behavior of La0.6Ca0.4− x Sr x MnO3 (x =0, 0.2 and 0.4) compounds has been investigated based on the data of static magnetic measurements in the vicinity of its critical temperature TC . Through various techniques such as modified Arrott plot, Kouvel–Fisher method and critical isotherm analysis, the estimated critical exponents are found to be (β =0.267, γ =0.992, δ =4.896 at TC =268.12), (β =0.501, γ =1.045, δ =2.992 at TC =344.37) and (β =0.386, γ =1.293, δ =4.88 at TC =371.02), for x =0, 0.2 and 0.4; close to tricritical mean field, mean field and 3D-Heisenberg model values, respectively. The reliability of the critical exponents values was confirmed by the Widom scaling relation and the universal scaling hypothesis. 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. Moreover, the local exponent n was studied in terms of the field dependence of the magnetic entropy change. It has been noted that n evolves with field in the entire studied temperature range for all samples. The invalidity of the mean field model for x =0 and 0.4 contents was confirmed at the peak temperature. Far above the transition temperature, the Curie–Weiss law is well satisfied. The differences observed in the n values below the transition are mentioned. Furthermore, unlike the modified Arrott or Kouvel–Fischer methods, the performed analysis is shown to be useful to examine critical exponents and their effects in mixed phases materials. [Copyright &y& Elsevier]

Abstract: The La0.6Ca0.4−x Sr x MnO3 (x=0, 0.2 and 0.4) samples have been elaborated by the solid-state method. X-ray powder diffraction shows that, for x=0, the sample crystallizes in orthorhombic phase, while, for x≥0.2 the structure becomes rhombohedral. The variation of magnetization as a function of temperature and applied magnetic field were carried out. All samples exhibit a PM-FM transition at the Curie temperature T C which increases with Sr2+ content. Magnetocaloric effect has been calculated in terms of isothermal magnetic entropy change. A large magnetocaloric effect has been observed in all samples, the maximum entropy change, , reaches the highest value of 6.70J/kgK under a magnetic field change of 5T with an RCP value of 285J/kg for La0.6Ca0.2Sr0.2MnO3 composition, which will be an interesting compound for application materials working as magnetic refrigerants near room temperature. The electrical transport behavior ρ(T) was also investigated. All the specimens undergo a metallic–semiconductor transition at the temperature T ρ . The ρ−T fit well with the phenomenological equation for conductivity under a percolation approach. [Copyright &y& Elsevier]

Abstract: AMn 1−x Fe x O 3 (A=La 0.75 Ca 0.08 Sr 0.17 and x=0–0.23) compounds, sintered at 700°C, were characterized by X-ray diffraction (XRD) at room temperature. Rietveld refinement has shown that samples can be indexed in the orthorhombic (Pnma) structure for low Fe-content (x≤0.046) and rhombohedral () structure for high Fe-content (x≥0.115). The transmission Mössbauer spectra have revealed the same isomer shift δ value assigned to Fe 3+ ion for all compounds. The magnetization behavior and the Curie temperature T C have shown a large dependence on the fractional composition x. In fact, the M(T) curves have revealed the presence of a long-range ferromagnetic state below T C for compounds with x ≤0.115, and a spin-glass state (SGS) at low temperature for high Fe-content (x ≥0.177). [Copyright &y& Elsevier]

Abstract: Polycrystalline perovskite manganites La0.8Cd0.2−x K x MnO3 (x =0.05, 0.075 and 0.1) were prepared by sol–gel method. The crystal structure examined by X-ray powder diffraction indicates that the samples were single phase and crystallize in a rhombohedral structure with increasing the K content. 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) increases from 260 to 282K as K-doping increases from 0.05 to 0.1.The resistivity measurements reveal that the samples exhibit a metallic to semiconductor transition and the electrical temperature transition T P presents a similar trend of T C, with increasing the K content. The magnetic entropy change |ΔS M | has been deduced by two methods: a Maxwell relation, and the Landau theory. The maximum value of the magnetic entropy change obtained from the M(H) plot data is for applied magnetic field of 2T. At this value of magnetic field the relative cooling power (RCP) is 62.59Jkg−1. Close to T C, large change in magnetic entropy has been observed in all samples. Our result on magnetocaloric properties suggests that La0.8Cd0.2−x K x MnO3 compounds are attractive as a possible refrigerant for near room temperature magnetic refrigeration. [Copyright &y& Elsevier]

Abstract: Polycrystalline perovskite manganites La0.7− x Eu x Ba0.3MnO3(x=0.05, 0.1 and 0.15) were prepared by sol–gel method. The prepared samples remain single phase with a perovskite structure, revealed by X-ray diffraction. The structure refinement of La0.7− x Eu x Ba0.3MnO3(x=0.05, 0.1 and 0.15) samples was performed in the hexagonal setting of the R3¯c space group. The dependence of magnetization M on applied magnetic field H and temperature T was measured carefully near the Curie temperature T C for all the samples. With the increasing Eu content, both the unit cell volume and Curie temperature T C of 298K has been detected with a maximum of magnetic entropy |ΔSM max| for the La0.7− x Eu x Ba0.3MnO3 with x=0.15, reaching a value of 2.3J/kgK when a magnetic field of 10kOe was applied and the relative cooling power (RCP) is 46J/kg. These results suggest that the material may be a suitable candidate as working substance in magnetic refrigeration near room temperature. [Copyright &y& Elsevier]