Magnetocaloric Properties Of La0 Research Articles

Magnetocaloric study, critical behavior and spontaneous magnetization estimation in La0.6Ca0.3Sr0.1MnO3 perovskite.

A detailed study of structural, magnetic and magnetocaloric properties of the polycrystalline manganite La0.6Ca0.3Sr0.1MnO3 is presented. The Rietveld refinement of X-ray diffraction pattern reveals that our sample is indexed in the orthorhombic structure with Pbnm space group. Magnetic measurements display a second order paramagnetic (PM)/ferromagnetic (FM) phase transition at Curie temperature Tc = 304 K. The magnetic entropy change (ΔSM) is calculated using two different methods: Maxwell relations and Landau theory. An acceptable agreement between both data is noted, indicating the importance of magnetoelastic coupling and electron interaction in magnetocaloric effect (MCE) properties of La0.6Ca0.3Sr0.1MnO3. The maximum magnetic entropy change (−ΔSmaxM) and the relative cooling power (RCP) are found to be respectively 5.26 J kg−1 K−1 and 262.53 J kg−1 for μ0H = 5 T, making of this material a promising candidate for magnetic refrigeration application. The magnetic entropy curves are found to follow the universal law, confirming the existence of a second order PM/FM phase transition at Tc which is in excellent agreement with that already deduced from Banerjee criterion. The critical exponents are extracted from the field dependence of the magnetic entropy change. Their values are close to the 3D-Ising class. Scaling laws are obeyed, implying their reliability. The spontaneous magnetization values determined using the magnetic entropy change (ΔSMvs. M2) are in good agreement with those obtained from the classical extrapolation of Arrott curves (μ0H/M vs. M2). The magnetic entropy change can be effectively used in studying the critical behavior and the spontaneous magnetization in manganites system.

Tuning the magnetic phase transition and the magnetocaloric properties of La0.7Ca0.3MnO3 compounds through Sm-doping

In this work, we point out that the width and the nature of the magnetic phase transition, TC value, and as well as magnetocaloric effect in La0.7-xSmxCa0.3MnO3 compounds can be easily modified through Sm-doped into La-site. With an increasing Sm concentration, a systematic decrease in the magnetization, TC, and magnetic entropy change (ΔSm) are observed. The Arrott-plot proveds that the samples with x = 0 and 0.1 undergoing a first-order phase transition. Meanwhile, sample x = 0.2 undergoes a second-order phase transition, which exhibits a high value of the relative cooling power (81.5 J/kg at ΔH = 10 kOe). An analysis of the critical behavior based on the modified Arrott plots method has been done for sample x = 0.2. The results proved a coexistence of the long- and short-range interactions in La0.5Sm0.2Ca0.3MnO3 compound.

The effect of cooling rate on the phase formation and magnetocaloric properties in La0.6Ce0.4Fe11.0Si2.0 alloys

In this work, the microstructure, phase formation behavior of the NaZn13-type 1:13 phase and related magnetocaloric effect have been investigated in La0.6Ce0.4Fe11.0Si2.0 as-cast bulk and melt-spun ribbons with different cooling rates. A multi-phase structure consisting of 1:13, α-Fe and La-rich phases is observed in the induction-melted sample with slow cooling. By fast cooling in the melt spinning processing, the La-rich phase can be almost eliminated and thus 1:13 phases with volume fraction as high as 74.4% directly form in the absence of further heat treatment. The resulting maximum magnetic entropy change of 3.1 J/kg K in 2 T field appears at its Curie temperature of 210 K for the La0.6Ce0.4Fe11.0Si2.0 ribbon prepared in 25 m/s.

Effect of Cu doping on the structural, magnetic and magnetocaloric properties of La0.7Sr0.25Na0.05Mn1−xCuxO3 manganites

The effect of Cu doping on structural, magnetic and magnetocaloric properties in La0.7Sr0.25Na0.05Mn1−xCuxO3 (x = 0, 0.05, 0.10, 0.15, 0.20) has been investigated. The samples were prepared by conventional solid-state reaction. Analysis of XRD patterns indicates that the samples are crystallized in a rhombohedral perovskite structure with R 3̅ c space group. Rietveld refinements reveal that the lattice parameter a and unit cell volume gradually increase up to x = 0.10 then decrease, while parameter c decreases with increasing Cu content. XPS spectra exhibit the coexistence of the Cu2+ and Cu3+ ions in the samples with x=0.15 and 0.20. Magnetization measurements show the Curie temperature Tc and the maximum magnetic entropy change ΔSM decrease with the increase in the Cu content, whereas the relative cooling power (RCP) is basically unaffected. The La0.7Sr0.25Na0.05Mn0.9Cu0.1O3 sample shows a maximum ΔSM of 1.75Jkg−1K−1 and a RCP of 87Jkg−1 at 320K under a magnetic field change of 20kOe, and can be one of the potential magnetic refrigerant materials for near room temperature application.

Magnetocaloric effect study of Pr0.67Ca0.33MnO3-La0.67Sr0.33MnO3 nanocomposite

The present study involves investigaton of magnetocaloric effect of Pr0.67Ca0.33MnO3-La0.67Sr0.33MnO3 nanocomposite materials above room temperature. From application point of view in magnetic refrigeration our study highlights the enhancement of operating temperature region compared to the well known La0.67Sr0.33MnO3 refrigerant material above room temperature. Comparison has also been made with the magnetocaloric properties of La0.67Sr0.33MnO3 nanomaterials. The modification of the magnetocaloric entropy changes (broadening of the temperature dependent magnetic entropy change) is addressed due to the effect of the gradual melting of antiferromagnetic charge ordered state of the Pr0.67Ca0.33MnO3 nanoparticles in such nanocomposite materials.

Magnetocaloric properties of La0.67Sr0.33MnO3 tunable by particle size and dimensionality

With a view to investigate the influence of nanosize on the magnetocaloric properties of the La0.67Sr0.33MnO3 nanoparticles, a systematic investigation of their temperature-dependant magnetic entropy change has been undertaken. The maximum of magnetic entropy change -ΔSMmax 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.

Potassium doping induced changes of magnetic and magnetocaloric properties of La0.78Cd0.22−xKxMnO3 (x = 0.00, 0.10, 0.15 and 0.20) manganites

In this paper, we have studied the effect of K substitution on the structural, magnetic and magnetocaloric (MCE) properties of the perovskite manganites La0.78Cd0.22−xKxMnO3 (x=0.00, 0.10, 0.15 and 0.20) which were prepared by standard solid-state reaction method. The phase purity of prepared samples were verified by analyzing the X-ray diffraction patterns and shows that all compositions crystallize in the rhombohedral structure with the R3‾c space group. The zero field cooled (ZFC) and field cooled (FC) magnetization measurements reveal that all the samples undergo a paramagnetic-ferromagnetic (PM-FM) phase transition and the transition temperature is found to increase from 202K for x=0.00 to 326K for x=0.20. Magnetic entropy change (ΔSM) was also studied which reaches a maximum values of 3.6, 4.86, 5.66 and 5.98J/kgK at 5T for x=0.00, 0.10, 0.15 and 0.20 composition, respectively. However, the relative cooling power (RCP) decreases with increasing K content from 274 (x=0.00) to 216 (x=0.20) J/kg for 5T due to the decrease of full width at half maximum of ΔSM curves with increasing K dopant. All the studied samples exhibit a second-order magnetic phase transition at TC. The field dependence of the magnetic entropy change curves show a power law dependence, ΔSMmax∞Hn, around the TC. The obtained n values are 0.89, 0.82, 0.86 and 0.75 for x=0.00, 0.10, 0.15 and 0.20 respectively, confirms not only the invalidity of the mean field model. Thus, the calculated ‘n’ values corroborate the absence of long range magnetic order and suggest the existence of magnetic inhomogeneities in all the samples reported here.

Effects of barium deficiency on structural, magnetic and magnetocaloric properties of La0.6Nd0.1Ba0.3−xMn0.9Cr0.1O3 manganites

ABSTRACTWe have investigated the effects of barium deficiency on structural, magnetic and magnetocaloric properties of La0.6Nd0.1Ba0.3−xMn0.9Cr0.1O3 (x = 0, 0.05 and 0.1) manganites prepared using the solid-state reaction. All the studied samples crystallize in the orthorhombic structure phase with Pnma space group. Magnetization versus temperature showed that the samples exhibit a second-order paramagnetic to ferromagnetic transition with a decrease of the Curie temperature (TC) from 275 K for x = 0–235 K for x = 0.1. The increase of barium deficiency leads to the decrease of the maximum magnetic entropy change and relative cooling power values from (4.40 J.kg−1 K−1 and 262.94 J.kg−1, for x = 0) to (2.78 J.kg−1 K−1 and 159.41 J.kg−1, for x = 0.1) for an applied magnetic field μ0H = 5 T. These values are compared favorably with those of some other reported manganites, making our samples promising candidates for the magnetic refrigeration technology.

Effect of Sodium Doping on Magnetic and Magnetocaloric Properties of La0.65Sr0.35MnO3 Manganites

A series of Na-doped manganites La0.65Sr0.35−x Na x MnO3 (x = 0.20, 0.25, 0.30, and 0.35) were synthesized via sol-gel method. The structural, magnetic, and magnetocaloric properties of the samples were investigated by XRD, TEM, Raman spectroscopy, and magnetization measurement. Rietveld refinements of XRD patterns shown that samples were single phase with a space group R-3c. The variation of magnetization versus temperature in a magnetic applied field demonstrated a phase transition from ferromagnetic to paramagnetic. The value of T C decreased from 345 to 330 K when x increases from 0.20 to 0.35. Arrott plots shown that all samples exhibit a second-order magnetic phase transition. The maximum absolute values of the magnetic entropy change were found to be 0.91, 0.93, 1.12, and 1.10 J/kg for x = 0.2, 0.25, 0.3, and 0.35, respectively. Moreover, relative cooling power has been discussed.

Investigation of the magnetic, electronic and magnetocaloric properties of La0.7(Ca,Sr)0.3Mn1-xGdxO3 manganites

La0.7(Ca,Sr)0.3Mn1−xGdxO3 (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), 55Mn and 139La nuclear magnetic resonance (NMR) spectroscopy and magnetometric measurements. The X-ray powder diffraction shows that all the prepared samples are single phase. La0.7Ca0.15Sr0.15MnO3 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 TC. The single double-exchange-narowed 55Mn NMR line, though broadened by Gd, demonstrates a metallic state in all samples. The current manganites exhibit a second-order magnetic phase transition at TC, 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 TFWHM of the entropy change peak as compared to the Gd-free materials, and have consequently potential applications in magnetic refrigeration.

Correlation between critical properties and magnetocaloric effect using phenomenological model in La0.7Ca0.2Ba0.1MnO3 compound

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 and the other for T > TC, indicating that the critical exponents obtained in this work are accurate.

Effects of rare earth ions substitution on the magnetocaloric and critical behavior of La0.6A0.2Sr0.2MnO3 (A=Pr, Nd, Ce) manganite

We have studied the influence of Ce, Pr and Nd elements substitution on the magnetic and magnetocaloric properties of La0.6A0.2Sr0.2MnO3 (A = Pr, Nd, Ce) polycrystalline manganites. X-ray diffraction patterns show that the samples crystallize in the rhombohedral structure with R-3C space group. The Pr and Nd doped samples are single phase, while Ce doped sample has a CeO2 secondary phase. The temperature dependent magnetization exhibits a sharp paramagnetic (PM)–ferromagnetic (FM) transition at 333, 252 and 243 K for Ce, Pr and Nd doped samples, respectively. The results show that the saturation magnetization of the pure and Nd doped samples are higher than Pr doped sample, while the Ce doped sample exhibits lowest magnetization. The magnetic entropy change (ΔSM) was calculated by applying the Maxwell equation and the estimated values in H = 25 kOe were found to be 3.20, 2.63, 3.34 and 3.50 J/kgK for pure, Pr, Nd and Ce doped samples, respectively. Also, improved relative cooling power was observed for the Pr and Nd doped samples. By using three different methods including analyzing magnetization data using Banerjee's criterion, normalizing entropy change versus reduced temperature and using ΔSM(T) data which is related to the local exponent (nL), it is found that all samples display a second-order magnetic phase transition. The critical exponents of the second-order magnetic phase transition for the samples has been calculated, using scaling law and Widom scaling relation and their reliability has also been confirmed with the scaling hypothesis.

Screening of the synthesis route on the structural, magnetic and magnetocaloric properties of La0.6Ca0.2Ba0.2MnO3 manganite: A comparison between solid-solid state process and a combination polyol process and Spark Plasma Sintering

La0.6Ca0.2Ba0.2MnO3 ceramics are prepared by an original route, combining soft chemistry and Spark Plasma Sintering, within a few minutes at 700 °C and by the solid-state reaction at high temperatures with an annealing temperature of 1200 °C. We have studied the leverage of the powder synthesis method on the structural, morphological, magnetic and magnetocaloric properties of the samples. X-ray diffraction analysis using Rietveld refinement revealed that our materials crystallize in the rhombohedral system with R3¯c space group for the sample prepared by the Polyol-Spark Plasma Sintering method and in the orthorhombic structure with Pbnm space group for the sample synthesized by the solid-state reaction. Magnetization measurements versus temperature under magnetic applied field of 0.05 T show a paramagnetic-ferromagnetic phase transition for both samples. The Arrott plots reveal that ours materials undergo a second-order phase transition. The maximum values of the magnetic entropy change (−ΔSMmax) under the magnetic field change of 5 T are 2.4 and 4.7 J/kg K for La0.6Ca0.2Ba0.2MnO3 synthesized by using solid-state reaction and Polyol-Spark Plasma Sintering methods respectively. The highest value of the relative cooling power RCP is found to be 244 J/kg for the Polyol-Spark Plasma Sintering sample under 5 T. These results are interesting enough and suggest that the Polyol-Spark Plasma Sintering synthesis method is a feasible route to prepare high quality perovskite material for magnetic cooling application.

Phenomenological model of the magnetocaloric effect and its correlation with critical behavior near room temperature in La0.7Ca0.2Sr0.1MnO3 manganite

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.

Large relative cooling power of Bi-doped La0.8−xBixSr0.08(Ca0.55Ba0.45)0.12MnO3 (x=0.0, 0.1 and 0.3) perovskites: Magnetic and magnetocaloric properties

We report magnetic and magnetocaloric properties of La0.8−xBixSr0.08(Ca0.55Ba0.45)0.12MnO3 (x=0.0, 0.1 and 0.3) perovskite manganites. Polycrystalline samples have been synthesized in air by the sol gel method at a sintering temperature of 1150°C. Powder X-ray diffraction data show that samples are phase pure and their cell parameters slightly decrease with increase in Bi content. Scanning electron micrographs show that the average particle size increases with increase in Bi content. The temperature dependent magnetization measurements show that the Curie temperatures decrease from 315K (x=0.0) to 140K (x=0.3) with increase in Bi content. The isothermal magnetization data is used to estimate the magnetic entropy changes (−ΔSM) and their calculated values are 1.12Jkg−1K−1, 1.96Jkg−1K−1 and 1.62Jkg−1K−1 for x=0.0, 0.1 and 0.3 samples respectively under an applied magnetic field of 2.0T. The corresponding values of relative cooling power (RCP) are 90Jkg−1, 180Jkg−1, 136Jkg−1 for x=0.0, 0.1 and 0.3 samples respectively. These results of magnetocaloric effect in our samples suggest that they are promising materials for the magnetic refrigeration applications.

Magnetocaloric properties of La0.666Sr0.373Mn0.943Cu0.018O3

Magnetocaloric properties of La0.666Sr0.373Mn0.943Cu0.018O3 (LSMCO) perovskite (such as magnetic entropy change, full-width at half-maximum, relative cooling power and magnetic specific heat change) at applied magnetic field of 0.05 T were calculated using the phenomenological model. The results indicate the prospective application of LSMCO due to high magnetocaloric effect near the Curie temperature. Furthermore, the magnetocaloric properties of LSMCO sample are comparable with magnetocaloric properties of MnAs film, La1-xCdxMnO3 and La1.25Sr0.75MnCoO6, and significantly larger than that of Gd1-xCaxBaCo2O5.5 and Ge0.95Mn0.05. It is recommended that magnetocaloric effect of LSMCO can be used as a promising practical material of an apparatus based on the active magnetic regenerator cycle.

Large magnetocaloric effect and critical behavior in La0.7Ba0.2Ca0.1Mn1−xAlxO3

The structural, magnetic and magnetocaloric properties of La0.7Ba0.2Ca0.1Mn1−xAlxO3 (0 ≤ x ≤ 0.1) perovskite manganite oxides have been investigated.

A comparative study of La0.65Ca0.2(Na0.5K0.5)0.15MnO3 compound synthesized by solid-state and sol-gel process

In this paper, we investigated the impact of the elaborating method on the structural, magnetic and magnetocaloric properties of La0.65Ca0.2(Na0.5K0.5)0.15MnO3 powder sample, synthesized by both methods: solid state (SS) and sol gel (SG) process. The two compounds were firstly analyzed by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) to determine the temperature transformation into the perovskite structure. The Rietveld refinement of the X-ray powder diffraction show that both samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. The surface morphology of the samples was carried out using scanning electron microscopy (SEM). Magnetization measurements versus temperature in a magnetic applied field of 0.05 T indicate that both samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. Curie temperature TC is found to be 296 and 260 K for SS and SG samples, respectively. The maximum of the magnetic entropy change, |ΔSMMax|, is lower in the SG sample than in the SS sample, but the thermal variation of −ΔSM is broader, resulting in a higher relative cooling power (RCP).

Study of magnetic, structural and magnetocaloric properties of La0.6Pr0.4Mn2Si2 under high pressures and magnetic field

The structural, magnetic and magnetocaloric properties of La0.6Pr0.4Mn2Si2 compound were measured in wide range of temperature, magnetic field and hydrostatic pressure. The structural study up to 10GPa confirmed the existence of critical Mn-Mn distance 0.2883nm for the ferromagnetic to antiferromagnetic transition at room temperature. The results demonstrated the crucial role of the volume in the suppression of the ferromagnetic phase above the transition temperature T1=168K under pressure. The huge pressure shift of the transition temperature T1, dT1/dp=230K/GPa, was observed. Based on our magnetization measurement the low temperature transition at T2=30K is connected with reorientation of Mn moment and the rare-earth sublattice is not ordered in this case. The direct magnetocaloric measurement showed moderate values of the adiabatic temperature change connected with the magnetic transition at Tc and T1 and confirmed the first order character of the transition at T1 and second order character of the transition at Tc.

Effect of trivalent rare earth doping on magnetic and magnetocaloric properties of La0.47(Y,Eu)0.2Pb0.33MnO3 manganites

The La0.47Ln0.2Pb0.33MnO3 (Ln=Eu and Y) polycrystalline has been synthesized using the solid state reaction method at high temperature. The X-ray diffraction shows that the materials crystallized in the orthorhombic structure. 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 value of the Curie temperatures are 275K and 264K for Ln=Eu and Y, respectively. The magnetic entropy change reaches a peak (−ΔSmmax) also decreases from 3.31J/kg. K for Ln=Eu to 2.97J/kg. K for Ln=Y, and the corresponding values of relative cooling power (RCP) reach 243.25 and 178.88J/kg, under a magnetic field of 5T. The results suggest that those polycrystalline could be useful for magnetic refrigeration in a broad temperature range.