Magnetocaloric Properties Of La0 Research Articles

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.

Influence of crystallite size reduction on the magnetic and magnetocaloric properties of La0.6Sr0.35Ca0.05CoO3 nanoparticles

In this paper, three samples of La0.6Sr0.35Ca0.05CoO3 with different crystallite sizes were prepared by a combination of the sol–gel and mechanical milling methods, with milling times tm of 0 (M0), 1h (M1) and 2h (M2). From the XRD and SEM analyses, it is confirmed that the grain size decreases with increased milling time. The value of the grain size observed from SEM is much larger than that observed from XRD analysis, which indicates that each particle observed by SEM consists of several crystallized grains. The reduction of the crystallite size (D) decreased the Curie temperature (TC) and magnetization values, and broadened the phase-transition region of the materials. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change. The maximum value of the magnetic entropy change of the M0 sample, obtained from the M(μ0H) plot data, is |ΔSMmax|=1.35J/kgK for an applied magnetic field of 5T. In addition, the μ0H/M versusM2 curves at temperatures around TC prove that the samples exhibit a second-order magnetic phase transition. The universal behavior obtained from the ΔSM variation curves confirmed the second-order transition for all the samples.

Vacancy effect in both calcium and barium on the physical properties of La0.6Ca0.2Ba0.2MnO3 polycrystalline manganite

In this paper, we report the effect of both calcium and barium (5%) on the structural, magnetic and magnetocaloric properties of La0.6Ca0.2Ba0.2MnO3 (LCBMO) polycrystalline manganite. Our powder specimens were synthesized using the solid-state reaction method at high temperatures with an annealing temperature of 1200 °C. The X-ray diffraction patterns refined using Rietveld method confirm that our compounds are single phase and crystallize in the orthorhombic perovskite structure (Pbnm space group). Magnetization measurements versus temperature under low magnetic applied field (0.05 T) show a paramagnetic-ferromagnetic transition for both compounds. The Curie temperature TC is found to be 302, 202 and 295 K for LCBMO, La0.6Ca0.15□0.05Ba0.2MnO3 (LC) and La0.6Ca0.2Ba0.15□0.05 MnO3 (LB) samples respectively.Using magnetization measurements as a function of magnetic applied field up to 5 T at several temperatures, we deduced the magnetic entropy change ΔSM. The |−ΔSMmax|, under a magnetic field change of 5 T is found to be 2.4; 2.69 and 2.84 Jkg−1K−1 for LCBMO, LC and LB, respectively. The obtained results are compared to calculated ones based on the Landau theory and a good concordance is observed.

Investigation on magnetic and magnetocaloric properties in the Pb-doped manganites La0.78Ca0.22−xPbxMnO3(x = 0, 0.05 and 0.1)

We present an investigation on structural, magnetic and magnetocaloric properties of La0.78Ca0.22−xPbxMnO3 (x = 0, 0.05 and 0.1) polycrystalline compounds prepared by conventional solid-state reaction method. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that all samples crystallize in the orthorhombic structure, with the Pnma space group. Magnetization as a function of temperature shows that all samples exhibit a paramagnetic (PM) – ferromagnetic (FM) phase transition at the Curie temperature TC which increases from 202 K to 242 K for x = 0–0.1, respectively. The magnetic-entropy changes,ΔSM, were calculated from the field dependence of magnetization data using the Maxwell's thermodynamic relation. The magnetic entropy change |ΔSMmax| decreases from 6.9 J kg−1 K−1 for x = 0 to 5.53 J kg−1 K−1 for x = 0.1, while the relative cooling power (RCP) also decreases from 274 to 241 J kg−1, respectively, under an applied magnetic field of 5 T. All of the investigated manganites exhibit a second-order magnetic phase transition at TC, which is also confirmed by Arrot plot and Landau's theory. Also, by normalizing the ΔSM(T,H) curves to their respective ΔS'(=ΔSM(T)/ΔSMmax) value we indicate that all these curves of the samples are collapsed onto a universal master curve. In addition, field dependence of the magnetic entropy change showing the power law dependenceΔSMmax∝(μ0H)n, at the TC is also analyzed. The obtained ‘n’ values are 0.64, 0.75 and 0.97 for x = 0, 0.05 and 0.1 respectively, which confirms that our samples does not follow the mean field model. The deviation from the mean field behavior for all the samples demonstrates an existence of short-range ferromagnetic order in the samples.

Prediction of Magnetocaloric Effect in Lanthanum Deficiency with Phenomenological Model

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

Tuning of Cr3+ ions doping on the magnetic and magnetocaloric properties of La0.5Sr0.5Mn1−xCrxO3

The effects of Cr3+ ions doping on the magnetic and magnetocaloric properties of manganites La0.5Sr0.5Mn1−xCrxO3 (x=0.05, 0.1, 0.15, and 0.2) have been investigated. The magnetization measurements show that a ferromagnetic cluster behavior is induced by Cr3+ dopants and the paramagnetic to ferromagnetic transition temperature TC decreases from 319 to 251K with increasing Cr3+ content from 0.05 to 0.2. The positive slope of the Arrott plots near TC indicates a second order phase transition. The magnetic entropy change (−ΔSM) is estimated from the isothermal magnetization measurements, and the maximum of the magnetic entropy change (−ΔSmaxM) near TC shows a power law dependence of magnetic field: −ΔSmaxM=m(μ0H)n with n being close to the predicted value ~2/3. The experimental results suggest that the magnetic entropy change and TC can be tuned by changing the Cr3+ ions doping level, which offers an effective method for finding an optimal doping level for magnetic refrigeration near room temperature.

Effect of barium-deficiency on the structural, magnetic, and magnetocaloric properties of La0.65Ba0.35−x□xMnO3 (0 ≤ x ≤ 0.2) manganites

Magnetic, and magnetocaloric properties of La0.65Ba0.35−x□xMnO3 (0 ≤ x ≤ 0.2) have been investigated, where □ is a barium deficiency. Our samples were synthesized using the solid-state reaction method at high temperatures. Rietveld analysis show that the vacancy induces a structural transition from orthorhombic (Pbnm) for x = 0 to rhombohedral (R3¯c) for x ≥ 0.05. Magnetization measurements versus temperature under a magnetic applied field of 0.05 T indicate that all our samples undergo a paramagnetic ferromagnetic transition. The Curie temperature TC are found to be 325, 345, 332 and 288 K for x = 0, 0.05, 0.10 and 0.20, respectively. The maximum value of the relative cooling power RCP is obtained for x = 0.2 and is found to be 231 J/Kg under a magnetic field change of 5 T, which is around 60% of that observed in pure gadolinium. This compound is considered as a good material for magnetic refrigeration near room temperature.

Magnetocaloric properties of La0.6Sr0.4MnO3 prepared by solid state reaction method

La0.6Sr0.4MnO3 composition was prepared by solid state reaction method. The structural, magnetic, and magnetocaloric properties were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and DC magnetization measurement. X-ray diffraction showed polycrystalline was in a rhombohedral (R-3c) structure and the SEM image as well as FT-IR spectroscopy indicated the formation of the perovskite structure. The magnetization measurement versus field at various temperatures demonstrated the second-order phase transition from the ferromagnetic to paramagnetic phase at around 361k. The magnetocaloric effect (MCE) study on La0.6Sr0.4MnO3 compound with micrometer scale showed that the maximum entropy change, ΔSMmax, was obtained near the PM-FM transition (361k) equal to 2.47 (J Kg−1 K−1). These results make this material a proper candidate in the magnetic refrigerator application above room temperature at moderate fields.

Effect of synthesis route on the structural, magnetic and magnetocaloric properties of La0.78Dy0.02Ca0.2MnO3 manganite: A comparison between sol-gel, high-energy ball-milling and solid state process

La0.78Dy0.02Ca0.2MnO3 compound has been synthesized using different methods: solid state reaction, sol-gel route and ball-milling process. The Rietveld refinement of X-ray powder diffraction shows that all our samples crystallize in the orthorhombic system with Pnma space group. Morphological properties investigated using Scanning Electron Microscopy (SEM), indicated various microstructure ranging from micrometric grain size (solid-state and sol-gel techniques) to an ultrafine grains one (ball-milling method). Based on Banerjee criterion, Landau theory and universal curve we successfully confirmed that the nature of the magnetic transition changes from first order for the sample elaborated by sol-gel route to second order transition for those synthesized by both solid-state route and ball-milling methods. Therefore, it can be deduced that the process of elaboration presents an intensive impact on the magnetic behavior. The compound elaborated by Ball-milling undergoes the larger magnetocaloric effect (MCE). It exhibits a large relative cooling power (RCP) of 346.70 J/Kg under 5 T. Thus it has the appropriate properties as suitable candidate for magnetic refrigeration application.

Effect of elaborating method on magnetocaloric properties of La0.7Ca0.2Ba0.1MnO3 manganite

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

Prediction of magnetocaloric effect in La0.8SrxCa0.2−xMnO3 compounds (x = 0.05, 0.1 and 0.15) with a first-order magnetic phase transition

In this paper, we have studied structural and magnetocaloric properties of La0.8SrxCa0.2−xMnO3 system with x = 0.05, 0.1 and 0.15. X-ray diffraction (XRD) indicates that samples with x = 0.05 and x = 0.1 crystallize in an orthorhombic structure in Pnma space group, whereas the sample with x = 0.15 crystallize in the rhombohedral structure with R3¯c space group. The field dependence of magnetocaloric properties of manganite La0.8SrxCa0.2−xMnO3 undergoing first order phase transition is investigated using a phenomenological model. The magnetic entropy change of the samples varies from 1.01 J/kg K for x = 0–1.57 J/kg K for x = 0.15 under the applied magnetic field of 12 kOe. These results indicate that the present compounds are one of candidate materials for magnetic refrigerators near room temperature.

Influence of Sn-doping on Magnetocaloric Properties of La0.7Ca0.3Mn1−xSnxO3(x = 0.0, x = 0.02 and x = 0.04) Compounds

Influence of Sn-doping on Magnetocaloric Properties of La0.7Ca0.3Mn1−xSnxO3(x = 0.0, x = 0.02 and x = 0.04) Compounds

Magnetic and magnetocaloric properties in La0.7Ca0.3−xNaxMnO3 exhibiting first-order and second-order magnetic phase transitions

Polycrystalline orthorhombic samples La0.7Ca0.3−xNaxMnO3 (x = 0–0.09) were prepared by solid-state reaction. The study of magnetic properties revealed that the ferromagnetic-paramagnetic (FM-PM) transition temperature (TC) increases from 255 to about 271 K with increasing Na-doping content (x) from 0 to 0.09, respectively. Around the TC, we have found the samples showing a large magnetocaloric (MC) effect with maximum values of magnetic entropy change (|ΔSmax|) of 7–8 J kg−1 K−1 and relative cooling power RCP = 232–236 J/kg for the samples x = 0.03–0.09 in a magnetic-field interval ΔH = 40 kOe. Detailed analyses of isothermal magnetization data M(T, H) based on Banerjee's criteria indicated a first-to-second-order magnetic-phase transformation taking place at a threshold Na-doping concentration xc ≈ 0.06. This could also be observed clearly from the feature of entropy universal curves. An assessment of the magnetic-ordering exponent N = dLn|ΔSm|/dLnH demonstrates an existence of short-range magnetic order in the samples. We believe that the changes of the magnetic properties and MC effect in La0.7Ca0.3−xNaxMnO3 caused by Na doping are related to the changes in the structural parameters and Mn4+/Mn3+ ratio, which are confirmed by the geometrical and electronic analyses based on X-ray diffraction and X-ray absorption fine structure.

Effect of Elaborating Technique on the Structural, Magnetic, and Magnetocaloric Properties of La 0.8 Ca 0.1 Na 0.1 Mno3 Manganite

In this study, we investigated the effect of structural, magnetic, and magnetocaloric properties of La0.8Ca0.1Na0.1MnO3 (LCNMO) prepared using both the conventional solid-state method with a consolidation stage at 1000 ∘C and the well-known sol–gel method combined to a sintering treatment at 950 ∘C. Rietveld refinement of the X-ray diffraction patterns indicates a rhombohedral structure with R-3C space group in both cases. It was also found that the magnetocaloric properties of LCNMO are strongly depended on the synthesis technique. In fact, a global magnetization reduction and a decrease in paramagnetic-ferromagnetic (PM-FM) transition temperature (TC) associated to an enhancement of the relative cooling power were noticed in sol–gel synthesized sample making it more suitable for magnetic refrigeration applications.

Influence of Ti Doping on the Critical Behavior and Magnetocaloric Effect in Disordered Ferromagnets La0.7Ba0.3Mn1−x Ti x O3

The Ti-substitution influence on the magnetic and magnetocaloric properties of La0.7Ba0.3Mn1−xTixO3 (x = 0.05 and 0.1) was investigated. Based on Banerjee’s criteria and Franco’s universal curves, we proved the existence of a second-order magnetic phase transition in the samples. Using the modified Arrott plot method, we determined the critical parameters TC ≈ 245 K, β = 0.374 ± 0.013, γ = 1.228 ± 0.045, and δ = 4.26 ± 0.03 for x = 0.05, and TC ≈ 169 K, β = 0.339 ± 0.001, γ = 1.307 ± 0.003, and δ = 4.78 ± 0.02 for x = 0.1. With these critical values, the predictable scaling behavior of the M(H) data above and below TC proves that the calculated exponents are unambiguous and intrinsic. The values β = 0.374 for x = 0.05 and β = 0.339 for x = 0.1 suggest that the magnetic phase transition of the samples falls into the three-dimensional (3D) Heisenberg and 3D Ising universality classes, respectively, corresponding to short-range ferromagnetic (FM) order due to FM clusters in a wide temperature range even above TC, as confirmed by electron spin resonance studies. In reference to the magnetocaloric effect around TC, the magnetic entropy change reaches maximum values (|ΔSmax|) of about 4 and 3 J kg−1 K−1 for x = 0.05 and 0.1, respectively, for a magnetic field change 50 kOe. Magnetic field dependencies of |ΔSmax| obey a power function |ΔSmax(H)| ∝ Hn, where exponent values n = 0.59 and 0.61 for x = 0.05 and 0.1, respectively, were determined from the relation n = 1 + (β-1)/(β + γ). The difference between the experimental n values and the theoretical value n = 2/3 of the mean field model is due to the presence of short-range FM order in the samples.

Theoretical Investigation of the Magnetocaloric Effect on Stochiometric and Deficient La0.7Ca0.3MnO3 Manganite at Room Temperature

In this paper, the magnetic and magnetocaloric properties of La0.7Ca0.3MnO3 (LCMO), La\(_{0.69}\square {~}_{0.01}\)Ca0.3MnO3 (L1) and La0.7Ca\(_{0.29}\square {~}_{0.01}\)MnO3 (L2) systems near a second-order phase transition from a ferromagnetic to a paramagnetic state, have been studied, using a phenomenological model. Based on this model, we are getting the better fits to magnetic transition and we can predict the values of the magnetocaloric effect such as magnetic entropy change, full-width at half-maximum, relative cooling power, and magnetic specific heat change from the calculation of magnetization as a function of temperature under different external magnetic fields. The maximum magnetic entropy change \({(-{\Delta } S}_{M}^{\max }) \)shifts to higher values with one percent of both calcium and lanthanum deficiencies, while the relative cooling power (RCP) and the full-width at half-maximum are reduced. According to the master curve behavior for the temperature dependence of ΔSM predicted for different maximum fields, this work has confirmed that the paramagnetic–ferromagnetic phase transition observed for our sample is of second order.

Annealing temperature effect on magnetic and magnetocaloric properties of manganites

In this work, we investigate the effect of annealing process at different temperatures (600 and 800 °C) on structural, magnetic and magnetocaloric properties of La0.7Ba0.3MnO3/xTiO2 system with x = 0.04 and 0.06. Crystal structure analysis shows the R-3c rhombohedral symmetry for composites in both annealing temperatures indicating structure stability. Magnetization and coercive field of doped composites increase with increasing annealing temperature, while there is no effect on their Curie temperature (Tc) that remains constant at 348 K due to the TiO2-La0.7Ba0.3MnO3 interaction lack. Increasing annealing temperature is found to be an effective process that can positively affect the magnetocaloric properties. Where, the relative cooling power of doped composites increases from 50 to 62 J/kg for x = 0.04 composite and from 54 to 66 J/kg for x = 0.06 composite with increasing annealing temperature from 600 to 800 °C. Moreover, the experimental results of magnetic entropy change have been modulated using Landau theory and the calculations have indicated the negligible contribution of elastic, magnetoelastic and magnetoelectronic coupling in the magnetocaloric properties of La0.7Ba0.3MnO3/xTiO2 system in both annealing temperatures.

Magnetic, Magnetocaloric and Master Curve Behaviors for La0.6Sr0.4Mn0.9V0.1O3 Compound

This paper reports the magnetic and magnetocaloric properties of La0.6Sr0.4Mn0.9V0.1O3 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 La0.6Sr0.4Mn0.9V0.1O3.

Particle size effects on La0.7Ca0.3MnO3: Griffiths phase-like behavior and magnetocaloric study

We report the particle size effects on the magnetic and magneto caloric properties of La0.7Ca0.3MnO3 nanoparticles. Raw samples, prepared by the reactive milling method, were annealed at different temperatures to produce samples with particle sizes of 21, 35 and 43 nm. The Curie temperature was found to decrease with increasing of grain size. The decrease in saturation magnetization was attributed to weakening of exchange interaction at the surface of the smaller particles. The existence of so-called “Griffiths singularity” above Curie temperature has been confirmed from non-Curie–Weiss behavior in samples. The magnetic entropy change was calculated by the phenomenological method using the experimental data of magnetization versus temperature. The maximum value of the magnetic entropy increased with increasing of grain size from 2.56 J/kg K for 21 nm sample to 2.68 J/kg K for 43 nm sample upon 6 T applied field change. Finally, the fact that the magnetic entropy change curves at different applied fields are collapsed onto a universal curve proves that the studied manganite undergoes a second order magnetic phase transition.

Influence of High-Pressure Nitrogenation on the Structural, Magnetic and Magnetocaloric Properties of La0.5Pr0.5Fe11.4Si1.6

Nitrogenation of La0.5Pr0.5Fe11.4Si1.6 with a particle size of 100–150 μm was performed in a high-purity N2 atmosphere of 40 MPa. La0.5Pr0.5Fe11.4Si1.6N0.3 nitrogenated at 480 °C exhibits an increase in the Curie temperature T C from 187 to 195 K. Moreover, for a field change from 0 to 1.5 T, the maximum hysteresis loss at T C is remarkably reduced from 53 to 3 J kg−1 and a large magnetic-entropy change ΔS m of over 10 J kg−1 K−1 is maintained. For a La0.5Pr0.5Fe11.4Si1.6N1.2 sample, nitrogenated at 550 °C, the XRD pattern clearly exhibits two 1:13 phases and, accordingly, the thermal magnetic curves exhibit two transitions, at 210 and at 295 K. The two transitions lead, for a field change of 5 T, to a ΔS m larger than 2 J kg−1 K−1 over a large temperature range from 200 to 310 K with a maximum value of 5.3 J kg−1 K−1 at 225 K. Upon further increase in the nitrogenation temperature to 650 °C, the amount of the nitrogen-poor phase strongly decreases and a large amount of α–Fe precipitates, resulting in a large reduction in the MCE.