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 La_0.6Ca_0.3Sr_0.1MnO₃ 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 T_c = 304 K. The magnetic entropy change (ΔS_M) 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 La_0.6Ca_0.3Sr_0.1MnO₃. The maximum magnetic entropy change (−ΔS^max_M) 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 T_c 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 (ΔS_Mvs. 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.

A detailed investigation was conducted on the magnetocaloric properties of La_0.6Ca_0.3Sr_0.1MnO₃ and its potential application in cooling fields.     

Study of the structural,electronic, magnetic and magnetocaloric properties of La0.5Ca0.5Mn0.9V0.1O3 sample: first-principles calculation (DFT–MFT)

This paper presents a correlation between experimental and theoretical approaches to study the structural, electronic, magnetic, and magnetocaloric properties of La_0.5Ca_0.5Mn_0.9V_0.1O₃. The studied compound crystallizes in the Pbnm orthorhombic space group. The calculated DOS using the DFT + U method proves that La_0.5Ca_0.5Mn_0.9V_0.1O₃ sample exhibits semi-metallic behavior, which is preferred in spintronic applications. The calculated PDOS proves that the high hydration among Mn 3d, V 3d and O 2p at the Fermi energy level is responsible for the FM behavior of La_0.5Ca_0.5Mn_0.9V_0.1O₃. The magnetic moment has been calculated using DFT results by estimating the valence electron population. The optical properties show high light absorption in the UV region. By using the Bean–Rodbell method, the magnetic phase shows a second-order transition where η = 0.85, and the exchange parameter λ is found to be 1.19 T g⁻¹ emu⁻¹. Based on the mean-field theory, the saturation magnetization (M₀), the Landé factor (g), and the total angular momentum (J) were determined. These parameters were used to simulate magnetization as a function of the magnetic field at different temperatures as well as the variation of the magnetic entropy change ΔS_M (T).

This paper presents a correlation between experimental and theoretical approaches to study the structural, electronic, magnetic, and magnetocaloric properties of La_0.5Ca_0.5Mn_0.9V_0.1O₃.     

Observation of enhanced magnetic entropy change near room temperature in Sr-site deficient La0.67Sr0.33MnO3 manganite

The effect of Sr-site deficiency on the structural, magnetic and magnetic entropy change of La_0.67Sr_0.33−yMnO_3−δ (y = 0.18 and 0.27) compounds was investigated. The compounds were prepared by the conventional solid-state route and powder X-ray diffraction technique along with Rietveld refinement was carried out to confirm the structure and phase purity. Lattice parameters and unit cell volumes are found to increase with the increase in Sr-deficiency due to the electrostatic repulsion from the neighbouring oxygen ions. A mixed valence state of Mn²⁺/Mn³⁺/Mn⁴⁺ was confirmed using the X-ray photoelectron spectroscopy technique and it was observed that the change of state from Mn³⁺ + Mn³⁺ pairs to Mn²⁺ + Mn⁴⁺ pairs is different for both the studied compounds. A second order ferromagnetic–paramagnetic transition with an enhancement in magnetization in comparison to the pristine compound (La_0.67Sr_0.33MnO₃) was observed due to multiple double exchange interactions. The La_0.67Sr_0.15□_0.18MnO_3−δ compound exhibits a magnetic entropy change (ΔS_M) of 4.61 J kg⁻¹ K⁻¹ at 310 K, and the La_0.67Sr_0.06□_0.27MnO_3−δ compound exhibits a ΔS_M of 4.11 J kg⁻¹ K⁻¹ at 276 K under a field of 50 kOe. In our previous work, we reported a large value of ΔS_M but at higher temperatures, around 350 K. However, in the present case, we have achieved a near room temperature (310 K) MCE with a significant ΔS_M value (4.61 J kg⁻¹ K⁻¹) which is larger than that reported for numerous perovskite manganites. Thus, the studied material could be a potential candidate for room temperature magnetic refrigeration applications.

The effect of Sr-site deficiency on the structural, magnetic and magnetic entropy change of La_0.67Sr_0.33−yMnO_3−δ (y = 0.18 and 0.27) compounds was investigated.     

Long-range ferromagnetic order in perovskite manganite La0.67Ba0.25Ca0.08Mn(1−x)TixO3 (x = 0.00, 0.05 and 0.10)

In this study, we report the effects of Ti on the critical behavior of La_0.67Ba_0.25Ca_0.08MnO₃ samples prepared by the flux method. Moreover, the critical exponents β, γ and δ are estimated through numerous techniques such as the modified Arrott plot, the Kouvel–Fisher method and critical isotherm analysis of the magnetic measurements on record near the Curie temperature. Compared to standard models, the estimated critical exponents are close to the theoretical values of the mean-field model for these samples. In order to estimate the spontaneous magnetization at a given temperature, we used a process based on the analysis, in the mean-field theory, of the magnetic entropy change (−ΔS_M) vs. magnetization (M). An excellent agreement was found between the spontaneous magnetization determined from −ΔS_Mvs. M² and the classical extrapolation from the Arrott curves (μ₀H/M vs. M²), thus confirming that −ΔS_M is a valid approach to estimate the spontaneous magnetization in this system. The accuracy of the critical exponent values was confirmed with the scaling hypothesis. The magnetization curves fall onto one of two sides, below and above T_C.

In this study, we report the effects of Ti on the critical behavior of La_0.67Ba_0.25Ca_0.08MnO₃ samples prepared by the flux method.     

Study of physical properties of a ferrimagnetic spinel Cu1.5Mn1.5O4: spin dynamics,magnetocaloric effect and critical behavior

The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu_1.5Mn_1.5O₄. The dynamic magnetic properties investigated using frequency-dependent ac magnetic susceptibility fitted using different phenomenological models such as Neel–Arrhenius, Vogel–Fulcher and power law, strongly indicate the presence of a cluster-glass-like behavior of Cu_1.5Mn_1.5O₄ at 40 K. The magnetization data have revealed that our compound displays an occurrence of second-order paramagnetic (PM) to ferrimagnetic (FIM) phase transition at the Curie temperature T_C = 80 K as the temperature decrease. In addition, the magnetic entropy change (ΔS_M) was calculated using two different methods: Maxwell relations and Landau theory. An acceptable agreement was found between both sets of data, which proves the importance of both electron interaction and magnetoelastic coupling in the magnetocaloric effect (MCE) properties of Cu_1.5Mn_1.5O₄. The relative cooling power (RCP) reaches 180.13 (J kg⁻¹) for an applied field at 5 T, making our compound an effective candidate for magnetic refrigeration applications. The critical exponents β, γ and δ as well as transition temperature T_C were extracted from various techniques indicating that the magnetic interaction in our sample follows the 3D-Ising model. The validity of the critical exponents is confirmed by applying the Windom scaling hypothesis.

The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu_1.5Mn_1.5O₄.     

Copper-doped lanthanum manganite La0.65Ce0.05Sr0.3Mn1−xCuxO3 influence on structural,magnetic and magnetocaloric effects

Bulk nanocrystalline samples of La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method. The effect of the substitution for Mn with Cu upon the structural and magnetic properties has been investigated by means of X-ray diffraction (XRD), Raman spectroscopy and dc magnetization measurements. The structural parameters obtained using Rietveld refinement of XRD data showed perovskite structures with rhombohedral (R$\bar{3}$c) symmetry without any detectable impurity phase. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing copper concentration. The analysis of the crystallographic data suggested a strong correlation between structure and magnetism, for instance a relationship between a distortion of the MnO₆ octahedron and the reduction in the Curie temperature, T_c. A paramagnetic to ferromagnetic phase transition at T_C is observed. The experimental results confirm that Mn-site substitution with Cu destroys the Mn³⁺–O²⁻–Mn⁴⁺ bridges and weakens the double exchange (DE) interaction between Mn³⁺ and Mn⁴⁺ ions, which shows an obvious suppression of the FM interaction in the La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ matrix. The maximum magnetic entropy change −ΔS^max_M is found to decrease with increasing Cu content from 4.43 J kg⁻¹ K⁻¹ for x = 0 to 3.03 J kg⁻¹ K⁻¹ for x = 0.15 upon a 5 T applied field change.

Bulk nanocrystalline samples of La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method.     

Study of magnetic and electrical properties of Pr0.65Ca0.25Ba0.1MnO3 manganite

The magnetic properties and magnetocaloric effect (MCE) in Pr_0.65Ca_0.25Ba_0.1MnO₃ have been investigated supplemented by electrical data. X-ray diffraction shows that the sample crystallizes in the distorted orthorhombic system with the Pnma space group. Pr_0.65Ca_0.25Ba_0.1MnO₃ undergoes paramagnetic–ferromagnetic (PM–FM) phase transition at T_C ∼ 85 K. For a magnetic field change of 5 T, the maximum value of the magnetic entropy change (−ΔS^max_M) is estimated to be 4.4 J kg⁻¹ K⁻¹ around T_C with a large relative cooling power (RCP) value of 263.5 J kg⁻¹. While the modified Arrott plots suggested that the magnetic transition belongs to the second order phase transitions, the universal curves of the rescaled magnetic entropy (ΔS_M) proved the opposite. The electrical properties of Pr_0.65Ca_0.25Ba_0.1MnO₃ have been investigated using impedance spectroscopy techniques. The dc-resistivity (σ_dc) study shows the presence of semiconductor behavior. Ac-conductivity (σ_ac) analysis shows that the conductivity is governed by a hopping process. From the analysis of the alternating regime, the exponent s variation obtained is in good agreement with Mott theory. The impedance spectrum analysis reveals the presence of a relaxation phenomenon. Based on these analyzes, the sample can be modeled by an electrical equivalent circuit.

The magnetic properties and magnetocaloric effect in Pr_0.65Ca_0.25Ba_0.1MnO₃ compound have been investigated supplemented by electrical data.     

Structural,magnetic and magnetocaloric properties of 0.75La0.6Ca0.4MnO3/0.25La0.6Sr0.4MnO3 nanocomposite manganite

The present study involves an investigation of structural, magnetic and magnetocaloric effect (MCE) properties of 0.75La_0.6Ca_0.4MnO₃/0.25La_0.6Sr_0.4MnO₃ composite material. Crystal structure analysis is performed by using Rietveld refinement of the X-ray diffraction patterns. The studied composite exhibits two structural phases; the rhombohedral and the orthorhombic structures corresponding to the mother compounds; La_0.6Ca_0.4MnO₃ and La_0.6Sr_0.4MnO₃, respectively. The scanning electron microscopy micrographs support our findings. Magnetic measurements as a function of temperature of the composite display two successive second order magnetic phase transitions at 255 and 365 K associated to both mother compounds. Therefore, a broadening of the magnetic entropy change peak is noted. A better relative cooling power (RCP) value of 360 J kg⁻¹ compared to those observed in mother compounds is obtained at μ₀H = 5 T, making of this material considered as a suitable candidate for magnetic refrigeration applications near room temperature. A consistent agreement between experimental results and numerical calculations based on the rule of mixtures has been shown. The theoretical modeling of the MCE using Landau theory reveals an acceptable concordance with experimental data indicating the importance of magnetoelastic coupling and electron interaction in the MCE properties of manganite systems. The field dependence of the magnetic entropy change is applied to study the critical behavior. Our results go in tandem with the values corresponding to the mean field model. The spontaneous magnetization values determined using the magnetic entropy change (ΔS_Mvs. M²) are in good agreement with those found from the classical extrapolation of Arrott curves (μ₀H/M vs. M²).

The present study involves an investigation of structural, magnetic and magnetocaloric effect (MCE) properties of a 0.75La_0.6Ca_0.4MnO₃/0.25La_0.6Sr_0.4MnO₃ composite material.     

Influence of Ni content on structural,magnetocaloric and electrical properties in manganite La0.6Ba0.2Sr0.2Mn1−xNixO3 (0 ≤ x ≤ 0.1) type perovskites

We present a detailed study on the physical properties of La_0.6Ba_0.2Sr_0.2Mn_1−xNi_xO₃ samples (x = 0.00, 0.05 and 0.1). The ceramics were fabricated using the sol–gel route. Structural refinement, employing the Rietveld method, disclosed a rhombohedral R$\bar{3}$c phase. The magnetization vs. temperature plots show a paramagnetic–ferromagnetic (PM–FM) transition phase at the T_C (Curie temperature), which decreases from 354 K to 301 K. From the Arrott diagrams M²vs. μ₀H/M, we can conclude the phase transition is of the second order. Based on measurements of the isothermal magnetization around T_C, the magnetocaloric effects (MCEs) have been calculated. The entropy maximum change (−ΔS_M) values are 7.40 J kg⁻¹ K⁻¹, 5.6 J kg⁻¹ K⁻¹ and 4.48 J kg⁻¹ K⁻¹, whereas the relative cooling power (RCP) values are 232 J kg⁻¹, 230 J kg⁻¹ and 156 J kg⁻¹ for x = 0.00, 0.05 and 0.10, respectively, under an external field (μ₀H) of 5 T. Through these results, the La_0.6Ba_0.2Sr_0.2Mn_1−xNi_xO₃ (0 ≤ x ≤ 0.1) samples can be suggested for use in magnetic refrigeration technology above room temperature. The electrical resistivity (ρ) vs. temperature plots exhibit a transition from metallic behavior to semiconductor behavior in the vicinity of T_M–SC. The adiabatic small polaron hopping (ASPH) model is applied in the PM-semiconducting part (T > T_MS). Throughout the temperature range, ρ is adjusted by the percolation model. This model is based on the phase segregation of FM-metal clusters and PM-insulating regions.

We present a detailed study on the physical properties of La_0.6Ba_0.2Sr_0.2Mn_1−xNi_xO₃ samples (x = 0.00, 0.05 and 0.1).     

Pr3+ doping at the A-site of La0.67Ba0.33MnO3 nanocrystalline material: assessment of the relationship between structural and physical properties and Bean–Rodbell model simulation of disorder effects

Bulk nanocrystalline samples of (La_1−xPr_x)_0.67Ba_0.33MnO₃ (0.075 ≤ x ≤ 0.30) manganites with a fixed carrier concentration are prepared by the sol–gel based Pechini method. Rietveld refinement of the X-ray diffraction patterns, shows the formation of single-phase compositions with rhombohedral symmetry. Upon Pr³⁺ doping at the A-site, the unit cell volume and the B–O–B bond angles are reduced. FTIR spectra present a prominent absorption peak of the in-phase stretching mode (B_2g mode) rising from the vibration of the Mn–O bond. Raman spectra at room temperature reveal a gradual shift toward lower frequencies in (E_g) phonon mode with increasing Pr³⁺ concentration. The M(T) measurements shows a clear ferromagnetic (FM)–paramagnetic (PM) phase transition with increasing temperature. An increase in resistivity and activation energy and a decrease in the metal–semiconductor transition (T_M–SC) and Curie temperatures (T_C) was observed as a consequence of Pr³⁺ doping. The results are discussed according to the change of A-site-disorder effect caused by the systematic variations of the A-site average ionic radius 〈r_A〉 and A-site-cation mismatch σ², resulting in the narrowing of the bandwidth and the decrease of the mobility of e_g electrons. The magneto-transport behavior in the whole measured temperature and a magnetic field can be described by a percolation model, which is in agreement with the limited experimental data of the samples for x = 0.075, 0.15 and 0.30. The experimental results confirm that A-site substitution with Pr³⁺ destroys the Mn³⁺–O²⁻–Mn⁴⁺ bridges and weakens the double exchange (DE) interaction between the Mn³⁺ (t³_2ge¹_g, S = 2) and Mn⁴⁺ (t³_2ge⁰_g, S = 3/2) ions. On the other hand, the Bean and Rodbell model has been successfully used to simulate the magnetization data of the samples with x = 0.15 and x = 0.22. The random replacement of La³⁺ by Pr³⁺ is shown to induce more disorder in the system, which is reflected in the increase of the fitted disorder parameter and spin value fluctuation. At a temperature close to room temperature, the maximum magnetic entropy change (ΔS_Max) and the relative cooling power (RCP) of La_0.52Pr_0.15Ba_0.33MnO_2.98 are found to be, respectively, 1.34 J kg⁻¹ K⁻¹ and 71 J kg⁻¹ for a 1.5 T field change.

Bulk nanocrystalline samples of (La_1−xPr_x)_0.67Ba_0.33MnO₃ (0.075 ≤ x ≤ 0.30) manganites with a fixed carrier concentration are prepared by the sol–gel based Pechini method.     

Structural study and large magnetocaloric entropy change at room temperature of La1−x□xMnO3 compounds

In this study, our central focus is to investigate the magnetocaloric characteristics of a La_1−x□_xMnO₃ (x = 0.1, 0.2 and 0.3) series prepared by a sol–gel technique published in Prog. Mater. Sci., 93, 2018, 112–232. The crystallographic study revealed that our compounds crystallize in a rhombohedral structure with R$\bar{3}$c. Ferromagnetic (FM) and paramagnetic (PM) characters were detected from the variation in magnetization as a function of magnetic fields at different temperatures. The second order transition was verified from the Arrott plots (M²vs. (μ₀H/M)), where the slopes have a positive value. In order to verify the second order, we traced the variation of magnetization vs. temperature at different magnetic fields for x = 0.2. This revealed a ferromagnetic (FM)–paramagnetic (PM) transition when temperature increases. Relying on the indirect method while using the Maxwell formula, we determined the variation in the entropy (−ΔS_M) as a function of temperature for different magnetic fields for the three samples. We note that all the studied systems stand as good candidates for magnetic refrigeration with relative cooling power (RCP) values of around 131.4, 83.38 and 57.26 J kg⁻¹ with magnetic fields below 2 T, respectively. Subsequently, the magnetocaloric effect was investigated by a phenomenological model for x = 0.2. The extracted data confirm that this phenomenological model is appropriate for the prediction of magnetocaloric properties. The study also demonstrated that this La_0.8□_0.2MnO₃ system exhibits a universal behaviour.

In this study, our central focus is to investigate the magnetocaloric characteristics of a La_1−x□_xMnO₃ (x = 0.1, 0.2 and 0.3) series prepared by a sol–gel technique.     

Large magnetic entropy change and prediction of magnetoresistance using a magnetic field in La0.5Sm0.1Sr0.4Mn0.975In0.025O3

A detailed study of the structural, magnetic, magnetocaloric and electrical effect properties in polycrystalline manganite La_0.5Sm_0.1Sr_0.4Mn_0.975In_0.025O₃ is presented. The X-ray diffraction pattern is consistent with a rhombohedral structure with R$\bar{3}$c space group. Experimental results revealed that our compound prepared via a sol–gel method exhibits a continuous (second-order) ferromagnetic (FM) to paramagnetic (PM) phase transition around the Curie temperature (T_C = 300 K). In addition, the magnetic entropy change was found to reach 5.25 J kg⁻¹ K⁻¹ under an applied magnetic field of 5 T, corresponding to a relative cooling power (RCP) of 236 J kg⁻¹. We have fitted the experimental data of resistivity using a typical numerical method (Gauss function). The simulation values such as maximum resistivity (ρ_max) and metal–semiconductor transition temperature (T_M–Sc), calculated from this function, showed a perfect agreement with the experimental data. The shifts of these parameters as a function of magnetic field for our sample have been interpreted. The obtained values of β and γ, determined by analyzing the Arrott plots, are found to be T_C = 298.66 ± 0.64 K, β = 0.325 ± 0.001 and γ = 1.25 ± 0.01. The critical isotherm M (T_C, μ₀H) gives δ = 4.81 ± 0.01. These critical exponent values are found to be consistent and comparable to those predicted by the three-dimensional Ising model with short-range interaction. Thus, the Widom scaling law is fulfilled.

Rietveld refinement for the sample LSSMIO. Experimental data (the point symbols), calculated data (the solid lines), difference between them is shown at the bottom of the diagram and Bragg positions are marked by vertical bars.     

Microstructural analysis,magnetic properties,magnetocaloric effect,and critical behaviors of Ni0.6Cd0.2Cu0.2Fe2O4 ferrites prepared using the sol–gel method under different sintering temperatures

This work focuses on the microstructural analysis, magnetic properties, magnetocaloric effect, and critical exponents of Ni_0.6Cd_0.2Cu_0.2Fe₂O₄ ferrites. These samples, denoted as S1000 and S1200, were prepared using the sol–gel method and sintered separately at 1000 °C and 1200 °C, respectively. XRD patterns confirmed the formation of cubic spinel structures and the Rietveld method was used to estimate the different structural parameters. The higher sintering temperature led to an increased lattice constant (a), crystallite size (D), magnetization (M), Curie temperature (T_C), and magnetic entropy change (−ΔS_M) for samples that exhibited second-order ferromagnetic–paramagnetic (FM–PM) phase transitions. The magnetic entropy changed at an applied magnetic field (μ₀H) of 5 T, reaching maximum values of about 1.57–2.12 J kg⁻¹ K⁻¹, corresponding to relative cooling powers (RCPs) of 115 and 125 J kg⁻¹ for S1000 and S1200, respectively. Critical exponents (β, γ, and δ) for samples around their T_C values were studied by analyzing the M(μ₀H, T) isothermal magnetizations using different techniques and checked by analyzing the −ΔS_Mvs. μ₀H curves. The estimated values of β and γ exponents (using the Kouvel–Fisher method) and δ exponent (from M(T_C, μ₀H) critical isotherms) were β = 0.443 ± 0.003, γ = 1.032 ± 0.001, and δ = 3.311 ± 0.006 for S1000, and β = 0.403 ± 0.008, γ = 1.073 ± 0.016, and δ = 3.650 ± 0.005 for S1200. Obviously, these critical exponents were affected by an increased sintering temperature and their values were different to those predicted by standard theoretical models.

This work focuses on the microstructural analysis, magnetic properties, magnetocaloric effect, and critical exponents of Ni_0.6Cd_0.2Cu_0.2Fe₂O₄ ferrites.     

Critical phenomena and estimation of the spontaneous magnetization from a mean field analysis of the magnetic entropy change in La0.7Ca0.1Pb0.2Mn0.95Al0.025Sn0.025O3

In the present work, we have studied the universal critical behavior in the perovskite-manganite compound La_0.7Ca_0.1Pb_0.2Mn_0.95Al_0.025Sn_0.025O₃. Experimental results revealed that all samples exhibit a second-order magnetic phase transition. To study the critical behavior of the paramagnetic–ferromagnetic transition, various techniques such as modified Arrott plots, the Kouvel–Fisher method and critical isotherm analysis were used to determine the values of the Curie temperature T_C, as well as the critical exponents β (corresponding to the spontaneous magnetization), γ (corresponding to the initial susceptibility) and δ (corresponding to the critical magnetization isotherm). The critical exponent values for our sample are consistent with the prediction of the mean field model (β = 0.46, γ = 1.0, and δ = 2.94 at an average T_C = 302.12 K), indicating that the magnetic interactions are long-range. The reliability of the critical exponent values was confirmed by the Widom scaling relation (WSR) and the universal scaling hypothesis. Moreover, to estimate the spontaneous magnetization of La_0.7Ca_0.1Pb_0.2Mn_0.95Al_0.025Sn_0.025O₃ perovskite, we used the magnetic entropy change (ΔS_M), obtained from isothermal magnetization. The results obtained through this approach are compared to those obtained from classical analysis using Arrott curves. An excellent agreement is found between this approach and the one obtained from the extrapolation of the Arrott curves.

In the present work, we have studied the universal critical behavior in the perovskite-manganite compound La_0.7Ca_0.1Pb_0.2Mn_0.95Al_0.025Sn_0.025O₃.     

The investigation of structural and vibrational properties and optical behavior of Ti-doped La0.67Ba0.25Ca0.08Mn(1−x)TixO3 (x = 0.00, 0.05 and 0.10) manganites

The influence of Ti⁴⁺ ions incorporated into the B site on the structural, vibrational and optical properties of La_0.67Ba_0.25Ca_0.08Mn_(1−x)Ti_xO₃ (LBCM_(1−x)T_x), a polycrystalline compound prepared by a molten salt method, was discussed. The X-ray diffraction (XRD) studies confirmed that at room temperature these compounds crystallize in the rhombohedral phases of R$\bar{3}$c. Rietveld refinement indicated that the octahedron (Mn/Ti)O₆ underwent a slight deformation and the θ_{(Mn/Ti)–O–(Mn/Ti)} bond angles decreased with the increase in the Ti content. Furthermore, Raman spectra were recorded at room temperature for the LBCM_(1−x)T_x ceramics to investigate the influence of incorporated Ti⁴⁺ ions in LBCM_(1−x)T_x. Moreover, we controlled the frequency and damping of the optic modes based on Ti incorporation. The infrared (IR) absorption spectrum (FTIR) analysis in the span of 420–750 cm⁻¹ supports the XRD results. The diffuse reflectance data at room temperature verified that both transition levels (⁵E_g → ⁵T_5g) and (⁴A_2g → ⁴T_2g) correspond to the Mn³⁺ and Mn⁴⁺ ions. The optical band gap (E_g) values decreased from 2.90 eV to 2.70 eV with the increase in the Ti⁴⁺ content, implying that our samples could be good candidates for some applications in luminescent devices, such as ultrafast optoelectronic devices. Moreover, the photoluminescence spectra (PL) features at room temperature decreased for all samples. CIE were estimated for all the concentrations of Ti⁴⁺ ions. The results indicated that are a shifts in the CIE values of the compounds.

The influence of Ti⁴⁺ ions incorporated into the B site on the structural, vibrational and optical properties of La_0.67Ba_0.25Ca_0.08Mn_(1−x)Ti_xO₃ (LBCM_(1−x)T_x), a polycrystalline compound prepared by a molten salt method, was discussed.     

Two 3D Mn-based coordination polymers: synthesis,structure and magnetocaloric effect

Two three-dimensional (3D) coordination polymers, namely Mn^II₆(CH₃COO)₂(HCOO)₂(IN)₈(C₄H₈O)₂(H₂O) and Mn^III₆Mn^II₁₂(μ₃-O)₆(CH₃COO)₁₂(IN)₁₈(H₂O)_7.5 (abbreviated as Mn^II₆ and Mn^II₁₂Mn^III₆ respectively; HIN = isonicotinic acid), were synthesized by the reaction of Mn(CH₃COO)₂·4H₂O and isonicotinic acid under solvothermal conditions. Magnetic studies revealed that antiferromagnetic interactions may be present in compounds Mn^II₆ and Mn^II₁₂Mn^III₆. Moreover, the values of −ΔS_m (26.27 (Mn^II₆) and 37.69 (Mn^II₁₂Mn^III₆) J kg⁻¹ K⁻¹ at ΔH = 7 T) are relatively larger than those of the reported Mn-based coordination polymers. This work provides a great scope in the magnetocaloric effect (MCE) of pure 3d-type systems.

Two 3D coordination polymers (Mn^II₆ and Mn^II₁₂Mn^III₆) were synthesized. Magnetic studies revealed that they are potential magnetic materials.     

Large magnetocaloric effect in manganese perovskite La0.67−xBixBa0.33MnO3 near room temperature

La_0.67−xBi_xBa_0.33MnO₃ (x = 0 and 0.05) ceramics were prepared via the sol–gel method. Structural, magnetic and magnetocaloric effects have been systematically studied. X-ray diffraction shows that all the compounds crystallize in the rhombohedral structure with the R$\bar{3}$c space group. By analyzing the field and temperature dependence of magnetization, it is observed that both samples undergo a second order magnetic phase transition near T_C. The value of T_C decreases from 340 K to 306 K when increasing x from 0.00 to 0.05, respectively. The reported magnetic entropy change for both samples was considerably remarkable and equal to 5.8 J kg⁻¹ K⁻¹ for x = 0.00 and 7.3 J kg⁻¹ K⁻¹ for x = 0.05, respectively, for μ₀H = 5 T, confirming that these materials are promising candidates for magnetic refrigeration applications. The mean-field theory was used to study the magnetocaloric effect within the thermodynamics of the model. Satisfactory agreement between experimental data and the mean-field theory has been found.

La_0.67−xBi_xBa_0.33MnO₃ (x = 0 and 0.05) ceramics were prepared via the sol–gel method.     

Donor–acceptor duality of the transition-metal-like B2 core in core–shell-like metallo-borospherenes La3&[B2@B17]− and La3&[B2@B18]−

Transition-metal doping induces dramatic structural changes and leads to earlier planar → tubular → spherical → core–shell-like structural transitions in boron clusters. Inspired by the newly discovered spherical trihedral metallo-borospherene D_3h La₃&B₁₈⁻ (1) (Chen, et al., Nat. Commun., 2020, 11, 2766) and based on extensive first-principles theory calculations, we predict herein the first and smallest core–shell-like metallo-borospherenes C_2v La₃&[B₂@B₁₇]⁻ (2) and D_3h La₃&[B₂@B₁₈]⁻ (3) which contain a transition-metal-like B₂ core at the cage center with unique donor–acceptor duality in La₃&B_n⁻ spherical trihedral shells (n = 17, 18). Detailed energy decomposition and bonding analyses indicate that the B₂ core in these novel complexes serves as a π-donor in the equatorial direction mainly to coordinate three La atoms on the waist and a π/σ-acceptor in the axial direction mainly coordinated by two B₆ triangles on the top and bottom. These highly stable core–shell complexes appear to be spherically aromatic in nature in bonding patterns. The IR, Raman, and photoelectron spectra of 2 and 3 are computationally simulated to facilitate their spectroscopic characterizations.

The smallest core–shell-like metallo-borospherenes C_2v La3&[B₂@B₁₇]⁻ and D_3h La₃&[B₂@B₁₈]⁻ have been predicted at first-principles theory level which contain a transition-metal-like B₂ core with unique donor–acceptor duality.     

Enhancing adsorption capacity and structural stability of Li1.6Mn1.6O4 adsorbents by anion/cation co-doping

Modifying the structure of Li_1.6Mn_1.6O₄ (LMO) to enhance its structural stability and adsorption capacity is an effective method to generate materials to recover Li⁺ ions from mixed solution. Herein, the co-doping of trace non-metal ion (S) and metal ion (Al) into Li_1.6Mn_1.6O₄ (LMO-SAl) is established and shows excellent Li⁺ adsorption capacity and Mn anti-dissolution properties. The adsorption capacity (when [Li⁺] is 6 mmol L⁻¹) is increased from 26.1 mg g⁻¹ to 33.7 mg g⁻¹. This is attributed to improved charge density via substitution of S at O sites, which facilitates the adsorption/desorption process. The Mn dissolution is also reduced from 5.4% to 3.0% for LMO-SAl, which may result from the stronger Al–O bonds compared to Li–O bonds that enhance the structural stability of the LMO. The ion-sieving ability of the co-doped material goes by the order of K_d (Li⁺ > Ca²⁺ > Mg²⁺ > Na⁺ > K⁺), indicating that Li⁺ can be efficiently separated from Lagoco Salt Lake brine. These results predict that lithium ions are effectively adsorbed from brine by the co-doped LMO material, which manifests the feasibility of lithium recovery and provides basic data for further industrial applications of adsorption.

Modifying the structure of Li_1.6Mn_1.6O₄ (LMO) to enhance its structural stability and adsorption capacity is an effective method to generate materials to recover Li⁺ ions from mixed solution.     

Improved electrical transport properties of polycrystalline La0.8(Ca0.12Sr0.08)MnO3 ceramics by Ag2O doping

Polycrystalline La_0.8(Ca_0.12Sr_0.08)MnO₃:mol%Ag_x (LCSMO:Ag_x, x = 0, 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized by the sol–gel technique. Structural, electrical and magnetic properties of the LCSMO:Ag_x ceramics were investigated in detail. X-ray diffraction (XRD) data analyses revealed that all the samples were crystalized in the orthorhombic structure with space group of Pnma. With the increase in Ag doping (x), the grain sizes of the LCSMO:Ag_x samples increased and the amount of grain boundaries (GBs) decreased accordingly. At the same time, the Mn–O bond distance and the Mn–O–Mn bond angles changed correspondingly, leading to the slight increase in the lattice constants (a, b and c) and slight expansion of cell volume (V). For the LCSMO:Ag_x sample with x = 0.3, the optimal values of temperature coefficient of resistivity (TCR) and magnetoresistance (MR) reached 16.22% K⁻¹ (265.1 K) and 42.07% K⁻¹ (270.48 K), respectively. In addition, the fitting analysis of ρ–T curves showed that the experimental data were consistent with the theoretical calculation data. In the T < T_MI (metal-insulator transition temperature) region, the electrical conduction mechanism of LCSMO:Ag_x was clarified by electron-magnon, electron–electron and electron-phonon scattering. In the T > T_MI region, the resistivity data were interpreted by using the adiabatic small-polaron hopping model. Furthermore, in the entire temperature range, the phenomenological equation called the percolation model was used to explain the resistivity data and the phase-separation mechanism of ferromagnetic metallic (FM) and paramagnetic insulating (PI) phases. All the obtained results indicated that the improvement in the electrical properties of the LCSMO:Ag_x samples was attributed to the doping of Ag, which changed the A-site (La, Ca and Sr ions) average ion radius, the Mn–O–Mn bond angles and the Mn–O bond distance. In addition, the grain size increased, which led to improvement in the Mn⁴⁺ ion concentration and the GBs connectivity in the LCSMO:Ag_x polycrystalline ceramics.

Polycrystalline La_0.8(Ca_0.12Sr_0.08)MnO₃:mol%Ag_x (LCSMO:Ag_x, x = 0, 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized by the sol–gel technique.