Arrott Curves Research Articles

Magnetothermal effect and first-principles calculations of Zn-doped Mn5Ge3-based alloys

This study investigates the compound system Mn5−xZnxGe3 (x = 0.1, 0.2, and 0.3) through experimental investigations and theoretical calculations. Zn doping lowers the Curie temperature and magnetic entropy change of Mn5−xZnxGe3 alloys. Analysis of phenomenological curves, including Landau theories, normalized curves, and Arrott curves during the study of isothermal magnetization curves, reveals a second-order phase transition in this system. Through an extensive investigation of critical behavior using critical isotherm curves and the Kouvel–Fisher (KF) method, the consistency and reliability of these critical indices are validated by the prediction of the scaling theory in the critical region. By scaling the dependence of |ΔSM| on M and applying crucial exponen21t values, an efficient new approach is utilized to calculate the spontaneous magnetization that agrees well with the values deduced from the KF method. Additionally, first-principles calculations reveal that the Mn atoms' 3d orbitals are more significantly close to the Fermi energy level, with Zn doping generally reducing both the electronic density of states and the total magnetic moment of the Mn 3d orbitals. Consequently, the introduction of Zn leads to a decrease in the Mn–Mn atom exchange coupling, resulting in a deterioration of the total exchange interaction. This phenomenon also explains the decrease in the Curie temperature TC due to Zn doping, aligning with experimental observations.

Magnetocaloric effect and critical exponents at near room temperature of CrTe

In this work, I investigated and studied the CrTe compound, which has a spin amplitude of about 2, to determine its critical behaviors at near room temperature, magnetocaloric cooling, and magnetic characteristics. For the purpose of this study, I used the Metropolis algorithm with the Monte Carlo approach. The Curie temperature of CrTe is around 326 K, which is determined through the magnetization M(T) and the inverse magnetic susceptibility (χ−1). The Arrott curves (H/M vs. M2) and the isothermal magnetization M(H) demonstrate a second-order ferromagnetic (FM) to paramagnetic (PM) state phase transition. The magnetic entropy change (-ΔSM), relative cooling power (RCP), and refrigeration capacity (Q) at 8 T are 1.31 J kg⁻1 K⁻1, 106 J kg⁻1, and 79 J kg⁻1, respectively. To calculate the critical exponents of CrTe, I used the Widom scaling relation and the modified Arrott plot (MAP). The critical exponent values were found to be in good agreement with those estimated using the renormalization group approach for a 3D-Ising model.

Fine tuning of Mn/Co vacancies for optimized magnetocaloric performance in MnCoGe alloys

As a family of rare-earth-free magnetocaloric materials, MnCoGe-based alloys have attracted intensive attention in the past few years. In this study, we reveal that the deficiency of either Mn or Co reduces the valence electron concentration of MnCoGe system, thereby lowering its structural transition temperature (Ttr) by pushing the Fermi level away from the Mn-Mn antibonding electronic states. Moreover, Ttr is found to be more sensitive to Co content. By systematically analyzing the temperature dependent magnetization plots and Arrott curves, it is proven that the magnetic and structural degrees of freedom are coupled in the Mn0.97CoGe alloy, resulting in a first-order magnetic phase transition. On the contrary, MnCo0.98Ge undergoes a second-order transition. As a consequence, the Mn0.97CoGe alloy exhibits a maximum magnetic entropy change of 27.6 J kg−1K−1 under a magnetic field of 5 T near the Curie temperature of 265 K, corresponding to a refrigeration capacity of 212.1 J kg−1. Our work demonstrates Mn/Co vacant MnCoGe alloy as a robust candidate of magnetic substance for room temperature magnetocaloric refrigeration.

STRUCTURAL, MAGNETIC AND MAGNETOCALORIC PROPERTIES OF La0.7Sr0.2Ba0.1MnO3 MANGANITE

In this present work, the structural, magnetocaloric and magnetic properties of La0.7Sr0.2Ba0.1MnO3 (LSBM) manganite were investigated. The material was synthesized using the sol-gel method and X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) devices were used to analyze structural properties such as crystal structure and surface morphology. XRD measurement revealed that the crystal structure of LSBM manganite is hexagonal. Based on the magnetic measurements, the TC value of La0.7Sr0.2Ba0.1MnO3 manganite compounds was calculated as 362 K. The ∆SM value of sample is established as 2.79 Jkg-1K-1 in an applied magnetic field of 5T. Arrott curves revealed that the phase transition was second order.

Enhancement of magnetocaloric effect by partial substitution of Bi in La0.60Dy0.10Sr0.30Mn(1−x)BixO3 manganites (x = 0, 0.01, 0.03, and 0.10)

In this study, the effects of Bi substitution for Mn on the magnetic and magnetocaloric properties of La0.60Dy0.10Sr0.30Mn(1−x)BixO3 manganites (x = 0, 0.01, 0.03, and 0.10) synthesized using the sol–gel method ​​were investigated. The samples x = 0, 0.01, and 0.03 had been indexed in an orthorhombic structure (space group Pnma), while sample x = 0.10 had been indexed in a hexagonal structure (space group R3c). The thermomagnetic measurements showed an increase in the Curie temperature (TC) with increasing Bi content, as well as an increase in magnetization at low temperatures. The TC values were determined as 322, 318, 327, and 360 K for x = 0, 0.01, 0.03, and 0.10 samples, respectively. Maximum magnetic entropy change (-ΔSMmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta {S}_{M}^{max}$$\\end{document}) values ​​obtained from isothermal magnetization measurements showed an increase with the amount of Bi. The -ΔSMmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta {S}_{M}^{max}$$\\end{document} value of 3.80 Jkg−1K−1 at 5 T for the x = 0 sample increased to 4.12 Jkg−1K−1 for the x = 0.10 sample with the highest Bi content. From the Arrott curves, it was observed that all samples exhibited a second-order magnetic phase transition. The obtained values of relative cooling power (RCP), which is an important factor in determining the performance of cooling material, are in the range of 282, 262, 251, and 232 Jkg−1 for x = 0, 0.01, 0.03, and 0.10, respectively.

Improved dielectric and ferroelectric properties near Morphotropic phase boundary in Sm3+ modified BZT-BCT ceramics

Lead free polycrystalline (1-x)BZT-xBSCT ceramics with x = 0.45, 0.50 and 0.55 were prepared by solid state reaction method. The samples were sintered at 1325 °C. XRD analysis confirms the perovskite structure in all the samples. The average grain size of ceramics decreases from 7.38 to 5.36 μm with the increase in the BSCT content. A maximum value of ε equal to 5715 at room temperature was found for sample with x = 0.50 and all the samples show diffused phase transition. PE loops were recorded at different temperatures to understand the ferroelectric nature. The polarization extension mechanism was found in sample with x = 0.50 through Arrott curves. The results show that the properties in solid solution of Sm3+ modified BCT ceramics with BZT, which makes the prepared ceramics as the potential candidates for several applications.

Evolution of magnetic and magnetocaloric behavior in Mn1-xCdxCoGe intermetallics

The hysteretic loss and evolution of magnetocaloric behavior in both increasing and decreasing fields of Mn1-xCdxCoGe (x = 0.02, 0.05, and 0.08) system prepared by conventional arc-melting technique were studied. Results show that Mn replacement by Cd could regulate Curie temperature from 318.1 K to 333.9 K as the x content increase without altering the original crystal structure. Meanwhile, the feature of magnetic phase transition was revealed by Arrott curves, n (T, H) plots, and universal behavior associated with its dispersion parameters. In addition, the critical parameters extracted by different techniques reveal the long-range ordering magnetic interactions. The Mn0.95Cd0.05CoGe sample presents the maximum magnetic entropy changes of 11.125 J/(kg·K) and 11.134 J/(kg·K) for Δμ0H= 7 T in increasing and decreasing modes with hysteretic loss of 1.13 J/kg. Furthermore, the evolution of temperature average entropy changes and normalized refrigerant capacity under increasing and decreasing fields were also introduced to further elaborate on the performance of magnetic refrigeration.

Magnetic properties of double perovskite oxide Gd1.8Ce0.2NiMnO6

In this paper, a double perovskite oxide Gd1.8Ce0.2NiMnO6 polycrystalline sample was prepared using a conventional high temperature and solid-state reaction method. The phase formation of sample was examined using X-ray diffractometry, and the magnetic properties were measured using a PPMS. The results showed that the sample was monophase and had a space group of monoclinic P21/n. At T > TG the sample was purely paramagnetic. At TC < T < TG paramagnetic and ferromagnetic states coexisted, and Griffiths-like phase appeared in the sample. In the lower temperature region (T < TN) there was competition between ferromagnetic and antiferromagnetic states, and cluster spin-glass behavior appeared. When a magnetic field of 7 T was applied, the double perovskite oxide Gd1.8Ce0.2NiMnO6 showed a maximum −ΔSM value of 3.12296 J · kg−1 · K−1 near Curie temperature with an RCP (Refrigeration Cooling Performance) of 231.09904 J/kg. Analysis of the Arrott, recalibration and Loop curves all proved that the sample underwent a second-order phase transition.

Landau mean-field analysis and estimation of the spontaneous magnetization from magnetic entropy change

We investigated the critical exponents for the compounds La1-x□xMnO3 (x = 0.1; 0.2 and 0.3) prepared bythe sol–gel method. Our samples show a second-ordertransition inferred from the positive slope, in accordance with the Banerjee Criterion. Using the slope of different models on the TC, the relative slope (RS) was traced. From this perspective, the best models for the three samples prove to be the mean field and thetricriticalmean field models. This model is characterized by critical exponents β, γ and δ which are determinedby many methods such as MAP, KF method and critical isotherm analysis.The theoritical methods and experimental results were in good agreement for the three compounds. The universality class has been shown. After determining the spontaneous magnetization for x = 0.2 from (-ΔSM) vs. M2, we detected a good agreement with those obtained from the classical extrapolation of Arrott curves (µ0H/M vs. M2). Furthermore, based on the magnetocaloric effect (MCE), Landau’s theory is valid for the compound x = 0.2.

Effect of Mn content on crystal structure, magnetic properties and magnetocaloric effect of NdCo2-xMnx compounds

ABSTRACT The crystal structure, magnetic properties and magnetocaloric effect (MCE) of NdCo2-xMnx (x = 0.0–0.5) compounds have been investigated. X-ray diffraction (XRD) analysis has revealed that all the compounds crystallize in the MgCu2-type cubic Laves phase structure (C15-type, Fd-3m). The lattice parameter a increases from 7.2987 Ǻ (x = 0.0) to 7.4020 Ǻ (x = 0.5) and the Curie temperature from 102 to 202 K as the Mn content increases to x = 0.5. Under an external field change from 0 to 5 T, a maximum magnetic entropy changes (ΔSM ) value of 8.75 J/kg K was obtained for NdCo2. With an increase of Mn content, the calculated ΔSM shows an obvious decrease with a broader peak. However, the relative refrigerating capacities (RCP) of the NdCo2–x Mn x compounds are larger than the parent compound. The Arrott curves and universal curves of the rescaled ΔSM confirmed that the NdCo2–x Mn x compounds undergo a second-order phase transition.

The analysis of magnetocaloric effect and magnetic critical behavior in Mn5Ge3−xAgx compounds

Structure, critical behavior and magnetic properties of Mn5Ge3−xAgx compounds with x = 0 and 0.1 have been investigated. With the substitution of Ge by Ag, the Curie temperature decreases from 299.8 to 295.1 K. Investigations for isothermal magnetization curves by Arrott curves, the Landau theory and phenomenological universal curves reveal that this system undergoes a second-order phase transition. To investigate the nature of magnetic transition, a detailed critical parameter study obtained by modified Arrott plots, Kouvel-Fisher method, and critical isothermal analysis has been performed. In comparison with the values given by standard models, these obtained critical parameters suggest a 3D long-range magnetic coupling with the exchange distance decaying as J(r) ≈ r−4.57 and J(r) ≈ r−4.67 for Mn5Ge3 and Mn5Ge2.9Ag0.1.

Long-range ferromagnetic ordering in La0.7Sr0.3Mn0.9Cu0.1O3 manganite

Nanosized La0.7Sr0.3Mn0.9Cu0.1O3 manganite was synthesized via the sol–gel procedures. The structural, morphological, magnetic and magnetocaloric properties as well as the critical phenomena were investigated. The sample was described by X-ray diffraction (XRD) technique at room temperature which confirms the single phase with a rhombohedral structure belonging to the R$$\overline{3}$$c space group. The magnetic measurements indicated the presence of a second-order ferromagnetic–paramagnetic phase transition at 320 K. According to hysteresis cycles, at 10 K a typical soft FM behavior with a low coercive field was observed. The critical exponents values (β, γ, and δ) as well as the Curie temperature TC were determined using different approaches such as the extrapolation of Arrott plots, Kouvel–Fisher (KF) method and critical isotherm analysis. The critical parameters values (β = 0.489 ± 0.003 with TC = 323.41 K ± 0.23, γ = 1.014 ± 0.020 with TC = 324.32 K ± 0.48 and δ = 3.074) are located near those theoretically predicted by mean-field theory, indicating the long-range ferromagnetic coupling in this system. The reliability of these critical parameters was confirmed by both the universal scaling hypothesis and the Widom scaling relation. Additionally, to estimate the spontaneous magnetization MS (T), we used a process which depends on the analysis of the magnetic entropy change (− ΔSM). A satisfactory agreement was found between the values of the spontaneous magnetization determined from the entropy change ((− ΔSM) vs. M2) and those obtained from the extrapolation of the Arrott curves (μ0H/M vs. M2).

Physical Properties of Sr-Doped Double Perovskite La2NiMnO6

A series of double perovskite manganese oxide La2−xSrxNiMnO6 (x = 0, 0.05, 0.1) samples were prepared by solid-state synthesis. The XRD patterns show that the three samples have perovskite crystal structures. The temperature dependence of the magnetization curves for La2−xSrxNiMnO6 (x = 0, 0.05, 0.1) near the Curie temperature indicates that Sr-doping weakens the ferromagnetism while enhancing the antiferromagnetism of this system, and the field-dependent magnetization curves further confirm this conclusion. The hysteresis loops, the enlarged views of the hysteresis loops at 2 K, and the Raman spectra of the three samples indicate that Sr-doping increases the antisite disorder degree, the number of antisite defects, and the antiphase boundaries, and the antiferromagnetic coupling between the antiphase boundaries and the surrounding ferromagnetic regions is enhanced. At the same time, the temperature dependence of the inverse magnetic susceptibility changes from an upward deviation from the Curie-Weiss law to a downward trend. This phenomenon can be explained by the opposing changes in the relative strength between the antisite defects and the antiferromagnetic coupling strength. After Sr-doping, the field-cooling curve and field-warming curve of the LSNMO system do not coincide, which is typical of a first-order phase transition. This phenomenon is further confirmed by the rescaling and arrott curves. The temperature dependence of the resistivity curves shows that the La2−xSrxNiMnO6 (x = 0, 0.05, 0.1) samples are all semiconductor materials. Following Sr-doping, the metal-insulator transition temperature of the system decreases, and the difference between the resistivity values measured at 0 T and 2 T increases.

Effect of partial substitution of Mn by Fe on the structure, magnetic phase transition and magnetocaloric response in La0.67Pb0.33Mn1−xFexO3 compounds

The compounds La0.67Pb0.33Mn1−xFexO3 (0 ≤ x ≤ 0.10) have been fabricated by ceramic procedures mainly to investigate their structure, magnetic phase transition and magnetocaloric effect. All samples have a rhombohedral structure belonging to $$R\overline {3} C$$ space group by structural analysis. As the Fe concentration x increases up to 0.10, Curie temperature value significantly decreases from 360 to 210 K. The maximum values of MEC (magnetic entropy change) are found to be 4.17, 2.99, 2.58 J kg−1 K−1 under 5 T field change for x = 0, 0.05, 0.10, respectively. The corresponding values of RCP (relative cooling power) are 229.8, 235.4, 216.5 J kg−1. The relatively large MEC, high RCP values and the convenient adjustment of the TC suggest that the prepared La0.67Pb0.33Mn1−xFexO3 compounds could be appropriate materials for magnetic cooling in a wide working temperature range. The analysis of isothermal magnetization using the Arrott curves and Franco’s universal method reveals that the La0.67Pb0.33Mn1−xFexO3 manganites show a second-order ferromagnetic–paramagnetic transition.

Ferromagnetic long-range ordering in nano-crystalline La0.7Ca0.3Mn1-xNixO3 (x = 0, 0.02) manganites

Abstract Nanosized La0.7Ca0.3Mn1-xNixO3 (x = 0, 0.02) manganites were synthesized via the auto-combustion method. The critical behavior of these samples was then carefully investigated by analyzing the results of static magnetic measurements near their critical temperatures. The samples exhibited second-order phase transition, and the effect of Ni doping was to lower the critical temperature. The analysis of the experimental data was carried out by means of various techniques, such as modified Arrott plots, the Kouvel-Fisher method, and critical isotherm analysis, which revealed that the values of the critical exponents β, γ, and δ are close to those theoretically predicted by mean-field theory. By using the Widom scaling relation and the universal scaling hypothesis, the dependability of the obtained values of the critical exponents was confirmed. Moreover, the temperature dependence of the spontaneous magnetization was estimated from the analysis of the variation of the magnetic entropy change with the magnetization within the framework of mean-field theory. Interestingly, the spontaneous magnetization determined from the entropy change and that obtained from classical extrapolation of the Arrott curves displayed high concordance. These results strongly suggested that the interactions among spins in the investigated compound are long-range.

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 La0.7Ca0.1Pb0.2Mn0.95Al0.025Sn0.025O3. 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 TC, 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 TC = 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 La0.7Ca0.1Pb0.2Mn0.95Al0.025Sn0.025O3 perovskite, we used the magnetic entropy change (ΔSM), 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.

Griffiths-like phase, critical behavior near the paramagnetic-ferromagnetic phase transition and magnetic entropy change of nanocrystalline La0.75Ca0.25MnO3

In this work, we report the structural and magnetic properties of La0.75Ca0.25MnO3 nanoparticles synthesized by the sol-gel route. Rietvield refinement of X-ray powder diffraction confirms that our sample is single phase and crystallizes in orthorhombic system with Pnma space group. The facts that effective magnetic moment is large and the inverse susceptibility deviates from the Curie Weiss lawn indicate the presence of Griffiths-like cluster phase. The critical exponents have been estimated using different techniques such as modified Arrott plot, Kouvel-Fisher plot and critical isotherm technique. The critical exponents values of La0.75Ca0.25MnO3 are very close to those found out by the mean-field model, and this can be explained by the existence of a long-range interactions between spins in this system. These results were in good agreement with those obtained using the critical exponents of magnetic entropy change. The self-consistency and reliability of the critical exponent was verified by the Widom scaling law and the universal scaling hypothesis. Using the Harris criterion, we deduced that the disorder is relevant in our case. The maximum magnetic entropy change (ΔSM) calculated from the M-H measurements is 3.47 J/kg K under an external field change of 5 T. The ΔSM-T curves collapsed onto a single master curve regardless of the composition and the applied field, confirming the magnetic ordering is of second order nature. The obtained result was compared to ones calculated based on the Arrott plot and a good concordance is observed. Moreover, the spontaneous magnetization obtained from the entropy change is in excellent agreement with that deduced by classically extrapolation the Arrott curves. This result confirms the validity of the estimation of the spontaneous magnetization using the magnetic entropy change.

Determination of the Transition Temperature of a Weak Ferromagnetic Thin Film by Means of an Evolution of the Method Based on the Arrott Plots

The ferromagnetic transition temperature (T c) of a weak ferromagnetic thin film Cu0.38Ni0.62 has been estimated by using an evolution of the Belov, Goriaga, and Arrott (BGA) model. In fact, the typically used measurements of the zero-field-cooled-field-cooled magnetic moment (m) as a function of temperature (T), the magnetic hysteresis loops (m(H)) as a function of field, and the temperature dependence of the remanent magnetic moment, performed on our sample, did not allow us to individuate precisely the value of T c, mainly due to the influence of thermal effects and noise on the weak ferromagnetic response of the sample, resulting in a large uncertainty in the estimation of T c. On the other hand, also the commonly used method of determining the T c by means of a linear extrapolation of the high-field region of m 2 as a function of the normalized magnetic field (H/m) at different temperatures (Arrott curves), working though for our analyzed material, could not completely fulfill the basic assumptions of the BGA model in general. For these reasons, we have considered the analysis of the derivatives of the Arrott curves, starting from observing that the T c of the sample corresponds to the temperature where the curvature of the Arrott curves at low fields inverts. In this way, the sensitivity in the determination of the Curie point from the inductive measurements of the magnetic moment is improved while the correct assumptions of the Arrott model are also fully respected.

Estimation of the spontaneous magnetization and the universal curve in MnCo1−xNbxGe alloys with long-range interactions

We report on the critical behavior, spontaneous magnetization, and universal curve of MnCo1−xNbxGe alloys. Results demonstrate that the replacement of Co by Nb produces a decrease in the Curie temperature, TC, from 259.3 K to 240.3 K. Critical exponents obtained by the modified Arrott plot technique, Kouvel-Fisher method, and critical isothermal analysis are close to the theoretical prediction of the mean-field model values, revealing the characteristic of long-range ferromagnetic interactions. The values of spontaneous magnetization Msp estimated from |ΔSM| vs. M2 plots are in good agreement with the classical extrapolation from the Arrott curves, proving the validity and usefulness of this approach to estimate the Msp. Moreover, the experimental magnetic entropy changes measured for different fields collapse onto a universal curve, confirming the universal behavior of the magnetocaloric effect in this system.

Landau mean-field analysis and estimation of the spontaneous magnetization from magnetic entropy change in La0.7Sr0.3MnO3 and La0.7Sr0.3Mn0.95Ti0.05O3

In this work, we present the research results of magnetocaloric property and spontaneous magnetization on polycrystalline compounds of La0.7Sr0.3MnO3 and La0.7Sr0.3Mn0.95Ti0.05O3. The magnetic entropy change ΔSM has been determined by two methods: Maxwell relation and Landau theory. The analysis of the ΔSM using the Landau theory are consistent with the experimental ones, indicating the importance of magneto-elastic coupling and electron interaction in the magnetocaloric effect properties of manganite. The critical exponents determined by analyzing the magnetic entropy change are close to the mean-field values. Moreover, the spontaneous magnetization determined using the entropy change is consistent with that deduced from the Arrott curves, confirming that the utilization of the magnetic field dependence of magnetic entropy change to determine the spontaneous magnetization is a valid method.