Entropy Change Curves Research Articles

Magnetoresistive and magnetocaloric properties of polycrystalline Sm0.50Sr0.50MnO3 compound with short range magnetic ordering

In this study, the magnetic and magneto-transport properties of polycrystalline Sm0.50Sr0.50MnO3 have been investigated. The presence of short-range magnetic order plays a crucial role in influencing electron transport, making it a promising pathway for tuning magnetoresistive properties for specific applications. This research focuses on the effects of magnetic nanoclusters on spin-dependent scattering and their impact on magneto-transport and magnetocaloric properties in polycrystalline Sm0.50Sr0.50MnO3. Experimental results reveal a significant magnetocaloric effect and notable magnetoresistance within the liquid nitrogen temperature range. At 100 K, the magnetoresistance reaches approximately 70% under an external magnetic field of 20 kOe. The magnetocaloric entropy change is calculated to be 3.5 J/kg-K for a 70 kOe magnetic field, with the entropy change curve exhibiting a broadened peak, leading to a substantial Relative Cooling Power (RCP). These findings enhance our understanding of the material’s behavior and highlight its potential for various technological applications.

Study of the Structure, Multiferroic, and Magnetic Order of Er0.9La0.1Cr0.8Fe0.2O3

Herein, the multiferroic perovskite Er0.9La0.1Cr0.8Fe0.2O3 was synthesized using the sol–gel method, and its structure and multiferroic properties were investigated. The magnetic order of Er0.9La0.1Cr0.8Fe0.2O3 was analyzed through magnetic entropy change curves. Furthermore, a four‐sublattice molecular field model was constructed to study the spin reorientation phenomena and explain the differences between various spin redirections through magnetic order correction. This work will provide a new perspective for studying the properties of type II multiferroic materials.

Comparison of two methods for achieving table-like magnetic entropy change in Eu-Ga-Ge clathrates

A novel method has been developed to efficiently produce composites of Eu-Ga-Ge clathrates through the process of spark plasma sintering (SPS) under varying pressures, temperatures, and times. This technique enables the adjustment of the α and β phase ratios, thereby allowing for the fine-tuning of material properties. The resulting composite exhibits a cohesive growth of both phases rather than a mere mechanical mixture, making it suitable not only for enhancing magnetic applications but also for improving various other physical properties including thermoelectric characteristics. The article focuses on the investigation of magnetocaloric properties in composites with different phase ratios. Remarkably, it was observed that an appropriately balanced ratio between the two phases yields a distinct table-like curve depicting magnetic entropy change, consequently leading to a enhanced refrigeration capacity (RC). Additionally, a hybrid sample was obtained through the mechanical mixing of several Eu-Ga-Ge β phases with different Tc values. The hybrid also exhibits a magnetic entropy change curve with a table-like shape. A comparative analysis between these two methods was conducted.

Structural, magnetic, magnetocaloric behavior and magneto-transport, electrical polarization study in 3d based bulk and nano-crystalline multiferroic double perovskite Dy2MnCoO6

In this paper, we report a detailed investigation of the crystal structure, magnetic, magnetocaloric, magneto-transport and electrical polarization properties of a new multiferroic material in the polycrystalline and nanocrystalline form of the Dy2MnCoO6 double perovskite. Both compounds crystallized in the monoclinic structure with P21/n space group. The magnetic properties of both systems are mainly dominant ferromagnetic (FM) and weak antiferromagnetic (AFM). The FM/AFM coupling is related by the competing and combining functions of the radius and the magnetic moments of rare earth ions (i.e. 3d–4f exchange interactions). The reduction of the saturation magnetization in the isothermal magnetization curves can be explained by the existence of anti-phase boundaries and local anti-site defects in the system. Moreover, these materials hold reasonable values of magnetocaloric parameters and the absence of hysteresis makes the system a potential candidate for magnetic refrigeration. These compounds revealed two magnetic phase transitions, according to the appearance of two peaks in the temperature dependence of magnetic entropy change curves. The temperature dependent resistivity data for both the systems display semiconductor nature near room temperature and insulating like behavior at low temperature regime. The variable-range hopping conduction mechanism is used to best understand their transport mechanism. In addition, the electrical polarization loop at low temperature confirms the presence of ferroelectricity for both the studied systems. The decreases polarization under an external magnetic field evidence the weak magnetoelectric coupling. The coexistence of FM ordering with insulating behavior and ferroelectricity at low temperature promises new opportunities and improvements in next generation applications for information storage, spintronic, and sensors.

Critical behavior and magnetocaloric effect in quasi-two-dimensional Mn3Si2Se6

The ferrimagnetic nodal-line semiconductor Mn3Si2Te6, featuring a quasi-two-dimensional crystal structure, has attracted significant attention owing to its rich physical properties. Here, we systematically investigate the magnetic properties of its isostructural compound, Mn3Si2Se6. The magnetism of this material is attributed to the Mn atoms, which exhibit antiferromagnetic interactions among the Mn atoms. The competition between antiferromagnetic exchange interactions results in an overall ferrimagnetic state, with a second-order transition from paramagnetic to ferrimagnetic occurring at 68 K. Critical exponents are derived using various common experimental techniques, including the modified Arrott plot, Kouvel-Fisher method, and critical isotherm analysis. The results indicate that the magnetism of Mn3Si2Se6 closely aligns with the mean-field model, with critical exponents β, γ, and δ determined as 0.475(3), 1.059(3), and 3.20(1), respectively, at the critical temperature of 68.3(2) K. Moreover, the curves of the magnetic entropy change − ΔSM(T, H) exhibit a peak around Tc, with −ΔSMmax amounts to 4.61 (3.63) J kg−1 K−1 for H∕∕ab (∕∕c) with a field change of 7 T. The estimated magnetic entropy value near Tc through specific heat is remarkably saller than the expected spin entropy of Mn2+ ions, indicating the presence of short-range interactions in the paramagnetic region.

Exploring the magnetic and magnetocaloric behavior of nanocrystalline melt-spun R2Fe17 (R = Pr, Nd) ribbons

Single-phase nanocrystalline R2Fe17 (R = Pr and Nd) ribbons with rhombohedral Th2Zn17-type crystalline structure (space group R3̅m) have been fabricated by melt-spinning technique. The microstructure of the polycrystalline ribbons is composed of quasi-spherical grains with an average size below 100 nm. Transmission electron microscopy reveals that these grains are formed by agglomeration of smaller nanocrystalline entities around 15 nm in diameter, separated by disordered boundaries where the long-range crystalline order is lost. Two different ferro-to-paramagnetic phase transitions are observed, one of them coincides with that of the parent bulk alloy (290 and 326 K for R = Pr and Nd, respectively), and the other one can be ascribed to the disordered boundaries (323 and 350 K for R = Pr and Nd, respectively). For R= Pr, this fact gives rise to a significant broadening (c.a. 120 K under a magnetic field change of 2 T) of the full-width at the half-maximum of the magnetic entropy change curve, |∆SM(T)| (that adopts a "table-like" shape), resulting in a considerable increase of the refrigerant capacity.

Assessing rapid solidification processing to produce magnetocaloric RFeSi alloys (R= Tb, Dy) for natural gas liquefaction

This work addressed the synthesis of melt-spun ribbons of the ternary intermetallic ferromagnetic phases RFeSi with R = Tb and Dy, presenting a thorough characterization of their structural, magnetic, and magnetocaloric behavior. Both compounds have been referred to as suitable magnetic refrigerants in the natural gas liquefaction temperature range. The primary phase in ribbon samples of both compounds shows the CeFeSi-type tetragonal crystal structure (space group P4/nmm), with Curie temperatures of 124 K and 89 K for TbFeSi and DyFeSi, respectively. Notably, a sizeable increase in the coercive field appeared below 20 K. However, for a magnetic field change of 2 T, the maximum values of the magnetic entropy change (|ΔSM|max) were 3.4 J kg−1 K−1 and 3.8 J kg−1 K−1 for TbFeSi and DyFeSi ribbon samples, respectively, reflecting a reduction of approximately 60% compared to reported findings for bulk alloys. In contrast, the refrigerant capacity under a magnetic field change of 2 T measured 120 J kg−1 for TbFeSi and 109 J kg−1 for DyFeSi. The reduction in |ΔSM|max is mainly due to a broader magnetic transition compared to the previous results for bulk alloys. Based on the RFeSi ribbons obtained, a biphasic magnetocaloric composite with a broad table-like magnetic entropy change curve, as that required for an Ericsson-type refrigeration cycle, is designed.

Cationic mismatch effect on structural and magnetic behavior of La0.5-xEuxCa0.5-yBayMnO3 charge-ordered manganites

In this research, we have tried to investigate the effect of the cationic disorder on charge ordering and magnetic phase separation in La0.5-xEuxCa0.5-yBayMnO3 (x = 0, 0.05, and 0.1) compounds synthesized by using the sol-gel method. All the samples possess the same average ionic radius at A site <rA> and the same Mn3+/Mn4+ ratio. Our analysis confirmed the chemical composition by energy dispersive X-ray spectroscopy and verified the structural integrity and purity of the phase by X-ray diffraction, revealing an orthorhombic structure with Pnma space group, which is in agreement with the tolerance factor. The important mismatch effect observed in the substituted specimens induces drastic effects on the structural and microstructural properties. Magnetic measurements indicate a great reduction of Curie temperature for substituted samples (from 250 K for x = 0 to 90 K for x = 0.05 and 85 K for x = 0.1), which indicates a weakening of ferromagnetic double exchange interactions induced by cationic disorder. The Arrott plots and the magnetocaloric study of the Eu−based samples indicate the persistence of the antiferromagnetic charge-ordered state characterizing the pristine compound (x = 0) as well as the presence of a first-ordered metamagnetic transition for all the studied samples, which is ascribed to the presence of antiferromagnetic domains. Such transition induced the appearance of a shoulder peak near 100 K in the magnetic entropy change curves for high magnetic field values, resulting in an extra cooling efficiency.

Influence of heat sintering on the physical properties of bulk La0.67Ca0.33MnO3 perovskite manganite: role of oxygen in tuning the magnetocaloric response.

The effect of heat treatments on bulk poly-crystalline La0.67Ca0.33MnO3 perovskite manganite is presented, to explore the possible enhancement in magnetocaloric performance. Samples were prepared via conventional solid-state reaction route with annealing and sintering at various temperatures. Detailed measurements of temperature-dependent and field-dependent magnetization were carried out to estimate the Curie point and order of magnetic transition. The increased sintering temperature results in a steep transition near the TC, and establishes the magnetic sensitivity as well as the active zone for substantial magnetocaloric performance, at about 168.2% for the LCM9 (sintered at 900 °C) sample. The cause for the significant improvement in the magnetic and magnetocaloric response is brought to light using detailed X-ray photoelectron spectroscopy (XPS) analysis, highlighting the role of oxygen in modifying the Mn3+/Mn4+ charge ratio. The maximum value of the isothermal magnetic entropy change for the optimized sample is found to be 6.4 J kg-1 K-1, achieved at 269 K, while temperature-averaged entropy change (TEC) values, TEC(ΔTH-C = 3 K) and TEC(ΔTH-C = 5 K), of 6 J kg-1 K-1 and 5.2 J kg-1 K-1, respectively, were obtained with a low magnetic field change of 20 kOe. The obtained isothermal entropy change at low field for the optimized La0.67Ca0.33MnO3 sample is higher than that of pure Gd and most oxide-based materials. The relative cooling power (RCP) value is around 93 J kg-1 (ΔH = 20 kOe). The order of the phase transition is examined with universal scaling; the scaled entropy change curves confirm the collapse onto a single curve for LCM9, asserting second-order character, whereas the breakdown of the curve with a dispersion relation (d) of 101.1% at Θ = -5 confirms the onset of intrinsic first-order nature in the case of the high-temperature-sintered samples. Calorimetry measurements show thermal hysteresis of 2.4 K and 7.1 K for LCM11 (sintered at 1100 °C) at ramp rates of 5 K min-1 and 10 K min-1, respectively, confirming the first-order nature of the magnetic transition.

Exploring thermodynamic characteristics and magnetocaloric effect of an edge-decorated Ising multilayer nanoparticle with graphene-like structure

In this paper, the thermodynamic characteristics, magnetocaloric effect and ground-state properties of an edge-decorated Ising multilayer nanoparticle with graphene-like structure are studied by Monte Carlo simulation. The results reveal that size effect, crystal field, exchange coupling, and applied magnetic field can control the magnetic behaviors of the system. In addition, the curves of magnetic entropy change and relative cooling power (RCP) are given induced by various physical parameters.

Critical behavior of the cubic ErNi2 Laves compound nearby the Ferro-paramagnetic phase transition

In this article, we analyze the critical behavior of the cubic Laves crystalline binary intermetallic compound ErNi2 near its second-order ferromagnetic (FM) to paramagnetic (PM) transition (6.9 K). Both the normalized thermal dependencies of the magnetic entropy change curves and the Banerjee criterion confirm the second order nature of the transition. By comparing the normalized slopes, we found that the Tricritical mean-field model is the best model to calculate the critical exponent value of ErNi2. Based on the modified Arrott plots, the final critical exponents are determined to be β = 0.164(2) and γ = 0.821(9), which are the closest to the Tricritical mean-field model, except for a litter differences. Moreover, the accuracy and reliability of these exponents were confirmed by both the Widom scaling relation and the scaling hypothesis. Our results provide new insight into understanding this compound's magnetic interactions.

Effect of thermal treatments below devitrification temperature on the magnetic and magnetocaloric properties in mechanically alloyed Fe70Zr30 powders

In this work, the relaxation of the amorphous structure of mechanically alloyed Fe70Zr30 powders has been analyzed through interrupted heating ramps below the devitrification temperature. As a result of such thermal treatment, Curie temperature and temperature at maximum magnetic entropy change curves shift to higher temperatures as the temperature of heating treatment increases. This effect can be attributed to both the release of the stress accumulated in the amorphous powder during the milling process and to the initiation of nucleation of α-Fe crystallites, as it has been shown by Mössbauer spectroscopy.

Enhanced magnetic refrigerant capacity power in Dy3Ni2 melt-spun ribbons by controlling the solidification rate

Both mechanical and magnetic properties of Dy3Ni2 ingots and melt-spun ribbons were investigated in the present work. The melt spinning rate has an important effect on their performance. The higher the melt spinning rate, the better the ductility, the larger the coercive force of ribbons. With increasing the spinning rate, the intensity of the diffraction peak suggesting the presence of polycrystalline becomes weaker and weaker, and eventually disappeared. The magnetic phase transition temperature is decreased from 66 K to 38 K with increasing the spinning rate. All samples undergo a second order paramagnetic-ferromagnetic phase transition. The full-width-at-half maximum of the temperature dependence of magnetic entropy change curve in Dy3Ni2 ribbons was much larger than that of Dy3Ni2 ingot. So a high refrigerant capacity power about 530 J.kg−1 of Dy3Ni2 ribbons was achieved.

Magnetocaloric effect of the Fe87M8B5 (M = Zr, Ce) amorphous alloys

The magnetic and magnetocaloric properties of the amorphous Fe87Ce8B5 ribbon were investigated in comparison with the Fe87Zr8B5 amorphous alloy (AA). It was found that the Fe87Ce8B5 AA shows a rather high maximum magnetic entropy change (−ΔSmpeak, ∼ 3.65 J/(kg × K) under 5 T and 1.47 J/(kg × K) under 1.5 T) near its Curie temperature (Tc, ∼ 283 K), which is much higher than the − ΔSmpeak of the Fe87Zr8B5 AA near 306 K. The mechanism for the enhanced − ΔSmpeak and decreased Tc by the Ce substitution for Zr in the Fe87M8B5 AAs were investigated. The results are helpful for achieving higher − ΔSmpeak of the iron-based AAs at the temperatures slightly lower than the room temperature, which is conducive to construct a table-like magnetic entropy change (−ΔSm) curve with higher average − ΔSm within the working temperature range of a domestic air conditioner.

Tuning structure and magnetic properties of table-like magnetocaloric effect in Er6MnSb2 by zirconium substitution

In this study, zirconium (Zr) successfully substituted for erbium (Er) in Er6–xZrxMnSb2 (x = 0, 0.5, 1, 1.5) of the Fe2P type, with comprehensive characterizations on crystal structure, electronic structure and magnetic properties. According to synchrotron powder X-ray diffraction data analysis and density functional theory calculation, Zr does not randomly but preferentially occupy during the doping process and results in weaker magnetic exchange interactions and depressed ordering temperatures. The electronic structure data show that the doping of Zr can weaken interaction between Er and Mn atoms. Owing to multiple transitions, the Er6–xZrxMnSb2 (x = 0, 0.5, 1, 1.5) exhibit table-like magnetocaloric effect. Er6MnSb2 displays wide δTFWHM (full width at half maximum of the magnetic entropy change curve) of 116 K and high relative cooling power of 388.62 J/kg for 3 T. The maximum magnetic entropy change of Er6–xZrxMnSb2 is increased from 3.81 to 7.69 J/(kg·K) with the Zr content up from x = 0 to x = 1.5.

Effect of heavy rare-earth (Dy, Tb, Gd) addition on the glass-forming ability and magneto-caloric properties of Fe89Zr7B4 amorphous alloy

In this paper, by adding rare-earth (RE) elements to Fe89Zr7B4 ternary amorphous alloy, we obtained a series of Fe87Zr7B4RE2 (RE = Dy, Tb, Gd) amorphous ribbons to further improve the magnetic refrigeration capacity of the basic alloy. Through the heavy RE element substitutions, the glass-formability of the Fe89Zr7B4 alloy was improved effectively. Besides, the Curie temperature Tc of the alloy system increased from 275 K to 342 K, obtaining a roughly linear correlation between the de Gennes factor and Tc. Through the recombination of ribbons with different Tc values, we designed potential amorphous composites with a "table-like" magnetic entropy change curve under different temperatures. This research promises to deepen understanding of the effect of RE additions on the magneto-caloric properties and enhance the performance of Fe-Zr-B amorphous refrigerants around room temperature.

Predicting the magnetic measurements of first- and second-order phase transition magnetocaloric materials with artificial neural networks

Due to the large innovative applications involving magnetocaloric materials, such as magnetic cooling devices and thermomagnetic engines, the number of studies on their characterization have been increasing over the past two decades. Although indispensable, magnetic measurements are considerably time-consuming, which sometimes hinder depth studies on the subject. We propose a method that uses artificial neural networks to predict magnetic measurements of magnetocaloric materials with first- and second-order phase transitions, aiming to reduce the required number of measured field dependent magnetization curves M(H) in standard studies. We validate the method for magnetic measurements of the first- and second-order phase transition materials Gd5Ge4 and Gd5Si2.4Ge1.6, respectively. The application of the proposed method results in very high accuracies, with r2>0.98, when comparing the prediction to measured M(H) curves. The entropy change vs temperature curves upon the application of 5 T magnetic fields are also predicted.

Effect of magnetocrystalline anisotropy on magnetocaloric properties of an AlFe2B2 compound

It is well known that the temperature dependence of the effective magnetocrystalline anisotropy energy obeys the $l(l+1)/2$ power law of magnetization in the Callen-Callen theory. Therefore, according to the Callen-Callen theory, the magnetocrystalline anisotropy energy is assumed to be zero at the critical temperature where the magnetization is approximately zero. This study estimates the temperature dependence of the magnetocrystalline anisotropy energy by integrating the magnetization versus magnetic field ($M\ensuremath{-}H$) curves, and found that the magnetocrystalline anisotropy is still finite even above the Curie temperature in the uniaxial anisotropy, whereas this does not appear in the cubic anisotropy case. The origin is the fast reduction of the anisotropy field, which is the magnetic field required to saturate the magnetization along the hard axis, in the case of cubic anisotropy. Therefore, the magnetization anisotropy and anisotropic magnetic susceptibility, which are the key factors of magnetic anisotropy, could not be established in the case of cubic anisotropy. In addition, the effect of magnetocrystalline anisotropy on magnetocaloric properties, as the difference between the entropy change curves of ${\mathrm{AlFe}}_{2}{\mathrm{B}}_{2}$ appears above the Curie temperature, is in good agreement with a previous experimental study. This is proof of magnetic anisotropy at slightly above Curie temperature.

Experimental and theoretical study of magnetic and magnetocaloric properties of the lacunar La0.8□0.2MnO2.8 compound: Bean-Rodbell model

In this paper, our research focuses on the correlation between structural and magnetic properties of the lacunar polycrystalline La0.8□0.2MnO2.8. The structural analysis proves a coexistence between R-3c and Pnma crystallographic structure. The analysis of the hysteresis loop shows that La0.8□0.2MnO2.8 sample is a Ferromagnetic soft material with an antiparallel magnetic coupled for both phases (Pnma and R-3c). Using servals theoretical approaches, the anisotropic parameters were estimated. The magnetocaloric properties were also investigated. A good result of the relative value of cooling power has been achieved (60% of that of Gd at 2 T) indicating that the material is a potential candidate for magnetic refrigeration application. The use of the Bean-Rodbell model based on the mean field theory allowed us to examine the nature of the magnetic transition and to calculate the magnetic and magnetocaloric properties with good accuracy. Moreover, within the framework of the mean-field theory, the spontaneous magnetization values MSp were estimated using the magnetic entropy change curves (-ΔS (M)).

The influence of Ti doping at the Mn site on structural, magnetic, and magnetocaloric properties of Sm0.6Sr0.4MnO3

Ti-doped Sm–Sr based manganites (Sm0.6Sr0.4Mn1-xTixO3, x ​= ​0, 0.1 and 0.15 denoted by S, S0.1, and S0.15 respectively) were prepared by the solid-state reaction method and the influence of Ti-doping at the Mn site on the structural, magnetic, and magnetocaloric properties were properly investigated. All the samples have orthorhombically distorted perovskite structures with pnma space group. S has peak magnetic entropy change 8.03Jkg−1K−1 ​at 100K for 14T magnetic field. For the same applied magnetic field, peak values of magnetic entropy change for S0.1 and S0.15 significantly reduce to 2.82 Jkg−1K−1 ​at 50K and 2.10 Jkg−1K−1 ​at 100K respectively. Relative cooling power (RCP) of S, S0.1, and S0.15 at 14T are 873Jkg-1, 271Jkg-1, and 204Jkg-1 respectively. Even though there is a reduction in RCP values, working temperature span (WTS) increases, and heat loss associated with magnetic hysteresis diminishes. Belov-Arrott plots and normalized magnetic entropy change curves suggest the presence of a field-induced first-order to second-order magnetic transition in the current samples.