Maximum Magnetic Entropy Change Research Articles

Structural, Optical, Magnetic, and Magnetocaloric Properties of Sn2Mn2O7 Pyrochlore

A new pyrochlore compound Sn2Mn2O7 has been synthesized to investigate its structural, optical, magnetic, and magnetocaloric properties. The refinement of the structure by Le Bail fitting reveals that the compound crystallizes into a monoclinic structure with P2/m space group. The reflectance spectrum has been recorded on a UV–vis spectrometer between the 200 and 800 nm wavelength range. The optical bandgap of the compound is found to be ≈3.06 eV. The skin depth, refractive index, extinction coefficient, and optical conductivity have also been computed. A magnetic transition has been observed at TC≈41 K in the magnetization versus temperature behavior. Arrott's plot confirms a second‐order magnetic phase transition, which is also established by the scaling analysis of magnetic entropy change. On the application of a 5 T magnetic field, the compound shows a maximum magnetic entropy change of 2.94 J kg−1 K−1 at a temperature ≈41 K with a relative cooling power of 41 J kg−1. The maximum magnetic entropy change values are higher than that reported for the Fe2Mn2O7 and smaller than for Al2Mn2O7 compound.

Mechanism for Improved Curie Temperature and Magnetic Entropy Change in Sm-Doped Fe88Zr8B4 Amorphous Alloys

In the present work, Fe88Zr8−xSmxB4 (x = 2, 4) amorphous alloys (AAs) were successfully synthesized into the shape of 40-micrometer-thick ribbons and their magnetic properties were measured. The Fe88Zr8−xSmxB4 (x = 2, 4) AAs exhibited a rather high maximum magnetic entropy change (−ΔSmpeak): ~3.53 J/(K × kg) near 317 K for x = 2 and ~3.79 J/(K × kg) near 348 K for x = 4 under 5 T. The effects of a Sm substitution for Zr on the Curie temperature (Tc) and −ΔSmpeak were studied and compared to those of Nd and Pr substitutions, for the purpose of revealing the mechanism involved in more detail.

Structural, Magnetocaloric, and Magnetic Properties in Heusler Ni50Mn35In10X5 (X = Ga, Fe and Al) Alloys

The structural, magnetocaloric, and magnetic characteristics in Heusler Ni50Mn35In10X5 (X = Ga, Fe, and Al) alloys were examined using X-ray diffraction and field-dependent magnetization measurements. All samples exhibited a mixture structure of cubic L21 and tetragonal L10 and underwent second-order magnetic transitions at TC(Al5) = 220 K, TC(Ga5) = 252 K, and TC(Fe5) = 298 K. The Ga5 alloy exhibited structural change as indicated by a thermal hysteresis that may be seen in the saturation magnetic field in the M(T) dependences. The transition at the TC point from a ferromagnetic to a paramagnetic state caused a drop in magnetization, supported by thermal hysteresis, at a low magnetic field (0.01 T). On the other hand, the Fe5 alloy presented a gradual decrease in magnetization with similar hysteresis behavior, also at a low magnetic field (0.01 T), whereas at 0.1 T of field, no features characteristic of this transition were detected. This could be due to a large difference in the metallic radius of Fe compared to that of In. Otherwise, magnetic investigations demonstrated that the replacement of In with Al may cause the structural transformation temperatures and TC to be shifted to low temperatures. The present results imply that the structural transformation temperatures and the transition itself are highly dependent on chemical composition. Furthermore, under a magnetic field change of 5 T, the maximum magnetic entropy changes of 0.6 J/kg K, 1.4 J/kg K, and 2.71 J/kg K for the Ga5, Fe5, and Al5 alloys, respectively, were determined by their TC. Refrigeration capacity values were found to be 25 J/kg, 74 J/kg, and 98 J/kg at µ0∆H = 5 T. These ribbons are viable candidates for multifunctional applications due to their cheaper cost and their physical characteristics disclosed during the magnetostructural transition, which takes place close to the room temperature.

Highly Anisotropic Magnetism and Nearly Isotropic Magnetocaloric Effect in Mn3Sn2 Single Crystals

Mn3Sn2 has been proposed as an ideal material for magnetic refrigeration. It undergoes two successive ferromagnetic transitions (T C1 = 262 K and T C2 = 227 K) and one antiferromagnetic transition (T N = 192 K). Herein we report, for the first time, the preparation of single crystals of Mn3Sn2 from Bi flux. The resultant anisotropic magnetic properties and magnetocaloric effect are investigated along the three principal crystallographic directions of the crystal. Significant anisotropy of magnetic susceptibility and multiple field-induced metamagnetic transitions were found at low fields, whereas the magnetocaloric effect was found to be almost isotropic and larger than that of the polycrystalline one. The maximum magnetic entropy change amounts to −ΔS M = 4.01 J⋅kg−1⋅K−1 near T C1 under a magnetic field change of μ 0ΔH = 5 T along the c-axis, with the corresponding refrigerant capacity of 1750 mJ⋅cm−3. Combined with a much wider cooling temperature span (∼ 80 K), our results demonstrate Mn3Sn2 single crystal to be an attractive candidate working material for active magnetic refrigeration at low temperatures.

Structural, magnetic properties and large cryogenic magnetocaloric effect (MCE) in RE2MgTiO6 (RE = Tb, Dy, Ho and Er) double perovskite (DP) oxides

We have systematically studied the crystal structure, cryogenic magnetic properties and MCE in RE2MgTiO6 (RE = Tb, Dy, Ho and Er) DP oxides. The four RE2MgTiO6 samples are all found to crystallize in a monoclinic DP structure (P21/n space group). The Néel temperature (TN) are found to be 4.7, 4.5, 3.1 and 2.1 K for RE2MgTiO6 (RE = Tb, Dy, Ho and Er) DP oxides, respectively. Moreover, the maximum magnetic entropy change (-ΔSMmax) together with relative cooling power (RCP) near TN under a magnetic field change (ΔH) of 0–7 T are evaluted to be 16.85, 360.59 for Tb2MgTiO6, 17.72, 381.05 for Dy2MgTiO6, 15.92, 398.14 for Ho2MgTiO6 and 22.95 J/kg K, 459.09 J/kg for Er2MgTiO6, respectively. The excellent cryogenic MCE suggest that RE2MgTiO6 (RE = Tb, Dy, Ho and Er) DP oxides can be used as a promising candidate material for cryogenic magnetic refrigeration.

Tuning of the magneto-caloric effects in Ni43Mn46In11 magnetic shape memory alloys by substitution of boron

In this study, we report the structural, magnetic, and magnetocaloric properties of B substitution on the Mn site in Ni43Mn46−x B x In11(x = 0.5, 1.0) Heusler alloys. Crystal structure analysis using room-temperature x-ray diffraction data reveals both samples have mixed phases composed of cubic and tetragonal phases. The structural and magnetic phase transition characteristic temperatures are determined using differential scanning calorimetry, isothermal magnetization (MT), and isofield magnetization (MH) measurements. Both alloys exhibit inverse and direct magnetocaloric effects in the vicinity of their magnetostructural transition and Curie temperature (T C), respectively. For Ni43Mn45.0B1.0In11 a maximum magnetic entropy change of 25.06 J kg−1 K−1 is observed at 250 K for a magnetic field change of 5 T.

Significant enhancement of magnetocaloric effects via tuning Curie temperature and magnetic anisotropy in rare-earth based compounds

Magnetic refrigeration (MR) research has been increasingly focused on targeting operation temperatures as low as 4.4–20 K, which is of strategic significance for liquid helium and hydrogen in various activities such as aerospace and highly advanced industries. To date, despite most research has been aimed at obtaining MR materials with large magnetic entropy change and adiabatic temperature change, the optimizing operation temperature to target the cooling range for helium-hydrogen liquefaction is highly desirable and valuable. Here, the significant enhancement in magnetocaloric effects (MCEs) and magnetic materials operating in the temperature range of 4.4–20 K are achieved. The magnetic properties and MCEs of HoCuAl are manipulated by substituting Er or Tm atoms with the lower de Gennes factor and various magnetic anisotropy. The maximum magnetic entropy change ((−ΔSM)max) and refrigeration capacity (RC) under 0–5 T for Ho0.9Er0.1CuAl increases by 25.8 % and 39.8 % respectively compared with HoCuAl compound. Additionally, the critical role of Curie temperature and magnetic anisotropy in the significant enhancement of MCEs is confirmed by the systematic macroscopic physical analysis and neutron diffraction measurements. The excellent MCEs, suitable operation temperature, and free of hysteresis loss demonstrate the promising application prospect in liquefaction of helium-hydrogen.

Study of magnetic properties and magnetocrystalline anisotropy of CoPb3 alloys by Ab initio calculations and Monte Carlo simulations for three-dimensional Ising, XY and Heisenberg models

The electronic and magnetic properties of CoPb3 compound have been calculated using the frst-principles density functional calculations and Monte Carlo simulation of Ising, XY and Heisenberg models. This compound exhibit metallic character. The total magnetic moments of CoPb3 using GGA and GGA + U approximations are 1.53874 and 2.1487 μB/f.u, respectively. The magnetic anisotropy shows that the easy axis is along the axis [100]. CoPb3 has perpendicular magnetic anisotropy (PMA) at T = 0 K. The critical temperature follows the trend Ising model > XY model > Heisenberg model using the MCS method. The isothermal magnetic entropy change was calculated. The maximum magnetic entropy changes are 0.24 J K−1 kg−1, 8.69 J K−1 kg−1 and 1.16 J K−1 kg−1 for Ising, XY and Heisenberg models respectively.

Exploration and quantification of magnetocaloric effect in EuTiO3 perovskite using extreme learning machine intelligent computational method

Perovskite EuTiO3 is a multi-ferroic titanate oxide material that exhibits huge magnetocaloric effect at low magnetic field without associated hysteresis loss due to the magnetic field and thermal energy. These unique features coupled with the presence of strong coupling existing between spin and lattice as well as the possibility to switch the magnetic ground state between ferromagnetism and anti-ferromagnetism, foster the potentials of this material for magnetocaloric effect based cooling technology application. Maximum magnetic entropy change of perovskite EuTiO3 determines the strength of magnetocaloric effect in the material and ultimately influences the usability of this material for cooling technology. However, experimental measurement of maximum magnetic entropy change is challenging and consumes appreciable resources and time. Maximum magnetic entropy change of intrinsic and doped EuTiO3 perovskite is modeled in this work using extreme learning machine intelligent algorithm (ELMIA) with the ionic radii, elemental concentration and applied magnetic field descriptors. The developed ELMIA-SINE with sine activation function performs better than ELMIA-SIG model with sigmoid activation function with performance superiority of 42.46%, 44.58% and 1.76% using root mean square error, mean absolute error and correlation coefficient performance yardstick, respectively. The developed ELMIA-SINE model further outperforms the existing particle swarm based support vector regression model with polynomial (PSVR-P) and Gaussian (PSVR-G) function with performance improvement of 37.03% and 14.11%, respectively. The dependence of applied magnetic field and dopant concentration on hugeness of magnetocaloric effect was established using the developed model. The precision and the ease of implementation of the developed ELMIA model as compared with the existing models would definitely facilitate exploration of magnetocaloric effect based system of refrigeration for addressing the present energy crisis.

Large magnetocaloric effect in Gd2Si2O7 and plateau-like magnetic entropy change in Dy2Si2O7

We report the magnetic properties and magnetocaloric effects (MCE) of R2Si2O7 (R = Gd, Dy) with different crystal structures. For the orthorhombic Gd2Si2O7 (Type E), no signature of long-range magnetic ordering is observed down to 2 K. What is very impressive is the maximum magnetic entropy change (−ΔSMmax) of 58.81 J kg–1 K–1 at 3 K, which is 82.1 % of the theoretical value 2Rln8 (71.637 J kg–1 K–1), for a field change of ΔB = 0 − 7 T. For the triclinic Dy2Si2O7 (Type B), it is long-range antiferromagnetically ordered at TN = 1.92 K. Importantly, the −ΔSMpresents a plateau-like behavior within 6–12 K with three local maxima. The value of −ΔSMmaxis about 20.33 J kg−1 K−1 for 0 − 7 T at 12 K (much higher than TN). Thus, the large MCE in Gd2Si2O7 and the plateau-like magnetic entropy change in Dy2Si2O7 make them potential candidates for magnetic refrigeration in the low temperature range.

Magnetic properties and magnetocaloric effect of a metallic triangular lattice antiferromagnetic DyAl2Ge2 single crystal

We report the synthesis, magnetic susceptibility, magnetization, electrical resistivity, heat capacity, and magnetocaloric properties of the metallic triangular lattice antiferromagnetic DyAl2Ge2 single crystal. High-quality rare-earth intermetallic compound DyAl2Ge2 single crystals were synthesized by the metallic flux method. DyAl2Ge2 crystallizes in a trigonal CaAl2Si2-type structure with Dy atoms forming a triangular lattice in the ab plane. The paramagnetic-antiferromagnetic transition occurs at 8 K, as determined by temperature dependencies of magnetic susceptibility and heat capacity. No observable hysteresis was found in the field-induced antiferromagnetic to the ferromagnetic metamagnetic transition of DyAl2Ge2. The electrical resistivity shows an overall metallic behavior with an upturn at the ordering temperature. For a magnetic field change of 0–70 kOe, the maximum magnetic-entropy change is −14.2 J kg−1 K−1 at 11 K and the relative cooling power is 327 J kg−1 with the applied magnetic field along the ab plane.

Pr/ Co co-doping endows perovskite manganite with enhanced magnetic refrigeration capacity

It is recognized that new environmentally friendly and economical cooling methods are needed. In this paper, we focus on the effect of different doping amounts of Pr on the performance of magnetic refrigeration materials in the presence of trace doping of Co ions at the B-site. The samples La0.67Sr0.33−xPrxMn0.975Co0.025O3 (LSPMCO x = 0.10,0.125 and 0.15) in this paper were prepared by sol-gel method. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) diffraction data determined that the samples were pure phases without impurities belonging to the R-3c space group (No. 167). Scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that the samples were not regular particles of submicron size, and the size of the grains decreased gradually with increasing Pr doping. The experimental data have shown that the samples underwent second order phase transitions near the Curie temperature (Tc). Tc is closest to room temperature at 300 K at a doping level of 0.10. The maximum magnetic entropy change (−∆SMmax) at 5 T is 3.79 (J/kg∙K) (x = 0.15) and the relative cooling power (RCP) is 352.78 (J/kg) (x = 0.15). The results demonstrated that the doping of Pr has an enhanced effect on the performance of the magnetic refrigeration La0.67Sr0.33Mn0.975Co0.025O3 material. This may provide a reference for improving the performance of magnetic refrigeration materials in future research.

On the origin of cracking in laser powder bed fusion processed LaCe(Fe,Mn,Si)13, and the impact of post-processing

LaCe(Fe,Mn,Si)13 magnetocaloric material printed by laser powder bed fusion (LPBF) has a huge potential for magnetic refrigeration. However, high crack and defect susceptibility in LPBF processing remains a limitation of its application. This study optimised the LPBF process parameters for optimally dense blocks. The volumetric energy density condition, EV = 250 J/mm3, showed the lowest crack density and porosity fraction. The behaviour and mechanism of different cracks and defects were revealed. The lower energy density parameter sets, caused by higher scanning speeds and hatch spacing, lead to the formation of lack-of-fusions. The hot cracking observed was attributed to stress concentration and a stable liquid film. The solid-state cracks observed were expected in the microstructure of the as-fabricated (AF) sample due to the poor toughness of the La/Ce/Si-rich phases. Thermal heat treatment and quenching increased the magnetocaloric effect (MCE) of the AF sample. The maximum magnetic entropy change (∆Smax) of the heat-treated sample was − 3.68 Jkg−1K−1 at 294 K, when applied to a 1 T field. The Curie temperature (Tc) (298 K when applied 0.01 T field) and superior MCE make the material an ideal choice for realising room-temperature magnetic refrigeration.

Tunning the magnetism and magnetocaloric effects of EuAl4 single crystals by Si and Cu doping

The effects of Si and Cu doping on crystal structures, magnetism, and the magnetocaloric effect of EuAl4 have been investigated. EuAl4, EuAl3.35Si0.65, and EuAl3.82Cu0.18 single crystals grown by the Al flux method are isotypic and crystallize in BaAl4-type structure with space group I4/mmm. Compared to the pristine compound EuAl4, the lattice parameter a keeps almost unchanged and c decreases obviously by Si doping, while a decreases and c increases upon Cu-substitution. These irregular changes in the lattice parameters may contribute to the electronegativity difference between Si and Cu. Cu and Si doping enhances the ferromagnetic interaction, and the direction of easy magnetization changes from the ab plane to the c axis upon the Cu-substitution. Multiple-step metamagnetic transitions are still observed in EuAl3.35Si0.65 as applying the magnetic field along the c axis, while EuAl3.82Cu0.18 shows ferromagnetic behavior along the ab plane and c axis. As a consequence, the low-field magnetocaloric effect is significantly enhanced. The maximum magnetic entropy change under a field change of 20 kOe increases from − 8.4 J/kg K for EuAl4 to − 12.9 J/kg K for EuAl3.35Si0.65 and − 15.9 J/kg K for EuAl3.82Cu0.18. The corresponding values of refrigerating capacity are 67, 140, and 147 J/kg, respectively. The remarkable magnetocaloric performances suggest that the Cu-doped EuAl4 compound is an excellent candidate material for low-temperature magnetic refrigeration.

Borderline first-order phase transition and large cryogenic magnetocaloric effect in PrNdIn

We report a large cryogenic magnetocaloric effect stemming from an unconventional borderline first-order magnetic phase transition with negligibly small thermomagnetic hysteresis in a rare-earth-based intermetallic compound PrNdIn. The sample exhibits maximum magnetic field-induced entropy change as large as −10 J/Kg K (for 20 kOe magnetic field change) near the boiling point of oxygen. Magnetocaloric properties of PrNdIn are comparable to those of other known potential magnetocaloric materials with operating temperatures ranging between 50 and 125 K. The magnetic properties of the present sample are qualitatively reminiscent of those of the binary Pr2In and Nd2In, including the emergence of a second low-temperature anomaly in the temperature dependence of magnetization.

Effect of annealing on magnetic and magnetocaloric properties of SmCo3B2 thin films

In this study, SmCo3B2 ternary thin films of manifold thickness were fabricated via e-beam evaporation technique. All the as-deposited SmCo3B2 thin films were subjected to electron beam rapid thermal annealing (ERTA). The X-ray diffraction studies showed amorphous nature for all the as deposited thin films and a highly crystalline hexagonal structure for all ERTA subjected thin films. The elemental composition, purity and surface morphology of the samples were analyzed using energy-dispersive x-ray spectroscopy (EDS) and High-resolution Scanning Electron Microscopy (HR-SEM). Furthermore, the study investigates the magnetocaloric properties of SmCo3B2 thin films, with significant changes depending on the thickness and annealing time. The thin films exhibited a magnetic phase transition around the Curie temperature (Tc) within the range of 40–46 K, attributed to the indirect exchange coupling of Sm–Sm sublattice interactions. Moreover, a significant shift in Tc towards higher temperatures with respect to thickness and annealing were observed in both as deposited and ERTA subjected thin films. The Arrot plots in the positive quadrant suggested the second order magnetic phase transition (SOPT) for all the films. The maximum magnetic entropy change (−ΔSm) of 1.172 Jkg−1K−1 accompanied by a relative cooling power of 5.33 Jkg-1 was achieved for 240 nm ERTA subjected thin film under a change in magnetic field of 5T. The study reveals the effect of ERTA and thickness dependent magnetic and magnetocaloric properties of SmCo3B2 thin films.

Effect of Minor Ce Substitution for Pr on the Glass Formability and Magnetocaloric Effect of a Fe88Zr4Pr4B4 Metallic Glass

In the present work, Fe88Zr4Pr3B4Ce1 metallic glass (MG) was successfully prepared by minor Ce substitution for Pr, and compared with Fe88Zr4Pr4B4 MG in terms of glass forming ability (GFA), magnetic and magnetocaloric properties. The GFA, Tc and the maximum magnetic entropy change (−ΔSmpeak) of the Fe88Zr4Pr3B4Ce1 MG were found to decrease slightly. At the same time, the possible interaction mechanism of minor Ce replacing Pr was also explained. The critical exponents (β, γ and n) obtained by the Kouvel–Fisher method indicate that Fe88Zr4Pr3B4Ce1 MG near Tc exhibits typical magnetocaloric behavior of fully amorphous alloys. The considerable maximum magnetic entropy change (−ΔSmpeak = 3.84 J/(kg × K) under 5 T) near its Curie temperature (Tc = 314 K) as well as RCP (~ 646.3 J/kg under 5 T) make the Fe88Zr4Pr3B4Ce1 MG a better candidate as a component of the amorphous hybrids that exhibit table-shape magnetic entropy change profiles within the operation temperature interval of a magnetic refrigerator.

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.

Tunable magnetic and magnetocaloric properties of scandium doped Gd3Fe5-xScxO12 garnet compound

This paper presents the tunable magnetic and magnetocaloric properties of Scandium-doped gadolinium iron garnets, Gd3 Fe5-xScxO12 (x = 0.0 to 0.25) compounds prepared by a facile auto-combustion method. The sample analyzed has a dominant cubic crystal structure (space group: Ia3¯d)) with a small fraction of an orthorhombic secondary phase, as determined by Rietveld analysis of X-ray diffraction patterns. The structural, magnetic, Mössbauer spectroscopy and first-principles density functional theory (DFT) studies show a preferential substitution of Sc3+ at the octahedral site of Fe3+ions. The ferrimagnetic (FIM) transition is present in all samples, with the transition temperature decreasing from 560 K for × = 0.0 to 521 K for × = 0.25. The Sc3+dopedGd3Fe4.75Sc0.25O12exhibits an improved magnetocaloric effect (MCE) with a maximum magnetic entropy change (-ΔSMmax)3.82 J kg-1K−1, and a higher relative cooling power (RCP) value of 408 J kg−1, which is ∼ 7 % higher than the Gd3Fe5O12(380 J kg−1) sample. These findings suggest that by incorporating Sc3+, the magnetic and magnetocaloric properties of Gd3Fe5-xScxO12 can be tailored for potential applications in low-temperature magnetic refrigeration.

Large table-like magnetocaloric effect in boron-doped Er5Si3B0.5 compound

In this work, Er5Si3B0.5 compound with the Mn5Si3-type hexagonal structure was synthesized, and the structure, magnetic properties, and the magnetocaloric effect were investigated theoretically and experimentally. The magnetic measurement results show a complex successive magnetic transition below TN. However, the magnetization of the Er5Si3B0.5 compound below TN is saturated under lower magnetic field relative to the Er5Si3 compound. Theoretical calculation indicates that this was attributed to the enhanced inter-orbital exchange interaction after doping B element. The complicated successive magnetic transitions contribute to the table-like magnetocaloric effect observed in the Er5Si3B0.5 compound with a wide temperature region. The maximum magnetic entropy change and the temperature averaged entropy change (30) are 10.1 and 9.02 J/kg K for the Er5Si3B0.5 compound under varying magnetic fields from 0 to 5 T, respectively. The temperature averaged entropy change (30) is reduced by just 11% compared to the maximum magnetic entropy change. While presenting an ideal magnetic refrigeration material with a large table-like magnetocaloric effect for hydrogen liquefaction, our work also demonstrates the feasibility of regulating magnetic behavior through enhanced orbital exchange interactions to develop magnetic refrigeration materials with outstanding performance.