Magnetic Entropy Change Research Articles

Evidence of a Large Refrigerant Capacity in Nb-Modified La1.4Sr1.6Mn2−xNbxO7 (0.0 ≤ x ≤ 0.15) Layered Perovskites

In this work, evidence of isothermal magnetic entropy change (∆SM) over a broad temperature region is presented in a series of La1.4Sr1.6Mn2−xNbxO7 Ruddlesden–Popper compounds with niobium modification (Nb) (0.0 ≤ x ≤ 0.15) at the manganese (Mn) site. The ceramic samples were obtained through a solid-state sintering method in optimized conditions. All compounds predominantly possessed Ruddlesden–Popper phase while a few additional reflections were resolved in Nb-doped compounds which indicates the separation of structural phases. These peaks are assigned to a separate layered perovskite and single perovskite with tetragonal symmetry and hexagonal symmetry, respectively. The microstructure of the pure sample reveals uniform grain morphology but in Nb-doped specimens chiefly three types of grains were found. It was assumed that the inter-connected large particles were of R-P phase which is dominant in both parent and x = 0.05 compounds, while the hexagonal and polygonal morphology of grains in higher concentrations of dopants directly corroborates with the symmetry of single perovskite and additional layered perovskite phases, respectively. The parent compound exhibits a single ∆SM curve, whereas all Nb-substituted samples display bifurcated ∆SM curves. This indicated two transition regions with multiple magnetic components, attributed to distinct structural phases. The highest ∆SM values obtained for components corresponding to the R-P phase are 2.32 Jkg−1k−1, 0.75 Jkg−1k−1, 0.58 Jkg−1k−1 and 0.43 Jkg−1k−1 and for the second component located around room temperature are 0.0 Jkg−1k−1, 0.2 Jkg−1k−1, 0.28 Jkg−1k−1 and 0.35 Jkg−1k−1 for x = 0.0, 0.05, 0.10 and 0.15 compositions, respectively, at 2.5 T. Due to the collective participation of both components the ∆SM was expanded through a broad temperature range upon Nb doping.

Magnetic properties and magnetocaloric effect of Borophyne structure: A Monte Carlo study

This study delves into the magnetocaloric effect of the Borophyne structure, employing a Monte Carlo method with a mixed spin composition of σ = 3/2 and S = 1. Each site within the structure is occupied by a spin, with pairwise interactions governed by exchange coupling parameters JSS, Jσσ, and JSσ, the interaction between two neighboring atoms is considered an antiferromagnetic for JSσ < 0 or ferromagnetic for JSσ > 0. The investigation focuses on determining magnetic entropy changes, relative cooling power, adiabatic temperature, and magnetic hysteresis cycles for a range of magnetic parameters. The results obtained from this study demonstrate that the structure under investigation exhibits highly intriguing properties. Through our simulations and analysis, we have uncovered a range of characteristics that highlight the unique behavior of the system.

Magnetocaloric effect at the reorientation of the magnetization in ferromagnetic multilayers with perpendicular anisotropy

We investigate the magnetocaloric effect obtained by the rotation of a magnetic field applied to an exchange-coupled multilayer system composed of two different ferromagnetic (FM) materials. We specifically consider a system in which the two FMs have perpendicular uniaxial anisotropy axes and utilize conditions which yield a reorientation of the total magnetization when compensation between the anisotropies of the two layers occurs. We calculate the consequent entropy change associated with the “artificial” reorientation. By using known parameters from MnBi and Co we predict an entropy change of Δs=0.34 J kg−1 K−1 for perfect coupling. Lastly, we study the behavior of the multilayer under a rotating magnetic field via a micromagnetic model. When the layer thicknesses are of the order of the local domain wall width, the magnetic field-induced entropy change can be obtained with magnetic fields one order of magnitude lower than in the uncoupled case.

A Monte Carlo investigation of the magnetic behaviors and magnetocaloric effect of the nanoporous graphenes of a mixed spin ferrimagnetic (2, 3/2)

Based on the Monte Carlo calculation, we have investigated the magnetic behavior and the magnetocaloric effect of the nanoporous graphenes of a mixed spin ferrimagnetic (2, 3/2). We start by discussing the ground state phase diagrams corresponding to several physical parameters at the temperature T=0 K. In addition, the reduced critical and compensation temperatures have been found with distinct values of the number of lattice sites (L). The influence of the parameter L, reduced exchange couplings Rσσ, Rsσ, and the reduced crystal field on the total magnetic and hysteresis cycles has also been studied. We begin by exploring the impact of the reduced external magnetic field on the specific heat (Cp), magnetic entropy change (-∆Sm), adiabatic temperature change (ΔTa), and relative cooling power (RCP). These results indicate that the nanoporous graphene compound could be a promising candidate for magnetic refrigeration technology.

Magnetic anisotropy and associated entropy change in textured TmGa

Since Warburg's discovery of the magneto-caloric effect (MCE) in 1881, researchers have invested decades exploring its applications in the realm of magnetic cooling not only at room temperature but also at cryogenic temperatures. TmGa has emerged as a focus due to its notably high MCE performance. However, discrepancies have surfaced between the findings on single-crystalline TmGa reported by Gao et al. in 2013 and subsequent reports on polycrystalline TmGa. These disparities present significant challenges for ongoing TmGa research. To address these inconsistencies, this study prepares TmGa in a textured polycrystalline form. Magnetic measurements along both parallel (H∥a) and perpendicular (H⊥a) to the a-axis reveal pronounced magnetic anisotropy between the two directions. Notably, a distinct and complex anisotropic field-dependence in magnetic interaction and corresponding transitions are observed. Furthermore, magnetic entropy changes (∆Sm) for both H∥a and H⊥a, along with the corresponding anisotropic entropy change (∆Sman), are computed based on Maxwell’s relations. This investigation discloses maximum values of ∆Sman, reaching 17.2 J/kg K at T = 16.5 K and 24.3 J/kg K at T = 11.5 K for fields of 20 and 50 kOe, respectively, which are close to the largest value to date. These findings provide insights into fundamental magnetic properties and their potential applications for rotational magneto-caloric effects.

Effect of synthesis method on structural and magnetic properties of La0.7Ca0.2Ba0.1MnO3

Abstract We study the effect of the synthesis method on the structural and magnetic properties of La0.7Ca0.2Ba0.1Mn03. The samples were synthesized by coprecipitation and solution combustion methods. X-ray diffraction and scanning electron microscopy were performed to investigate the crystallographic structure, showing that both methods produced La0.7Ca0.2Ba0.1Mn03 monophasic samples. From magnetization measurements a second-order, ferromagnetic to paramagnetic, phase transition was observed. The Curie temperature is found to be 272 K for the sample obtained by coprecipitation and 283 K for the sample obtained by solution combustion. There is a small magnetic hysteresis for both samples. The magnetocaloric parameters were obtained using a phenomenological model; the magnetic entropy change and relative cooling power factor are higher in the sample synthesized by combustion.

Magnetothermal properties including magnetocaloric performance of the ternary rhombohedral Laves phase of Pr2Rh3Ge

The article presents the study of the magnetocaloric effect (MCE) for the rhombohedral Laves phase of Pr2Rh3Ge, which shows a magnetic order below TC=8.5 K. We have established that the compound exhibits a continuous second-order type of transition which was demonstrated and confirmed by several different techniques, mainly by analyzing universal curves of normalized entropy change as a function of scaled temperature. The observed MCE, in our opinion, is a consequence of an indirect exchange coupling between the magnetic sublattices of the rare earth ions, which, however, does not exclude the potential contribution of sublattice-containing transition metals. In this paper, the procedure to evaluate the MCE from magnetization and specific heat data is described. As a result, important parameters such as the isothermal magnetic entropy change (ΔSM), adiabatic temperature change (ΔTad), relative cooling power (RCP), and the temperature averaged entropy change (TEC) were determined. The highest values of −ΔSM, ΔTad, and RCP for a field change (Δμ0H) of 5 T at TC are 5.96 J/kgK, 3.87 K, and 72.62 J/kg, respectively. These results obtained for Pr2Rh3Ge seem to be, however, low compared to the values obtained for the rhombohedral Laves phases, belonging to the group of ternary germanides RE2Rh3Ge containing heavy rare earth metals (RE = Gd, Tb, Ho, and Er). Nevertheless, we believe that the results presented in this work extend and complement the current knowledge on the magnetocaloric properties of this family of materials.

The study of structural, electronic, magnetic and magnetocaloric properties of antiperovskite carbides M3AlC (M=Mn and Fe): DFT combined with Monte Carlo simulation

This work aims to investigate the structural stability, magnetic and electronic properties of M3AlC antiperovskites using density functional theory (DFT) and Monte Carlo simulation. The obtained ground state results reveal that the antiperovskites M3AlC are stable in the ferromagnetic (FM) state with a metallic character. The calculated total magnetic moments are 5.21[Formula: see text] and 3.34[Formula: see text] for Mn3AlC and Fe3AlC, respectively, with the total moments mainly from the M atom. The ferromagnetic behavior is confirmed by computing the density of state at Fermi level and verified the Stoner criterion. The magnetic and magnetocaloric behavior of M3AlC is investigated using Monte Carlo simulation and the obtained results demonstrate that the transition from ferromagnetic to paramagnetic state occurs at [Formula: see text][Formula: see text]K and [Formula: see text][Formula: see text]K for Mn3AlC and Fe3AlC, respectively. These values of [Formula: see text] are in good agreement with the experimental results. The magnetocaloric effect and critical behavior are studied and the obtained values of magnetic entropy change [Formula: see text] at 4.5[Formula: see text]T is about 4.242[Formula: see text]J/kg.K and 3.666[Formula: see text]J/kg.K and the relative cooling power (RCP) are 342.434[Formula: see text]J/kg.K and 325.26[Formula: see text]J/kg.K for Mn3AlC and Fe3AlC at 4.5T, indicating that these compounds are more appropriate for magnetic refrigeration. Finally, the critical exponents ([Formula: see text],[Formula: see text],[Formula: see text]) are calculated and the obtained values are close to the values of mean-field model.

The large magnetocaloric effect in GdErHoCoM (M = Cr and Mn) high-entropy alloy ingots with orthorhombic structures

High-entropy alloys (HEAs) with significant magnetocaloric effects (MCEs) have attracted widespread attention due to their potential magnetic refrigeration applications over a much more comprehensive temperature range with large refrigerant capacity (RC). However, most of them are metallic glasses (MGs) with problems of limited size, resulting in the difficulty of further applications. Therefore, research on HEAs with crystalline structures and giant MCE is urgently needed. In this paper, GdErHoCoM (M = Cr and Mn) rare-earth HEA ingots with orthorhombic structures are developed, and their magnetic behavior and MCE are studied in detail. Phase investigations find that the main phase of GdErHoCoM ingots is probably (GdErHo)Co with an orthorhombic Ho3Co-type structure of a space group of Pnma. The secondary phases in GdErHoCoCr and GdErHoCoMn are body-center-cubic Cr and Mn-rich HoCo2-type phases, respectively. Magnetic investigations reveal that both ingots undergo a first-order magnetic phase transition below their respective Neel temperatures. Above their respective Neel temperatures, a second-order transition is observed. The Neel temperatures are 40 and 56 K for GdErHoCoCr and GdErHoCoMn, respectively. Additionally, the GdErHoCoCr and GdErHoCoMn ingots exhibit maximum magnetic entropy changes and RC values of 12.29 J/kg/K and 746 J/kg and 10.13 J/kg/K and 606 J/kg, respectively, under a magnetic field of 5 T. The ingots GdErHoCoM (M = Cr and Mn) show excellent MEC properties and can be manufactured easily, making them promising for magnetic refrigerant applications.

Magnetocaloric effect in Gd1-xCexNi (x = 0–0.6): A cost-effective approach to tuning Curie temperature from 70 K to 30 K

Magnetic refrigeration is a promising alternative to traditional gas compression refrigeration technologies, as it offers significantly higher energy efficiency. One factor hindering the widespread implementation of magnetic refrigeration is the dependence on expensive and critical rare earth elements needed to produce a strong magnetocaloric effect. Inside this work we explore substituting a non-critical rare earth element, Ce, into an established magnetocaloric material of choice, GdNi. Structural characteristics are investigated via x-ray powder diffraction, and the magnetocaloric effect is evaluated indirectly from heat capacity measurements as well as calculated using the mean field method. Our results show that small substitutions of Ce into GdNi results in the dilution of the magnetocaloric effect while maintaining relative cost effectiveness for small substitutions of Ce. As Ce content is increased, the cost effectiveness of the adiabatic temperature change (ΔTad) increases as high as 20% for (Gd0.4Ce0.6)Ni while the magnetic entropy change (-ΔSm) shows minimal improvement in cost effectiveness, falling from 3.93 J/kg*K in GdNi to 1.75 J/kg*K in (Gd0.4Ce0.6)Ni at 1 T applied field. This demonstrates that using Ce substitutions can be a powerful tool in both tuning Curie temperature and mitigating the reliance on critical elements as we look to develop towards a more sustainable future.

Weak magnetic doping effect on the magnetic transition, magnetocaloric properties, and super-invar behavior in TbCo2Vx system

In this work, the V-doped effect on the magnetic transition and magnetocaloric properties have been studied systematically for TbCo2Vx (0 ≤ x ≤ 0.2) series. All samples were characterized by powder X-ray diffraction (XRD) as cubic structures (Fd-3 m) at room temperature. The Curie temperatures TC of TbCo2Vx decrease monotonically from 234 K (x = 0) to 214 K (x = 0.2) corresponding to a monotonically increasing value of lattice a. The slightly diminished magnetic saturation moment MS from 6.35 μB/f.u to 6.12 μB/f.u with the x value increasing indicates weak magnetic doping in this system, which can also be reflected in the slight decrease of the maximum values of magnetic entropy change (-ΔSM) from 6.23 J kg-1K−1 to 5.27 J kg-1K−1 (0–5 T). X-ray photoelectron spectrum (XPS) measurements confirm that the weak magnetic doping originates from the multivalences of V2+ and V4+, compared with other normally nonmagnetic V-doped cases reported before. Both the Banerjee criteria and rescaled magnetic entropy change lines deny the first-order transition in parent compound TbCo2 as reported recently. Almost zero thermal expansion near TC in TbCo2 with thermal expansion coefficient αl = -1.43 × 10-6 K−1 indicates weak magnetostriction, which is another experimental hint for second-order transition. The deviation of the critical exponents to Mean-field theory in TbCo2 implies some crystal defects and inhomogeneous polycrystalline distribution inside, which should also be a key point for the divergence of first-order and second-order transition in different samples of TbCo2 as reported before. Super-invar behavior with αl = 4.4 × 10-7 K−1 was found in the x = 0.2 component by macro-thermal expansion measurement.

Hysteresis-free reversible magnetocaloric effect and critical behavior of Ni39.56Fe7.27Co2.97Mn40.65Sn9.55 full heusler alloy

Utilizing the magnetocaloric effect (MCE), magnetic refrigeration technology offers an advantage over traditional gas-based refrigerators, which produce harmful gases. Herein, we study the MCE and critical magnetic behavior of Fe and Co substituted Ni39.56Fe7.27Co2.97Mn40.65Sn9.55 Heusler alloy near the paramagnetic (PM) to ferromagnetic (FM) transition temperature. With Fm3̅m space group, the present sample crystallizes in cubic L21 structure. Arrott plots and hysteresis-free continuous phase transition confirm a second-order transition from FM to PM. Again, this second-order transition is verified by collapsing scaled entropy curves for various fields into a single universal curve. The critical exponent values obtained using several analytical techniques, like the Kouvel-Fisher method, modified Arrott plot, and critical isotherm, correspond to the mean-field theory universality class having long-range ordering. The above findings suggest our sample to be a suitable magnetic refrigerant by overcoming the difficulty of obtaining a reversible and high value of magnetic entropy change along with substantial relative cooling power across the second-order phase transition.

Growth and magnetocaloric effect of Na2Gd2(BO3)2O crystal

High-quality Na2Gd2(BO3)2O crystals have been successfully grown using the top-seeded solution growth method (TSSG), employing a Na2O - NaF - B2O3 flux system with optimal molar ratios of Na2Gd2(BO3)2O : Na2CO3 : NaF : H3BO3 = 1:2:6:4. The magnetic and magnetocaloric properties were investigated including magnetic susceptibility (χ), magnetization (M), and isothermal magnetic entropy change (−ΔSm) measurements. Na2Gd2(BO3)2O exhibits a large magnetocaloric effect with a maximum − ΔSm of 41.6 J·kg−1·K−1 at 2 K and 7 T, which is higher than that of commercial Gd3Ga5O12 (GGG, −ΔSm = 38.4 J·kg−1·K−1 at 2 K and 7 T) and most other Gd3+-based borates, showing the potential application in the field of magnetic refrigeration.

Research on the hydrogenation behavior of magnetocaloric La0.8Ce0.2Fe11.51Mn0.19Si1.3 hot-pressed plates

The fabrication of La(Fe, Si)13Hy plates is very challenging owing to the poor mechanical stability. In this work, La(Fe, Si)13 plates synthesized by hot-pressing remain mechanically robust after optimizing the hydrogenation process. The hydrogenation behavior was investigated through characterizing the phase structures and magnetocaloric effects of La0.8Ce0.2Fe11.51Mn0.19Si1.3 hydride plates. The saturated hydrogenation plates exhibit the large magnetic entropy change (12.98 J/kg·K), excellent mechanical properties (bending strength ∼ 213 MPa) and good stability under the conditions of the hydrogenating temperature of 593 K, the pressure of 0.13 MPa for 210 min.

Coexisting magnetic interaction, critical behavior and magnetocaloric effect at high temperature in Fe50Ni50 soft ferromagnetic alloy

Herein, we report the structural, magnetic and magnetocaloric properties of Fe50Ni50 alloy prepared through the planetary ball-mill. Rietveld analysis of the X-ray profiles confirmed the cubic crystallographic phase with the Fm-3 m space group. The magnetic characterization demonstrates that Fe50Ni50 alloy exhibits the coexistence of magnetic interaction within the ferromagnetic phase with Curie temperature 762 K. The Arrott plot results confirmed the second-order nature of the alloy. Critical exponents were also determined using the modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis. Obtained results indicated coexisting magnetic behavior, i.e., long-range ferromagnetism and inhomogeneous magnetic state. This alloy also noted a significant magnetocaloric parameters, i.e., magnetic entropy change (−ΔSM ∼ 2.3 J/kg-K) and relative cooling power (RCP ∼ 230 J/kg) at 30 kOe applied field. Both parameters followed power law dependence of magnetic field, and the exponent value supports the ferromagnetic nature along with the coexisting magnetic state. By normalizing the ΔSM curve with rescaled temperature, a universal master curve is also constructed for this alloy, reiterating the second-order nature of the magnetic transition.

Tailoring the cryogenic magnetism and magnetocaloric effect from Zr substitution in EuTiO3 perovskite

Refrigeration in the liquid helium temperature range provides vital technological support for many scientific frontiers and engineering technologies. The considerable magnetocaloric effect (MCE) makes EuTiO3 a potential candidate for magnetic refrigeration near liquid helium temperature. More interestingly, the magnetic transition from antiferromagnetism to ferromagnetism offers the possibility to tailor the magnetism and improve the MCE of this magnetic system. In this study, the magnetic properties and MCE of EuTi0.875Zr0.125O3 were systematically investigated by first-principles calculation and experiments. The substitution of Zr induces a significant lattice expansion and alters the electronic interactions, leading to a dominance of ferromagnetism in the compound. Remarkable low-field MCE performance has been achieved attributed to the enhanced ferromagnetism and low saturation field. Under the field change of 0–1 T, the maximum magnetic entropy change (−ΔSMmax) and adiabatic temperature change (ΔTadmax) are 17.9 J kg−1 K−1 and 6.1 K, respectively. It is worth noting that the −ΔSMmax of EuTi0.875Zr0.125O3 reaches 10.3 J kg−1 K−1 for a field change of 0–0.5 T, making it one of the best magnetocaloric materials ever reported operating in the liquid helium temperature range.

Magnetocaloric effect in Er[formula omitted]Gd[formula omitted]Al2 ([formula omitted]) alloys

Measurements of magnetization (M) were performed on a series of Er1−xGdxAl2 (x= 0.1, 0.25, and 0.5) alloys. ErAl2 and GdAl2 are ferromagnets with the Curie temperatures (TC) of 14 K and 168 K, respectively. Er1−xGdxAl2 also showed a ferromagnetic order at TC= 21 K for x= 0.1, 57 K for x= 0.25, and 89 K for x= 0.5. Upon cooling, M(B) curves of Er1−xGdxAl2 for 0.1≤x≤0.5 exhibited a metamagnetic behavior. The field cooled M for Er1−xGdxAl2 increased below 30 K, indicating a spin-reorientation transition. The magnetic entropy change (ΔSm) for x=0.1 peaked at TC, while a peak or kink was observed for x= 0.25 and 0.5 in ΔSm near 25 K, distinct from a ferromagnetic order. The spin-reorientation due to the Gd substitution is attributed to the magnetic properties and broadened ΔSm(T) curves for Er1−xGdxAl2 alloys.

Magnetism, heat capacity, magnetocaloric effect, and magneto-transport properties of heavy fermion antiferromagnet CeGaSi

We synthesize high-quality single crystal of CeGaSi by a Ga self-flux method and investigate its physical properties through magnetic susceptibility, specific heat and electrical resistivity measurements as well as high pressure effect. Magnetic measurements reveal that an antiferromagnetic order develops below T m ∼ 10.4 K with magnetic moments orientated in the ab plane. The enhanced electronic specific heat coefficient and the negative logarithmic slope in the resistivity of CeGaSi indicate that the title compound belongs to the family of Kondo system with heavy fermion ground states. The max magnetic entropy change −ΔSMmax (μ 0 H⊥c, μ 0 H = 7 T) around T m is found to reach up to 11.85 J⋅kg−1⋅K−1. Remarkably, both the antiferromagnetic transition temperature and −lnT behavior increase monotonically with pressure applied to 20 kbar (1 bar = 105 Pa), indicating that much higher pressure will be needed to reach its quantum critical point.

Wide temperature span and giant refrigeration capacity magnetic refrigeration materials for hydrogen liquefaction

Based on theoretical calculations and experiments, the crystal structure, electronic structure, magnetism, and magnetocaloric effect (MCE) of the Ho5B2C5 compound have been systematically investigated. The Ho5B2C5 compound with a typical metallic nature was found to crystallize in a tetragonal structure belonging to space group P4/ncc (No. 130), and its magnetic ground state was identified as ferromagnetic (FM) ordering based on theoretical and experimental results. Additionally, a second-order magnetic phase transition from FM to paramagnetic around approximately 27 K was observed in the Ho5B2C5 compound, resulting in a large MCE. Under varying magnetic fields (ΔH) from 0 to 7 T, the maximum magnetic entropy change (−ΔSMmax), refrigeration capacity (RC), and δTFWHM are 21.3 J/kg K, 1001.6 J/kg, and 60.2 K (a wide temperature range from 15.2 to 75.4 K), respectively. The outstanding MCE performance of the Ho5B2C5 compound is expected to facilitate the progress of magnetic refrigeration for hydrogen liquefaction.

Tailoring the cryogenic thermal conductivity in EuTiO3-based magnetic refrigeration materials

As one of the core components of a magnetic refrigerator, magnetic refrigeration materials are expected to have not only a considerable magnetocaloric effect but also excellent thermal conductivity. The poor thermal conductivity of many competitive oxide-based magnetic refrigerants, exemplified by EuTiO3-based compounds, acts as a major limitation to their practical application. Therefore, improving the thermal conductivity of magnetic refrigeration materials has become a research emphasis of magnetic refrigeration in recent years. In this work, a series of EuTiO3 (ETO)/Cu composites with different copper additives was prepared using a solid-phase reaction method by introducing appropriate amounts of copper powder. The influence of the introduction of copper on the phase composition, microstructure, thermal conductivity, and magnetocaloric effect of the composites was systematically investigated. Unexpectedly, the thermal conductivity of the composites is enhanced by up to 260% due to copper addition, accompanied by only a 5% decrease in magnetic entropy change and refrigerating capacity. Copper additive forms localized thermal conductive networks and promotes the densification process, resulting in significantly enhanced thermal conductivity of the composites. This work demonstrates the feasibility of improving the thermal conductivity of oxide-based magnetic refrigeration materials by introducing highly thermally conductive substances.