Magnetocaloric Research Articles

Magnetocaloric properties of Nd-doped Gd5Si4 microparticles and nanopowders

Abstract The preparation of materials with enhanced magnetocaloric properties is crucial for magnetic refrigeration. In this study, Nd-doped Gd5Si4 microparticles and nanomaterials were synthesized using the reduction–diffusion method. The impact of Nd doping with varying compositions on the structure and entropy change properties of the materials was investigated. The Curie temperatures of both the micron- and nano-sized materials ranged from 190 K to 210 K, which were lower than previously reported values. Micron-sized samples doped with 1% Nd exhibited superior magnetocaloric properties, demonstrating a maximum entropy change of 4.98 J⋅kg−1⋅K−1 at 5 T, with an entropy change exceeding 4 J⋅kg−1⋅K−1 over a wide temperature range of approximately 70 K. Conversely, the nanomaterials had broader entropy change peaks but lower values. All samples exhibited a second-order phase transition, as confirmed by the Arrott plots.

The structural, electronic and magnetic properties of [formula omitted] anti-perovskite

A comprehensive exploration of the structural, electronic, and magnetic attributes of anti-perovskite Fe3ZnC carbides was carried out using Density Functional Theory (DFT) and Monte Carlo Simulation (MCS). These anti-perovskite materials possess a unique structure where cation and anion positions are interchanged within the perovskite framework. Our study involves a comparative analysis of the electronic band structures and density of states (DOS) for Fe3ZnC, considering prior theoretical and experimental research. Understanding these anti-perovskite materials' band structures and DOS is pivotal for their effective utilization in magnetic sensors and magnetic refrigeration applications. Our results indicate that Fe3ZnC displays ferromagnetic metallic behavior, particularly when applying the Generalized Gradient Approximation (GGA). Notably, there is a significant overlap between the valence (VB) and conduction (CB) bands. Furthermore, MCS predicts a second-order ferromagnetic-to-paramagnetic transition in the anti-perovskite Fe3ZnC compound, characterized by a notably high Curie temperature. These insights advance our understanding of these materials, paving the way for their effective utilization in magnetic technologies.

Magnetic transition magnetocaloric and supercapacitor behavior in synthesized Sn0.6Mn0.1Ge0.3Te alloys

This study comprehensively investigates the structural, microstructural, vibrational, magnetic, and magnetocaloric properties of novelty Sn0.6Mn0.1Ge0.3Te alloys synthesized using the sealed tube solid-state reaction method. The observed magnetic behavior showcases a transition from paramagnetic (PM) to ferromagnetic (FM) phases at the Curie temperature TC = 29 K. Notably, magnetic entropy change (−ΔSM), relative cooling power (RCP), and refrigerant capacity (RC) are calculated as 1.5 J/kg-K, 42.05 J/kg, and 37.39 J/kg, respectively, under a magnetic field of 60 kOe. Arrott curve analysis further validates the magnetic phase transition, affirming a second-order transition between FM and PM phases. Critical exponents (β, γ, and δ) are derived from field-dependent magnetic entropy changes around the second-order transition and strongly agree with the mean field model. These critical exponents establish a clear correlation between critical behavior and magnetocaloric effects, reinforcing the potential of Sn0.6Mn0.1Ge0.3Te alloys for magnetocaloric applications. Investigations into the electrochemical properties of the alloy have indicated that it exhibits a specific capacitance of 152.9 F/g at a scan rate of 20 mV/s, demonstrating a predominantly pseudocapacitive charge storage mechanism. Additionally, the alloy has proven to be highly stable, retaining 94.2 % of its specific capacitance after 10,000 cycles.

Supercooling Phenomenon of Magnetic Field-Assisted Freezing and its Impacts on Quality Preservation of Frozen Fruits and Vegetables

Supercooling Phenomenon of Magnetic Field-Assisted Freezing and its Impacts on Quality Preservation of Frozen Fruits and Vegetables

Synthesis, Characterization, and Magnetocaloric Properties of the Ternary Boride Fe2AlB2 for Caloric Applications.

The ternary transition metal boride Fe2AlB2 is a unique ferromagnetic "MAB" phase that demonstrates a sizable magnetocaloric effect near room temperature-a feature that renders this material suitable for magnetic heat pump devices (MHP), a promising alternative to conventional vapor compression technology. Here, we provide a comprehensive review of the material properties of Fe2AlB2 (magnetofunctional response, transport properties, and mechanical stability) and discuss alloy synthesis from the perspective of shaping these materials as porous active magnetic regenerators in MHPs. Salient aspects of the coupled magnetic and structural phase transitions are critically assessed to elucidate the fundamental origin of the functional response. The goal is to provide insight into strategies to tune the magnetofunctional response via elemental substitution and microstructure optimization. Finally, outstanding challenges that reduce the commercial viability of Fe2AlB2 are discussed, and opportunities for further developments in this field are identified.

Optimization research of salt pill in an ultra-low temperature adiabatic demagnetization refrigerator

Adiabatic demagnetization refrigeration is a crucial technology for cooling bolometric infrared detectors and cryogenic X-ray detectors in the sub-Kelvin temperature range (below 1 K). To improve the cooling performance and reduce the total mass of a four-stage continuous adiabatic demagnetization refrigerator (ADR) (operating between 4 K and 50 mK) for future space missions, a two-dimensional transient ADR model has been developed. Through this model, the effects of salt pill’s aspect ratio on the cooling performance (holding-time) and total mass of the ADR have been studied. As the salt pill’s aspect ratio increased, the holding-time of ADR gradually decreased, while the total mass of the ADR firstly increased and then decreased. The optimal aspect ratios of stage 1 ∼ stage 4 ADRs have been 2.4, 2.2, 1.3 and 1.4, with efficiencies of 56.20 %, 82.78 %, 75.45 %, and 88.36 % respectively. Additionally, the effects of the thermal bus diameter and the volume ratio of magnetocaloric material in the salt pill have also been investigated. With a thermal bus diameter of 0.2 mm, the maximum holding-times achievable for stage 2, stage 3, and stage 4 ADRs have been 1711 s, 1832 s, and 4050 s, and the corresponding optimal number of thermal buses have been 459, 1957, and 505 respectively.

Phase shift in AC magnetocaloric effect measurements as an indicator of the order of magnetic phase transitions

Phase shift in AC magnetocaloric effect measurements as an indicator of the order of magnetic phase transitions

Influence of high-pressure heat treatment on magnetocaloric effects and phase transition critical behavior in La0.75Sr0.25Mn0.9Co0.1O3

Influence of high-pressure heat treatment on magnetocaloric effects and phase transition critical behavior in La0.75Sr0.25Mn0.9Co0.1O3

Enhanced magnetocaloric and cold storage properties in HoCu2-xNix (x=0.05–0.5) compounds for hydrogen liquefaction

Based on first-principle calculations and experiments, the electronic structure, magnetism, magnetocaloric effect and cold storage properties of HoCu2-xNix (x=0.05–0.5) compounds have been investigated. The theoretical calculations revealed that the magnetic interactions of the HoCu2-xNix compounds were gradually transformed to ferromagnetic states when the Ni element was added above 0.0625. In addition, the Ni element leads to a decreasing Fermi energy level, which results in a significant enhancement of orbital hybridization around the Fermi surface, which may be responsible for the magnetic jump. The magnetic phase transition temperatures of the HoCu1.75Ni0.25 and HoCu1.5Ni0.5 compounds are 14.4 K and 26.0 K, respectively. The ferromagnetic state transition is responsible for the excellent magnetocaloric effect of the HoCu2-xNix compounds under low magnetic fields. The maximum magnetic entropy changes of the HoCu1.75Ni0.25 and HoCu1.5Ni0.5 compounds were 14.7 J/kg K and 11.5 J/kg under varying magnetic fields from 0 to 2 T. In addition, the Ni element make the HoCu2 compound exhibit more excellent cold storage capability. The peak of specific heat capacities of HoCu1.75Ni0.25 and HoCu1.5Ni0.5 compounds were 0.6 J/cm−3K−1 and 0.9 J/cm−3K−1 under 0 T. The present results indicate that HoCu2-xNix (x=0.05–0.5) compounds have promising applications in cryogenic cold storage and magnetic refrigeration.

The effect of metal/non-metal ratio on the microstructure and magnetic properties of (MnFe)x(P0.5Si0.5) microwires

The effects of metal/non-metal ratio (M/NM ​= ​x: 1) on the microstructure and magnetocaloric properties of promising melt-extracted Mn–Fe–P–Si microwires with short heat treatment have been investigated here. More Fe2P principal phase, which is considered favorite for magnetocaloric effect (MCE), should achieve at low M/NM ratio and the fraction of Fe2P phase increased with the reduction of x. Meanwhile, the (Mn, Fe)3Si impurity phase is formed for x ​= ​2.00–1.90 whereas change to (Mn, Fe)5Si3 structure for x ​= ​1.85. It's worth noting that a metal deficiency resulted in the thermal hysteresis (Thys) and the magnetic hysteresis loss (Wy) decreased by ∼40 ​%., The magnetic transition temperature (Ttran), peak value of isothermal magnetic entropy change (−ΔSisopeak), refrigerant capacity (RC) and effective refrigerant capacity (RCE) first increased then decreased with the decrease of x, and reached the maximums at x ​= ​1.90, i.e., 370 ​K, 26.0 ​J ​kg−1 ​K−1, 367.4 and 339.8 ​J ​kg−1, respectively. Therefore, the customizable microstructure and magnetic properties of the melt-extracted (MnFe)x(P0.5Si0.5) microwires will be achievable effectively by tuning M/NM ratio x, and optimized Mn–Fe–P–Si compounds with novel thermomagnetic properties will be obtained.

Effects of Moving Magnetic Materials in and out of Superconducting Magnet for Active Magnetic Regenerative Refrigeration System

Effects of Moving Magnetic Materials in and out of Superconducting Magnet for Active Magnetic Regenerative Refrigeration System

Stellated cuboctahedron of FeIII

AbstractThe solvothermal reaction of FeCl2 ⋅ 4H2O and H4TBC[4] in a basic dmf/EtOH solution affords an [FeIII18] Keplerate conforming to a stellated cuboctahedron. Magnetic and heat capacity measurements reveal spin frustration effects arising from the high symmetry. A crossover between inverse and direct magnetocaloric effects is observed at ~10 K for applied‐field changes lower than 3 T.

Development of a Superconducting Magnet System for Magnetic Refrigeration Using a Switching Power Supply

Development of a Superconducting Magnet System for Magnetic Refrigeration Using a Switching Power Supply

Direct measurement of magnetocaloric effect (MCE) in frustrated Gd-based molecular complexes

AbstractGeneration of low temperatures below 1 K has been required for applications and fundamental research, given this, development of new materials utilized for demagnetization cooling has extensively been performed in recent years. Here, we studied two polynuclear Gd3+-based molecular compounds of Gd0.33[Gd4(OH)4(OAc)3][Rh4Zn4(L-cys)12]·32H2O (1Gd) and Gd0.33[Gd4(OH)4(OAc)3][Ir4Zn4(L-cys)12]·28H2O (2Gd) (L-cys = L-cysteinate) which show paramagnetic even at low temperatures due to their frustrated arrangement of Gd3+ ions. We discuss the magnitude of the magnetocaloric effect (MCE) in them inferred from the isothermal magnetic entropy change ($${\Delta S}_{\text{M}}$$ Δ S M ) from isothermal magnetization data. The − $$\Delta S_{{\text{M}}}^{{{\text{max}}}}$$ Δ S M max of 1Gd and 2Gd are 15.15 J kg−1 K−1 and 17.49 J kg−1 K−1 occur at 2.0 K under an applied field from 0 to 7 T, respectively. We also discussed the results of heat capacity measurement under magnetic fields to confirm the validity of the entropy change for 1Gd. Furthermore, with an aim of detecting their MCE directly, we have developed a new non-magnetic and metal-free magnetocaloric measurement cell. The adiabatic temperature change ($$\Delta T_{{{\text{ad}}}}$$ Δ T ad ) occurs in a small amount of sample on an order of 102-microgram with the application and removal of various magnitude magnetic fields starting from several initial temperatures were detected directly, to evaluate the potential of them to be a refrigerant for an adiabatic demagnetization refrigerator. The instrumental design for direct measurements of MCE is described along with the construction details.

Cryogenic temperature magnetocaloric effect and critical behavior of GdDyErAlM (M=Fe, Co, Ni) high entropy amorphous alloys

High entropy amorphous alloys (HE AMs) have attracted extensive interest lately due to their superior magnetocaloric properties. However, the critical behavior and mechanical properties have received less research, which restricts their applications. This work presented a comprehensive investigation of the magnetocaloric effect (MCE), critical behavior, and mechanical performance of quinary Gd20Dy20Er20Al20M20 (M = Fe, Co, Ni) HE AMs. All samples exhibited distinct spin glass-like behavior below TC and competitive MCE around hydrogen liquefaction temperature range. Excellent MCE was achieved by the HE AMs through a second-order phase transition from paramagnetic state to ferromagnetic state at 79 K for Fe, 41 K for Co, and 36 K for Ni. Among them, the maximum magnetic entropy change (-ΔSM)max of Gd20Dy20Er20Al20Co20 amorphous alloys was 9.59 J kg−1 K−1 under 0–5 T. Furthermore, RC and RCP of Gd20Dy20Er20Al20Fe20 amorphous alloys were respectively 519 J kg−1 and 613 J kg−1, larger than that of most RE-based amorphous alloys. For all samples, the critical behavior of the phase transition approached the mean field model, and this responded to the long-range ordering of the magnetic interaction. The bending plasticity of Gd20Dy20Er20Al20M20 (M = Fe, Co, Ni) HE AMs were 0.78, 1.03, 0.89, respectively. The adjustable Tc, large (-ΔSM), high RCP, and outstanding mechanical properties suggested Gd20Dy20Er20Al20M20 (M = Fe, Co, Ni) HE AMs may find utility as magnetic refrigerants in low-temperature applications.

A Homochiral Hexagadolinium Phosphonate Cluster: Structure, Chiral Electrochemical Recognition and a Large Magnetocaloric Effect

AbstractChiral lanthanide clusters have promising applications in chiral recognition, magneto‐optical memories, and spintronic devices. Nonetheless, the precise prediction and controlled development of homochiral polynuclear Ln‐complexes is still a challenge. Herein, through multidentate chelate synthetic strategy, a new homochiral hexagadolinium phosphonate cluster designated as R/S‐[Gd6(pmhpH)8(NO3)2(H2O)8]⋅19H2O (R/S‐1) was successfully obtained by reacting chiral phosphonomethylhomoproline(pmhpH3) with Gd(III) salt. The cluster, shaped like a lantern, is constructed from {GdO8} polyhedra and {PO3C} tetrahedra surrounded by eight pmhpH2− ligands. Within the structure, two types of gadolinium ions with different coordination modes are observed. Each Gd(III) ion is bound to two carboxylate oxygens and six phosphonate oxygens from the coordinated pmhpH2− ligands. Circular dichroism spectra comfirmed that R/S‐1 exists as a pair of enantiomers. Moreover, the cluster exhibits high thermal stability, decomposing at temperatures exceeding 335 °C. Notably, the chiral cluster materials can be used for enantiomeric recognition for tryptophan (Trp) with the differential pulse voltammetry (DPV) peak current ratio (ID/IL) 2.74. Besides, the magnetic measurements revealed that compound R‐1 exhibits a good magnetocaloric effect (MCE) with a maximum entropy change of −ΔSmmax=36.84 Jkg−1 K−1 at T=2 K and ΔH=7 T.

3D-Ising-type magnetic interactions stabilized by the extremely large uniaxial magnetocrystalline anisotropy in layered ferromagnetic Cr2Te3

We investigate the magnetocrystalline anisotropy, critical behavior, and magnetocaloric effect in ferromagnetic-layered Cr2Te3. We have studied the critical behavior around the Curie temperature (TC) using various techniques, including the modified Arrott plot (MAP), the Kouvel-Fisher method (KF), and critical isothermal analysis (CI). The derived critical exponents β = 0.353(4) and γ = 1.213(5) fall in between the three-dimensional (3D) Ising and 3D Heisenberg type models, suggesting complex magnetic interactions by not falling into any single universality class. On the other hand, the renormalization group theory, employing the experimentally obtained critical exponents, suggests 3D-Ising-type magnetic interactions decaying with distance as J(r) = r−4.89. We also observe an extremely large uniaxial magnetocrystalline anisotropy energy (MAE) of Ku = 2065 kJ/m3, the highest ever found in any CrxTey based systems, originating from the noncollinear ferromagnetic ground state as predicted from the first-principles calculations. The self-consistent renormalization theory (SCR) suggests Cr2Te3 to be an out-of-plane itinerant ferromagnet. Further, a maximum entropy change of -ΔSMmax≈ 2.08 J/kg − K is estimated around TC for the fields applied parallel to the c-axis.

Effect of gadolinium particle size on the performance of a magnetic refrigeration system

This study investigates the influence of gadolinium particle size on Magnetic Refrigeration (MR) system performance. Understanding how particle size of Magnetocaloric Materials (MCMs) within a fixed Active Magnetic Regenerator (AMR) volume affects cooling capacity and Coefficient of Performance (COP) is crucial for MR system design. However, research on this influence, especially using an experimental approach, has been surprisingly rare. This is despite the importance of considering various factors like total MCM mass, porosity, and pressure drop. The particles were categorized into five cases based on their sizes, which ranged from 0.50 to 2.00 mm opening sizes of the meshes. The magnetic field source produced the maximum 0.815 and 0.069 T for magnetization and demagnetization, respectively. A total four of AMRs were installed in the MR system for each case study. First, the porosity of the AMRs mostly increased as finer particles were filled up. This led to a tendency of lower mass of the MCMs in the same volume of the AMRs with smaller particles. Second, the temperature span showed the most outstanding value of 11.1 K in the 0.20 utilization factor using the finest particles (0.50–0.85 mm) in a no-load test. It also achieved a wider 8.3 K temperature span under 3.8 W of thermal load, outperforming the other sizes despite the least total mass of the MCMs. The major contribution to these results was the larger heat transfer area between the MCMs and heat transfer fluid inside the AMRs with the smaller particles. Nevertheless, the case with the second-finest particles (0.80–1.18 mm) exhibited the highest COP of 2.6, due to their favorable combination of moderately significant cooling capacity, reasonably small particle size, and elevated porosity that reduced pumping power demand and magnetic force.

Magnetocaloric Properties of Melt-Extracted Medium Entropy Gd33Co33Al34 Microfibers

In this paper, a new medium entropy alloy with nominal composition of Gd33Co33Al34 was designed and fabricated into microfibers by a melt-extraction method. The microstructure, thermophysical parameters, and magnetocaloric properties of the obtained fibers were systematically analyzed. The results showed that the as-cast fibers show an amorphous matrix with embedded in situ nano crystals. The fibers show a good magnetocaloric effect with the maximum magnetic entropy change of ~6 J/kg·K for a field change of 5 T. Notably, the fibers show excellent cooling efficiencies with an RCP and RC of ~611.72 and ~487.38 J/kg, respectively. Though the as-cast fibers possess an amorphous/nanocrystal bi-phase structure, they still exhibit a second-order transition near a Curie temperature of ~96 K. Our findings provide a promising pathway towards developing new magnetocaloric materials with good magnetocaloric performances.

Dynamic magnetic and magnetocaloric behaviors of a Kagome-like cluster

By utilizing the Monte Carlo simulation, how different physical parameters affect the dynamic magnetic properties and magnetocaloric effects of a Kagome-like cluster with mixed spins (3/2, 2) are explored. The findings show that changing the values of the exchange coupling |J|, |Js|, and |J2| had no impact on the saturation order parameters of the system. Under specific parameter conditions, the magnetization susceptibility curve displays double peaks, and compensation phenomena are noted. The impacts of hbias and hosc on the blocking temperature of the system are opposite. In addition, the effects of various parameters on the magnetization, magnetic entropy change, and relative cooling power of the ferromagnetic system under a static magnetic field are given. The strong exchange coupling is found to negatively affect the magnetic refrigeration efficiency of the material, while a strong magnetic field enhances the system's relative cooling power.