Magnetic Refrigerant Capacity Research Articles

Lattice and spin entropy changes in B2-type magnetocaloric Al–Mn–Ni alloy

Abstract Understanding the electronic, lattice, and magnetic contributions to the magnetocaloric effect in magnetic materials can help to elucidate and optimize their performance. In this work, the structural and magnetocaloric properties of Al–Mn–Ni alloy are experimentally determined and theoretically analyzed based on ab initio calculations. The dominating B2 phase associated with the Mn-rich sublattice is found to be responsible for the observed magnetocaloric properties. The magnetic entropy change, refrigerant capacity, and adiabatic temperature change are evaluated. Through the analysis of the data, we find that for the B2 phase, changing from ferromagnetic to paramagnetic configurations results in a pronounced elastic hardening despite the volume expansion. The decrease in lattice entropy is significant and contributes negatively to the magnetic and electronic entropy changes. Our work emphasizes the critical role of the lattice sector in the magnetocaloric effect, and provides an in-depth understanding of the individual entropy terms in magnetic solid solutions.

Multiphase critical point type phase boundary induced superior magnetocaloric properties in ferromagnetic Tb1-xGdxCo2 alloys

In this work, we report an exotic combination of magnetic entropy change (ΔSM =4.56 Jkg-1K−1), refrigerant capacity (RC=190.6 J kg−1) and adiabatic temperature change (ΔTad=6.8 K) for varying magnetic fields (ΔH) from 0 to 5 T, with near-zero hysteresis loss at the critical point of multiphase coexistence of rhombohedral, cubic and tetragonal phases at x=0.9 in Tb1−xGdxCo2 alloys. Additionally, the ΔSM curves cover a broad temperature range of 42 K. Further analysis demonstrates that the excellent magnetocaloric performance observed at the multiphase coexistence point stems from the flattening free energy, which provides minimal energy barriers, enabling magnetic spins to switch between different crystal symmetries.

Critical behavior and tunable magnetocaloric effect in (Gd1-xErx)3Al2 alloys

The magnetic properties, magnetocaloric effect, and the critical behavior near Curie temperature (TC) were systematically studied in a series of (Gd1-xErx)3Al2 (x = 0, 0.1, 0.2, 0.3) alloys. As the Er content increases, both the TC and lattice constant gradually decrease. The maximum magnetic entropy change and refrigerant capacity remain relatively high, ranging from −5.8 to −8.5J/kg K and 209.0 to 290.8 J/kg respectively, for a field change of 5 T. The critical exponents, derived from the field dependence of magnetic entropy change, conform to scaling theory and are consistent with those obtained using the Kouvel–Fisher method. These findings suggest that the reliability of the obtained critical exponents and imply the presence of long-range exchange interactions in (Gd1-xErx)3Al2 alloys.

Structural, magnetic, and magnetocaloric characterizations of geometrically-frustrated SrRE2O4 (RE = Gd, Dy, Ho, Er) oxides for low-temperature cooling applications

The magnetocaloric (MC) properties of many rare earth (RE)-based magnetic solids have been intensively investigated. This research aims to develop suitable MC materials for low-temperature cooling application and to better elucidate their intrinsic properties. We have fabricated four single-phase SrRE2O4 (RE = Gd, Dy, Ho, Er) oxides and conducted a systematic experimental investigation into their structural, magnetic, and low-temperature MC properties. All these SrRE2O4 oxides crystallize in an orthorhombic structure (space group Pnma) and exhibit typical geometrical frustration. This frustration arises from the one-dimensional RE ion zigzag ladders along the c-axis, which link the two-dimensional honeycomb lattice in the ab plane. The elements in SrRE2O4 oxides are uniformly distributed and present with valence states of Sr2+, RE3+, and O2−, respectively. Large low-temperature MC effects and notable performances are realized in these SrRE2O4 oxides, determined by the MC parameters of magnetic entropy change, refrigerant capacity, and temperature-averaged entropy change (with a lift of 5 K). These MC parameters under a magnetic field change of 0–70 kOe are as follows: 34.18 J/kgK, 275.88 J/kg, and 30.74 J/kgK for SrGd2O4; 18.13 J/kgK, 253.83 J/kg, and 17.54 J/kgK for SrDy2O4; 18.81 J/kgK, 354.77 J/kg, and 18.61 J/kgK for SrHo2O4; and 22.63 J/kgK, 284.25 J/kg, and 21.97 J/kgK for SrEr2O4. These values are comparable to those of most recently updated low-temperature MC materials with remarkable performances, making these SrRE2O4 oxides highly interesting for practical cooling applications.

Structural, Magnetic, and Magneto-Thermal Properties of Rare Earth Intermetallic GdRhIn.

We study the structural, magnetic, and magneto-thermal properties of the GdRhIn compound. The room-temperature X-ray diffraction measurements show a hexagonal crystal structure. Temperature and field dependence of magnetization suggest two magnetic transitions-antiferromagnetic to ferromagnetic at 16 K and ferromagnetic to paramagnetic at 34 K. The heat capacity measurements confirm both the magnetic transitions in GdRhIn. The magnetization data were used to calculate isothermal magnetic entropy change and refrigerant capacity in GdRhIn, which was found to be 10.3 J/Kg-K for the field change of 70 kOe and 282 J/Kg for the field change of 50 kOe, respectively. The large magnetocaloric effect in GdRhIn suggests that the material could be used for magnetic refrigeration at low temperatures.

Excellent magnetocaloric effect near the hydrogen liquefaction temperature of a binary Er67.5Co32.5 metallic glass

We reported the excellent magnetocaloric effect of a binary Er67.5Co32.5 metallic glass (MG) near the hydrogen liquefaction temperature. The binary MG ribbon was fabricated by a melt-spinning method. The Er67.5Co32.5 alloy exhibits a better glass formability than most of other rare earth (RE)-Co binary alloys. The maximum magnetic entropy change (−ΔSmpeak) and refrigeration capacity (RC) of the Er67.5Co32.5 amorphous ribbon under 0–5 T reach to 17.47 J/(kg × K) near its Curie temperature (Tc, ∼ 11 K) and 472 J/kg, both of which are rather high among the RE-based MGs with a Tc around 10 K and imply the potential application perspective as magnetic refrigerants for hydrogen liquefaction. The magnetization as well as magnetocaloric behaviors of the binary MG were observed, and the mechanism involved was investigated.

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.

Magnetocaloric effect and phase transformation of Zn-doped Ni–Mn–Ti all-d metal Heusler alloys

Ni–Mn–Ti Heusler alloys have gained a great consideration recently due to their important magnetoresistance and magnetocaloric properties. Herein, the structure, martensitic transition (MT), and magnetocaloric effect (MCE) of Ni50-xZnxMn35Ti15 (x = 0, 2, 4, and 6) Heusler alloys have been studied. XRD results show that the studied alloy with x = 0 display a monoclinic (5 M) martensite phase. Besides, the examined alloy with x = 2 presents a combination of monoclinic (5 M) martensite and cubic (B2) austenite phases, whereas the alloys with x = 4 and x = 6 exhibit only a cubic (B2) austenite phase. By increasing Zn content x up to 6, the Curie temperature of austenite decreases from 283 K to 132 K, and the MT temperatures decrease from ferromagnetic austenite to weak-magnetic martensite, which is apparently due to the exchange interaction of Mn–Mn and the low power of d-d hybridization between the A/C and B(D) sites. The best maximum magnetic entropy change (ΔSM, max) and refrigeration capacity (RC) are for the studied alloy with x = 4 (5.22 J kg−1K−1 and 217 J kg−1 at 120 kOe, respectively). The Zn addition not only facilitates the formation of B2-type Heusler phases but also offer the possibility to tune the MT and establish strong ferromagnetic coupling.

Magnetic properties and magnetocaloric effect in the multiple rare-earth-containing MRE2Cu2In compounds

In this study, two Mo2FeB2-type multiple rare-earth-containing MRE2Cu2In (MRE = Dy1/3Ho1/3Er1/3 and Ho1/3Er1/3Tm1/3; space group P4/mbm, No. 127) compounds are prepared via arc-melting method and systematically determined regarding their structural and magnetic properties, magnetic phase transition (MPT), and magnetocaloric (MC) performances. They undergo typical second-order MPT at low temperatures. The MC effect and MC performances of the present MRE2Cu2In compounds at low temperatures are assessed using magnetic entropy changes, refrigerant capacity, and temperature-averaged entropy changes. The values of these parameters are comparable to most updated candidate materials for low-temperature magnetic cooling, making the present MRE2Cu2In compounds considerable for practical applications.

Hydrogen-annealing modulated magnetocaloric effect and critical behavior of Weyl semimetallic Co3Sn2S2

Modulating the electron interaction and magnetic domains is an essential strategy to evoke novel physical properties, both for fundamental research and for related magnetic applications. The emerging annealing process attracted attention due to its capability of tuning the magnetic performance, but it has been rarely studied. Herein, we conducted hydrogen annealing on the Weyl semimetallic Co3Sn2S2 and investigated the magnetic interaction, critical behavior, and magnetocaloric effect (MCE). Hydrogen-annealed Co3Sn2S2 (HA-Co3Sn2S2) exhibits a distinct anisotropy-dependent magnetic behavior, where a typical second-order transition with an easy magnetization process is observed under H//c. However, a frustrated magnetic state composed of ferromagnetic (FM), antiferromagnetic (AFM), and/or spin glass phases is observed when H//ab. Critical analyses illustrate that the ground state of HA-Co3Sn2S2 lies between the 3D-Ising model and the Mean-filed model, indicating the presence of both long-range and short-range magnetic interactions in the system. Additionally, we found that HA-Co3Sn2S2 exhibits an enhanced saturation magnetization (Ms) and magnetic refrigeration capacity, both showing anisotropic dependence, compared to the pristine Co3Sn2S2. Our work develops hydrogen annealing to modulate electron coupling and magnetic domains, paving the way for further studies of anisotropic magnetic behavior and applications in magnetic refrigeration.

Magnetic phase transition and large cryogenic magnetocaloric effect in the gallides RE2Rh3Ga (RE = Gd, Dy, Ho, Er)

We herein provide an experimental investigation of the gallides RE2Rh3Ga (RE = Gd, Dy, Ho, Er) regarding their magnetic properties and magnetocaloric effect (MCE). All of these RE2Rh3Ga intermetallic compounds crystallized with the Mg2Ni3Si type structure, space group R–3 m and are ordered magnetically at low temperatures. Large reversible MCEs around their own ordering temperature were observed in all RE2Rh3Ga compounds and their magnetocaloric parameters including the maximum magnetic entropy change, refrigerant capacity, and temperature-averaged entropy change are comparable to those of some recently reported candidate materials with prominent performances, making them considerable for cryogenic MR applications.

Magnetic properties and magnetocaloric performances in the (Dy0.25Ho0.25Er0.25Tm0.25)2Cu2In high-entropy compound

We herein fabricated the (Dy0.25Ho0.25Er0.25Tm0.25)2Cu2In high-entropy (HE) compounds and systematically determined its structural, magnetic, and magnetocaloric properties. The (Dy0.25Ho0.25Er0.25Tm0.25)2Cu2In HE compound was found to crystalize in a tetragonal Mo2B2Fe type structure (P4/mbm space group) and undergoes typical second order type magnetic transition. Large MCE and prominent cryogenic magnetocaloric performances were observed in (Dy0.25Ho0.25Er0.25Tm0.25)2Cu2In HE compound. The evaluated values of magnetic entropy change and refrigerant capacity of (Dy0.25Ho0.25Er0.25Tm0.25)2Cu2In HE compound under magnetic field change of 0–7 T are 17.1 J/kgK and 398.0 J/kg which are comparable with the reported candidate materials for cryogenic magnetic cooling, making the present (Dy0.25Ho0.25Er0.25Tm0.25)2Cu2In HE compound also considerable for practical applications.

Structural and magnetic properties of Gd4Ga2O9 oxide with a large cryogenic magnetocaloric effect

The magnetocaloric effect has been extensively investigated in various types of magnetic solids to not only develop practical magnetic cooling applications but also deepen the understanding of these materials’ underlying inherent properties. Through experimental determination and theoretical calculation, we conducted a systematic investigation of Gd4Ga2O9 oxide in terms of its structural, magnetic, and magnetocaloric properties and found it to crystallize in a monoclinic structure belonging to the space group P21/c and to possess an antiferromagnetic semiconducting ground state. The consistent elements were uniformly distributed up to the nanoscale and presented as Gd3+, Ga3+, and O2 states, respectively. The magnetocaloric performances of Gd4Ga2O9 oxide were checked according to the parameters of maximum magnetic entropy change, refrigerant capacity, and temperature-averaged entropy changes (lift of 5 K), which were determined to be 25.77 J/kgK, 218.27 J/kg, and 23.43 J/kgK under 0–7 T magnetic field change. These parameters of Gd4Ga2O9 oxide are comparable to those of some recently reported materials with prominent performances, which means that it can be considered for cryogenic magnetic cooling applications.

Structure, magnetic properties and cryogenic magnetocaloric performances of perovskite-type Gd(4TM0.25)O3 and Gd(5TM0.2)O3 high-entropy oxides

We herein fabricated two gadolinium-transition metal-based high entropy (HE) oxides of Gd(Mn0.25Fe0.25Al0.25Cr0.25)O3 [denoted as Gd(4TM0.25)O3] and Gd(Mn0.2Fe0.2Al0.2Co0.2Ni0.2)O3 [denoted as Gd(5TM0.2)O3] and determined their structural, magnetic, and magnetocaloric properties. Both of present HE oxides are found to crystallize in the single-phase perovskite-type orthorhombic structure with a homogeneous microstructure and exhibit prominent cryogenic magnetocaloric performances. The values of magnetic entropy change, refrigerant capacity, and temperature-averaged entropy change (6K-lift) under the magnetic field change of 0–7 T are estimated to be 20.34 J/kgK, 295.4 J/kg, and 19.56 J/kgK for Gd(4TM0.25)O3, and to be 22.45 J/kgK, 258.2 J/kg, and 20.79 J/kgK for Gd(5TM0.2)O3, respectively, which are comparable with recently reported candidate materials for practical magnetic cooling. These findings not only indicate potential applications of present perovskite-type Gd(4TM0.25)O3 and Gd(5TM0.2)O3 HE oxides, but also provide meaningful clues for exploring HE oxides with prominent cryogenic magnetocaloric performances.

Large reversible magnetocaloric effects originating from ferromagnetic phase transition in Gd(Cu1−xNix)2 (x = 0.12, 0.15)

Here, the significant increase in MCE without any hysteresis loss was achieved through the substitution of nickel for a portion of the copper in GdCu2 compound. The values of maximum magnetic entropy changes (−ΔSMmax) and refrigeration capacity (RC) for Gd(Cu1-xNix)2 (x = 0.12, 0.15) compounds are 10.3 J/kg K, 455.3 J/kg, 9.3 J/kg K and 461.2 J/kg under varying magnetic fields from 0 to 5 T, respectively. The refrigeration capacity of Gd(Cu1−xNix)2 (x = 0.12, 0.15) is improved by an order of magnitude compared to the GdCu2 compound under varying magnetic fields from 0 to 5 T. While providing an ideal magnetocaloric refrigerated material for hydrogen liquefaction, our work also suggests a promising approach to the development of new magnetocaloric refrigerated materials.

Modeling magnetic refrigeration capacity of doped EuTiO3 magnetocaloric compounds using swarm based intelligent computational method

This work models the magnetic refrigeration capacity (MRC) of doped europium titanate (EuTiO3) at different applied magnetic field using hybrid particle swarm optimization based support vector regression (SW-SVR) algorithm with ionic radii dopant descriptors. The developed model with Gaussian function (SW-SVR-Gas) shows better performance as compared with polynomial based model (SW-SVR-Pol) with improvement of 35.76 %, 0.13 % and 45.76 % using mean absolute error (MAE), correlation coefficient (CC) and root mean square error (RMSE) performance yardsticks, respectively. The developed SW-SVR-Gas model investigates the behavior of Eu1-xBaxTiO3 and EuTi1-xNixO3 doped europium titanate at different dopants concentration as well as applied field. Novelties of the developed model include circumvention of experimental difficulties associated with magnetic refrigeration capacity determination, implementation of simple molecular descriptors with high precision and accuracy. The demonstrated uniqueness of the developed model would strengthen exploration of refrigeration capacity of europium titanate based compounds for addressing global refrigeration crisis.

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.

Giant low-field magnetocaloric effect in unstable antiferromagnetic Tm1–xErxNi2Si2 (x = 0.2, 0.4) compounds

Magnetic refrigeration (MR) technology is regarded as an ideal solution for cryogenic applications, relying on magnetocaloric materials which provide necessary chilling effect. A series of polycrystalline Tm1–xErxNi2Si2 (x = 0.2, 0.4) compounds was synthesized, and their magnetic properties, magnetic phase transition together with magnetocaloric effect (MCE) were studied. The Tm1–xErxNi2Si2 (x = 0.2, 0.4) compounds display a field-induced metamagnetic transition from antiferromagnetic (AFM) to ferromagnetism (FM) in excess of 0.2 T, respectively. Meanwhile, the AFM ground state is unstable. Under the field change of 0–2 T, the values of maximal magnetic entropy change (−ΔSMmax) and refrigerant capacity (RC) for Tm0.8Er0.2Ni2Si2 compound are 17.9 J/(kg·K) and 83.5 J/kg, respectively. The large reversible MCE under low magnetic fields (≤2 T) indicates that Tm0.8Er0.2Ni2Si2 compound can serve as potential candidate materials for cryogenic magnetic refrigeration.

Magnetocaloric and thermoelectric properties of two-phase composite Eu8Ga15.25Ge30.75

A novel Eu8Ga15.25Ge30.75 composite clathrate with α and β phases coexisting were synthesized for the first time. The composite exhibits two consecutive magnetic transitions at temperatures of 12 and 32 K corresponding to the TC of α and β phases, respectively. The magnetic entropy change with temperature reveals two distinct peaks, resulting in a broader −∆SMT curve and an enhanced magnetic refrigeration capacity compared to single phase clathrate. Furthermore, the interactive growth of the α and β phases in the composite acts to reduce the lattice thermal conductivity. Specifically, at 600 K, the lattice thermal conductivity κL reaches its minimum value of 0.39 W/m·K. The zT value increases from 0 to 0.24 as the temperature ranges from 2 to 773 K.

Large rotating magnetocaloric effects in polycrystalline Ni-Mn-Ga melt-spun ribbons

In this study, the different wheel speeds Ni53Mn23.5Ga23.5 alloy ribbons were prepared by melt-spun method. The morphology and crystal structure, martensitic phase transformation, magnetocrystalline anisotropy, in situ technique magnetization observation and the magnetic refrigeration capacity resulting were tested. The ratio of the length to width for the columnar crystals is approximately 2.5:1.0 in the sample created at a wheel speed of 12 m s−1, and it increases to 5:1 in the sample produced at a wheel speed of 18 m s−1. It is found that a sample with 18 m s−1 ha−1s−1 a large rotating magnetocaloric effect in polycrystalline alloys, with the results of 2 K with different directions. It can be designed as a working substance for rotary refrigeration machines that make full use of their anisotropic characteristics. The in situ atomic force microscope observation of the technological magnetisation has provided an important exploration for a better understanding of the magnetisation.