Large Magnetic Entropy Change Research Articles

Phase transformation and magnetocaloric effect of Co-doped Mn–Ni–In melt-spun ribbons

Ribbon-shaped magnetocaloric materials are favorable to achieve high heat-transfer efficiencies due to their large specific surface area. In this work, Mn50Ni41−xIn9Cox (0 ≤ x ≤ 4) ribbons were prepared using a melt-spinning technique, and the corresponding phase transformation and magnetocaloric properties were studied. The large temperature gradient during melt-spinning caused the initial austenite in the ribbons to form typical columnar-shaped grains with a strong ⟨001⟩A preferred orientation perpendicular to the ribbon plane. After cooling, the ribbons undergo martensitic transformation from cubic austenite to monoclinic eight-layered modulated (8 M) martensite. High angle annular dark field-scanning transmission electron microscopy observations indicate that martensite lattice modulation is inhomogeneous at atomic scales. Co substitution for Ni not only strongly influences the phase transformation temperatures but also greatly enhances ferromagnetic coupling. As a result, an enlarged magnetization difference across the martensitic transformation under a field change of 5 T in the Mn50Ni38In9Co3 ribbon induces a large magnetic entropy change up to 12.1 J kg−1 K–1 and a refrigeration capacity of 197 J kg–1 around room temperature. In addition, a wide operational temperature region up to 31 K is obtained in the Mn50Ni37In9Co4 ribbon due to the enhanced sensitivity of the transformation temperature shift under a magnetic field.

Existence of short-range magnetic correlation and observation of large magnetocaloric effect in BiGdO3 compound

In the present study, we have investigated the detailed magnetic and magnetocaloric properties of the rare-earth-based polycrystalline BiGdO3 compound, synthesized by the solid-state reaction method. Detailed magnetic measurements show the absence of long-range magnetic ordering down-to 2 K. Zero-field heat capacity study also supports this result. However, all these magnetic and heat capacity measurements reveal the possibility of having a weak short-range antiferromagnetic correlation in this system below 40 K. Detailed analysis of the magnetic isotherms (using modified Langevin function) and field-dependent magnetic entropy change (using mean-field theory) nicely represent the existence of short-range antiferromagnetic correlation in this system. The prepared material also exhibits a large magnetic entropy change of about 25 J kg−1 K−1 at 2.6 K and a large adiabatic temperature change of 14.8 K at 12 K for the magnetic field change of 0–70 kOe. This observed large magnetocaloric effect at this low temperature region is possibly a consequence of the absence of long-range magnetic ordering and the presence of field-induced ferromagnetic behaviour in this BiGdO3 compound.

Large Barocaloric Effect with High Pressure-Driving Efficiency in a Hexagonal MnNi0.77Fe0.23Ge AlloySupported by the National Natural Science Foundation of China (Grant No. 51722106), the National Key R&D Program of China (Grant No. 2019YFA0704904), Users with Excellence Program of Hefei Science Center CAS (Grant No. 2019HSC-UE009), and Fujian Institute of Innovation, Chinese Academy of Sciences.

The hydrostatic pressure is expected to be an effective knob to tune the magnetostructural phase transitions of hexagonal MM’X alloys (M and M’ denote transition metals and X represents main group elements). We perform magnetization measurements under hydrostatic pressure on an MM’X martensitic MnNi20.77Fe0.23Ge alloy. The magnetostructural transition temperature can be efficiently tuned to lower temperatures by applying moderate pressures, with a giant shift rate of –151 K/GPa. A temperature span of 30 K is obtained under the pressure, within which a large magnetic entropy change of –23 J⋅kg−1K−1 in a field change of 5 T is induced by the mechanical energy gain due to the large volume change. Meanwhile, a decoupling of structural and magnetic transitions is observed at low temperatures when the martensitic transition temperature is lower than the Curie temperature. These results show a multi-parameter tunable caloric effect that benefits the solid-state cooling.

New DyHoCo medium entropy amorphous microwires of large magnetic entropy change

Abstract We report upon the excellent magnetocaloric effect in melt-extracted DyHoCo medium entropy microwires. The magnetic entropy change (-ΔSM) reaches a large value of ∼11.2 J kg−1 K−1 for a field change (μ0ΔH) of 5 T. The large value of -ΔSM is resulted from the large magnetic moments of Dy and Ho. In addition, the DyHoCo microwires show a good cooling efficiency; RC1, RC2 and RC3 are evaluated to be ∼530 J kg−1, ∼417 J kg−1 and ∼279 J kg−1, respectively, at μ0ΔH = 5 T. The DyHoCo microwires undergo a second-order paramagnetic-ferromagnetic transition at the Curie temperature of ∼35 K. The excellent magnetocaloric property makes the melt-extracted DyHoCo microwires a promising refrigerant for cryogenic cooling application.

Conventional and Inverse Magnetocaloric Effect in Ni-Rich Ni-Mn-Ga and Ni-Mn-Sn Heusler Alloy: A Comparison

Magnetic and magnetocaloric effect of Ni-rich Ni52Mn34Sn14 (Ni-Mn-Sn) and Ni54Mn17Ga29 (Ni-Mn-Ga) Heusler alloys have been investigated up to a magnetic field of 5T and within a temperature range of 4.2 – 325 K. In this study, we report a systematic comparison between Ni-rich Ni52Mn34Sn14 and Ni54Mn17Ga29 alloys in the light of their magnetocaloric effect (MCE). In both the samples, a large magnetic entropy change was observed (~96 J kg-1 K-1 for Ni-Mn-Ga), but for the alloy Ni-Mn-Sn the MCE becomes negative/inverse. From various magnetic measurements it have been observed that in Ni-Mn-Sn alloy the martensite to austenite transition accompanied by lower to higher magnetization whereas for Ni-Mn-Ga alloy reverse situation occurred. The different type of magnetocaloric effect, i.e. inverse and direct can be explained by considering magneto-crystalline anisotropy and different state of magnetization of the martensite and austenite phase of the alloys.

Machine learning the magnetocaloric effect in manganites from lattice parameters

Efficient solid-state refrigeration techniques have drawn increasing attention due to their potential for improving energy efficiency of refrigeration temperature control systems without using harmful gas as in conventional gas compression techniques. Research on magnetocaloric lanthanum manganites with a large maximum magnetic entropy change near room temperature shows promising results for further developments of magnetic refrigeration devices. By incorporating chemical substitutions, oxygen content modifications, and various synthesis methods, these manganites experience lattice distortions from perovskite cubic structures to pseudocubic, orthorhombic, and rhombohedral structures. Further changes in lattice parameters can also be achieved by the introduction of strain due to lattice mismatches. Empirical results and previous models through thermodynamics and first principles show that changes in lattice parameters correlate with those in MMCE, but correlations are merely general tendencies and obviously not universal. In this work, the Gaussian process regression model is developed as a machine learning tool to find statistical correlations between the MMCE and lattice parameters among lanthanum manganites. More than 100 lattices, cubic, pseudocubic, orthorhombic, and rhombohedral, with the MMCE ranging from 0.65 to $$8.00\,\hbox {J}\,\hbox {kg}^{-1}\,\hbox {K}^{-1}$$ under a field change of 5 T are explored for this purpose. The modeling approach demonstrates a high degree of accuracy and stability, contributing to efficient and low-cost estimations of the magnetocaloric effect. Furthermore, the machine learning algorithm predicts close MMCE results on epitaxial films with strained lattices against experimental results, which can provide guidance on thin film structure design and help understandings of magnetic phase transformations and magnetocaloric effects.

Magnetocaloric performance and its linear relationship with magnetoresistance in Gd-Al-Cu metallic glass

The magnetocaloric property and magneto-resistance (MR) of Gd83Cu9Al8 metallic glass (MG) showing a second order ferromagnetic-paramagnetic transition have been investigated. A large maximum magnetic entropy change of 9.7 J/kg.K under a field change of 5 T was obtained, indicative of its attractiveness as magnetic refrigerants. Importantly, a linear relationship was observed between magnetic entropy change, ΔSm, and MR in both the ferromagnetic and paramagnetic states, which is different from that of the reported rare earth based MGs and intermetallics. The diversiform relationships of MR vs ΔSm in MGs imply the complexity of their underliying mechanisms. The linear ΔSm-MR relationship sheds new light on the magnetocaloric effect of MGs, and can guide the design of amorphous magnetic refrigerants.

Giant low field magnetocaloric effect near room temperature in isostructurally alloyed MnNiGe-FeCoGe systems

According to the strategy of isostructural alloying, the magnetostructural coupling was realized by doping appropriate stable hexagonal Ni2In-type FeCoGe alloy into MnNiGe systems, which results in the achievement of large magnetization difference and giant low field magnetic entropy change (ΔSm) in the isostructurally alloyed (MnNiGe)-(FeCoGe) systems. Giant ΔSm as much as −51.3 J∙kg-1K−1 at 296 K and −56.2 J∙kg-1K−1 at 275 K under 5 T magnetic field have been observed in (MnNiGe)0.91-(FeCoGe)0.09 and (MnNiGe)0.89-(FeCoGe)0.11 alloys, respectively. Moreover, the ΔSm of (MnNiGe)0.89-(FeCoGe)0.11 alloy are reached −25.6 J∙kg-1K−1 (2 T) and −43.6 J∙kg-1K−1(3 T), respectively. The observed values of -ΔSM under the magnetic field of 2 T and 3 T are larger than most of the reported MnMX(M = Co, Ni and X = Ge, Si) based systems.

Magnetocaloric effect in ercu-based metallic glass composite

In order to reduce the worsen effects of strong antiferromagnetic coupling between Er and Fe, Co, Ni elements on the magnetocaloric effect of Er based amorphous alloys, an Er45Cu45Al10 metallic glass composite is fabricated and its magnetocaloric effect is studied. The alloy exhibits large magnetic entropy change (14.6 Jkg−1K−1) and high refrigerant capacity (330 Jkg−1) under a magnetic field of 5 T, which is a promising candidate for a magnetic refrigerant in helium liquefaction temperature range. It is intriguing that the entropy change normalized to the rare earth elements for this Er45Cu45Al10 alloy is much higher than other Er-based metallic glasses, which is attributed to the weaker antiferromagnetic interactions between Er and Cu. These results are helpful for designing advanced rare earth-based magnetocaloric materials.

The Gigantic {Ni36Gd102} Hexagon: A Sulfate-Templated "Star-of-David" for Photocatalytic CO2 Reduction and Magnetic Cooling.

Gigantic coordination molecules assembled from a large number of metal ions and organic ligands are structurally and functionally challenging to characterize. Here we show that a heterometallic cluster [Ni36Gd102(OH)132(mmt)18(dmpa)18(H2dmpa)24(CH3COO)84(SO4)18(NO3)18(H2O)30]·Br6(NO3)6·(H2O)x·(CH3OH)y, (1, x ≈ 130, y ≈ 60), shaped like a "Star of David", can be synthesized using a "mixed-ligand" and "sulfate-template" strategy. In terms of metal nuclearity number, 1 is the second largest 3d-4f cluster to date. In the solid state, 1 is porous after removing the lattice guests. The N2 adsoption experiment reveals that the BET and Langmuir surface areas are 299.8 and 412.0 cm2 g-1, respectively. CO2 adsorption at 298 K gives the amount of 45 cm3 g-1 for 1. More importantly, 1 is soluble in common organic solvents and exhibits high solution stability revealed by high resolution MALDI-TOF mass spectroscopy, small-angle X-ray scattering (SAXS), and low-dose transmission electron microscopy. The solubility and the potential open metal sites owing to the labile coordinating components prompted us to investigate the photocatalytic properties of 1, which displays high selectivity and efficiency for reduction of CO2 to CO with turnover number and turnover frequency of 29700 and 1.2 s-1, respectively. These values are higher than most catalysts working under the same conditions, presumably due to the strong Ni-CO2 binding effect. In addition, the large percentage of Gd(III) in 1 leads to a large magnetic entropy change (41.3 J·kg-1·K-1) at 2.0 K for ΔH = 7 T.

Magnetocaloric effect in 2D-alkylammonium copper halides layered inorganic-organic systems

Two-dimensional inorganic–organic hybrids are important due to tunable physical properties and their suitability in the data storage, memory devices, low-temperature magnetic refrigeration technology, energy storage, and other applications. The significance of such lead-free layered hybrids is in the ease of synthesis and material stability against heat, humidity, temperature, and other environmental conditions. Here, we report the magnetic properties of (C12H25NH3)2Cu(Br1 – xClx)4 and (C6H9C2H4NH3)2Cu(Br1 – xClx)4 systems that are self-assembled layered structures formed by solution processing. The systems exhibit paramagnetic to ferromagnetic transition with the Curie temperature and amount of magnetization both controllable by halogen content in the stoichiometric composition. Magnetocaloric properties have been investigated to find out the suitability of highly stable (C12H25NH3)2CuCl4 in environment friendly low-temperature magnetic refrigeration technology. A large magnetic entropy change varying from ∼0.6 J kg−1 K−1 to larger than 2.0 J kg−1 K−1 is measured from isothermal magnetization data around the Curie temperature at field variations 0–10 kOe and 0–60 kOe, respectively. Characteristic critical exponents from the field-dependent magnetic entropy changes have been determined, which show excellent agreement with the three-dimensional Heisenberg model.

Magnetostructural transitions in V-doped MnCoGe compounds

MnCoGe1-xVx (x = 0.005, 0.01, 0.015, 0.02, 0.03, and 0.04) compounds were synthesized and investigated in view of the effect of transition metals on main-group-element sites to the magnetostructural transition. A small amount of V doping results in a decrease of the martensitic transformation temperature, while a further increase of V disturbs the Co-Ge bonds hence destabilizing the MM’X phase. Therefore, the transformation temperature returns to high temperature, and the expected Curie temperature window becomes incomplete. Accordingly, a large magnetic entropy change of about 10 J/kg·K and a refrigerant capacity of about 129.5 J/kg is obtained in the series.

Large magnetic entropy change and refrigeration capacity around room temperature in quinary Ni41Co9-xFexMn40Sn10 alloys (x= 2.0 and 2.5)

We report the magnetocaloric properties of two Fe-containing quinary bulk polycrystalline alloys of nominal compositions Ni41Co7Fe2Mn40Sn10 and Ni41Co6.5Fe2.5Mn40Sn10 that were determined by indirect and direct methods. Both samples showed a large refrigeration capacity RC and maximum magnetic entropy change ΔSMpeak around room temperature. For a magnetic field change of 2 T (5 T), a large magnetic entropy change of 18.9 (22.4) J kg−1 K−1 and 11.8 (16.8) J kg−1 K−1 and a refrigeration capacity of 128 (396) J kg−1 and 99 (313) J kg−1 were found in Ni41Co7Fe2Mn40Sn10 and Ni41Co6.5Fe2.5Mn40Sn10 alloys, respectively. RC for the alloy Ni41Co7Fe2Mn40Sn10, is among the largest value reported so far for Ni–Mn based Heusler alloys. Under a 1.5 T field change, the direct measurements showed the maximum adiabatic temperature changes ΔTadmax of −0.8 K and −1.5 K for these two alloys, respectively. The present findings point out the potential of Fe-alloyed Ni41Co9Mn40Sn10 Heusler alloys as room-temperature magnetic refrigerants.

Plastically deformed La–Fe–Si: Microstructural evolution, magnetocaloric effect and anisotropic thermal conductivity

La(Fe,Si)13-based alloys are considered to be one of the most promising magnetocaloric materials for solid state cooling. However, the intrinsic brittleness of NaZn13-type functional phase (1:13 phase) obstructs the shaping of La–Fe–Si alloys into desired geometries for the applications in magnetic cooling devices. Here, by exploiting the excellent deformability of α-Fe phase, we propose a near-net shaping method of open die-forging to prepare La–Fe–Si thin plates. This novel approach is demonstrated for the first time to exhibit several advantages including producing full-dense materials, facilitating the phase formation, and maintaining large magnetocaloric effect. The microstructural and texture evolution have been systematically investigated for the pre-deformed and annealed La–Fe–Si alloys. Large magnetic entropy change of 14 J/kg K at 2 T is obtained in the annealed sample and 11 J/kg K for the hydrogenated sample without hydrogen-induced cracking. Furthermore, a unique dual-phase structure consisting of aligned α-Fe phase and non-equiaxial 1:13 grains brings about the significant anisotropic thermal conductivity in cross-plane and in-plane directions for the plastically-deformed plates. This new insight would greatly benefit the design of high efficient magnetic refrigerator with one-way enhanced thermal conduction.

Hysteresis loss reduction and magnetocaloric effect improvement in the Ni-Co-Mn-In alloys

In this work the magnetocaloric effect (MCE) and hysteresis losses of Ni45Co5Mn(37-x)In(13+x) alloy (x= 0, 0.4) are studied. Also we propose a new approach in calculating the average entropy change to eliminate the overestimation of the magnetic entropy change calculation using Maxwell’s relations which is commonly seen in the indirect MCE calculation in the literature. The attributes of magnetostructural coupling have an important role in the magnetic behavior of these magnetofunctional alloys. This work exhibits that a strong magnetostructural coupling can be achieved over a wide temperature range in this alloy family which results in a higher MCE and relative cooling power (RCP) compared to other Ni-Mn-In based Heusler alloys. It’s shown that by increasing the applied field the peak of the entropy change curves shifts to lower temperatures. Additionally, a small variation in the stoichiometry composition broadens the magnetic entropy change curve and shifts the critical temperatures by about 36 K to around room temperature. Furthermore, due to the enhancement in ferromagnetic exchange interactions in austenite, the magnetization change accompanying the martensitic transformation is greatly improved, resulting in a large magnetic entropy change of 31 Jkg-1K-1 under 5T field. The broadened and higher peak of the entropy change curves produced a significantly high relative cooling power in Ni45Co5Mn36.6In13.4 (488 JKg-1) and Ni45Co5Mn37In13 (317 JKg-1) under 5T field. These results are especially promising in finding low-cost, high-performance magnetocaloric material for magnetic refrigeration systems.

Large magnetic entropy change and magnetostrain in a directionally solidified Ni45.7Co4.2Mn37.3Sb12.8 alloy

Heusler-type Ni-(Co)-Mn-X (X = In, Sn, Sb) meta-magnetic alloys can exhibit various magneto-functional behaviors due to the strong coupling between the magnetic and structural orders. Here, we demonstrate large magnetocaloric effect and magnetic shape memory effect in a directionally solidified Ni45.7Co4.2Mn37.3Sb12.8 alloy with 〈5 5 3〉A preferred orientation. It is shown that large magnetic entropy change up to 27.4 J kg−1 K−1 can be achieved under the field change of 5 T. Moreover, a large magnetic field-induced strain of 0.42% was also obtained with no-prestrain through inverse martensitic transformation induced by applying a magnetic field of 7 T. The present magnetostain is much higher than those in polycrystalline Ni-(Co)-Mn-Sb based alloys reported previously. Such enhanced magneto-functional behavior could be attributed to the highly textured microstructure and enlarged lattice distortion through Co addition.

Melt-extracted Gd73.5Si13B13.5/GdB6 ferromagnetic/antiferromagnetic microwires with excellent magnetocaloric properties

A novel class of magnetocaloric microwires composed of antiferromagnetic GdB6 nanocrystals embedded in an amorphous ferromagnetic Gd73.5Si13B13.5 matrix is reported. These composite microwires were created directly from a melt-extraction process. XRD, TEM, HRTEM and SAED confirm the formation of GdB6 nanocrystals (∼10 nm) in the amorphous Gd73.5Si13B13.5 matrix. As a second-order magnetic material, the Gd73.5Si13B13.5/GdB6 microwires exhibit an excellent magnetocaloric response, with a large magnetic entropy change ΔSM ∼6.4 J kg−1 K−1 at ∼120 K, a large temperature interval δTFWHM ∼130 K, and the large refrigerant capacity RC ∼890 J kg−1 for a field change of 5 T. Such microwires are a promising candidate for active magnetic refrigeration in the temperature range of 10–200 K.

On the giant magnetocaloric and mechanical properties of Mn–Fe–P–Si-Ge alloy

We report the magnetocaloric properties of Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 alloy prepared by mechanical alloying followed by spark plasma sintering and annealing the spark plasma sintered alloy. The X-ray diffraction pattern confirms the presence of hexagonal Fe2P-type phase in both (as-prepared and annealed) alloys. Annealing of the spark plasma sintered alloy leads to the increase of the volume fraction of the Fe2P phase from 87% to 98% and a decrease in the lattice volume. Thermo-magnetic measurements show that Curie temperature (TC) decreases from 291 K to 289 K after annealing the spark plasma sintered alloy. Thermal hysteresis reduces from 19 K to 9 K after annealing the spark plasma sintered alloy. The magnetic entropy evaluated from magnetization measurements was found to be 8 J/kg-K in the spark plasma sintered alloy and it increases to 19 J/kg-K in the annealed spark plasma sintered alloy under 3 T magnetic field. The refrigerant capacity of the annealed spark plasma sintered alloy was found to be 200 J/kg at 3 T. The adiabatic temperature change of the annealed alloy has been estimated from the heat capacity measurements and it was found to be 1.9 K at 1 T and increases to around 2.7 K under a magnetic field of 3 T. Annealing the spark plasma sintered alloy leads to decrease in the hardness and it is observed that both the alloys crack after thermal cycling. However, the large change in magnetic entropy and adiabatic temperature change very near to the room temperature makes Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 alloy a promising magnetocaloric material.

Effect of Ti doping on the phase transitions, magnetocaloric effect, and exchange bias in Ni43Mn46Sn11−xTix Heusler alloys

In this work, we systematically studied the influence of Ti doping on the crystal structure, martensitic transition, magnetocaloric effect, and exchange bias in Ni43Mn46Sn11−xTix alloys. With the increase of Ti concentration, the martensitic transformation temperature increases gradually due to the effect of lattice contraction, and the ferromagnetic ordering windows in the martensitic and austenitic regions are closed at x = 1 and x = 2, respectively. This study demonstrates that relatively large magnetic entropy changes can be obtained around the paramagnetic-paramagnetic martensitic transformation under high magnetic field. Another effect of Ti doping is the enhancement of antiferromagnetic interaction, which resulting in the transformation of ground state from reentrant-spin-glass to canonical spin-glass for x⩾1. The zero-field-cooled exchange (ZEB) was realized in the composition range of 1⩽x⩽4, of antiferromagnetic interactions is a viable way to achieve ZEB in NiMn-based Heusler alloys.

Magnetocaloric materials with ultra-small magnetic nanoparticles working at room temperature

Through the use of the Monte Carlo simulations utilising the mean-field approach, we show that a dense assembly of separated ultra-small magnetic nanoparticles embedded into a non-magnetic deformable matrix can be characterized by a large isothermal magnetic entropy change even upon applying a weak magnetic field with values much smaller than one Tesla. We also show that such entropy change may be very significant in the vicinity of the room temperature which effect normally requires an application of a strong external magnetic field. The deformable matrix chosen in this work as a host for magnetic nanoparticles adopts a thin film form with a large surface area to volume ratio. This in turn in combination with a strong magneto-volume coupling exhibited by this material allows us to show its suitability to be used in the case of a variety of applications utilising local cooling/heating such as future magnetic refrigerants.