Large Magnetocaloric Effect Research Articles

Large Refrigerant Capacity Induced by Table‐Like Magnetocaloric Effect in High‐Entropy Alloys TbDyHoEr

Rare‐earth‐based high‐entropy alloys (HEAs) with large magnetocaloric effect (MCE) have been recently recognized as good candidates for magnetic refrigeration. Herein, the complex magnetic transition, MCE, refrigerant capacity (RC), and magnetic‐phase diagram of single‐phase TbDyHoEr HEA are studied. It is showed in the results that due to complex magnetic transition and an ideal table‐like MCE, the RC of TbDyHoEr is significantly improved from 883.19 to 1049.22 J kg−1by melt‐spun treatment. In terms of RC value and hysteresis performance, the melt‐spun treatment significantly improves the application potential of TbDyHoEr HEA as a high‐efficient magnetic refrigeration material, and the ideal table‐like MCE in a large temperature range enables this material to meet the requirements of both cryogenic refrigeration and mesothermal refrigeration for an Ericsson cycle.

Large magnetocaloric effect near room-temperature by tuning the magneto-structural transition in (Mn, Fe)(Ni, Fe)Si alloy

The observation of near room-temperature coupling of both magnetic and structural transitions in Fe substituted Mn-Ni-Si alloy leads to an interesting magneto-structural transition (MST) phenomenon which intensifies the required magnetocaloric parameters for magnetic cooling applications. The crystal structure analysis reveals that temperature as well as Fe substitution work as the driving forces for deforming the orthorhombic unit cell and to stabilize the hexagonal phase. The correlation between the unit cell parameters of both phases confirms that a large change in unit cell volume (∼2.9%) is mainly responsible for the structural transition. The simultaneous substitution of Fe across Ni and Mn sites helps to tune the MST temperature. Both magnetization and calorimetric studies confirm the existence of first-order type structural transition across MST. The [Mn0.64 Ni0.64 Fe0.72 Si] alloy exhibits a large isothermal magnetic entropy change (ΔS M ) of −19.2 0.4 J kg−1 K−1 accompanied by a large value of effective refrigerant capacity (RC effe ) of 181.8 3.7 J kg−1 due to a magnetic field change of 0–30 kOe. The estimated total entropy change associated with the complete structural transition from the calorimetric studies sets an upper limit for the entropy change of the system. The low cost and non-toxic nature of constituent elements, composition-dependent tunability of the transition temperature, and near room-temperature large magnetocaloric parameters make this alloy potentially suitable to be used as a refrigerant in solid-state magnetic cooling technology.

{Gd44Ni22}: a gigantic 3d–4f wheel-like nanoscale cluster with a large magnetocaloric effect

A previously undiscovered gigantic 3d–4f wheel-like nanoscale cluster, {Gd44Ni22}, exhibits a large magnetocaloric effect (−ΔSm = 44.9 J kg−1 K−1 at 2.0 K for ΔH = 7 T).

A new method to enhance the magnetocaloric effect in (Sc,Ti)Fe2 via magnetic phase separation

Magnetic refrigeration based on the magnetocaloric effect (MCE) is a novel refrigeration technology that will replace traditional vapor-compression refrigeration in the future. Improvement in the performance of MCE materials is crucial for the development of magnetic refrigeration technology. This study presents a new method that enhances the MCE performance of (Sc,Ti)Fe2 via magnetic phase separation. The maximum magnetic entropy change induced by the coexistence of an in-plane ferromagnetic phase (FMab) and a canting antiferromagnetic phase (CAFM) in Sc0.3Ti0.7Fe2 is twice that found in other (Sc,Ti)Fe2 compounds. Variable-temperature neutron diffraction experiments directly reveal that the large magnetic entropy change in Sc0.3Ti0.7Fe2 is dominated by the transformation from a highly ordered FMab state to a CAFM state with a lower magnetic order. The magnetic phase separation is a direct transition from a higher-ordered state with a larger lattice to a lower-ordered state with a smaller lattice that induces a large magnetic order change and lattice contraction. The combination of the metamagnetic transition and negative thermal expansion leads to enhanced MCE. This study suggests the possibility that magnetic phase separation can be an effective approach to achieving and controlling a large MCE in magnetic materials.

Octanuclear Ln(III)-Based Clusters Assembled by a Polydentate Schiff Base Ligand and a β-Diketone Co-Ligand: Efficient Conversion of CO2 to Cyclic Carbonates and Large Magnetocaloric Effect

A series of new Ln8 clusters [Ln8(acac)4(HL)4(L)2(μ3-O)4(C2H5O)4]·2C2H5OH·2CH2Cl2 (Ln(III) = Gd (1), Dy (2), and Ho (3); Hacac = acetylacetone and H2L = 2-hydroxy-benzoic acid (5-hydroxymethyl-furan-2-ylmethylene)-hydrazide) have been designed and constructed using a multiple coordination site Schiff base ligand (H2L) as well as a β-diketonate auxiliary ligand. The structures, magnetic properties, and catalytic performance of clusters 1–3 have been studied. X-ray crystallography data revealed that clusters 1–3 possess similar structures with two chair-form Ln4 cores bridged by four μ3-O atoms. Clusters 1–3 display extensive and high solvent stability. Magnetic analysis exhibits that cluster 1 possesses a comparably large magnetocaloric effect (−ΔSm = 33.06 J kg–1 K–1 at 2.0 K and 7.0 T). AC susceptibility measurement suggests that cluster 2 exhibits single-molecule magnet behavior under zero-field conditions. What’s more, all clusters can effectively convert CO2 with epoxides. The highest yield is 98% at 70 °C 0.1 MPa catalyzed by 1. In addition, cluster 1 can be reused three times with a negligible loss of catalytic activity.

Large magnetocaloric effect in the frustrated antiferromagnet EuIr[formula omitted]P[formula omitted

We present a theoretical analysis of the magnetocaloric effect in the frustrated antiferromagnet EuIr2P2. Monte Carlo simulations indicate a large magnetic entropy change ΔSMmax∼5 J kg−1 K−1 at T=2.45 K for a moderate change in the external magnetic field ΔB=1.2 Tesla. The highest value of ΔSM seems to be associated with the presence of a multicritical point in the magnetic field versus temperature phase diagram (at Bm∼1.2 Tesla and Tm∼2.2 K) but it persists with similar large values for a broad range of temperatures T≲Tm. Single crystal EuIr2P2 magnetization vs magnetic field experiments allowed us to obtain the magnetocaloric effect for T>2 K. The results are consistent with the theoretical analysis and show a large magnetocaloric effect for T∼2.5 K. Finally, we present a phenomenological Landau functional analysis that provides a simplified description of the phase diagram and of the magnetocaloric effect. Although the magnetic frustration in this system leads to a rich phase diagram, we found no clear indication that it plays a significant role enhancing the magneticaloric effect, other than by reducing the transition temperatures and fields.

Study on the critical behavior and magnetocaloric effect of RCrO3 (R = Gd, Dy)

In this study, we aim to examine the critical behavior and magnetocaloric effect of RCrO3 (R = Gd, Dy) polycrystal synthesized by solid-state sintering. As per the heat capacity fitting curves, GdCrO3 and DyCrO3 fit the 3D-XY and 3D-Ising models, respectively. The analysis of heat capacity curves, field cooling (FC), and zero-field cooling (ZFC) curves reveals two magnetic phase transitions in the samples, with TNCr = 174 K, TNGd = 3.7 K and TNCr = 152 K, TNDy = 3.5 K for GdCrO3 and DyCrO3, respectively. Under a 50 kOe magnetic field, the maximum magnetic entropy change (−ΔSmmax) and relative cooling efficiency (RCP) of the sample are 39.9 J/kg K, 373.4 J/kg and 15.9 J/kg K, 276 J/kg for the two samples, respectively. We believe that the significant magnetocaloric effect of GdCrO3 is associated with its critical behavior. This provides an additional reference for the origin of the large magnetocaloric effect of materials.

Assembly of tetra-nuclear lanthanide compounds: Structures, magnetic refrigeration and slow relaxation of magnetization

Two novel tetranuclear lanthanide compounds with the formula [Ln4(L1)2(L2)2(μ2- OCH3)2(CH3OH)2]·CH3OH (Ln = Gd (1), Dy (2), H2L1 = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-8-hydroxyquinoline, H3L2 = 2-[(2-(N'-acetylhydrazino)propanehydrazide)methyl]-8-hydroxyquinoline) were successfully prepared, and structurally and magnetically characterized. Crystal structural analyses reveal that two compounds are isostructural and they all consist of a tetranuclear Ln4 cluster. All Ln(III) ions in them are eight-coordinated and located in a distorted triangular dodecahedron geometry. Magnetic studies indicate that 1 exhibits large magnetocaloric effect with the entropy change (-ΔSm) of 32.10 J Kg−1 K−1 (at T = 2.0 K and ΔH = 7 T), and 2 displays slow magnetic relaxation behaviors.

Unusual first-order magnetic phase transition and large magnetocaloric effect in Nd2In

A large magnetocaloric effect with its maximum near the boiling point of natural gas occurs in a rare-earth intermetallic compound ${\mathrm{Nd}}_{2}\mathrm{In}$. While behaviors of physical properties indicate that paramagnetic-ferromagnetic transformation supporting the large magnetocaloric effect is first order in nature, temperature-dependent crystallographic study reveals no changes in lattice symmetry and lack of discontinuities either in phase volume or lattice parameters. The borderline first-order nature of phase transformation in ${\mathrm{Nd}}_{2}\mathrm{In}$ is markedly different from conventional first-order magnetic transitions occurring in other members of the family -- isostructural ${\mathrm{Pr}}_{2}\mathrm{In}$ and nonisostructural ${\mathrm{Eu}}_{2}\mathrm{In}$.

Complete and reversible magnetostructural transition driven by low magnetic field in multiferroic NiCoMnIn alloys

Magnetic-field-induced first-order magnetostructural transition (MFI-FOMST) brings about an ample variety of intriguing magnetoresponsive effects including magnetocaloric effect, magnetoresistance and magnetostrain. Metamagnetic shape memory alloys (MSMAs) exhibit MFI-FOMST and thus giant magnetoresponsive effects, but the critical field for complete and reversible MFI-FOMST, (μ0∆H)min, is too high (usually >5 T), which has been a longstanding bottleneck for practical applications. Here, we successfully achieved complete and reversible MFI-FOMST under a low field of 1.5 T, which can be generated by permanent magnets, in a prototype MSMA. The significant reduction of (μ0∆H)min is realized by simultaneously enlarging the distance between Curie transition and magnetostructural transition and manipulating the geometric compatibility between the transforming phases. The low (μ0∆H)min provides a great opportunity for attaining low-field-induced large reversible magnetoresponsive effects. For instance, a large reversible magnetocaloric effect is achieved under 1.5 T. Our realization of low-field-induced complete and reversible first-order magnetostructural transition may push a significant step forward towards the practical use of MSMAs. This work is instructive for developing novel magnetic materials with low-field-actuated first-order phase transition for applications as magnetic actuators, magnetoresistors and solid-state refrigerants.

Structure, magnetic and magnetocaloric properties of polycrystalline Er3AlC compound

The development of magnetic materials with large magnetocaloric effects for solid state refrigeration technology is receiving increasing attention. In this work, the crystal structure, magnetic and magnetocaloric properties of polycrystalline Er3AlC compound are investigated. Powder X-ray diffraction indicate that Er3AlC crystallizes in the inverse perovskite structure, belonging to the space group Pm3¯m(221). The polycrystalline sample exhibits two successive magnetic transitions: antiferromagnetic-ferromagnetic below 2 K and ferromagnetic–paramagnetic transition around 4.1 K. The value of the maximum magnetic entropy changes are 13.9 J/kg K and 30.5 J/kg K under the field changes of 0–2 T and 0–5 T, respectively. The large magnetic entropy change under low fields makes Er3AlC compound a potential candidate for cryogenic magnetic refrigeration.

Structural and cryogenic magnetic properties of the RE2MoO6 (RE = Er and Ho) compounds

The rare earth (RE) based magnetic materials with large low temperature magnetocaloric effect (MCE) have attracted much research interest due to their potential application for the environment-friendly magnetic refrigeration (MR) technology. Herein, a systematic investigation on the crystal structure, micro morphology together with the low temperature magnetic properties and MCE performances have been conducted on the RE2MoO6 (RE = Er and Ho) compounds. Both compounds crystallize in monoclinic structure and exhibit large reversible low temperature MCE. The maximum magnetic entropy changes (−ΔSMmax) at magnetic field change (ΔH) of 0–5 T reach 15.3 and 15.8 J kg−1 K−1 for Er2MoO6 and Ho2MoO6, respectively. The corresponding relative cooling power/refrigeration capacity (RCP/RC) values are 197.4/149.7 and 286.0/222.3 J/kg. These obtained MCE parameters for present RE2MoO6 compounds are close to those of reported RE based MCE materials, which make them of potential for low temperature MR application.

Contrasting response on magnetocaloric effect and refrigeration capacity due to Ni or Mn substitution by Fe in Ni-Mn-In-Co-Fe alloys

We set the composition of two Ni-Mn-In-Co-Fe alloys as (Ni46.8Fe1.2)Co2Mn36.5In13.5 and Ni48Co2(Mn34.5Fe2)In13.5 in order to display the martensitic transformation near to room temperature. Under a magnetic field change of 5 T the polycrystalline low Co content alloys displayed a large magnetocaloric effect ΔSMag of 15.5 and 20.0 Jkg-1K-1; and giant refrigeration capacity RCFWHM up to 422 and 292 Jkg-1 for (Ni46.8Fe1.2)Co2Mn36.5In13.5 and Ni48Co2(Mn34.5Fe2)In13.5, respectively. The XRD patterns showed cubic L21 structure with space group 225 in both alloys and via Rietveld refinement negligible differences were found in lattice parameter of 0.598(7) and 0.598(9) nm for (Ni46.8Fe1.2)Co2Mn36.5In13.5 and Ni48Co2(Mn34.5Fe2)In13.5, respectively. Nevertheless, the magnetocaloric response in the alloys exhibited remarkable dissimilarities. Whilst the applied magnetic field shifted the martensitic transformation − 3.4 KT-1 in the Ni48Co2(Mn34.5Fe2)In13.5 alloy this sensibility increased up to − 6.8 KT-1 in the (Ni46.8Fe1.2)Co2Mn36.5In13.5 alloy; consequently the span in the Full Width Half Maximum of the ΔSMag(T) curve was 17 and 32 K, respectively.

Strain manipulation of magnetocaloric effect in a Ni39.5Co8.5Mn42Sn10 melt-spun ribbon

Heusler-type Ni-Mn-based alloys can demonstrate large magnetocaloric effect through magnetic field-induced phase transformation, but it usually occurs in a relatively narrow temperature region. In this work, we fabricate a bilayer composite with a Ni39.5Co8.5Mn42Sn10 ribbon adhered to a Ni50Ti50 substrate in order to manipulate the magnetocaloric properties by using the recovery strain of the predeformed substrate. The transformation temperatures of the ribbons can be effectively shifted to higher temperature region through the external strain transferred from the substrate, which contributes to the extended cooling temperature region. Moreover, the effective refrigeration capacity can also be improved by such strain manipulation.

Incommensurate spin density wave and magnetocaloric effect in the metallic triangular lattice HoAl2Ge2

We report the magnetic structure and the magnetocaloric effect (MCE) of the ternary compound $\mathrm{Ho}{\mathrm{Al}}_{2}{\mathrm{Ge}}_{2}$ with a trigonal ${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$-type crystal structure. A neutron powder diffraction experiment reveals that $\mathrm{Ho}{\mathrm{Al}}_{2}{\mathrm{Ge}}_{2}$ exhibits an incommensurate spin density wave (SDW) with a propagation vector $\mathbit{k}=(0.23,\phantom{\rule{0.28em}{0ex}}0,\phantom{\rule{0.28em}{0ex}}0.06)$. The special arrangement of magnetic moments in $\mathrm{Ho}{\mathrm{Al}}_{2}{\mathrm{Ge}}_{2}$ induces interesting physical phenomena and large magnetocaloric effects. The rise in resistivity at low temperatures indicates the effect of the SDW state in the electronic transport. The maximum magnetic-entropy change is $\ensuremath{-}16.1\phantom{\rule{0.16em}{0ex}}\mathrm{J}/\mathrm{kg}\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ under a magnetic field change of 0--70 kOe for an isotropic $\mathrm{Ho}{\mathrm{Al}}_{2}{\mathrm{Ge}}_{2}$ powder and it increases to $\ensuremath{-}17.9\phantom{\rule{0.16em}{0ex}}\mathrm{J}/\mathrm{kg}\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for a single crystal when the magnetic field ($H$) is applied parallel to the $ab$ plane. A large rotating magnetic-entropy change of $\ensuremath{-}5.1\phantom{\rule{0.16em}{0ex}}\mathrm{J}/\mathrm{kg}\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $H=20\phantom{\rule{0.16em}{0ex}}\mathrm{kOe}$ in a $\mathrm{Ho}{\mathrm{Al}}_{2}{\mathrm{Ge}}_{2}$ single crystal is obtained, which is closely associated to the magnetic anisotropy of the SDW order and its response to the external magnetic field. We discuss the large MCE in terms of the field-induced metamagnetic transition from the incommensurate SDW order to the ferromagnetic order. Our study establishes the triangular lattice $R{\mathrm{Al}}_{2}{\mathrm{Ge}}_{2}$ ($R$ = rare-earth elements) as a unique family of compounds to explore the existence of the incommensurate spin density waves and the correlated physical properties.

Exchange bias effects and a large magnetocaloric effect arising out of the second-order transition in suction cast Ni50Mn36Sn14

Exchange bias effects and a large magnetocaloric effect arising out of the second-order transition in suction cast Ni50Mn36Sn14

Enhanced and giant low-field magnetocaloric effects in Eu(Ti,Nb,M)O3 (M=Cu or Zn) compounds

For more practical applications, research on magnetic refrigeration has been gradually focused on developing refrigerants with large magnetocaloric effect (MCE) under low magnetic fields (≤2 T). EuTiO3 exhibits considerable low-field MCE near ordering temperature, meanwhile the magnetic switch from antiferromagnetic to ferromagnetic (AFM-FM) in it provides the feasibility of improving the magnetocaloric performance. In this study, a series of Eu(Ti,Nb,M)O3 (M=Cu or Zn) compounds were synthesized, and the crystal structure, magnetic properties together with cryogenic MCEs were investigated in detail. The co-substitution contributes to an FM coupling domination in all the compounds. Besides, significantly enhanced and giant low-field MCEs were detected in these compounds. Under the field change of 1 T, all the samples possess remarkable magnetic entropy change (>15 J·kg-1·K-1) around 5 K without hysteresis. The corresponding refrigerating capacities are calculated to be 68.0, 72.6, 76.0, and 69.6 J·kg-1, respectively, exhibiting an increase of 149–178% than EuTiO3. The outstanding magnetocaloric performances make the Eu(Ti,Nb,M)O3 (M=Cu or Zn) compounds competitive candidates for cryogenic magnetic refrigeration.

Microstructure, magnetism and magnetocaloric effect of Gd3NixAl2‒x alloys

The microstructure, magnetic and magnetocaloric properties of the Gd3NixAl2‒x (x = 0, 0.1, 0.2, 0.3) alloys were systematically studied. Three phases of Gd3Al2, GdAl and Gd2Al were observed in the Gd3Al2 alloy. The lamellar GdAl and Gd2Al phases were dispersed in the main phase of Gd3Al2 alloy, which was not conducive to the plasticity of the alloy. It was demonstrated that the introduction of a small amount of Ni changed the phase composition. The Gd3NixAl2‒x (x = 0, 0.1, 0.2, 0.3) alloys underwent second-order magnetic phase transition around their Curie temperatures (TC) of 275 K, 274.5 K, 271 K and 269.5 K, respectively. The maximum isothermal magnetic entropy changes (‒ΔSM)max were 2.95 J kg−1 K−1, 2.45 J kg−1 K−1, 2.02 J kg−1 K−1 and 1.42 J kg−1 K−1 under the magnetic field change of 0–2 T. The maximum adiabatic temperature changes (ΔTad)max were 2.74 K, 2.18 K, 1.56 K and 1.14 K for Gd3NixAl2‒x alloys with x = 0, 0.1, 0.2 and 0.3, respectively. Compared with pure Gd, the Gd3NixAl2‒x (x = 0, 0.1, 0.2, 0.3) alloys exhibited weaker comprehensive magnetocaloric effect due to the reduction of magnetization caused by the addition of a large amount of Al. However, the cheaper raw material price and relatively large magnetocaloric effect make the Gd3NixAl2‒x (x = 0, 0.1, 0.2, 0.3) alloys be the potential magnetic refrigerants at near room temperature.

Large magnetocaloric and magnetoresistance effects during martensitic transformation in Heusler-type Ni44Co6Mn37In13 alloy

NiMn-based Heusler alloys are promising materials in the multi-functional applications due to their ample magneto-responsive effects across martensitic transformation, such as magnetocaloric effect, magnetostriction and magnetoresistance. In this work, the evolution of microstructure, large magnetocaloric and magnetoresistance effects during martensitic transformation are systematically studied in a Ni44Co6Mn37In13 alloy. Magnetic and caloric measurements verify that the martensite in weak magnetic state would gradually transform to be ferromagnetic austenite upon heating. The temperature dependence of microstructure observed in an in-situ optical microscopy unambiguously verify the ‘kinetic arrest’ of martensitic transformation. Most importantly, due to the high sensitivity of transformation to the magnetic field, large magnetocaloric and magnetoresistance effects near room temperature are obtained, including magnetic entropy changes of 8.4 Jkg-1K−1, effective refrigerant capacity of 181 Jkg−1 and magnetoresistance change of 75 % under the field change of Δμ0H = 0–5 T, making the studied sample promising for room temperature magnetic refrigeration and magnetic storage.

Electronic structure and magnetic properties of 3d−4f double perovskite material

Double perovskite-based magnets wherein frustration and competition between emergent degrees of freedom are at play can lead to novel electronic and magnetic phenomena. Herein, we report the electronic structure and magnetic properties of an ordered double perovskite material Ho2CoMnO6. In the double perovskite with general class A2BB'O6, the octahedral B and B'-site has a distinct crystallographic site. The Rietveld refinement of XRD data reveals that Ho2CoMnO6 crystallizes in the monoclinic P21/n space group. The X-ray photoelectron spectroscopy confirms the charge state of cations present in this material. The temperature dependence of magnetization and specific heat exhibit a long-range ferromagnetic ordering at Tc ~ 76 K owing to the presence of super exchange interaction between Co2+ and Mn4+ moments. Furthermore, the magnetization isotherm at 5 K shows a hysteresis curve that confirms ferromagnetic behavior of this double perovskite. We observed a re-entrant glassy state in the intermediate temperature regime, which is attributed to inherent anti-site disorder and competing interactions. A large magnetocaloric effect has been observed much below the ferromagnetic transition temperature. The temperature-dependent Raman spectroscopy studies support the presence of spin-phonon coupling and short-range order above Tc in this double perovskite. The stabilization of magnetic ordering and charge states is further analyzed through electronic structure calculations. The latter also infers the compound to be a narrow band gap insulator with the gap arising between the lower and upper Hubbard Co-d subbands. Our results demonstrate that anti-site disorder and complex 3d-4f exchange interactions in the spin-lattice account for the observed electronic and magnetic properties in this promising double perovskite material.