Large Magnetic Entropy Change Research Articles

Magnetic Properties and Magnetocaloric Effect of Fe90–<italic>x</italic>Nd<italic>x</italic>Zr10 Rapidly Quenched Alloys

In this paper, we present the results of a systematic study of Fe90– x Nd x Zr10 ( ${x} = 1$ , 2, 3, 4, and 5) alloy ribbons with a thickness of $\sim 15~\mu \text{m}$ , which were prepared by melt-spinning on a single roller system. X-ray diffraction patterns of the ribbons manifest their almost amorphous structure. Magnetization measurements show that the Curie temperature of the alloy can be tuned from 262 to 350 K by varying Nd concentration. Saturation magnetization of the alloy is found to increase with increasing Nd concentration. All the ribbons reveal a soft magnetic behavior with low coercivity ( $H_{\mathbf {c}} Oe). The ribbons exhibit large magnetocaloric effect ( $\vert \Delta \text{S}_{\mathrm {m}}\vert _{\max } > 1.6~\text{J}\,\cdot \,\, \text{kg}^{-1}\,\cdot \, \text{K}^{{-1}}$ for a magnetic field change of 12 kOe) at room temperature. In addition, a large working temperature range ( $\delta _{\text {TFWHM}} >60$ K) is found, which together with the large magnetic entropy change yields the large cooling efficiency desirable for active magnetic refrigeration.

Enhanced magnetocaloric effect in Ni-Mn-Sn-Co alloys with two successive magnetostructural transformations

High magnetocaloric refrigeration performance requires large magnetic entropy change ΔSM and broad working temperature span ΔTFWHM. A fourth element doping of Co in ternary Ni-Mn-Sn alloy may significantly enhance the saturation magnetization of the alloy and thus enhance the ΔSM. Here, the effects of Co-doping on the martensite transformation, magnetic properties and magnetocaloric effects (MCE) of quaternary Ni47−xMn43Sn10Cox (x = 0, 6, 11) alloys were investigated. The martensite transformation temperatures decrease while austenite Curie point increases with Co content increasing to x = 6 and 11, thus broadening the temperature window for a high magnetization austenite (13.5, 91.7 and 109.1 A·m2/kg for x = 0, 6 and 11, respectively). Two successive magnetostructural transformations (A → 10 M and A → 10 M + 6 M) occur in the alloy x = 6, which are responsible for the giant magnetic entropy change ΔSM = 29.5 J/kg·K, wide working temperature span ΔTFWHM = 14 K and large effective refrigeration capacity RCeff = 232 J/kg under a magnetic field of 5.0 T. These results suggest that Ni40.6Mn43.3Sn10.0Co6.1 alloy may act as a potential solid-state magnetic refrigerant working at room temperature.

The phase transitions, magnetocaloric effect, and exchange bias in Mn49Ni42-xCoxSn9 alloys

The structure, phase transitions, magnetocaloric effect, and exchange bias effect in Mn49Ni42-xCoxSn9 (x = 0, 1, 3 and 5) ferromagnetic shape memory alloys have been systematically investigated. X-ray diffraction results measured at room temperature reveal that Mn49Ni42-xCoxSn9 alloys with x = 0, 1 present martensite structure, and Mn49Ni42-xCoxSn9 alloys with x = 3, 5 exhibit mixture phases of both martensite and austenite. The martensitic transformation and exchange bias field (HEB) are very sensitive to the Co content. In addition, large positive magnetic entropy changes were observed in these alloys due to the magnetic-field-induced transition from the paramagnetic martensitic phase to the ferromagnetic austenitic phase, and a large effective refrigeration capacity of 230.8 J/kg was obtained under the magnetic field change of 70 kOe in Mn49Ni37Co5Sn9 alloy. We realized a continuous tuning of the HEB from 534.7 Oe to 1113.0 Oe after field cooling in presence of 10 kOe.

Effects of the thermal and magnetic paths on first order martensite transition of disordered Ni45Mn44Sn9In2 Heusler alloy exhibiting a giant magnetocaloric effect and magnetoresistance near room temperature

The existence of a first order martensite transition in off-stoichiometric Ni45Mn44Sn9In2 ferromagnetic shape memory Heusler alloy has been clearly observed by thermal, magnetic, and magneto-transport measurements. Field and thermal path dependence of the change in large magnetic entropy and negative magnetoresistance are observed, which originate due to the sharp change in magnetization driven by metamagnetic transition from the weakly magnetic martensite phase to the ferromagnetic austenite phase in the vicinity of the martensite transition. The noticeable shift in the martensite transition with the application of a magnetic field is the most significant feature of the present study. This shift is due to the interplay of the austenite and martensite phase fraction in the alloy. The different aspects of the first order martensite transition, e.g. broadening of the martensite transition and the field induced arrest of the austenite phase are mainly related to the dynamics of coexisting phases in the vicinity of the martensite transition. The alloy also shows a second order ferromagnetic → paramagnetic transition near the Curie temperature of the austenite phase. A noticeably large change in magnetic entropy (ΔSM = 24 J kg−1 K−1 at 298 K) and magnetoresistance (= −33% at 295 K) has been observed for the change in 5 and 8 T magnetic fields, respectively. The change in adiabatic temperature for the change in a magnetic field of 5 T is found to be −3.8 K at 299 K. The low cost of the ingredients and the large change in magnetic entropy very near to the room temperature makes Ni45Mn44Sn9In2 alloy a promising magnetic refrigerant for real technological application.

Large reversible magnetic entropy change in rapidly solidified Ni0.895Cr0.105MnGe1.05 melt-spun ribbons

The crystal structure, and magnetic and magnetocaloric properties of rapidly solidified Ni0.895Cr0.105MnGe1.05 melt-spun ribbons is reported. The ribbon samples crystallize into a single-phase hexagonal Ni2In-type structure at room temperature. The as-quenched ribbons showed a second order magnetic transition at 192 ± 1 K at μoH = 5 mT. A magnetic-field-induced transition from an antiferromagnetic (AFM)-like to a ferromagnetic (FM) state of martensite structure was observed in annealed ribbons below the temperature of the martensitic transformation (TM ∼ 245 ± 1 K). The annealed ribbons undergo a first-order magnetostructural transition (MST) with a large maximum reversible magnetic entropy change of ΔSM = 16.1 J kg−1 K−1 (this is about a four-fold increase compared to the ΔSM observed for the bulk sample of the same nominal composition) and RC = 144 J kg−1 for μoΔH = 5 T at temperature T = TM ∼ 245 ± 1 K. The increase in the ΔSM peak value leads to an improved RC compared to that of the bulk sample (122 J kg−1). The observed MCE and quasi-reversible character of ΔSM at the MST illustrates the potential of Ni0.895Cr0.105MnGe1.05 ribbons for magnetic cooling technology.

Microstructure, Martensitic Transformation, and Inverse Magnetocaloric Effect in Ni48Mn39.5Sn12.5−xAlx Metamagnetic Shape Memory Alloys

The effect of Al substitution on microstructure, martensitic transformation and magnetocaloric properties in Ni48Mn39.5Sn12.5−xAlx (x = 0, 1, 2, 3) alloys is reported. At room temperature, depending on Al concentration, the alloys have typical Heusler L21 austenite structure and/or orthorhombic martensite structure with Pmma space group. A secondary Ni-Mn-Al phase also appears already for low Al concentrations (x ≥ 1). On cooling, irrespective of Al substitution, all the samples show ferromagnetic type ordering below 303 K in the austenite phase. The martensitic transition temperature varies with Al content. All the alloys undergo magnetic field-induced reverse martensitic transformation giving rise to an inverse magnetocaloric effect. The largest magnetic entropy change (8.5 J·kg−1·K−1) is observed near 280 K for the Ni48Mn39.5Sn12.5 alloy.

Reversibility of magnetostructural transition and associated magnetocaloric effect above room temperature in Ni-Co-Mn-In-Gd polycrystal

The magnetocaloric effects (MCE) in polycrystalline Ni45Co5Mn35In14Gd1 alloy were investigated. The magnetic-field-induced phase transformation from martensite to austenite phase is confirmed. Both inverse and an conventional magnetocaloric effects are attained at a magnetic field up to 5 T. Above room temperature (328 K), high inverse magnetic entropy change of 26.8 J/kg K under a 5 T magnetic field is observed around first order magnetostructural transition. The large magnetic entropy change in Ni-Co-Mn-In-Gd alloy is promising for magnetic refrigeration.

Second-Order Magnetic Transition and Low Field Magnetocaloric Effect in Nanocrystalline $$\hbox {Pr}_ {5}\hbox {Co}_{19}$$ Pr 5 Co 19 Compound

Magnetic and magnetocaloric properties have been studied for the $$\hbox {Pr}_{5}\hbox {Co}_{19}$$ compound crystallized in the Ce $$_{5}\hbox {Co}_{19}$$ -type structure (space group $$R\bar{3}m$$ ). We report a large magnetic entropy change ( $$-\triangle S_{{\mathrm{M}}}^{\max }$$ ) at Curie temperature, using the thermodynamic Maxwell’s relation, which reaches a maximum of 5.2 J/(kg K) under a low magnetic field of 0-1.5 T. The temperature dependence of the magnetization and the Arott plots around the second order magnetic transition for this compound are also reported. The temperature dependence of the Landau coefficients has been derived by fitting the magnetization, using the Landau expansion of the magnetic free energy.

Series of Highly Stable Lanthanide-Organic Frameworks Constructed by a Bifunctional Linker: Synthesis, Crystal Structures, and Magnetic and Luminescence Properties.

By utilizing a preselected functional ligand produced by 1 H-imidazole-4,5-dicarboxylic acid, three isostructural lanthanide coordination polymers (CPs), denoted as {[Ln2(OH)2(L)2]·(DMF)·(H2O)4} n (Ln = Gd (1), Eu (2), Dy (3); L = 1-(4-carboxybenzyl)imidazole-4-carboxylic acid), containing a 1D infinite [Ln4(OH)4] subchain have been successfully constructed. The highly connected mode between the multifunctional ligand and 1D building units is responsible for the exceptional chemical stability of three lanthanide CPs. In addition, a study of the magnetic properties reveals that 1 displays a large magnetic entropy change (-Δ Sm = 30.33 J kg-1 K-1 with T = 2 K and Δ H = 7 T). Furthermore, genetic algorithm and quantum Monte Carlo methods were combined to simulate the magnetic coupling parameters of compound 1, shedding light on the effect of linking bridges on magnetic propagation. 2 shows intense luminescence in the range of 350-710 nm. Comparably, magnetic studies of 3 reveal the existence of a metamagnetic transformation from an antiferromagnetic interaction to a ferromagnetic interaction along with a decrease in temperature. Through fitting of the results of HF-EPR measurements, a component of the g tensor is obtained, g|| = 16.4(5), indicating the large anisotropy of 3.

Behavior of the magnetocaloric effect in La0.7Ba0.2Ca0.1Mn1-xSnxO3 manganite oxides as promising candidates for magnetic refrigeration

The magnetocaloric effect along with magnetic phase transition in the peroveskite polycrystalline samples La0.7Ba0.2Ca0.1Mn1-xSnxO3 (x = 0 and 0.1) was investigated. The samples were synthesized using conventional solid state reaction at 1400 °C temperature. Magnetization vs. temperature measurements, under a magnetic field of μ0H = 0.05 T, showed a paramagnetic-ferromagnetic transition at Curie temperature, TC, which decreases from 310 K for x = 0–290 K for x = 0.1. A large magnetic entropy change |ΔSM| deduced from isothermal magnetization curves, has been observed in our samples with a peak centered on their respective TC. Interesting values of the relative cooling power (RCP), 237 J kg-1 for x = 0 and 248 J kg-1 x = 0.1, make these samples promising candidates for magnetic refrigeration around room temperature.

High temperature martensitic transformation and giant magnetocaloric effect in Ni40Co10Mn41Sn9 melt-spun ribbons

We report a large magnetic entropy change associated with a high-temperature martensitic transformation in Ni40Co10Mn41Sn9 (at. %) melt-spun ribbons. The ribbons underwent a first-order forward martensitic transition and a reverse structural transition from the paramagnetic six-layered modulated martensite to a ferromagnetic austenite in the temperature range of 395–380 K. For a magnetic field change of 5 T (2 T), extremely large magnetic entropy changes of 33.9 (25) J kg−1 K−1 and 53 (22) J kg−1 K−1 upon reverse and forward martensitic transformations occurred. These values are among the largest for Ni-Mn based Heusler alloys reported so far. As compared with the large values upon heating, hysteresis losses upon cooling were negligibly low (only 0.36 J kg−1). The present findings open up the possibility of elevated temperature magnetic cooling.

A large reversible room temperature magneto-caloric effect in Ni-TM-Co-Mn-Sn (TM = Ti, V, Cr) meta-magnetic Heusler alloys

Herein, we achieved a large reversible room temperature magneto-caloric effect (MCE) through synergic tuning of martensitic transformation (MT) temperatures and transition entropy change (ΔStr) via micro-alloying with transition metals (Ti, V, and Cr) in Ni45Co5Mn40Sn10 meta-magnetic Heusler alloys (MHAs). By the minor addition of TM, MT temperatures were brought down to below room temperature and ΔStr was reduced while maintaining narrow MT temperature range (ΔT) and large difference in magnetization (ΔM) of Ni45Co5Mn40Sn10 MHA. In particular, Ni43.8Cr1.2Co5Mn40Sn10 MHA exhibited a very large reversible room temperature magnetic entropy change (ΔSM) of 24.5 J/kg·K with a broad operating temperature window of ∼11 K at 5 T. Indeed, the MHA exhibited a very effective refrigeration capacity (RCeff) of 276 J/kg for 5 T, which is the largest value among the reported Ni-Mn-based MHAs. The decrease of ΔStr reduces the magnetic field required for completely reversible MT and accelerates the saturation of ΔSM, which leads to maximum RCeff value in the composition of MHA. Thus, we can conclude that smaller ΔStr with narrow ΔT and large ΔM is a key variable to develop MHA with reversible MCE under low magnetic field, which will ultimately give us a guideline for the tailor-made design of high-performance magneto-caloric materials.

Magnetocaloric effects and electrical resistivity of Ni2Mn0.55CoxCr0.45-xGa – A Heusler alloy system exhibiting a partially-decoupled first-order phase transition

The phase transitions and associated magnetocaloric properties of the Ni2Mn0.55CoxCr0.45-xGa (0 ≤ x ≤ 0.25) Heusler alloy system have been investigated. All samples exhibit a first-order martensitic phase transition, evidenced by a sharp drop in the resistivity versus temperature data and a thermomagnetic irreversibility in the dc magnetization data of the respective samples. Large magnetic entropy changes have also been observed near the phase transitions. The martensitic transformation temperature increases as Cr is partially replaced with Co. Additionally, this substitution leads to a partial decoupling of the magnetic and structural phase transitions, dramatically suppressing any magnetic hysteresis losses. Furthermore, the change in electrical resistivity during the phase transition remains relatively constant across the system, despite major changes in the degree of structural disorder and magnetostructural phase transition coupling. Detailed experimental results and conjectures as to the origin of these behaviors have been provided.

Magnetocaloric effect in the layered organic–inorganic hybrid (CH3NH3)2CuCl4**Project supported by the National Natural Science Foundation of China (Grant Nos. 51371193 and 11534015), the Youth Innovation Promotion of the Chinese Academy of Sciences (Grant No. 2013004), and the Science Fund from the Chinese Academy of Sciences (Grant Nos. XDB07030200 and KJZD-EW-M05).

We present a study of magnetocaloric effect of the quasi-two-dimensional (2D) ferromagnet (CH3NH3)2CuCl4 in ab plane (easy-plane). From the measurements of magnetic field dependence of magnetization at various temperatures, we have discovered a large magnetic entropy change associated with the ferromagnetic–paramagnetic transition. The heat capacity measurements reveal an abnormal adiabatic change below the Curie temperature Tc ~ 8.9 K, which is caused by the nature of quasi-2D layered crystal structure. These results suggest that perovskite organic–inorganic hybrids with a layered structure are suitable candidates as working substances in magnetic refrigeration technology.

Giant magnetic entropy change in gadolinium orthoferrite near liquid hydrogen temperature

The magnetic properties and giant magnetic entropy change in gadolinium orthoferrite have been investigated for their potential application as magnetic refrigeration working media. We found GdFeO3 polycrystalline sample exhibits a large magnetic entropy change value (–ΔSM = 50.2 J/kg K at 70 kOe) near the liquid hydrogen temperature, which is much larger than those of other oxide magnetic refrigerators. The large magnetocaloric effect is related to the half-filled 4f electronic state in rare earth-transition oxides. The large values of these parameters, together with negligible hysteresis, suggest that GdFeO3 multiferroic ferrite could be potential materials for magnetic refrigeration in low-temperature region.

Large magnetic entropy change and prediction of magnetoresistance using a magnetic field in La0.5Sm0.1Sr0.4Mn0.975In0.025O3.

A detailed study of the structural, magnetic, magnetocaloric and electrical effect properties in polycrystalline manganite La0.5Sm0.1Sr0.4Mn0.975In0.025O3 is presented. The X-ray diffraction pattern is consistent with a rhombohedral structure with R3̄c space group. Experimental results revealed that our compound prepared via a sol–gel method exhibits a continuous (second-order) ferromagnetic (FM) to paramagnetic (PM) phase transition around the Curie temperature (TC = 300 K). In addition, the magnetic entropy change was found to reach 5.25 J kg−1 K−1 under an applied magnetic field of 5 T, corresponding to a relative cooling power (RCP) of 236 J kg−1. We have fitted the experimental data of resistivity using a typical numerical method (Gauss function). The simulation values such as maximum resistivity (ρmax) and metal–semiconductor transition temperature (TM–Sc), calculated from this function, showed a perfect agreement with the experimental data. The shifts of these parameters as a function of magnetic field for our sample have been interpreted. The obtained values of β and γ, determined by analyzing the Arrott plots, are found to be TC = 298.66 ± 0.64 K, β = 0.325 ± 0.001 and γ = 1.25 ± 0.01. The critical isotherm M (TC, μ0H) gives δ = 4.81 ± 0.01. These critical exponent values are found to be consistent and comparable to those predicted by the three-dimensional Ising model with short-range interaction. Thus, the Widom scaling law is fulfilled.

Magnetic and magnetocaloric effects of Eu<sub>0.9</sub><i>M</i><sub>0.1</sub>TiO<sub>3</sub> (<i>M</i>=Ca, Sr, Ba, La, Ce, Sm) compounds

EuTiO<sub>3</sub> is a direct band-gap semiconductor material and exhibits antiferromagnetism with large magnetic entropy change around the liquid helium temperature. The ferromagnetic state can be changed into antiferromagnetic state through lattice constant change and electron doping by element substitution due to strong spin-lattice coupling coexistence of ferromagnetic coupling, and antiferromagnetic coupling. The values of magnetic entropy change can be effectively improved under low magnetic field change after changing into ferromagnetism. Samples of EuTiO<sub>3</sub> and Eu<sub>0.9</sub><i>M</i><sub>0.1</sub>TiO<sub>3</sub> (<i>M</i>=Ca, Sr, Ba, La, Ce, Sm) are prepared by the sol gel method. The Eu<sub>0.9</sub>Ca<sub>0.1</sub>TiO<sub>3</sub> exhibits the antiferromagnetism due to similar ion radius. The ferromagnetic coupling between Eu<sub>0.9</sub>Sr<sub>0.1</sub>TiO<sub>3</sub> and Eu<sub>0.9</sub>Ba<sub>0.1</sub>TiO<sub>3</sub> is enhanced, for alkaline earth metal (Sr and Ba) has larger ion radius, which is beneficial to improving the magnetocaloric effect under low magnetic field. Electron doping can inhibit the antiferromagnetic coupling because the extra carrier may occupy the Ti 3d and reduce the hybridization of Eu 4f-Ti 3d-Eu 4f. When the electron doping concentration is greater than 10%, the spin polarization rate of Ti 3d state on the Fermi surface is negative, resulting in the transition from antiferromagnetic to ferromagnetic state. When the Eu ions are replaced with the Sm ions (Sm ion radius is similar to Eu ion radius), the ferromagnetic coupling is enhanced. However, when the Eu ions are replaced with the La or Ce ions, the samples show strong ferromagnetism, for the lattice constant and electron doping are increased. A giant reversible magnetocaloric effect and large refrigerant capacity for each of Eu<sub>0.9</sub><i>M</i><sub>0.1</sub>TiO<sub>3</sub> (<i>M</i>=Sr, Ba, La, Ce) compounds are observed. Under the magnetic field change of 1 T, the values of maximum magnetic entropy change and refrigeration capacity are 9.8 J/(kg·K) and 36.6 J/kg for Eu<sub>0.9</sub>Sr<sub>0.1</sub>TiO<sub>3</sub>, and 10 J/(kg·K) and 45.1 J/kg for Eu<sub>0.9</sub>Ba<sub>0.1</sub>TiO<sub>3</sub>. The values of maximum magnetic entropy change of Eu<sub>0.9</sub>La<sub>0.1</sub>TiO<sub>3</sub> and Eu<sub>0.9</sub>Ce<sub>0.1</sub>TiO<sub>3</sub> are 10.8 J/(kg·K) and 11 J/(kg·K), respectively, which are larger than that of EuTiO<sub>3</sub> (9.8 J/(kg·K)). The values of refrigeration capacity are 39.3 J/kg and 51.8 J/kg, which are also improved compared with those of EuTiO<sub>3</sub>. In a word, the results suggest that these compounds could be considered as good candidates for low-temperature and low-field magnetic refrigerant.

Magnetic and thermodynamic properties of the Pr-based ferromagnet PrGe2−δ

We investigated the magnetization, M, and specific heat, C, of ThSi2-type PrGe2−δ. A polycrystalline sample of PrGe2−δ was prepared by arc-melting. Magnetization divided by magnetic field, M/B, increased sharply and C showed a clear jump at the Curie temperature, TC, of 14.6 K; these results indicate that PrGe2−δ ordered ferromagnetically. The magnetic entropy at TC reached Rln 3, indicating a quasi-triplet crystalline electric field (CEF) ground state. The maximum value of magnetic entropy change was 11.5 J/K kg with a field change of 7 T, which is comparable to those of other right rare-earth based magnetocaloric materials. This large magnetic entropy change was attributed to the quasi-triplet ground state of the CEF.

Effect of Bi substitution on the magnetic and magnetocaloric properties of Ni50Mn35In15-xBix Heusler alloys

The structural, magnetic, magnetocaloric, and transport properties of Ni50Mn35In15-xBix (x = 0, 0.25, 0.5, 1, 1.5) compounds has been studied through X-ray diffraction (XRD), differential scanning calorimetry, and magnetization measurements. A mixture of high temperature austenite phase (AP) and low temperature martensitic phase (MP) was observed from the XRD at room temperature. The saturation magnetization MS at 10 K was found to decrease with increasing Bi content. A shift in the martensitic transition temperature (TM) relative to the parent compound was observed with a maximum shift of ∼ 36 K for x = 1.5. Abnormal shifts in TC and TM to higher temperatures were observed at high field for x ≥ 0.5. Large magnetic entropy changes (ΔSM) of about 40 J/kg K (x = 0) and 34 J/kg K (x = 0.25) were observed at TM with H = 5 T, which reduced significantly for higher Bi concentrations. The doping of small amounts of Bi in the In sites increased the peak width of the ΔSM curves at the second order transition, leading to larger values of relative cooling power. A significant magnetoresistance (-30%) was observed near TM with ΔH = 5T for x = 0.5.

Table-like magnetocaloric effect and large refrigerant capacity in Gd65Mn25Si10-Gd composite materials for near room temperature refrigeration

Amorphous Gd65Mn25Si10 as well as crystalline Gd have technologically significant Curie temperature and large magnetic entropy change. Two types of composite materials Gd65Mn25Si10-Gd were fabricated: laminating Gd sheets and amorphous Gd65Mn25Si10 ribbons (multilayer composite) and hot pressing a mixture of amorphous Gd65Mn25Si10 thin ribbons, Gd particles and a small amount of Sn powders (bulk composite). A table-like magnetocaloric effect (MCE) in a wide, commercially useful, temperature span of 73 K (220 K-293 K) were observed in these composites. The values of full-width at half maximum of (−ΔSM) − T plots (ΔTFWHM) and enhanced refrigerant capacity (RC) for the multilayer and bulk composites are 212 K, 724 J/kg, and 248 K, 617 J/kg, respectively, for a field of 5 T. Large ΔTFWHM and RC values and the table-like (−ΔSM)max feature suggest that both multilayer and bulk Gd65Mn25Si10-Gd composites can meet the requirements of different magnetic refrigeration based on Ericsson-cycle.