Low-field Magnetic Entropy Change Research Articles

Magnetic properties and large low-field magnetocaloric effect of RFe2Si2 (R = Ho, Tm) compounds

Nowadays, magnetic refrigerant technology has drawn much attention for its environmental friendliness. Those magnetic materials possessing giant low-field magnetocaloric effect (MCE) performance are of great importance for practical applications, especially at low temperatures. Herein, we present a detailed study on polycrystalline magnetocaloric compounds HoFe2Si2 and TmFe2Si2. HoFe2Si2 exhibits a transition from antiferromagnetic to paramagnetic phase at 2.2 K, while no long-range magnetic ordering is observed in TmFe2Si2 even temperature down to 2 K. For both compounds, they showed large low-field magnetic entropy change (−ΔSM) with the peak values of 10.6 and 7.9 J kg−1 K−1 under field change of 0–2 T for HoFe2Si2 and TmFe2Si2, respectively, which is comparable or even larger than some low-temperature magnetocaloric materials. In addition, the characteristic of second-order magnetic transitions of both compounds were confirmed on basis of Arrott plots and mean-field theory criterion. The low magnetic ordering temperatures, large low-field MCE performance along with the feature of second order phase transition for HoFe2Si2 and TmFe2Si2 indicate that both compounds are promising candidate for magnetic refrigerant materials at liquid helium temperature.

La0.6X0.1Te0.3MnO3 system with significant refrigerant capacity at low magnetic field and double magnetic entropy change peaks: effect of ball-milling time on physical and critical behaviors

We have investigated the ball-milling time effect on different physical properties of La0.6X0.1Te0.3MnO3 (X is a lacuna) system (LT) milled for 1 h (LT-1h), 3 h (LT-3h), and 6 h (LT-6h). According to Williamson-Hall method, as the ball-milling duration is increased, the material’s crystallite size decreases from approximately 145 to 99 nm for LT-1h and LT-6h, respectively. Electronic study was also investigated. The Zero-Field-Cooling and Field-Cooling (ZFC/FC) magnetization measurements illustrated that all the systems are presenting a ferromagnetic to paramagnetic phase transition around Curie temperature (TC). This transition is around 176, 182, and 183 K accompanied by a decrease in the magnitude in both ZFC and FC data. Thus, increasing the ball-milling time of the sample leads to the elevation of TC and does not enhance the magnitude of the magnetization the fact that it affects the magnetic interactions between atoms. By increasing the ball-milling duration, the proportion of homogeneity is increased, and the material becomes slightly more resilient, according to the Curie-Weiss law. Additionally, it is accompanied with an increase in coercivity and a decrease in the saturation magnetization and remanence. Based on the AC-susceptibility, raising the ball-milling time facilitates the appearance of a spin-glass (SG) state. The relative cooling power (RCP) value in the LT-1h sample at 2 T is 108% (211.758 J kg−1) compared to that of the Gd at 2 T. Consequently, the LT sample could be a permanent magnet in a magnetic refrigerator. Noting that raising the ball-milling time weakens the RCP. Both LT-1h and LT-3h systems are belonging to the tricritical mean field model. However, for LT-6h, the model changed and the best one became the 3D-Ising model. Hence, the ball-milling time influences also the universality class.

Giant low-field magnetocaloric effect in ferromagnetically ordered Er1–xTmxAl2 (0 ≤ x ≤ 1) compounds

Magnetocaloric material is the key working substance for magnetic refrigerant technology, for which the low-field and low-temperature magnetocaloric effect (MCE) performance is of great importance for practical applications at low temperatures. Here, a giant low-field magnetocaloric effect in ferromagnetically ordered Er1–xTmxAl2 (0 ≤ x ≤ 1) compounds was reported, and the magnetic structure was characterized based on low-temperature neutron powder diffraction. With increasing Tm content from 0 to 1, the Curie temperature of Er1–xTmxAl2 (0 ≤ x ≤ 1) compounds decreases from 16.0 K to 3.6 K. For Er0.7Tm0.3Al2 compound, it showed the largest low-field magnetic entropy change (–ΔSM) with the peak value of 17.2 and 25.7 J/(kg K) for 0–1 T and 0–2 T, respectively. The (–ΔSM)max up to 17.2 J/(kg K) of Er0.7Tm0.3Al2 compound for 0–1 T is the largest among the intermetallic magnetocaloric materials ever reported at temperatures below 20 K. The peak value of adiabatic temperature change (ΔTad)max was determined as 4.13 K and 6.87 K for 0–1 T and 0–2 T, respectively. The characteristic of second-order magnetic transitions was confirmed on basis of Arrott plots, the quantitative criterion of exponent n, rescaled universal curves, and the mean-field theory criterion. The outstanding low-field MCE performance with low working temperatures indicates that Er1–xTmxAl2 (0 ≤ x ≤ 1) compounds are promising candidates for magnetic cooling materials at liquid hydrogen and liquid helium temperatures.

Efficiently increasing low-field magnetic entropy by incorporating SO32- into Gd22Ni21 clusters.

The distinct nanosized cluster Gd22Ni21 was isolated using a mixture of anions (SO32- and SO42-) as templates, and to the best of our knowledge, this was the first such 3d-4f cluster to have been developed. Additionally, of a number of 3d-4f heterometallic clusters, Gd22Ni21 showed the largest low-field magnetic entropy change (26.1 J kg-1 K-1) at 2.0 K and ΔH = 2.0 T.

The chain-shaped coordination polymers based on the bowl-like Ln18Ni24(23.5) clusters exhibiting favorable low-field magnetocaloric effect

The design of assembling high-nuclearity transition-lanthanide (3d-4f) clusters along with excellent magnetocaloric effect (MCE) is one of the most prominent fields but is extremely challenging. Herein, two heterometallic metal coordination polymers are constructed via the “carbonate-template” method, formulated as {[Gd18Ni24(IDA)22(CO3)7(μ3-OH)32(μ2-OH)3(H2O)5Cl]·Cl8·(H2O)14}n and {[Eu18Ni23.5(IDA)22(CO3)7(μ3-OH)32(H2O)5(IN)(CH3COO)2(NH2CH2COO)Cl]·Cl6·(H2O)17}n [abbreviated as 1-(Gd18Ni24)n and 2-(Eu18Ni23.5)n respectively; H2IDA = iminodiacetic acid; HIN = isonicotinic acid]. Concerning the structures, compounds 1-(Gd18Ni24)n and 2-(Eu18Ni23.5)n both feature the one-dimensional (1D) chain-like structure which is rarely reported in high-nuclearity metal complexes. Meanwhile, the large presences of Gd3+ ions in compound 1-(Gd18Ni24)n are conducive to the fantastic MCE, and the value of −∆Sm is 35.30 J kg−1 K−1 at 3.0 K and ∆H = 7.0 T. And more significantly, compound 1-(Gd18Ni24)n shows the large low-field magnetic entropy change (−∆Sm = 20.95 J kg−1 K−1 at 2.0 K and ∆H = 2.0 T) among the published 3d-4f mixed metal clusters.

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.

Magnetic phase diagram, magnetocaloric effect, and exchange bias in Ni43Mn46Sn11−xGax Heusler alloys

Abstract In this work, the effect of Ga substitution on the crystal structure, phase transitions, magnetocaloric effect, and exchange bias properties, was systematically investigated in Ni43Mn46Sn11−xGax alloys. With increasing Ga content, the Curie temperature of austenite slightly decreases, while the martensitic transformation temperature shifts to a higher temperature and finally disappears, due to the emergence of γ phase. Large low-field magnetic entropy changes around the martensitic transformation were observed as the transition from a paramagnetic martensitic phase to a ferromagnetic austenitic phase took place. Ni43Mn46Sn11 has a reentrant-spin-glass ground state, and Ga doping can enhance the antiferromagnetic interaction arising from lattice contraction, leading to close of intermediate ferromagnetic windows and establishment of canonical spin-glass for x > 2. Prominently, the zero-field-cooled exchange was achieved in the spin-glass region with 5 ⩽ x ⩽ 10 .

The structural, magnetic and above room temperature magnetocaloric properties of La0.5Sr0.5MnO3 compound

We have carried out the structural properties, magnetization measurements and magnetocaloric effects in La0.5Sr0.5MnO3 perovskite prepared by the solid-state reaction formula. Crystallographic analysis was realized by Rietveld refinement of experimental X-ray diffraction data. Results show that this material has tetragonal crystal structure and exhibits a sharp ferromagnetic-paramagnetic (FM-PM) transition at a Curie temperature TC (352 K). The experimental magnetic entropy change −ΔSM and the relative cooling power (RCP) have been determined. The magnetocaloric data show a moderate low field magnetic entropy change above room temperature. In addition, the RCP values vary from 46.40 to 228.35 J kg−1 upon variation of the applied magnetic field at 1 and 5 T, which is about 56% of the conventional refrigerant Gd material under 5 T. A good agreement is found between the experimental −ΔSM and the one estimated by the Landau theory at the ferromagnetic region. However, the discrepancy at paramagnetic region was assigned to the contribution of itinerant electron to the large magnetic entropy change.

Improvement of low-field magnetic entropy change by increasing Fe concentration in solid-state reactive sintered La(FexSi1−x)13

Solid-state reactive sintering has been carried out in order to fabricate La(FexSi1−x)13 specimens with a higher Fe concentration. No trace of α-Fe was confirmed for x=0.90, while a residual amount of α-Fe less than 0.6vol.% was observed for x=0.91. The net value of the Fe concentration for the La(FexSi1−x) phase in both specimens is confirmed to be close to the nominal value based on the energy dispersion X-ray analyses. Magnetic entropy changes ΔSM=–23 and –24J/kgK is obtained even under the low field change of 0.6T for x=0.90 and 0.91, respectively. Therefore, the low field response of ΔSM is improved owing to an increase in the net value of the Fe concentration in La(FexSi1−x) by the sintering method.

Magnetic properties and magnetocaloric effect in the RCu2Si2 and RCu2Ge2 (R = Ho, Er) compounds

The magnetic properties and magnetocaloric effect (MCE) in RCu2Si2 and RCu2Ge2 (R = Ho, Er) compounds have been investigated. All these compounds possess an antiferromagnetic (AFM)-paramagnetic (PM) transition around their respective Neel temperatures. The RCu2Si2 compounds undergo spin-glassy behavior above Neel temperature. Furthermore, a field-induced metamagnetic transition from AFM to ferromagnetic (FM) states is observed in these compounds. The calculated magnetic entropy changes show that all RCu2Si2 and RCu2Ge2 (R = Ho, Er) compounds, especially, ErCu2Si2 exhibits large MCEs with no thermal hysteresis and magnetic hysteresis loss. The value of −ΔSMmax reaches 22.8 J/Kg K for magnetic field changes from 0 to 5 T. In particular, for field changes of 1 and 2 T, the giant reversible magnetic entropy changes −ΔSMmax are 8.3 and 15.8 J/kg K at 2.5 K, which is lower than the boiling point of helium. The low-field giant magnetic entropy change, together with ignorable thermal hysteresis and field hysteresis loss of ErCu2Si2 compound is expected to have effective applications in low temperature magnetic refrigeration.

Low-field giant reversible magnetocaloric effect in intermetallic compound ErCr2Si2

A giant low-field reversible magnetocaloric effect was reported in ErCr2Si2 compound at ∼4.5 K, which is just above the boiling point of helium. Under a field change of 2 T, the maximum values of magnetic entropy change and adiabatic temperature change are achieved: 24.1 J kg−1 K−1 and 8.4 K, respectively. The low-field giant magnetic entropy change, together with the absence of thermal and field hysteresis, makes the ErCr2Si2 compound an attractive candidate for low temperature magnetic refrigeration.

Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn1+xCo1−xGe alloys

We have investigated the magnetic transition and magnetocaloric effects of Mn1+xCo1−xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn (x = 0.11) gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.

Low-field magnetic entropy changes in (Gd 1–xY x) 3Al 2 alloys

The effects of Y substitution on the magnetic properties and magnetocaloric effect of (Gd 1– x Y x ) 3Al 2 ( x=0-0.3) alloys were investigated by X-ray diffraction and magnetization measurements. All samples crystallized in single phase with Zr 3Al 2-type tetragonal structure. The lattice parameters and magnetic transition temperature decreased obviously with increasing Y content. The magnetic entropy change and refrigerant capacity of these alloys were calculated. The adjustable transition temperature and favorable properties of magnetocaloric effect made these alloys potential candidate as magnetic refrigerant in the temperature range of 190–290 K.

Large reversible high-temperature magnetocaloric effect in [formula omitted] alloys

Accompanied by a second-order paramagnetic to ferromagnetic transition, a large reversible negative Δ S m above room temperature has been observed in Ni 50 − x Mn 38 + x Sb 12 alloys besides low-field magnetic entropy change Δ S m around/below room temperature. A − Δ S m max of 5.21 J kg −1 K −1 is acquired at 347 K in nominal Ni 49 Mn 39 Sb 12 alloy for a magnetic-field change from 0 to 5 T, with a refrigerant capacity of 184 J kg −1. The large reversible Δ S M and the high reversible refrigerant capacity indicate that Ni 49 Mn 39 Sb 12 alloy may be a promising candidate for magnetic refrigeration above room temperature.

Dynamic inverse-magnetocaloric and martensite transition in Ni49Mn38Sn13 nanocrystals in low magnetic fields

Ni49Mn38Sn13 nanocrystals exhibit a sharp transition from a paramagnetic martensite MP to a strongly ferromagnetic austenite phase AF, with a well-defined peak of magnetotherm at 288.1 K (∼15 K peak-width) upon heating in a low magnetic field (a few tens of mT). The Curie point of the austenite phase, = 305 K lies well above the MF phase ( = 228 K). A kind of spin-superheating promotes fast reordering of the nanocrystals with a spin → lattice heat transfer. The low-field magnetic entropy changes as much as 6.8 mJ g−1 K−1 at 1.4 T. Cooling via shows a smaller enthalpy change (−) 8.35 J g−1 from forward transition of 9.18 J g−1 (in part with the superheating) in a calorimetric peak at 284.4 K, with a small hysteresis (−) 12.1 K. A model phase diagram is proposed to describe the transitions with intermediate spin-transport processes.

Structures, magnetic properties, and magnetocaloric effect in MnCo 1−xGe (0.02⩽ x⩽0.2) compounds

The crystalline structures, magnetic properties and magnetocaloric effect (MCE) of MnCo 1− x Ge alloys (0.02⩽ x⩽0.2) have been reported. The crystalline structures of MnCo 1− x Ge ( x⩽0.06) alloys are mainly of TiNiSi-type phase, and Ni 2In-type structure dominates for x>0.06. With decreasing Co concentrations the saturated magnetization of these compounds decreases. Large low-field magnetic entropy change −Δ S M of about 2.3 J/kg K in MnCo 0.94Ge alloy has been obtained for a magnetic field change of 1 T. Moreover, it is found that TiNiSi-type phase exhibits larger −Δ S M than Ni 2In-type one. For MnCo 0.94Ge alloy, considerable low-field refrigerant capacity (RC) (∼460 mJ/cm 3), low coercivity and easy synthesis make these alloys potential candidates for near-room temperature magnetic refrigerants.

Effect of lattice contraction on martensitic transformation and magnetocaloric effect in Ge doped Ni–Mn–Sn alloys

The composition dependences of the structure, martensitic transformation and the magnetocaloric effect in Ni 43Mn 46Sn 11− x Ge x ( x = 0, 1, 2) ferromagnetic shape memory alloys are investigated. These samples all have L2 1 Heusler type structure at room temperature. With the increase of Ge content, the cell volume decreases, and the martensitic transformation temperatures increase rapidly. Large low-field magnetic entropy changes around the martensitic transformation temperatures are observed. Compared to the conventional way to control martensitic transformation temperatures by the adjustment of valence electron concentration, our results indicate that the adjustment of cell volume provides an alternative way to tailor the martensitic transformation and the magnetocaloric effect in ferromagnetic shape memory alloys.

Long-range ferromagnetism and giant magnetocaloric effect in type VIII Eu8Ga16Ge30 clathrates

Long-range ferromagnetism and low-field giant magnetocaloric effect are observed in Eu8Ga16Ge30 with the type VIII clathrate crystal structure, a material that is better known for its thermoelectric properties. Magnetization and modified Arrott plots indicate that the system undergoes a second-order ferromagnetic-paramagnetic phase transition at ∼13K. The low-field giant magnetic entropy change (−ΔSM∼11.4J∕kgK for Δμ0H=3T) coupled with the absence of thermal hysteresis and field hysteresis makes the system very attractive for low temperature magnetic refrigeration. The giant magnetic entropy change originates from the large magnetization (7.97μB per Eu ion) and the sharp change with temperature at the paramagnetic-ferromagnetic transition.

Giant low-field magnetic entropy changes in Ni45Mn44−xCrxSn11 ferromagnetic shape memory alloys

A series of Ni45Mn44−xCrxSn11 (x = 0, 1, 2) ferromagnetic shape memory alloys were prepared. With slight doping of Cr, the martensitic transition temperatures decrease rapidly. The magnetic entropy changes at a low magnetic field were investigated in these alloys. The maximum value of ΔSM is 23.4 J kg−1 K−1, which was observed in Ni45Mn43CrSn11 alloys. The origin of the magnetic entropy changes in these alloys has been discussed. The giant low-field magnetic entropy changes and low cost make Ni45Mn44−xCrxSn11 alloys a promising candidate for magnetic refrigeration.

The study of low-field positive and negative magnetic entropy changes in Ni43Mn46−xCuxSn11 alloys

A series of Ni43Mn46−xCuxSn11 (x=1, 2, and 3) alloys was prepared by the arc melting method. The martensitic transition shifts to a higher temperature with increasing Cu concentration. The isothermal magnetization curves around the martensitic transition temperature show a typical metamagnetic behavior. Under a low applied magnetic field of 10kOe, positive values of magnetic entropy change around the martensitic transition temperature are 14.1, 18.0, and 15.8J∕kgK for x=1, 2, and 3, respectively. While in the vicinity of the Curie temperature of the austenitic phase, these negative values are 1.1, 1.0, and 0.9J∕kgK for x=1, 2, and 3, respectively. The origin of the large entropy changes and the potential application for Ni43Mn46−xCuxSn11 alloys as a working substance for magnetic refrigeration are discussed.