Value Of Magnetocaloric Effect Research Articles

Hourglass-Shaped Homo- and Heteronuclear Nonanuclear Lanthanide Clusters: Structures, Magnetism, Photoluminescence, and Theoretical Analysis.

Synthesis of nonameric cationic clusters [Dy9(acac)16(μ3-OH)8(μ4-OH)2]OH·6H2O (1), [Dy8Tb (acac)16(μ3-OH)8(μ4-OH)2]OH·2H2O (2), and [Gd9(acac)16(μ3-OH)8(μ4-OH)2]OH·6H2O (3) (acac = acetylacetonate) is reported. The emission spectrum of 1 shows Dy(III) ion characteristic bands assignable to the 4F9/2 → 6HJ (J = 15/2 to 9/2) transitions. Emission due to both Dy(III) and Tb(III) ions is observed for 2 in the visible range, with Tb(III) specific bands appearing due to the 5D4 → 7FJ (J = 6, 4, and 3) transitions. Cluster 3 exhibits a significant magnetocaloric effect (MCE), with -ΔSm values increasing with decrease in temperature and increase in field, reaching -ΔSmmax = 20.98 J kg-1 K-1 at 2 K and 9 T. Isotropic magnetic coupling constants (Js) in 3 derived from density functional theory (DFT) calculations reveal that the exchange interactions are antiferromagnetic and weak. Compound 3 possesses S = 7/2 ground state arising from the central Gd(III) ion along with several nested excited states due to competing antiferromagnetic interactions that yield reasonably large MCE values. Utilizing computed exchange coupling interactions, we have performed ab initio CASSCF/RASSI-SO/POL_ANISO calculations on antiferromagnetic 1 and 2 to estimate the exchange interactions using the Lines model. For 2, Dy(III)···Tb(III) exchange interactions were extracted for the first time and were found to be weakly antiferromagnetically coupled.

Sublimed fine-grained dysprosium: Significant magnetocaloric effect

As is known, rare-earth metals (REMs) are promising magnetocaloric materials. The magnitude of the magnetocaloric effect (MCE) of REMs significantly depends on their purity. This paper presents results of studies of the magnetic and magnetocaloric properties of sublimed dysprosium, prepared in the course of the present study, with an emphasis on its impurity and structure perfection. The comprehensive analysis of the chemical composition of sublimed dysprosium, which was performed for the first time by atom probe tomography, showed that the metal corresponds to high-purity rare-earth metals (3 N+). The MCE effect was studied using direct measurements of the adiabatic temperature change (ΔTad) in pulsed (up to 50 T) and steady (up to 14 T) magnetic fields. The studies of the MCE of polycrystalline sublimed Dy by direct method showed that the high ΔTad value for sublimed Dy are comparable with those obtained for single-crystal Dy in magnetic fields up to 5 T. The vacuum sublimation, which is more economical and technologically advanced in contrast to single crystal growing, can be used to create magnetocaloric REM-based materials with high MCE values.

Phase transitions and the magnetocaloric effect in (Gd,Tb)5Si2Ge2 compounds doped with Ti

We have conducted the study of structural, magnetic, magnetothermal, and magnetoelastic properties of four rare-earth compounds: Gd4.5Tb0.5Si2Ge2, Gd4TbSi2Ge2, Gd4.4Tb0.5Ti0.1Si2Ge2, and Gd3.9TbTi0.1Si2Ge2 in the vicinity of magnetically induced phase transitions. We demonstrate that the introduction of Ti into the rare-earth sublattice separates the structural and magnetic phase transitions and changes the order of magnetic phase transition from type I to II, while preserving high values of magnetocaloric effect (MCE). Additionally, incorporating a small quantity of Tb enables the creation of compounds with enhanced MCE values over a specific temperature range of 240–290 K. The observed phenomena can be attributed to the combined effects of forced magnetization and alteration of magnetic susceptibility during the structural phase transition that accompany the magnetic phase changes in these compounds.

Magnetocaloric Effect in Half-Doped and Self-Doped Manganites: A Study to Green Refrigeration

Magnetic refrigeration has emerged as a promising and environmentally friendly technology due to its high efficiency and eco-friendly nature. It is becoming a strong competitor to traditional gas refrigeration and is often referred to as a green refrigeration technique. This technique utilizes the magnetocaloric effect (MCE) or inverse magnetocaloric effect (IMCE) to achieve a change in temperature after adiabatic demagnetization. Among various magnetocaloric materials, perovskite manganites have drawn significant attention due to their abundance and low field MCE. In this paper, a comparative study of MCE has been presented for two different types of manganites. The self-doped La0.9MnO3 shows a considerable amount of MCE (2.5 J/Kg-K) at an applied magnetic field of 10 kOe around 255 K. In contrast, Pr0.5Sr0.5Mn0.98Cr0.02O3another manganite, shows a comparably lower value of MCE (0.55 J/Kg-K) around 220 K under the same magnetic field, but it exhibits a large IMCE (1.26 J/Kg-K) around 150 K. This comparative study provides insights into the magnetocaloric properties of these manganites, which could have potential applications in green refrigeration.

Adjusting of the performance characteristics of the La(Fe,Si)13 compounds and their hydrides for multi-stimuli cooling cycle application

The use of multi-stimuli materials is a promising approach for increasing the cooling capacity of magnetic refrigerators. The working body undergoes both a magnetic field and an external compressive pressure during cooling. The proposed material must have outstanding magnetocaloric and mechanical properties. The magnetocaloric properties should provide a high adiabatic temperature change value in a limited field range. Mechanical stability at high pressures and adequate geometry are required to ensure high heat transfer values. The compounds La(Fe,Si)13 and their hydrides are the most suitable for the manufacture of such devices. They are able to work at both room and cryogenic temperatures. In the article, we present the results of direct measurements of the magnetocaloric effect and mechanical compression tests of the cast and hydrogenated La(Fe,Si)13Hδ rods. The samples were reinforced with a secondary alpha-iron phase, which ensured their mechanical integrity during hydrogenation and cycle performance. The addition of a secondary alpha-iron phase leads to a decrease in the magnetocaloric effect value. Therefore, we determine the optimal content of the secondary phase, which provides a balance between the caloric and mechanical alloy properties.

Structure of Ni44.4Mn36.2Sn14.9Cu4.5 alloy applicable for thermomechanical treatment

Ni-Mn-Sn Heusler alloys exhibit a significant value of magnetocaloric effect. A disadvantage of these alloys is their high brittleness in the as-cast state, but their ductility can be increased by a thermomechanical treatment. The results of a study of thermal treatment for achieving a structure of Ni44.4Mn36.2Sn14.9Cu4.5 alloy applicable for further thermomechanical treatment are presented. It is shown that after argon-arc melting and cooling of the ingot in a water-cooled copper crucible, the structure is characterized by two phases that are quite similar in composition and have no clear phase boundaries. After homogenization annealing at 860°C for 24 hours and slow cooling, a two-phase state with regions enriched in Cu atoms is observed. It is possible to preserve the single-phase structure of the high-temperature state by quenching from the annealing temperature. In order to imitate the temperature regime of thermomechanical treatment, the alloy in the single-phase quenched state was subjected to annealing at 700°C for 1 hour and slow cooling. An analysis of the microstructure shows that, as a result, it remains in the same single-phase state. Thus, a mode of heat treatment of the Ni44.4Mn36.2Sn14.9Cu4.5 alloy, which makes it possible to achieve the applicable structure for further thermomechanical treatment, was selected.

Room temperature giant magnetocaloric effect in Pd doped FeRh and the effect of martensitic transition

FeRh 0.8 Pd 0.2 is known to exhibit near room-temperature first-order antiferromagnetic (AF)–ferromagnetic (FM) transition, typical of chemically ordered FeRh system. In addition, it is also reported to show martensitic transition at a lower temperature. In this work, the effect of sample history on transition temperature (Tt) and the magnetocaloric effect (MCE) have been studied. The experimentally determined MCE parameters across FM to AF transition induced either by isothermal magnetic field sweep or by temperature sweep showed a large isothermal change in entropy around room temperature, i.e., 14 J/kg K for 50 kOe magnetic field change, whereas MCE corresponding to AF–FM transition depends on cooling history. Our study shows that in the presence of martensite phase, the peak value of MCE is shifted to higher temperatures but with significantly reduced magnitude.

Magnetocaloric properties of La0.9Pr0.1Fe11.2Co0.7Si1.1 compound through direct measurements under cyclic magnetic fields up to 30 Hz

Direct measurements of the adiabatic temperature change (ΔTad) in cyclic magnetic fields with a frequency of up to 30 Hz in the La0.9Pr0.1Fe11.2Co0.7Si1.1 alloy were carried out. For this alloy, the magnetocaloric effect (MCE) under magnetic field change of 1.8 T is 2.8 K and the temperature hysteresis does not exceed 0.5 K. Under magnetic field change of 0.62 T with frequencies of up to 20 Hz, the MCE shows a weak frequency dependence (less than 5%), while under magnetic field change of 1.2 T the frequency dependence is clear pronounced. Long-term exposure to a low frequency cyclic magnetic field does not result in a change in the MCE value, while at frequencies more than 10 Hz noticeable degradation of the MCE is observed. The results of the study show that the upper limit of the operation of magnetic refrigerators can reach several tens of Hz.

Effects of composition variation and hydrogenation on magnetocaloric properties of the (Gd1-xTbx)Ni (x = 0.1; 0.9) compounds

To identify promising magnetic refrigerant materials, we have studied the influence of composition variations and hydrogenation on the magnetocaloric effect (MCE) of the (Gd1-xTbx)Ni compounds. The end compositions of the series, Gd0.9Tb0.1Ni and Gd0.1Tb0.9Ni crystallize in orthorhombic CrB-type and monoclinic TbNi-type structures, respectively. Hydrogenation boosts the unit cell volume of (Gd,Tb)Ni by more than 20 % upon absorption of 4 at.H/f.u. Hydrogen absorption changes the structure type from TbNi to the CrB-type in Gd0.1Tb0.9Ni. Decrease of the Curie temperature in hydrides reaches ∼ 60 K. The magnetocaloric effect in (Gd,Tb)NiHy (y = 0 and 4) obtained by indirect method in the vicinity of TC revealed similar values of the maximum of specific isothermal entropy change -ΔST = 20.5 J kg−1 K−1 for Gd0.9Tb0.1Ni and its hydride Gd0.9Tb0.1NiH4 at μ0ΔH = 7 T. We show that the controlled synthesis of hydrides allows us to tailor the magnetocaloric effect in the multicomponent rare earth intermetallics and obtain materials with largely different TCs but with the same MCE values that are attractive for use in low-temperature magnetic cooling applications.

Magnetocaloric Effect in a Ni2.25Mn0.75Ga0.93Si0.07 Alloy

The results of a study of the magnetocaloric effect (MCE) in Ni2.25Mn0.75Ga0.93Si0.07 alloy are presented in the cast state and in the state after multi-axial isothermal forging (MIF) at 700°C and true degree of deformation e = 3.19. It is shown that as a result of MIF, the initial equiaxed microstructure is transformed into a bimodal one in which large grains 100–200 μm in size are surrounded by a layer of fine-grained microstructure.As a result of MIF, the range of martensitic transformation is slightly shifted to the region of low temperatures by about 5°C. The analysis of phase transformations in the region of room temperatures shows that the intervals of martensitic and magnetic phase transformations are superimposed on each other. The MCE value in a magnetic field of 1.8 T is 0.59ºC in the initial cast state, and as a result of forging it decreases to 0.55°C.

Inverse Magnetocaloric Effect in Mn5Si3 Compound

A direct method was used to study the magnetocaloric effect (MCE) for samples of the compound Mn5Si3 under adiabatic conditions in magnetic fields up to 2 T at cryogenic temperatures in the range from 25 to 125 K. According to the results of measurements, it is shown that at temperatures near the first-order metamagnetostructural phase transition from a noncollinear antiferromagnetic to a collinear antiferromagnetic state, both inverse and сonventional MCE are observed. The maximum value of the inverse MCE was ΔTad = –0.27 K at initial temperature T0 = 55 K in a magnetic field of 2 T. Conventional MCE with maximum value ΔTad = +0.23 K is observed at T0 = 70 K in a field of 2 T.

Unravelling the nature of spin reorientation transition in quasi-2D vdW magnetic material, Fe[formula omitted]GeTe[formula omitted

Fe4GeTe2, a recently discovered van der Waals magnet, hosts rather complex magnetic phases with two distinct transitions: paramagnetic to ferromagnetic at around TC∼ 266 K and another spin reorientation transition (SRT) at around TSRT∼ 100 K, unlike the other family member (Fe3GeTe2). Understanding the magnetic phases, nature of phase transitions and magnetic anisotropy have both fundamental and technological importance. Here, we report a detailed investigation of magnetization (M (T, H)), magneto-caloric effect (MCE), and heat capacity (Cp) in Fe4GeTe2 single crystal prepared via chemical vapor transport (CVT) method to shed light on the nature the magnetic transitions and the magnetic anisotropy, in particular, near the spin reorientation transition. M (T) measurements exhibit a prominent thermal hysteresis in proximity to TSRT, implying the first-order nature of SRT. A change in magnetic easy axis around SRT observed from M (T) and M (H) concludes a magnetic anisotropy is present at around TSRT. SRT is further observed in Cp (T) measurement, in terms of a prominent anomaly around SRT, suggesting the transition as real thermo-magnetic. Not only that we observe a higher MCE value near TSRT in comparison to near TC (near TC, -ΔSMmax = 1.95 and 1.99 J Kg−1K−1 and near TSRT, -ΔSMmax= 3.9 and 2.4 J Kg−1K−1 along H∥ab and H∥c, respectively, at 50 kOe magnetic field). The scaling analysis of MCE at TC, shows that the rescaled ΔSM(T,H) follows a universal curve confirming the second-order character of the ferromagnetic transition, while the same analysis breaks down at TSRT, suggesting that SRT is indeed not a second order phase transition. Thus, our experimental findings not only confirm the first-order nature of SRT at round 100 K in Fe4GeTe2, but provide additional insight into the complex spin texture with the possibility of canted or ferrimagnetic ordering.

Elastocaloric-like effect in strain-mediated Mn3SnC/PZT magnetoelectric hetero-composite for solid-state refrigeration

Concerning the part of global warming caused by conventional refrigerant gasses, past decades of research on solid-state cooling technologies based on caloric effects present an attractive alternative with zero-greenhouse gas emission and higher operating efficiency. However, the search for materials with large caloric effects near room temperature has become a challenge in modern material physics. Mn-based antiperovskite compounds are favorable caloric materials which generate a reversible enthalpy change by applying an external field. We report a novel approach of piezo-enhanced elastocaloric-like effect on Mn3SnC for solid-state refrigeration application. In the as-designed Mn3SnC/PZT magnetoelectric hetero-composite, the reversible caloric effect of Mn3SnC was regulated by the electric field-induced strain in the PZT piezoelectricity layer without any external magnetic field. In addition, we proposed an experimental setup for the direct adiabatic temperature change measurement of the caloric effect. The adiabatic temperature change is as high as ∼ 0.57 K at 280 K under an electric field of 0.8 kV/cm, which is approximately 2 factors larger than that of the magnetocaloric effect value of Mn3SnC under 3 T. By adopting the first-principles theory, we estimated the entropy change is approximately 2.6 J Kg−1 K−1 at 280 K which is close to the previous reports. This work demonstrates a novel approach to effectively enhance reversible caloric effects in first-order phase transition materials via electric fields.

Effect of Mn-site doping on the magnetofunctional behaviors of Mn5Si3 alloy

Present work reports a detailed investigation on the magnetoresistance and magnetocaloric behavior of Ni and Cr-doped Mn5Si3 alloys with general formula Mn5−xAxSi3 (where A = Ni/Cr; x = 0, 0.05, 0.1 and 0.2). Both pure (undoped) and doped alloys show a reasonably large amount of magnetoresistance (MR). Doping at Mn-site, both by Ni and Cr, results in a monotonic decrease in MR values. Magnetocaloric effect (MCE), on the other hand, is found to be interesting, and all the alloys show both conventional and inverse MCE around the magneto-structural transition temperature. Among the two types of MCE observed, the inverse MCE is found to decrease with increasing doping concentration and consistent with the MR behavior, whereas doping results in a significant increase in conventional MCE values.

Magnetocaloric and Mössbauer effects studies of the multicomponent Tb-Dy-Ho-Co-Fe-H compounds with a Laves phase structure near the Curie temperature

In this work, the effects of substitutional elements on the magnetism of complex rare-earth-transition metal compounds RT2 with the Laves phase structure are studied with the aim to find new materials with high magnetocaloric effect (MCE) above room temperature. We determine the main regularities in the MCE magnitude variation when varying composition of the Tb-Dy-Ho-Co-Fe alloys and also after hydrogenation. The crystal structure of the compounds is characterized by X-ray diffraction in a wide temperature range while information on the magnetic properties of the 3d-transition metal sublattice is accessed by means of the 57Fe Mössbauer effect studies. We design a series of Tbx(Dy0.5Ho0.5)1-xCo1.75Fe0.25 samples with constant MCE values, suitable for the use as cooling elements of devices operating at elevated temperatures.

Study of Heat Treatment Effect in MnCoGe Compound on Stucture and Electric Properties

A comprehension about magnetic refrigeration which develops strong materials as the refrigerant will be explained and develop in this project. Magnetic refrigeration comes from magnetocaloric effect (MCE) which is magnetic material known as refrigerant that react with a magnetic and demagnetic field. Refrigerant plays the roll in control the performance of magnetic refrigerator. One of interesting refrigerant is MnCoGe compound which found very favourable in produce high value of MCE. From this point of view, the process of producing of MnCoGe using ball milling treatment and heat treatment had been studied. Variable of temperature in heat treatment process and following by cooling down to room temperature have been implemented in order to produce good structure of MnCoGe compound. Furthermore, from structure properties measurement found this compound produce three type of structures which are hexagonal, orthorhombic and mix structure (hexagonal and orthorhombic). Based on the different temperature of heat treatment, it indicate for 1500o C and 1200o C treatment are dominant to the hexagonal structure type, then for 1000o C dominant to the orthorhombic structure and lastly for 1100o C dominant to mix structure. Electric properties measurement found the frequency play the role in change the structure as well as in 1000o C compound was found below 5M Hz frequency show the hexagonal structure and when increasing above 5M Hz the pattern change to orthorhombic structure respectively. Moreover, for the permittivity measurement it gives the information about conductivity and tan delta value. Systematically at 1000o C compound found this material is more to conductor behavior compare others compound. Therefore, when the temperature is increased to 1100o C, 1200o C and 1500o C then the conductivity value decreasing and its resistivity value become increasing.

Table-like shape magnetocaloric effect and large refrigerant capacity in dual-phase HoNi/HoNi2 composite**Project supported by the National Natural Science Foundation of China (Grant No. 51690162), Science and Technology Committee of Shanghai, China (Grant No. 19ZR1418300), Independent Research and Development Project of State Key Laboratory of Advanced Special Steel, Shanghai Key Laboratory of Advanced Ferrometallurgy, Shanghai University (Grant No. SKLASS 2019-Z003), and

Nowadays, magnetic cooling (MC) technology by using the magnetocaloric effect (MCE) has attracted extensive research interest for its promising practical applications. A constant large/giant MCE covers wide refrigeration temperatures (denote as table-like shape) is beneficial for obtaining high efficiency performance for MC. In this paper, the HoNi/HoNi2 composite was successfully synthesized by arc-melting method and proved to be composed of HoNi and HoNi2 crystalline phases with weight ratios of 52.4 wt.% and 47.6 wt.%, respectively. The maximum magnetic entropy change () is 18.23 J/(kg⋅K), and the refrigerant capacity values RC1, RC2, and RC3 are 867.9 J/kg, 676.4 J/kg, and 467.8 J/kg with ΔH = 0–70 kOe, respectively. The table-like shape MCE and large refrigerant capacity values make the composite attractive for cryogenic MC using the Ericsson cycle.

Large rotational magnetocaloric effect in GdVO4 single crystal

The magnetic properties and magnetocaloric effect (MCE) in GdVO4 single crystal have been investigated systematically. In addition to the previously reported spin-flop transition at 1 T along the c-axis, other spin-flop transitions also occur along the a and b axes at 1.7 T. Meanwhile, prominent magnetic anisotropy is observed below the paramagnetic temperature, which leads to evident distinction of negative magnetic entropies along the a, b, and c axes. The maximum negative magnetic entropy −ΔSM along the three axes are 45.91, 46.17, and 56.03 J/kg × K, respectively, at H = 7 T. The anisotropic MCE between the c and a, b axes also induces large rotational MCE (RMCE) in the bc plane, with the maximum value −ΔSR,bc reaching 10.1 J/kg × K at H = 7 T. These remarkable MCE and RMCE values at low temperatures make the GdVO4 single crystal a potential candidate for applications in cryogenic magnetic refrigeration areas.

Specific heat, electrical resistivity, and magnetocaloric study of phase transition in Fe48Rh52 alloy

In this paper, we focus on understanding the magnetic field and temperature dependences of the heat capacity CP, electrical resistivity ρ, and magnetocaloric effect ΔTad in Fe48Rh52 alloy near room temperatures. The phase diagram is constructed according to the CP(H, T) and ρ(H, T) data, and the field shift of the critical temperature is found to be 9.6 K/T. The experimental results on the heat capacity do not confirm the existing assumption about the electronic nature of the antiferromagnet–ferromagnet phase transition in the FeRh alloy. An increase in resistance through the ferromagnetic–antiferromagnetic phase transition is explained by a sharp decrease of the carrier density and simultaneously the appearance of an additional conducting channel. The adiabatic temperature change ΔTad at a field change of 1.8 T equals −9.8 K, and the maximum value of the entropy change ΔS estimated from CP(H, T) and ΔTad(H, T) data is equal to 12.8 J/kg K. The differences in the magnetocaloric effect values in the heating and cooling run in weak magnetic fields are explained based on the thermal expansion data. An almost reversible degradation of the magnetocaloric effect was discovered upon the continuous application of a cyclic magnetic field at temperatures near the magnetostructural transition.

Multifunctional phenomena in Tb-Dy-Gd(Ho)-Co(Al) compounds with a Laves phase structure: Magnetostriction and magnetocaloric effect

Abstract This paper presents a review and results of a comparative study of the magnetocaloric and magnetostriction properties for the four multicomponent systems TbxDyyGdzCo2, TbxDyyHozCo2, TbxDyyGdz(Co,Al)2 and TbxDyyHoz(Co,Al)2 (x + y + z = 1). All compounds have a Laves-phase MgCu2-type structure at room temperature. A magneto-structural phase diagram is constructed for the compounds under study. We showed that the Curie temperatures (TC), the values of magnetocaloric effect (MCE) and volume or anisotropic magnetostriction can be tuned by variation of element concentration in the rare-earth and cobalt sublattices. When lattice parameter a increases from ∼0.718 to 0.722 nm for Al-free compositions, the Curie temperature grows (from ∼100 to 300 K), respectively. Partial substitution of Co by Al in the studied compounds also leads to an increase in Curie temperature. An important feature of multicomponent RCo2-type compounds (unlike pseudo-binary systems, e.g. (Tb,Dy)Co2) is a weak MCE and volume magnetostriction dependence on the composition both within each of the systems and between the groups (TbxDyyGdzCo2 and TbxDyyGdz(Co,Al)2) when the Curie temperatures of the samples TC > 170 K. Regular recurrence and/or change of the magnetic properties across the varied composition of the compounds allows us to find materials with desired magnetic characteristics such as TC, MCE, and magnetostriction, to use them in practice.