Tunable Magnetocaloric Effect Research Articles

Critical behavior and tunable magnetocaloric effect in (Gd1-xErx)3Al2 alloys

The magnetic properties, magnetocaloric effect, and the critical behavior near Curie temperature (TC) were systematically studied in a series of (Gd1-xErx)3Al2 (x = 0, 0.1, 0.2, 0.3) alloys. As the Er content increases, both the TC and lattice constant gradually decrease. The maximum magnetic entropy change and refrigerant capacity remain relatively high, ranging from −5.8 to −8.5J/kg K and 209.0 to 290.8 J/kg respectively, for a field change of 5 T. The critical exponents, derived from the field dependence of magnetic entropy change, conform to scaling theory and are consistent with those obtained using the Kouvel–Fisher method. These findings suggest that the reliability of the obtained critical exponents and imply the presence of long-range exchange interactions in (Gd1-xErx)3Al2 alloys.

Electron tailoring of thermal and magnetocaloric properties in Tb55TM17.5Al27.5 (TM = Fe, Co, and Ni) metallic glasses

Transition metal (TM) elements play a key role in determining properties of magnetocaloric materials. However, the effect of TM elements on the thermodynamic behavior and magnetocaloric effect (MCE) of metallic glasses (MGs) remains elusive. In this work, ternary Tb55TM17.5Al27.5 (TM = Fe, Co, and Ni) MGs without the complexities induced by high-entropy effects were designed. It is found that both the glass transition temperature (Tg) and the initial crystallization temperature (Tx) significantly increase with decreasing 3d electron number. It leads to the low values of Trg, γ, and γm for Tb55Fe17.5Al27.5, which is consistent with its poor glass forming ability (GFA) as evidenced by the obvious lattice fringes and structural order. Despite the mediocre value of magnetic entropy change (|ΔSMpk|) for Tb55Fe17.5Al27.5, its broader magnetic transition temperature of 110.4 K associated with ∼26% evident structural order yields the maximum relative cooling power (RCP) of 546.04 J kg−1 among three MGs. Moreover, a novel weighted method for evaluating 3d electron number by consideration of the concentration and species of TM elements was adopted to reveal an inverse correlation between the 3d electron number and Tg/Tx, as well as curie temperature (Tc), |ΔSMpk|, and RCP. It is found that with the decrease of the weighted 3d electron number of TM elements, the thermal stability of rare-earth-base MGs is effectively enhanced ascribed to the strong f - d orbital hybridization effect, along with the enhanced 3d - 3d exchange interaction that induces a high Tc. This work would help us more deeply understand the role of TM elements from the perspective of electronic structure, which is crucial for designing the novel MGs with a tunable MCE and GFA applied in various cryogenic refrigeration fields.

Tunable magnetocaloric effect towards cryogenic range by varying Mn:Ni ratio in all-d-metal Ni(Co)-Mn-Ti Heusler alloys

Cryogenic magnetic refrigeration is a highly efficient and environmentally friendly technique for gas liquefaction. However, refrigerant materials undergoing large magnetocaloric response at the interesting cryogenic range are dominated by critical elements (mainly rare-earth elements) which impedes practical applicability of such refrigeration systems. Therefore, there is a need for dedicated investigations on optimization of magnetocaloric response at cryogenic range by utilizing compositions that are rare-earth free. In this work, we synthesize the mechanically stable and rare-earth free, all-d-metal Ni35Co15Mn35Ti15 Heusler alloys and investigate the role of varying Mn:Ni ratio on the magnetostructural and magnetocaloric properties of the alloy system. The results of the microstructural characterization indicate homogenous composition for the investigated alloy series. As the Mn:Ni ratio increases from 1.01 to 1.10, the martensitic transition shifts from near-room temperature down to cryogenic region (120–140 K) while the magnetization of the austenitic phase remains unaltered. Isothermal entropy change as high as ∼ 13 J kg−1 K−1 at 1.5 T is achieved for the sample with the highest Mn:Ni ratio at the temperature region for natural gas liquefaction, which significantly surpasses the values previously reported in the literature for similar alloys. In addition to large magnetocaloric response, the martensitic transformation falls in an interesting temperature of the cryogenic region, paving the way for various low-temperature magnetocaloric applications.

Investigation of magnetocaloric effect in La0.67Sr0.33Mn1-xZrxO3

The influence of Zr-doping on the magnetocaloric effect of La0.67Sr0.33Mn1-xZrxO3 manganese perovskites in low magnetic field has been investigated. Using Hamad’s phenomenological model, we have estimated the important magnetocaloric properties, for example, the thermal magnetization, the change of magnetic entropy and the relative cooling power. We have shown that the magnetocaloric properties decrease as the increase of the dopant amount. Tunable magnetocaloric effect in these compounds is advantageous to magnetic refrigeration applications in wide temperature ranges. Therefore, these compounds are good candidates for working materials in magnetic refrigeration.

Estimation of magnetocaloric effect by means of phenomenological model in La0.67Ca0.33-xSrxMnO3 (x=0.035, 0.065) perovskite manganite

The magnetocaloric effect in the perovskite manganite La0.67Ca0.33-xSrxMnO3 with x=0.035, 0.065 have been investigated. Using Hamad’s phenomenological model, we have estimated the important magnetocaloric properties, for example, the thermal magnetization, the change of magnetic entropy and the relative cooling power. Considerable and tunable magnetocaloric effect in these compounds is advantageous to applications in near-room-temperature magnetic refrigeration. Therefore, these compounds are good candidates for working materials in magnetic refrigeration.

Tunable magnetocaloric effect at approximately room temperature by Y-substitution in Ho2Fe17

The structure, magnetic transition and magnetocaloric effect of the intermetallic compounds (Ho2-xYx)Fe17 (x = 0, 0.5, 1 and 1.5) were investigated. The compounds crystallize into a Th2Ni17-type structure with the P63/mmc space group, as determined by Rietveld refinement of the XRD powder diffraction patterns. All the samples undergo a second-order magnetic transition from the ferromagnetic to paramagnetic state, and the Curie temperature decreases from 334 K (x = 0) to 314 K (x = 1.5) with increasing Y content. In the paramagnetic region, the reciprocal magnetic susceptibilities χ−1 for (Ho2-xYx)Fe17 (x = 0.5, 1 and 1.5) obey the Curie-Weiss law. The effective magnetic moment was determined to be 28.97 μB/f.u., 32.88 μB/f.u. and 33.78 μB/f.u., respectively, with corresponding paramagnetic Curie temperatures of 323 K, 308 K and 304 K. The maximum magnetic entropy changes for (Ho2-xYx)Fe17 (x = 0, 0.5, 1 and 1.5) are 3.0 J/kg K, 3.5 J/kg K, 3.8 J/kg K and 4.6 J/kg K, with corresponding refrigerant capacity values of 168 J/kg, 197 J/kg, 263 J/kg and 342 J/kg for a field change of 0–5 T. The tunable Curie temperature and considerable magnetocaloric effect indicate that (Ho2-xYx)Fe17 (x = 0, 0.5, 1 and 1.5) compounds are candidates for room-temperature magnetic refrigerants.

Tunable magnetocaloric effect in Gd-based metallic glasses microalloying elements with different magnetism

In this work, the thermal properties, magnetic behavior and magnetocaloric effect of the Gd55Co17.5Al24.5M3 (M = Mn, Fe and Cu) metallic glasses with minor substitution of elements exhibiting varying magnetisms were investigated. The metallic glasses exhibited good glass-forming ability and underwent a second-order magnetic transition. As compared with the original composition, the Curie temperature was improved by microalloying the antiferromagnetic Mn, nonmagnetic Cu and ferromagnetic Fe. The magnetocaloric properties of the BMGs could be tuned by the microalloying elements with varying magnetisms. The competitive magnetic entropy change of 8.94 J kg−1K−1 and a large relative cooling power of 940 J kg−1 under a field change of 5 T were obtained for the Fe-substituted and Mn-substituted BMGs, respectively. A combination of the large refrigeration capacity and considerable magnetic entropy change makes the Gd55Co17.5Al24.5M3 (M = Mn, Fe and Cu) BMGs attractive refrigerant candidates for application in the active magnetic refrigerators.

Large and tunable magnetocaloric effect in gadolinium-organic framework: tuning by solvent exchange

Magnetic properties of three variants of MOF-76(Gd), {[Gd(BTC)(H2O)]·G}n (BTC = benzene-1,3,5-tricarboxylate, G = guest molecules) were investigated by static susceptibility, isothermal magnetization and specific heat capacity measurements. In the study we used as synthesized MOF-76(Gd)-DMF (1) (G = DMF = dimethylformamide), containing DMF molecules in the cavity system, compound MOF-76(Gd) (2), activated complex without solvents in the cavities and water exchanged sample MOF-76(Gd)-H2O (3). A pronounced change in the magnetic entropy was found near the critical temperature for all three compounds. It was shown, that magnetic entropy change depends on the solvatation of the MOF. The highest value entropy change, ΔSMpk(T) was observed for compound 2 (ΔSMpk(T) = 42 J kg−1 K−1 at 1.8 K for ΔH = 5 T). The ΔSMpk(T) for the compounds 1, 2 and 3 reached 81.8, 88.4 and 100% of the theoretical values, respectively. This suggests that in compound 3 Gd3+···Gd3+ antiferromagnetic interactions are decoupled gradually, and higher fields promote a larger decoupling between the individual spin centers. The observed entropy changes of compounds were comparable with other magnetic refrigerants proposed for low-temperature applications. To study the magnetothermal effect of 2 (the sample with largest −ΔSMpk), the temperature-dependent heat capacities (C) at different fields were measured. The value of magnetic entropy S obtained from heat capacities (39.5 J kg−1 K−1 at 1.8 K for an applied magnetic field change of 5 T) was in good agreement with that derived from the magnetization data (42 J kg−1 K−1 at 1.8 K).

Tunable Magnetocaloric Effect in Ni-Mn-Ga Microwires

Magnetic refrigeration is of great interest due to its high energy efficiency, environmental friendliness and low cost. However, undesired hysteresis losses, concentrated working temperature interval (WTI) and poor mechanical stability are vital drawbacks that hinder its practical application. Off-stoichiometric Ni-Mn-Ga Heusler alloys are capable of giant magnetocaloric effect (MCE) and tunable transformation temperatures. Here, by creating Ni-Mn-Ga microwires with diameter of 35–80 μm using a melt-extraction technique, negligible hysteresis and relatively good mechanical stability are found due to the high specific surface area (SSA) that reduces incompatibility between neighboring grains. The high SSA also favors the element evaporation at high temperatures so that the transformation temperatures can be feasibly adjusted. Tunable magnetocaloric effect owing to different magneto-structural coupling states is realized by (i) composition design and subsequent tuning, which adjusts the temperature difference between the martensite transformation (MT) and the magnetic transition, and (ii) creation of gradient composition distribution state, which manipulates the MT range. Magnetic entropy change ΔSm ~−18.5 J kg−1 K−1 with relatively concentrated WTI and WTI up to ~60 K with net refrigeration capacity ~240 J kg−1 at 50 kOe are demonstrated in the present Ni-Mn-Ga microwires. This criterion is also applicable for other small-sized materials.

Tunable magnetocaloric effect around room temperature by Fe doping in [formula omitted] compound

In this work, we present an investigation of the magnetic and magnetocaloric properties of Mn0.98Cr(0.02-x)FexAs compounds with x=0.002, 0.005 and 0.010. Our findings show that as Fe content increases the unit cell volume decreases, which indicates that Fe doping emulates the pressure effect on the crystalline structure. The transition temperature TC decreases as x increases and it can be set at approximate value of room temperature by changing the doping level. In addition, the magnetic entropy change ΔSM was determined using a discontinuous measurement protocol, and realistic values from the magnetocaloric effect presented by MnAs-type compounds under pressure (emulated pressure) could be obtained. The values of ΔSMMAX are very large, around −11Jkg-1K-1 with ΔH=15kOe, which is higher than that observed for most compounds with TC around room temperature. However, ΔSM is confined to a narrow temperature range of 11K. To overcome this drawback, the composition of a theoretical composite formed by our samples was calculated in order to obtain a table-shaped ΔSM curve. The simulated composite showed a high value of full width at half maximum δTFWHM of 33K, which is much higher than that of single sample.

Magnetocaloric response of amorphous and nanocrystalline Cr-containing Vitroperm-type alloys

The broad compositional range in which transition metal (TM) based amorphous alloys can be obtained, yields an easily tunable magnetocaloric effect (MCE) in a wide temperature range. In some TM-based alloys, anomalous behaviors are reported, as a non-monotonous trend with magnetic moment (e.g. FeZrB alloys). Moreover, in certain Cr-containing Vitroperm alloys anomalously high values of the magnetic entropy change were published. In this work, a systematic study on MCE response of Cr-containing amorphous alloys of composition Fe74-xCrxCu1Nb3Si15.5B6.5 (with x=2, 8, 10, 12, 13, 14 and 20) has been performed in a broad Curie temperature range from 100K to 550K. Curie temperature and magnetic entropy change peak of the amorphous alloys decrease with the increase of Cr content at rates of −25.6K/at% Cr and −54mJkg−1K−1/at% Cr, respectively, following a linear trend with the magnetic moment in both cases. The presence of nanocrystalline phases has been considered as a possible cause in order to explain the anomalies. The samples were nanocrystallized in different stages, however, the magnetocaloric response decreases as crystallization progresses due to the large separation of the Curie temperatures of the two phases.

Study of Magnetic and Magnetocaloric Behaviour of (1 - Y)La0.7Ca0.3MnO3/(Y)MnFe2O4, (1 - Y)La0.7Ca0.3MnO3/(Y)Ni0.9Zn0.1Fe2O4 Composites.

We report the structural, magnetic and magnetocaloric properties of (1 - Y)La0.7Ca0.3MnO3/ (Y)MnFe2O4 (LCMO/MFO) and (1 - Y)La0.7Ca0.3MnO3/(Y)Ni0.9Zn0.1Fe2O4 (LCMO/NZFO) composites. Polycrystalline LCMO/MFO samples were prepared using the conventional solid-state reaction technique. The results of X-ray diffraction indicates mainly LCMO phase without characteristic lines of the MFO and NZFO phase. The magnetic study has revealed that the Curie temperature was influenced by the concentration of MFO and NZFO phases. A large magnetic entropy change has been observed for La0.7Ca0.3MnO3 compound. The value of the maximum magnetic entropy change was found to decrease in the composites samples with increasing the concentration of the MFO and NZFO phases. This investigation suggests that LCMO/MFO and LCMO/NZFO types of composites can give a new kind of refrigeration candidates, which can easily provide the tunable magnetocaloric effect.

Tunable magnetocaloric effect in transition metal alloys.

The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants.

Tunable magnetocaloric effect in Gd-based glassy ribbons

The series of glassy ribbons Gd60M30In10 (M = Mn, Co, Ni, Cu) was synthesized by melt-spinning. The change of transition element M in these Gd-based metallic glasses was proven to induce huge variations of the Curie temperature TC, magnetic entropy change peak values ΔSmpeak, and widths at half maximum values of the magnetic entropy change δT. When M is non magnetic (M = Co, Ni, Cu), the samples behave similarly: they display high values of ΔSmpeak (between -6.6 and -8.2 J/kg K in a magnetic field variation of 4.6 T), average δT values (between 77 and 120 K) and no magnetic hysteresis. On the contrary, when M carries a magnetic moment (M = Mn), some irreversibility appears at low temperature, ΔSmpeak is lower (only 3.1 J/kg K for μ0H = 4.6 T) and the magnetic transition is very large (δT = 199 K for μ0H = 4.6 T). These features are explained by some antiparallel coupling between Mn atoms randomly located in the metallic glass. This leads to the occurrence of a cluster-glass behavior at low temperature (35 K), following the ferromagnetic transition observed at 180 K when the temperature is decreased. Also, power law fittings of ΔSmpeak and δT versus μ0H were performed and show that δT is less field dependent than ΔSmpeak. We could then identify an interesting way of improving the refrigeration capacity of the material at low magnetic field.

Tunable magnetocaloric effect around hydrogen liquefaction temperature in Tb 1−xY xCoC 2 compounds

The magnetic properties and magnetocaloric effect of Tb 1− x Y x CoC 2 ( x=0, 0.1, 0.2, 0.3, 0.4) compounds have been investigated systematically. All the compounds undergo second-order transitions from paramagnetic to ferromagnetic states without thermal and magnetic hysteresis. With increasing Y content from 0 to 0.4, the Curie temperatures decrease nearly linearly from 28 to 18 K. The nature of the second-order phase transitions can be confirmed by Arrott plots. For Tb 0.6Y 0.4CoC 2 compound, the maximum value of the magnetic entropy change –Δ S M at 20 K is 9.35 J kg −1 K −1 for an external field change of 5 T (5.14 J kg −1 K −1 for 2 T). The large reversible magnetic entropy change makes Tb 0.6Y 0.4CoC 2 compound an attractive candidate for the application at hydrogen liquefaction temperature.

Tunable magnetocaloric effect in ceramic perovskites

A large entropy variation (magnetocaloric effect) has been discovered in ceramic perovskites with the formulas La0.65Ca0.35Ti1−xMnxO3−z and La0.5+x+yLi0.5−3yTi1−3xMn3xO3−z. Both Curie temperature and entropy change were studied from 4.2 to 400 K for different stoichiometric compositions and applied magnetic fields. Our conclusion is that these materials are excellent candidates for working materials in magnetic refrigeration and liquefaction devices in a wide temperature range.