Giant MCE Research Articles

Anisotropic Metamagnetic Spin Reorientation and Rotational Magnetocaloric Effect of Single Crystal NdAlGe.

Magnetic anisotropy strongly influences the performance of the magnetocaloric effect. We investigated the magnetocaloric properties of the NdAlGe single crystal with I41md structure. The temperature-dependent magnetization revealed significant anisotropic properties; stable antiferromagnetic transition at TN = 6 K for H//a and meta-magnetic spin reorientation at low temperature (T ≤ 5 K) within an intermediate field (H = 2 T) for H//c. During the metamagnetic spin reorientation, the abrupt change of the magnetic entropy leads to a significant magnetocaloric effect with negative magnetic entropy change (∆SM) by -13.80 J kg-1 K-1 at TC = 5.5 K for H = 5 T along the H//c axis. In addition, the antiferromagnetic state for H//a shows the inverse magnetocaloric effect(I-MCE) by positive entropy change ∆SM = 2.64 J kg-1 K-1 at TN = 6 K for H = 5 T. This giant MCE accompanied by the metamagnetic transition resulted in a significantly large relative cooling power (158 J/kg at H = 5 T) for H//c. The giant MCE and I-MCE can be applied to the rotational magnetocaloric effect (R-MCE) depending on the crystal orientations. NdAlGe exhibits rotational entropy change ∆Sc-a = -12.85 J kg-1 K at Tpeak = 7.5 K, H = 5 T. With comparison to conventional MCE materials, NdAlGe is suggested as promising candidate of R-MCE, which is a novel type of magnetic refrigeration system.

Transformation of magnetic ordering in MnCo1-xNixGe (x = 0–0.6) alloys, its investigations on structural, transport, magnetic, and magnetocaloric properties

In the latest study, physical behaviour of (structure, transport, magnetism, and magnetocaloric effect, critical exponents studies) MnCo1-xNixGe (x = 0, 0.2, 0.4, 0.6) intermetallic alloys are enquired. The parental MnCoGe reveals doublet-orthorhombic at ambient temperature, while doping up Ni crystallographic structure is renovated from the mixed-phase of Orthorhombic-Hexagonal to complete hexagonally crystallized by confirmation of high-temperature XRD. From the transport measurements, Semiconductor (x = 0.2) to metallic (x = 0.4, 0.6) transitions are appeared. The suppression of magneto-structural transitions (MST’s), First [(AFM-FM)-(TM)] to Second [(FM-PM)-(TCA)] order transformation are recognized from thermo-magnetic measurements [M (T)]. The presence and absence of Field-Induced Meta Magnetic Transitions (FIMMT) for parent (x = 0) and doped (x = 0.2, 0.4, 0.6) samples have appeared from isothermal magnetization curves [M (H)]. Giant MCE is perceived near RT (303 K) for x = 0 and decreases for Ni-doped samples by dropping temperatures. The change in magnetic entropy (ΔSM) decreases with increasing Ni substitution. Refrigeration capacity (RC) linearly increases with magnetic field for all samples and decreases with Ni compositions.

Tuning transition temperature of magnetocaloric Mn1.8Fe0.2(P0.59Si0.41)x alloys for cryogenic magnetic refrigeration

Giant magnetocaloric effect in Mn1.8Fe0.2(P0.59Si0.41)x ( x = 1.00, 1.01, 1.02, 1.03, 1.04) alloys is assessed for cryogenic temperature applications. We found that the Curie temperature can be tuned from. 300 K to 99 K by increase of Mn/Fe and P/Si ratios. We systematically optimized metal/non-metal ratio and homogenization condition to maximize the volume fraction of the Fe2P-type phase. A giant isothermal magnetic entropy changes of 10.6 and 14.0 J/kgK under a magnetic field of 2.0 and 5.0 T is obtained at 117.0 K for Mn1.8Fe0.2(P0.59Si0.41)1.03 alloy. This work demonstrates low-cost Mn-Fe-P-Si alloys with giant MCE are competitive candidates compare to the rare-earth-containing magnetocaloric compounds for cryogenic applications.

Investigations on Cu induced couple-decoupled magneto-structural transition in MnCoGe alloys

We have investigated structural, transport, magnetic, and magnetocaloric properties of MnCo1−xCuxGe (x = 0, 0.2, 0.4, 0.6) alloys. The non-magnetic (Cu) atom is doped at the Co site which modifies both the structure and electrical properties. The magneto-structural transition changes the order of transition [1st (AFM-FM) to 2nd (FM-PM)]. Giant MCE is observed ∼RT (307 K) for (x = 0) and it’s decreases for doped samples. The change in magnetic entropy (∆SM) decreases with Cu doping. Refrigeration Capacity (RC) linearly increases with magnetic field and decreases with Cu doping. The order of transitions are confirmed for x = 0.2, 0.4, 0.6 alloys by the analysis of critical exponents via modified Arrott plots and Kouvel-Fisher method. The Landau coefficients, spontaneous magnetizations and local exponent from isothermal curves are also estimated. The both value of Sommerfeld and Debye coefficients are seen to increas by Cu substitution.

Giant low-field magnetic refrigeration in EuTi1−xAlxO3 (x = 0.05, 0.1 and 0.15) compounds

Abstract The EuTi1−xAlxO3 (x = 0.05, 0.1 and 0.15) compounds exhibit the ferromagnetic state. A giant reversible MCE of EuTi1−xAlxO3 (x = 0.05, 0.1, 0.15) compounds was observed, which was attributed to the increase of ferromagnetic ordering. With increasing the Al content, the value of −ΔSMmax is increased from 11.6 J/kg K to15.6 J/kg K for EuTi1−xAlxO3, and the RC values are 48.4 J/kg for EuTi0.95Al0.05O3, 53.1 J/kg for EuTi0.9Al0.1O3 and 58.2 J/kg for EuTi0.85Al0.15O3 with magnetic field change 0–1 T. Additionally, the maximum value of ΔTad is 4.7 K for EuTi0.85Al0.15O3 compound as magnetic field changes 1 T. The EuTi1−xAlxO3 with giant −ΔSM, large RC and large ΔTad suggest an important material for magnetic refrigerant at low-temperature.

A giant magnetocaloric effect in EuTi0.875Mn0.125O3 compound

The magnetic properties and magnetocaloric effect of EuTi0.875Mn0.125O3 compounds are investigated. EuTi0.875Mn0.125O3 compounds show the ferromagnetic to paramagnetic magnetic transition at Tc = 5.5 K. There are 15.48% Eu2+ ions that change into Eu3+, because the concentrations of Mn2+ and Mn4+ are 7.74% and 4.76% in the EuTi0.875Mn0.125O3 compounds. Although, the magnetic moments were decreased, the utilization of spin entropy of Eu2+: 4f7 localized moments was improved. A giant reversible magnetocaloric effect was observed in EuTi0.875Mn0.125O3 compounds. The maximum value of magnetic entropy change are (12.3 and 23.3 J/kg K), and the values of RC were evaluated to be 46 and 123 J/kg for a field change of 1 and 2 T, without thermal and field hysteresis loss. Therefore, the giant reversible MCE and large RC make the EuTi0.875Mn0.125O3 compound a good candidate for magnetic refrigerant working at low-temperature and low-field.

Effects of Mn-doping on the giant magnetocaloric effect of EuTiO3 compound

The magnetic properties and magnetocaloric effect of EuTi1−xMnxO3 (x = 0–0.1) compounds are investigated. When the Ti4+ was substituted by Mn2+, the lattice constants were changed, the Eu3+ state and the oxygen vacancy generated. The exchange mechanisms were more complex among the Mn2+ 3d, the Eu 5d and Eu2+ 4f. The FM phase was dominant between AFM and FM as Mn substitute for Ti, which improve the MCE under low magnetic field. The values of −ΔSMmax are evaluated to 11.7 and 11.1 J/kg K for EuTi0.975Mn0.025O3 and EuTi0.95Mn0.05O3 compounds, under a magnetic field change of 1 T. And, the values of RC were obviously enhanced under the magnetic field changes of 1 and 2 T. Therefore, the giant reversible MCE makes these compounds promising candidates for magnetic refrigeration.

Enhancement of magnetocaloric effect in mischmetal doped La-Fe-Si alloys

The influence of partial substitution of mischmetal on the structure, Curie temperature and magnetocaloric effect has been investigated in La1-xMxFe11.5Si1.5 alloys. X-ray diffraction patterns indicate the alloys crystallize mainly in NaZn13-type cubic structure and the amount of secondary α-Fe phase obviously reduces in the mischmetal doped alloys. As the content of mischmetal increases, the Curie temperature is reduced from 198.1 K for x = 0 to 184.2 K for x = 0.3 and the thermal hysteresis is enlarged from 3.5 K for x = 0 to 8.2 K for x = 0.3. Upon a field change from 0 to 3 T, the obtained maximum isothermal entropy change values are 17.2, 19.8, 37.8 and 47.9 J/kgK for x = 0, 0.1, 0.2 and 0.3, respectively. The entropy changes due to the latent heat of first-order transitions are estimated to be 11.3, 14.7, 18.5 and 23.4 J/kgK for x = 0, 0.1, 0.2 and 0.3, respectively. The enhancement of giant magnetocaloric MCE in La1-xMxFe11.5Si1.5 alloys originates from the strengthened itinerant electron metamagnetic transitions by adding the mischmetal. Our result suggests that the mischmetal doped NaZn13-type La-Fe-Si alloys are potential candidates of refrigerants for magnetic refrigeration.

Influences of La and Ce doping on giant magnetocaloric effect of EuTiO**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFB0702704), the National Natural Science Foundation of China (Grant Nos. 11504266, 51676198, and 51371075), the Tianjin Natural Science Foundation, China (Grant No. 17JCQNJC02300), and the National Key Foundation for Exploring Scientific Instrument of China (Grant

Giant reversible magnetocaloric effects and magnetic properties in Eu0.9R0.1TiO3 (R = La, Ce) are investigated. The antiferromagnetic ordering of pure EuTiO3 can significantly change to be ferromagnetic as substitution of La (x = 0.1) and Ce (x = 0.1) ions for Eu2+ ions. The values of and RC are evaluated to be 10.8 J/(kgK) and 51.8 J/kg for Eu0.9Ce0.1TiO3 and 11 J/(kgK) and 39.3 J/kg for Eu0.9La0.1TiO3 at a magnetic field change of 10 kOe, respectively. The large low-field enhancements of and RC can be attributed to magnetic phase transition. The giant reversible MCE and large RC suggest that Eu0.9R0.1TiO3 (R = La, Ce) compounds could be promising materials in low temperature and low magnetic field refrigerants.

Giant magnetocaloric effect induced by reemergence of magnetostructural coupling in Si-doped Mn0.95CoGe compounds

It has been reported that the martensitic structural transformation temperature (Tstr) can be lowered and even depressed by Mn vacancy in MnCoGe-based alloys. In the present work, the structural transformation is tuned to reappear and the Tstr increases significantly by substituting Si for Ge in Mn0.95CoGe system, and thus the magnetostructural transition from paramagnetic Ni2In-type phase to ferromagnetic TiNiSi-type phase is again realized around room temperature. Meanwhile, the working temperature window is enhanced to be 22% wider than that of Mn1−xCoGe system. The history-dependent phase transitions have been discussed by measuring the M-H curves in different processes. Mn0.95CoGe0.9Si0.1 experiences a forward martensitic transition in loop process, and then a field-induced metamagnetic transition (FIMT) with large magnetic hysteresis can be observed around Tstrcooling. On the other hand, a reverse martensitic transition is observed in standard process, and the FIMT is depressed by thermal disturbance at higher temperatures. Large MCE is obtained due to the reemergence of magnetostructural transition, e.g., the maximum −ΔSM is 15.0J/kgK for a relatively low field change of 2T, which is larger than those of Mn1−xCoGe system and some other typical magnetocaloric materials in similar temperature range. The comprehensive advantages including giant low-field MCE, wide working temperature range, and lower cost of Si than Ge, suggest that Mn0.95CoGe1−xSix compounds could be promising materials for room temperature magnetic refrigeration.

Enhanced magnetic entropy change and working temperature interval in Ni–Mn–In–Co alloys

High magnetic entropy change and wide working temperature interval are both of great importance for the application of magnetic refrigerant working materials. Here Ni–Mn–In–Co alloys with oligocrystalline structure were produced by annealing heat treatment and the giant magnetocaloric effect and large working temperature interval were confirmed. The annealing increases the magnetization difference ΔM between martensite and austenite. The annealed alloy subjects to a reverse martensite to austenite and an intermediate phase transformation upon heating. The two-stage field-induced reverse transformation, contribute to a maximum magnetic entropy change of 37.1 J/kgK at 309 K under a magnetic field of 50000 Oe, were observed for the first time. In addition, a broadened working temperature interval of ∼22 K was obtained owing to the intermediate phase transformation. The giant room-temperature MCE in quaternary Ni–Mn–In–Co alloys is promising for magnetic refrigeration.

Observation of giant magnetocaloric effect in EuTi1-xCrxO3

The magnetic properties and magnetocaloric effect in EuTi1−xCrxO3 (x = 0, 0.02, 0.04, 0.1) compounds are investigated. The magnetic ground state (AFM) of pure EuTiO3 can be significantly changed to be FM with slight Cr-doping. A giant reversible MCE and large RC in EuTi1−xCrxO3 compounds were observed. The value of −ΔSMmax reaches to 40.3 J/kg K for EuTiO3 under the magnetic field change of 5 T. Especially, under the magnetic field changes of 1 and 2 T, the values of −ΔSMmax are evaluated to be 12.5 and 22.5 J/Kg K and the maximum values of RC are 64 and 127 J/kg, without magnetic and thermal hysteresis for EuTi1−xCrxO3 system. Therefore, the giant reversible MCE and large RC make the EuTi1−xCrxO3 compounds could be considered as a good candidate material for low-temperature and low-field magnetic refrigerant.

Observation of giant magnetocaloric effect in EuTiO3

A giant reversible MCE and large RC in EuTiO3 compound were observed. Under the magnetic field changes of 5T, the maximum value of −ΔSM is evaluated to be 40.4J/kg K, and the value of RC is 328J/kg in EuTiO3 compound. Especially, for the magnetic field changes of 1 and 2T, the large values of −ΔSM are 11 and 22.3J/Kg K without magnetic and thermal hysteresis are also obtained, respectively. The giant MCE is attributed to field-induced AFM-FM transition and FM-PM transition. Therefore, the giant reversible MCE and large RC make the EuTiO3 compounds could be considered as a good candidate material for low-temperature and low-field magnetic refrigerant.

Magnetocaloric refrigerant with wide operating temperature range based on Mn5−xGe3(Co,Fe)x composite

The Curie temperature of Mn5Ge3 was raised or lowered by alloying the compound with Fe or Co; hence, the temperature at which maximum magnetocaloric effect manifested was easily manipulated by forming Mn5−xGe3(Co,Fe)x alloys to ultimately develop a composite magnetic refrigerant consisting of multiple Mn5Ge3 – based alloys. The composite refrigerant was designed to produce a table-like ΔSM–T curve and to maximize the RC value near room temperature. Linear combination of the ΔSM–T curves for the constituent materials showed that a composite composed of physical mixture of four different Mn5Ge3-based compounds: Mn5Ge3, Mn5.1Ge2.9, Mn4.75Co0.25Ge3 and Mn4.75Fe0.25Ge3, generated an optimal ΔSM–T curve with a table-like shape. The composite refrigerant with refrigeration capacity of 52Jkg−1, peak entropy change at 300K, and operating temperature range of 45K under ΔH=10kOe was suitable for room-temperature magnetic refrigeration. Moreover, by changing the relative fraction of each constituent material in the composite, it was shown that the operating temperature range could be fine-tuned as needed. The calculated ΔSM–T curve for the composite refrigerant by linear combination reasonably well matched the experimental ΔSM–T curve estimated from the M–H curves of the composite refrigerant, suggesting that the simple linear combination of the experimental ΔSM–T curves can be used to predict the performance of the composite magnetic refrigerants whose MCE was originated from the second order magnetic transition. In conclusion, being rare-earth free and lacking thermal or magnetic hysteresis, the Mn5Ge3 – based composite can be a competitive candidate magnetic refrigerant material operating at room temperature in terms of both economy and reliability compared to the giant MCE materials such as Gd – based intermetallic compounds or Heusler alloys.

First-order magnetostructural transformation in Fe doped Mn–Co–Ge alloys

• We have achieved FOMT by substituting Mn by Fe atoms in off-stoichiometric MnCoGe. • A giant MCE (△ S m = −9.74 J kg −1 K −1 at △ H = 0–5 T for Mn 0.89 Fe 0.11 CoGe) was obtained. • Large lattice strain up to ∼12% accompanied by the transformation was observed. Substitution of Fe for Mn atoms in Mn–Co–Ge alloys was employed for tailoring concurrent structural and magnetic phase transitions. First-order magnetostructural transition from paramagnetic hexagonal Ni 2 In-type parent phase to ferromagnetic orthorhombic TiNiSi-type martensite was achieved. A giant magnetocaloric effect of △ S m = −9.74 J kg −1 K −1 was obtained under magnetic field change of 5 T in the vicinity of phase transition temperature. This result indicates that Fe doped Mn–Co–Ge alloys are ideal candidates for magnetic refrigeration applications. Furthermore, the magnetic field-induced martensitic transformation, associated with a large lattice strain of ∼12%, was directly evidenced by in situ synchrotron high-energy X-ray diffraction.