Giant Reversible Magnetocaloric Effect Research Articles

Giant low-field magnetocaloric effect in EuTi1 − xNbxO3 (x = 0.05, 0.1, 0.15, and 0.2) compounds**Project supported by the Science & Technology Development Fund of Tianjin Education Commission for Higher Education, China (Grant No. 2017KJ247).

The magnetic properties and magnetocaloric effect (MCE) of EuTi1 − xNbxO3 (x = 0.05, 0.1, 0.15, and 0.2) compounds are investigated. Owing to electronic doping, parts of Ti ions are replaced by Nb ions, the lattice constant increases and a small number of Ti4+ (3d0) ions change into Ti3+ (3d1). It is the ferromagnetism state that is dominant in the derivative balance. The values of the maximum magnetic entropy change () are 10.3 J/kg · K, 9.6 J/kg · K, 13.1 J/kg · K, and 11.9 J/kg · K for EuTi1 − xNbxO3 (x = 0.05, 0.1, 0.15, and 0.2) compounds and the values of refrigeration capacity are 36, 33, 86, and 80 J/kg as magnetic field changes in a range of 0 T–1 T. The EuTi1 − xNbxO3 (x = 0.05, 0.1, 0.15, and 0.2) compounds with giant reversible MCE are considered as a good candidate for magnetic refrigerant working at low-temperature and low-field.

Giant reversible magnetocaloric effect in orthorhombic GdScO3

Abstract The magnetic and magnetocaloric properties were studied in orthorhombic polycrystalline GdScO3. GdScO3 possesses an antiferromagnetic ordering below the Neel temperature ∼2.8 K. Negligible thermal and magnetic hystereses were both observed in GdScO3, indicating a second-order feature of phase transition and a reversible magnetocaloric effect (MCE). In the magnetic field changes of 0–50 kOe and 0–70 kOe, giant maximum magnetic entropy changes of 39.39 J/kg K and 50.77 J/kg K were obtained near the liquid helium temperature, respectively. The giant reversible MCE indicates the polycrystalline GdScO3 is a very promising refrigerant candidate for the low-temperature magnetic refrigeration.

Low-field induced giant magnetocaloric effect in EuTi1-xNixO3 (x = 0.05, 0.1) compounds

Abstract The FM exchange is gradually enhanced in the EuTi1-xNixO3 (x = 0.05, 0.1) compounds. There are two successive magnetic transitions around liquid helium temperature, and exhibit a giant reversible magnetocaloric effect. The maximum values of magnetic entropy change are 41.9 and 45.5 J/kg K, and the refrigerating capacity were evaluated to be 336.5 and 359.5 J/kg for a field change of 5 T. Especially, for a field change of 1 T, the maximum value of magnetic entropy change is 13.7 J/kg K, the refrigerating capacity reach to 53.4 J/kg, and adiabatic temperature change is 4.1 K for EuTi0.9Ni0.1O3, respectively.

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.

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.

Observation of giant magnetocaloric effect under low magnetic fields in EuTi1–xcoxo3**Project supported by the National Natural Science Foundation of China (Grant Nos. 11504266, 51271192, 51322605, and 51371075) and the Natural Science Foundation of Tianjin, China (Grant No. 17JCQNJC02300).

The magnetic properties and magnetocaloric effect (MCE) in EuTi1−xCoxO3 (x = 0, 0.025, 0.05, 0.075, 0.1) compounds have been investigated. When the Ti4+ ions were substituted by Co2+ ions, the delicate balance was changed between antiferromagnetic (AFM) and ferromagnetic (FM) phases in the EuTiO3 compound. In EuTi1−xCoxO3 system, a giant reversible MCE and large refrigerant capacity (RC) were observed without hysteresis. The values of were evaluated to be around 10 J⋅kg−1⋅K−1 for EuTi0.95Co0.05O3 under a magnetic field change of 10 kOe. The giant reversible MCE and large RC suggests that EuTi1−xCoxO3 series could be considered as good candidate materials for low-temperature and low-field magnetic refrigerant.

Effects of Sr-doping on the giant magnetocaloric effect of EuTiO3

The magnetic properties and magnetocaloric effect of Eu1−xSrxTiO3 (x=0–0.1) compounds are investigated. With slight Sr-doping, the ferromagnetic (FM) coupling significantly increased and FM exchange is dominant in the delicate balance. A giant reversible magnetocaloric effect (MCE) and large refrigerant capacity (RC) for Eu1−xSrxTiO3 compounds were observed. The values of −ΔSMmax are evaluated to be around 10J/kg K under a magnetic field change of 1T and 21J/kg K under a magnetic field change of 2T, respectively. But, the values of RC are increased with the more Eu in EuTiO3 to be substituted by Sr. Therefore, the giant reversible MCE and large RC make the Eu1−xSrxTiO3 compound a good candidate for magnetic refrigerant working at low-temperature and low-field.

Observation of giant magnetocaloric effect under low magnetic field in Eu1−xBaxTiO3

The magnetic properties and magnetocaloric effect in Eu1−xBaxTiO3 (x = 0, 0.04, 0.08, 0.1) compounds are investigated. With slight Ba-doping, the antiferromagnetic ordering of pure EuTiO3 can be significantly changed to ferromagnetic due to the size Ba2+ ion bigger than Eu2+. A giant reversible magnetocaloric effect and large RC in Eu1−xBaxTiO3 compounds were observed. The maximum value of magnetic entropy change (−ΔSMmax) reaches to 41.4 J/kg K for Eu0.92Ba0.08TiO3 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 23.4 J/kg K and the maximum values of RC are 54 and 119 J/kg, without magnetic and thermal hysteresis for Eu0.92Ba0.08TiO3. Therefore, the giant reversible magnetocaloric effect and large RC make the Eu1−xBaxTiO3 compounds could be considered as a good candidate material for low-temperature and low-field magnetic refrigerant.

Magnetic properties and giant reversible magnetocaloric effect in GdCoC2

The crystal structure, magnetic properties and magnetocaloric effect (MCE) of GdCoC2 have been studied.

Giant low field magnetocaloric effect and field-induced metamagnetic transition in TmZn

The magnetic properties and the magnetocaloric effect (MCE) in TmZn have been studied by magnetization and heat capacity measurements. The TmZn compound exhibits a ferromagnetic state below a Curie temperature of TC = 8.4 K and processes a field-induced metamagnetic phase transition around and above TC. A giant reversible MCE was observed in TmZn. For a field change of 0–5 T, the maximum values of magnetic entropy change (−ΔSMmax) and adiabatic temperature change (ΔTadmax) are 26.9 J/kg K and 8.6 K, the corresponding values of relative cooling power and refrigerant capacity are 269 and 214 J/kg, respectively. Particularly, the values of −ΔSMmax reach 11.8 and 19.6 J/kg K for a low field change of 0–1 and 0–2 T, respectively. The present results indicate that TmZn could be a promising candidate for low temperature and low field magnetic refrigeration.

Large reversible magnetocaloric effect in antiferromagnetic HoNiSi compound

Magnetic properties and magnetocaloric effect (MCE) of intermetallic HoNiSi compound have been investigated systematically. It is found that HoNiSi exhibits antiferromagnetic (AFM) state below the Néel temperature TN of 3.8 K, which is quite close to the liquid helium temperature (4 K). A giant MCE without hysteresis loss is observed in HoNiSi, which is related to the field-induced first-order metamagnetic transition from AFM to ferromagnetic states. For a magnetic field change of 2 T, the maximum values of magnetic entropy change (−ΔSM) and adiabatic temperature change (ΔTad) are 17.5 J/kg K and 4.5 K, respectively. In addition, HoNiSi presents both large values of positive and negative ΔSM for the low field changes, i.e., the maximum −ΔSM values are 9.2 J/kg K around TN and −7.2 J/kg K below TN for the field changes of 1 and 0.5 T, respectively. A universal curve of ΔSM is successfully constructed by using phenomenological procedure, proving the applicability of universal ΔSM curve for AFM materials. The giant reversible MCE for relatively low magnetic field change makes HoNiSi attractive candidate for magnetic refrigerant materials around liquid helium temperature.

A giant reversible magnetocaloric effect in Ho2PdSi3 compound

The magnetic properties and magnetocaloric effect (MCE) in Ho2PdSi3 compound are investigated. Ho2PdSi3 compound exhibits a giant reversible MCE, the value of -ΔSMmax and RC are 27.5J/kgK and 427J/kg without thermal and field hysteresis loss, for field changes of 5T, respectively. Especially, under field changes of 2T, the value of -ΔSMmax is 15.3J/kgK and ΔTadmax is 4.2K, respectively. The giant reversible −ΔSM, ΔTad and large RC together with the absence of thermal and field hysteresis indicate that Ho2PdSi3 compound could be a promising candidate for magnetic refrigeration at low temperatures.

Magnetic properties and magnetocaloric effect of the HoAgGa compound

Magnetic properties and magnetocaloric effect (MCE) of the HoAgGa compound are investigated by magnetization and heat capacity measurements. A giant reversible MCE was observed around TC = 7.2 K. The maximum values of magnetic entropy change and adiabatic temperature are found to be 16 J kg−1 K−1 and 6 K, respectively, with a refrigerant capacity value of 262 J kg−1 for field change of 5 T. These magnetocaloric parameters also remain large for a wide range of temperature above TC. The large MCE as well as no hysteresis loss make HoAgGa an attractive candidate for low temperature magnetic refrigerant.

Giant reversible magnetocaloric effect in flower-like β-Co(OH)2 hierarchical superstructures self-assembled by nanosheets

A facile hydrothermal strategy is proposed to synthesize flower-like β-Co(OH)2 hierarchical microspherical superstructures with a diameter of 0.5-1.5 μm, which are self-assembled by β-Co(OH)2 nanosheets with the average thickness ranging between 20 and 40 nm. The magnetocaloric effect associated with magnetic phase transitions in Co(OH)2 superstructures has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a filed-induced transition from the antiferromagnetic to the ferromagnetic state below the Neel temperature. The large reversible magnetic-entropy change -ΔSm (13.4 J/kg K at 15 K for a field change of 5 T) indicates that flower-like Co(OH)2 superstructures is a potential candidate for application in magnetic refrigeration in the low-temperature range.

Giant reversible magnetocaloric effect in ErMn2Si2 compound with a second order magnetic phase transition

The magnetic properties and magnetocaloric effect (MCE) in the ternary intermetallic compound ErMn2Si2 have been studied by magnetization and heat capacity measurements. A giant reversible MCE has been observed, accompanied by a second order magnetic phase transition from paramagnetic to ferromagnetic at ∼4.5 K. Under a field change of 5 T, the maximum value of magnetic entropy change (−ΔSMmax) is 25.2 J kg−1 K−1 with no thermal and field hysteresis loss, and the corresponding maximum value of adiabatic temperature change (ΔTadmax) is 12.9 K. Particularly, the values of −ΔSMmax and ΔTadmax reached 20.0 J kg−1 K−1 and 5.4 K for a low field change of 2 T, respectively. The present results indicate that the ErMn2Si2 compound is an attractive candidate for low temperature magnetic refrigeration.

A sign of field-induced first order magnetic state transition and giant reversible magnetocaloric effect in cobalt hydroxide nanosheets

We report the synthesis of β−Co(OH)2 nanosheets using microwave assisted hydrothermal and conventional chemical reaction methods. A magnetic transition at an onset temperature, T1∼96 K, and a sign of antiferromagnetic state transition at the Néel temperature, TN=9∼10 K, can be determined from M-T curves and M-H curves magnetic properties investigation. It is found that a sign of field-induced first order transition below 9 K, act as a role of reversing the magnetocaloric effect from negative to positive value. The large reversible magnetic-entropy change (ΔSM) of 17 J/kg K around 11 K for a field change of 5 T indicates that this material is useful for refrigeration applications at low temperatures.

Giant reversible magnetocaloric effect in metamagnetic HoCuSi compound

The magnetic properties and magnetocaloric effect (MCE) of antiferromagnetic HoCuSi compound have been studied. It is found that HoCuSi undergoes a field-induced first order metamagnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) states below the Néel temperature (TN). A giant MCE without hysteresis loss is observed in HoCuSi around TN. The maximal magnetic entropy change (−ΔSM) and refrigerant capacity are 33.1 J/kgK and 385 J/kg, respectively, for a field change of 0–5 T. The excellent magnetocaloric properties can result from the field-induced AFM-FM transition below TN and the increase in magnetization change caused by the change in lattice volume at TN.

Giant reversible magnetocaloric effect in antiferromagnetic superconductor Dy0.9Tm0.1Ni2B2C compound

The magnetic properties and magnetocaloric effect in antiferromagnetic superconductor Dy0.9Tm0.1Ni2B2C compound have been studied. The magnetic phase transition TM (∼9.2 K) occurs above the superconducting transition temperature Tc (∼4.5 K). A giant reversible magnetocaloric effect has been observed, which is related to a field-induced first order metamagnetic transition from antiferromagnetic to ferromagnetic state. The values of maximum magnetic entropy change (−ΔSMmax) reach 14.7 and 19.1 J kg−1 K−1 for the field change of 5 and 7 T with no obvious hysteresis loss around 13 K, respectively. These results indicated that Dy0.9Tm0.1Ni2B2C could be a promising candidate for magnetic refrigeration at low temperatures.

Giant reversible magnetocaloric effect in antiferromagnetic GdCo2B2 compound

The magnetocaloric effect of GdCo2B2 was studied by magnetization and heat capacity measurements. A giant reversible magnetocaloric effect has been observed which is related to a field-induced first order metamagnetic transition from antiferromagnetic to ferromagnetic state. The values of maximum magnetic entropy change (−ΔSMmax) reach 9.3 and 21.5 J kg−1 K−1 for the field change of 2 and 7 T with no obvious hysteresis loss around 25 K, respectively. The corresponding maximum adiabatic temperature changes (ΔTadmax) are evaluated to be 6.7 and 18.9 K. These values are even larger than some of potential magnetic refrigerant materials reported in the same temperature range and also comparable to the room temperature giant magnetocaloric materials. These results indicated that GdCo2B2 could be a promising candidate for magnetic refrigeration at low temperatures.

Giant reversible magnetocaloric effect in cobalt hydroxide nanoparticles

The magnetocaloric effect associated with magnetic phase transitions in β-Co(OH)2 nanoparticles has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a field-induced transition from the antiferromagnetic to the ferromagnetic state below the Néel temperature. The large reversible magnetic-entropy change −ΔSm (20.9 J/kg K at 15 K for a field change of 7 T) indicates that β-Co(OH)2 is a potential candidate for application in magnetic refrigeration in the low-temperature range.