Reversible Magnetic Entropy Change Research Articles

Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18 K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (∼8 K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications.

High-temperature solvothermal synthesis and magnetic properties of nearly monodisperse CdCr2S4 nanocrystals

Magnetic spinel CdCr2S4 nanocrystals have been synthesized using a high-temperature solvothermal method, which exhibit a large reversible magnetic entropy change over a wide temperature span.

Modeling of Thermomagnetic Phenomena in Active Magnetocaloric Regenerators

The active magnetic regenerator (AMR) consists of a porous matrix heat exchanger whose solid phase is a magnetocaloric material (solid refrigerant) that undergoes a reversible magnetic entropy change when subjected to a changing magnetic field. The cooling capacity of the cycle is proportional to the mass of solid refrigerant, operating frequency, volumetric displacement of the heat transfer fluid and regenerator effectiveness. AMRs can be modeled via a porous media approach and a model has been developed in this work to simulate the time-dependent fluid flow and heat transfer processes in the regenerator matrix. Gadolinium (Gd) is usually adopted as a reference material for magnetic cooling at near room temperature and its magnetic temperature change and physical properties were accounted for through a combination of experimental data and the Weiss-Debye-Sommerfeld (WDS) theory. In this paper, the interaction of the applied magnetic field waveform with the heat transfer fluid displacement profile and the influence of demagnetizing effects on the AMR performance are investigated numerically. The numerical model is evaluated against experimental data for a regenerator containing spherical Gd particles.

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.

Magnetic properties and magnetocaloric effect in the HoNi1−xCuxIn (x=0, 0.1, 0.3, 0.4) intermetallic compounds

The magnetic properties and magnetocaloric effect (MCE) in HoNi1−xCuxIn (x=0, 0.1, 0.3, 0.4) compounds have been investigated. With the substitution of Cu for Ni, the Ho magnetic moment will cant from the c-axis, and form a complicated magnetic structure. These compounds exhibit two successive magnetic transitions with the increase in temperature. The large reversible magnetocaloric effects have been observed in HoNi1−xCuxIn compounds around Tord, with no thermal and magnetic hysteresis loss. The large reversible isothermal magnetic entropy change (−ΔSM) is 20.2J/kgK and the refrigeration capacity (RC) reaches 356.7J/kg for field changes of 5T for HoNi0.7Cu0.3In. Especially, the value of −ΔSM (12.5J/kgK) and the large RC (132J/kg) are observed for field changes of 2T for HoNi0.9Cu0.1In. Additionally, the values of RC are improved to 149J/K for the field changes of 2T due to a wide temperature span for the mix of HoNi0.9Cu0.1In and HoNi0.7Cu0.3In compounds with the mass ratio of 1:1. These compounds with excellent MCE are expected to have effective applications in magnetic refrigeration around 20K.

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.

Magnetic and Magnetocaloric Properties of Er2TiMnO7 Compound

Magnetic properties and magnetocaloric effects of the Er2TiMnO7 compound have been evaluated by magnetization and heat capacity measurements. The reversible magnetic-entropy change is found to be just above the boiling point of helium and hydrogen liquefaction temperature range of 2 to 50 K.

Mechanism of the giant irreversible positive magnetic entropy change in a Tb-based bulk metallic glass

A suitable coherent description of the reversible and irreversible magnetic entropy changes in a Tb-based metallic glass with strong random magnetic anisotropy (RMA) is presented. A giant irreversible positive magnetic entropy change is observed from magnetic measurements at low temperatures, which is found to arise from the entropy production, while a small negative one is obtained from heat capacity measurements. The temperature dependences of the irreversible positive magnetic entropy change under a field change of 5 T and the internal entropy production in the initial magnetization process can be described by an exponential law, which is determined by RMA.

Irreversible and reversible magnetic entropy change in a Dy-based bulk metallic glass

The magnetic entropy change of a Dy-based bulk metallic glass (BMG) was investigated in the temperature range of 2–94 K. The alloy shows spin glass like freezing process around 18.5 K. Above the spin freezing temperature, the magnetic entropy change is negative with a minimum about −8.3 J⋅kg−1K−1, demonstrating its good magnetocaloric effect (MCE) performance. Below the spin freezing temperature, irreversible positive magnetic entropy change is obtained with a maximum of 27.7 J⋅kg−1K−1 indicating large internal entropy production, which relates to the random magnetic anisotropy.

Large magnetic entropy change and refrigerant capacity in rare-earth intermetallic RCuAl (R=Ho and Er) compounds

The magnetic properties and the magnetocaloric effects of RCuAl (R=Ho and Er) compounds have been investigated. Both HoCuAl and ErCuAl just undergo a second-order ferromagnetic–paramagnetic phase transition at TC. Large reversible magnetic entropy changes (ΔSM) are observed around their respective Curie temperatures due to the ferromagnetic–paramagnetic phase transition. For a field change of 0–5T, the peak values of −ΔSM of RCuAl (R=Ho and Er) compounds are 23.9 and 22.9Jkg−1K−1 at TC, with the values of refrigerant capacity of 393 and 321Jkg−1, respectively. These properties suggest that RCuAl (R=Ho and Er) compounds could be considered as attractive magnetic refrigerants working in low temperature range.

The magnetic and magnetocaloric properties of NdFe12−xMox compounds

The crystal structure and magnetic properties of NdFe12−xMox (x = 2.25, 2.5, 2.75, 3.0) compounds were synthesized and investigated. These compounds crystallized in ThMn12-type single phase, and the Curie temperature decreased with increasing Mo content. NdFe9.5Mo2.5 has a Curie temperature around room temperature, and a reversible magnetic entropy change was observed ∼290 K due to the second-order magnetic transition. The maximum value of −ΔSM is 2.38 J kg-1 K-1 at 290 K for a magnetic field change of 50 kOe. The working temperature span is more than 150 K and the relative cooling power reaches 357 J/kg, which makes the compound a promising candidate for magnetic refrigerator vicinal room temperature.

Abnormal magnetic behaviors and large magnetocaloric effect in MnPS3 nanoparticles

A nanostructured honeycomb lattice consisting of MnPS3 nanoparticles synthesized via the ion-exchange technique was found to have restacked molecular layers stabilized by H2O insertion between the layers. Susceptibility (χ) and heat capacity measurements showed the absence of long range magnetic ordering, at least down to 2 K. However, the χ data showed that the system possesses a high effective Curie temperature, suggesting that the system is in a high spin lattice disordered state. Evaluation of the magnetocaloric effect indicates that the system has a large reversible magnetic-entropy change (−ΔSm) of 6.8 and 12.8 J/kg K and an adiabatic temperature change (ΔTad) of 3.8 K and 8 K at 2.85 K for magnetic field changes of 3 T and 9 T, respectively.

Field-induced reversible magnetocaloric effect in CoCl 2

A sign change of 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 of CoCl 2 nanoparticles. The reversible magnetic-entropy change −Δ S m (4.1 and 11.5 J kg −1 K −1 at 27 K for a field change of 3 and 7 T, respectively) almost without hysteresis and the large cooling power (83.4 and 148 J kg −1, correspondingly) indicates that CoCl 2 is a potential candidate for application in magnetic refrigeration in the low-temperature range.

Giant irreversible positive to large reversible negative magnetic entropy change evolution in Tb-based bulk metallic glass

We study the effects of amorphous structure and random anisotropy on the magnetic entropy change in a series of Tb-based amorphous alloys. The amorphous structure broadens the peak of magnetic entropy change and facilitates the adjustment of properties. The peak magnetic entropy change above the spin freezing temperature first depends on the average magnetic moment approximately linearly and second on the exchange interaction and random anisotropy. Large and broad reversible negative magnetic entropy changes are observed above the spin freezing temperature and giant positive irreversible magnetic entropy changes which associate with the internal entropy production are obtained well below.

Magnetic properties and magnetocaloric effect in Nd5Si3 compound

The structure and magnetic properties of Nd5Si3 compound have been investigated. A reversible magnetic entropy change was observed at about 112 K accompanied with a second-order magnetic transition from the ferromagnetic to paramagnetic state. The maximum value of −ΔSM is 5.0 J kg−1 K−1 at 112 K for a magnetic field change of 50 kOe. The relatively large magnetic entropy change and broad working-temperature span (about 57 K) of the reversible magnetocaloric effect make the present compound a potential candidate for the practical magnetic refrigeration in this temperature range.

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.

Large reversible magnetocaloric effect of light rare-earth intermetallic compound Pr 5Si 3

The structure and magnetic properties of Pr 5Si 3 compound have been investigated. A large reversible magnetic entropy change was observed at about 47 K accompanied with a second-order magnetic transition from the ferromagnetic to paramagnetic state. The maximum values of −Δ S M are 11.6 and 6.0 J kg −1 K −1 at 47 K, corresponding to the applied magnetic field changes of 50 and 20 kOe, respectively. The study on the magnetocaloric effect of the light rare-earth based compound, may open a field in searching for new magnetic refrigerant materials.

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.

Hysteresis of the martensitic phase transition in magnetocaloric-effect Ni-Mn-Sn alloys

We have investigated the hysteresis of the temperature- and magnetic field--induced martensitic phase transition in ${\text{Ni}}_{50.4}{\text{Mn}}_{34.0}{\text{Sn}}_{15.6}$. Specifically, we have characterized the fraction of martensite and cubic Heusler phase present along a variety of temperature and magnetic field paths using magnetization as a proxy for the fraction of phases present. We present these results and discuss (1) the thermodynamics of the thermal- and magnetic field--induced hysteresis and (2) the impact of this hysteresis on the magnetocaloric effect of the alloy. We demonstrate that both temperature and magnetic field are equivalent driving forces for the phase transition and result in equivalent hysteresis behavior linked through the magnetic Gibbs free energy. The hysteresis reduces the useful magnetocaloric effect of the alloy by allowing only a limited fraction of the alloy to transform cyclicly between the martensite and the austenite phase under application and removal of magnetic fields up to 9 T, and by dissipating work through irreversible energy loss. While the importance of a large thermodynamically reversible magnetic entropy change is generally accepted, our results suggest that the hysteresis behavior is equally critical in evaluating the effective magnetocaloric effect of a material.

Large reversible magnetocaloric effect in Tb 2In

The intermetallic compound Tb 2In exhibits two magnetic phase transitions: a paramagnetic-ferromagnetic transition at T C of 165 K and a ferromagnetic–antiferromagnetic one at 45 K. A large reversible magnetocaloric effect is observed in Tb 2In. For a magnetic field change of 5 T, the maximum magnetic entropy change − Δ S M is 6.6 J/kg K at T C . Meanwhile, the full width at half maximum ( δ T FWHM ) of the − Δ S M − T curve has a very high value of 100 K and relative cooling power (RCP) is as high as 660 J/kg with no hysteresis loss. In particular, the large reversible − Δ S M (3.5 J/kg K), δ T FWHM (57 K) and RCP (200 J/kg) are achieved for a low field change of 2 T. The large reversible magnetic–entropy changes, together with high δ T FWHM and RCP values indicate that Tb 2In is a suitable candidate material for magnetic refrigeration.