Low Temperature Magnetic Refrigeration Research Articles

Large reversible magnetocaloric effect in RE2Cu2In (RE = Er and Tm) and enhanced refrigerant capacity in its composite materials

The magnetic properties and magnetocaloric effect (MCE) in RE2Cu2In (RE = Er and Tm) compounds and its composite materials have been investigated. A large reversible MCE is observed at around their own Curie temperature of TC ~ 39.4 and 31.6 K for Er2Cu2In and Tm2Cu2In, respectively. Under a magnetic field change of 0–7 T, the maximum values of magnetic entropy change () are estimated to be 18.4 and 18.2 J kg−1 K−1 for Er2Cu2In and Tm2Cu2In, respectively. A table-like MCE at a temperature of 20–50 K and enhanced refrigerant capacity (RC) are realized in the Er2Cu2In–Tm2Cu2In composite materials. For magnetic field changes of 0–5 and 0–7 T, the maximum improvements of RC reach 32% (12%) and 28% (14%), in comparison with that of the individual compound Er2Cu2In (Tm2Cu2In), respectively. The excellent MCE properties make the RE2Cu2In composite materials attractive for low-temperature magnetic refrigeration.

Magnetic phase transition and giant anisotropic magnetic entropy change in TbFeO3 single crystal

The magnetocaloric effect (MCE) is an intrinsic property of magnetic materials that enable magnetic refrigeration devices without using the traditional vapour-compression. Temperature sensitive and anisotropic magnetic solids might give rise to a large rotating MCE for building compact and efficient magnetic cooling systems by simply rotating the sample. Here, we report an unprecedented maximal refrigeration capacity of 497.36 J/kg (at 70 kOe) in perovskite TbFeO3 single crystal, resulting from its giant anisotropic magnetic entropy change along a axis. Our paper reveals that interaction between Fe-3d and Tb-4f electrons drives extremely interesting spin reorientation transition, which is highly sensitive to magnetic field and temperature. These findings highlight potential applications of an emerging material for high efficient low temperature magnetic refrigeration, which is compact and quiet, and does not use ozone-depleting coolant gases.

Giant low-field magnetocaloric effect in single-crystalline EuTi0.85Nb0.15O3

The magnetocaloric effect in ferromagnetic single crystal EuTi0.85Nb0.15O3 has been investigated using magnetization and heat capacity measurements. EuTi0.85Nb0.15O3 undergoes a continuous ferromagnetic phase transition at TC = 9.5 K due to the long range ordering of magnetic moments of Eu2+ (4f7). With the application of magnetic field, the spin entropy is strongly suppressed and a giant magnetic entropy change is observed near TC. The values of entropy change ΔSm and adiabatic temperature change ΔTad are as high as 51.3 J kg−1 K−1 and 22 K, respectively, for a field change of 0–9 T. The corresponding magnetic heating/cooling capacity is 700 J kg−1. This compound also shows large magnetocaloric effect even at low magnetic fields. In particular, the values of ΔSm reach 14.7 and 23.8 J kg−1 K−1 for field changes of 0–1 T and 0–2 T, respectively. The low-field giant magnetocaloric effect, together with the absence of thermal and field hysteresis makes EuTi0.85Nb0.15O3 a very promising candidate for low temperature magnetic refrigeration.

High-performance low-temperature magnetic refrigerants made of gadolinium-hydroxy-chloride

Two new gadolinium(iii)-hydroxy-chloride materials with large magnetocaloric effects were facilely synthesized by using Cl− as the template.

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.

Giant magnetocaloric effect in Gd2NiMnO6 and Gd2CoMnO6 ferromagnetic insulators

We have investigated the magnetocaloric effect in double perovskite Gd2NiMnO6 (GNMO) and Gd2CoMnO6 (GCMO) samples by magnetic and heat capacity measurements. Ferromagnetic ordering is observed at ~130 K (~ 112 K) in GNMO (GCMO), while the Gd exchange interactions seem to dominate for T < 20 K. In GCMO, below 50 K, antiferromagnetic behaviour due to the 3d–4f negative exchange interaction is observed. A maximum entropy (−ΔSM) and adiabatic temperature change of ~35.5 J Kg−1 K−1 (~ 24 J Kg−1 K−1) and 10.5 K (6.5 K) is observed in GNMO (GCMO) for a magnetic field change of 7 T at low temperatures. Absence of magnetic and thermal hysteresis and their insulating nature make them promising for low temperature 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.

Giant rotating magnetocaloric effect induced by highly texturing in polycrystalline DyNiSi compound.

Large rotating magnetocaloric effect (MCE) has been observed in some single crystals due to strong magnetocrystalline anisotropy. By utilizing the rotating MCE, a new type of rotary magnetic refrigerator can be constructed, which could be more simplified and efficient than the conventional one. However, compared with polycrystalline materials, the high cost and complexity of preparation for single crystals hinder the development of this novel magnetic refrigeration technology. For the first time, here we observe giant rotating MCE in textured DyNiSi polycrystalline material, which is larger than those of most rotating magnetic refrigerants reported so far. This result suggests that DyNiSi compound could be attractive candidate of magnetic refrigerants for novel rotary magnetic refrigerator. By considering the influence of demagnetization effect on MCE, the origin of large rotating MCE in textured DyNiSi is attributed to the coexistence of strong magnetocrystalline anisotropy and highly preferred orientation. Our study on textured DyNiSi not only provides a new magnetic refrigerant with large rotating MCE for low temperature magnetic refrigeration, but also opens a new way to exploit magnetic refrigeration materials with large rotating MCE, which will be highly beneficial to the development of rotating magnetic refrigeration technology.

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.

Large entropy change accompanying two successive magnetic phase transitions in TbMn2Si2 for magnetic refrigeration

Structural and magnetic properties in TbMn2Si2 are studied by variable temperature X-ray diffraction, magnetization, electrical resistivity, and heat capacity measurements. TbMn2Si2 undergoes two successive magnetic transitions at around Tc1 = 50 K and Tc2 = 64 K. Tc1 remains almost constant with increasing magnetic field, but Tc2 shifts significantly to higher temperature. Thus, there are two partially overlapping peaks in the temperature dependence of magnetic entropy change, i.e., −ΔSM (T). The different responses of Tc1 and Tc2 to external magnetic field, and the overlapping of −ΔSM (T) around Tc1 and Tc2 induce a large refrigerant capacity (RC) within a large temperature range. The large reversible magnetocaloric effect (−ΔSMpeak ∼ 16 J/kg K for a field change of 0–5 T) and RC (=396 J/kg) indicate that TbMn2Si2 could be a promising candidate for low temperature magnetic refrigeration.

Novel route to prepare HoN nanoparticles for magnetic refrigerant in cryogenic temperature

Holmium nitride (HoN) nanocrystallites were synthesized by a plasma arc discharge technique and characterized to study their magnetocaloric properties. HoN was formed under the influence of nitrogen–argon mixed gas. N2 gas was used as an active element for arc discharge between two electrodes maintained at a constant current. In addition, N2 gas played an important role not only as a reducing agent but also as an inevitable source of excited nitrogen molecules and nitrogen ions for the formation of HoN phase. The ratio of partial pressure between Ar and N2 was systematically varied to obtain single phase HoN with minimal impurities. Magnetocaloric properties were measured by applying fields up to 50 kOe in the temperature range from 6 K to 60 K. The as-synthesized HoN nanoparticles have shown a change in magnetic entropy of 27.5 J/kgK with a transition temperature at 14.2 K thereby demonstrating their ability to be applied as an effective low temperature magnetic refrigerant material towards the re-liquefaction of H2.

Experimental and theoretical investigations on magnetic and related properties of ErRuSi

We report experimental and theoretical studies of magnetic and related properties of ErRuSi compound. Various experimental techniques such as neutron diffraction, magnetization, magneto-thermal, magneto-transport, optical conductivity have been used to investigate this compound. Neutron diffraction shows ferromagnetic ordering at low temperatures with moments aligned in the ab plane. Neutron diffraction and magnetization data indicate the influence of crystalline electric field effects in the moment at low temperatures. The compound shows good magnetocaloric properties with a low-field adiabatic temperature change of 4.7 K, which is larger than that of many proposed low temperature magnetic refrigerant materials. Magnetoresistance (MR) shows large negative value at 8 K, which changes its sign and increases in magnitude with decrease in temperature and/or increase in field. The positive MR at low temperatures is attributed to the Lorentz force effect. The electronic structure calculations accounting for electronic correlations of the 4 f electrons of Er elucidate the ferromagnetic ordering and effective paramagnetic moment. Interband transitions between the Ru and the Er d states and the Er f states in one spin projection are found to form the main feature of the measured optical conductivity in this compound.

Magnetic properties and low-temperature large magnetocaloric effect in the antiferromagnetic HoCu0.33Ge2 and ErCu0.25Ge2 compounds

Magnetic properties and magnetocaloric effect (MCE) of HoCu0.33Ge2 and ErCu0.25Ge2 compounds have been investigated. The compounds were determined to be antiferromagnetic with the Néel temperatures TN=9K and 3.9K, respectively. The critical transition magnetic fields for the metamagnetic transition from antiferromagnetic to ferromagnetic state below TN were determined to be 10kOe for HoCu0.33Ge2 at 5K and 6kOe for ErCu0.25Ge2 at 2K. Large MCE with the maximal values of magnetic entropy changes (ΔSM) as −10.2J/kgK at 10.5K were found in HoCu0.33Ge2 for field changes of 0–70kOe and −10.5J/kgK at 5.5K in ErCu0.25Ge2 for field changes of 0–50kOe, respectively. The large ΔSM around TN as well as no hysteresis loss made RCuxGe2 competitive candidates as low temperature magnetic refrigerant.

Structural, magnetic and magnetocaloric properties of La0.67Ba0.22Sr0.11Mn1 − xFexO3 nanopowders

The influence of Fe-doping on the structural, magnetic and magnetocaloric properties of La0.67Ba0.22Sr0.11Mn1 − xFexO3 perovskite was investigated. These samples were synthesized by Sol–Gel method. X-ray diffraction (XRD) measurements for all samples indicates that all samples, except that with x = 0.2 and 1.0, crystallize in the orthorhombic single-phase with Pnma space group. The Rietveld refinement of the X-ray nanopowder data confirms this result. Room-temperature transmission Mössbauer spectra for all samples except that with x = 1.0 consisted of doublets with similar isomer shift (δ) values consistent with Fe3+ valence state. The spectrum for the sample with x = 1.0 showed the presence of an additional magnetically ordered phase and showed evidence of the presence of Fe4+ valence state. Magnetization measurements versus temperature under magnetic applied field of 0.05 T showed that all of our investigated samples exhibit a paramagnetic–ferromagnetic transition at low temperature except that with x = 1.0. The Curie temperature decreased with increasing Fe content from 345 K for x = 0–80 K for x = 0.3. The magnetic entropy change |ΔSM| for the parent compound was evaluated using Maxwell's relation. The maximum value of the magnetic entropy change obtained from the M(H) plot data is |ΔSMMax| = 2.26 J kg−1 K−1 for applied magnetic field of 5 T. Our result on magnetocaloric properties suggests that the parent sample La0.67Ba0.22Sr0.11MnO3 could be a candidate refrigerant for low temperature magnetic refrigeration.

Ground State, Magnetization Process, and Magnetocaloric Effect of the Exactly Tractable Spin-Electron Tetrahedral Chain

A hybrid spin-electron system on one-dimensional tetrahedral chain, in which the localized Ising spin regularly alternates with the mobile electron delocalized over three lattice sites, is exactly investigated using the generalized decoration-iteration transformation. The system exhibits either the ferromagnetic or antiferromagnetic ground state depending on whether the ferromagnetic or antiferromagnetic interaction between the Ising spins and mobile electrons is considered. The enhanced magnetocaloric effect during the adiabatic demagnetization suggests a potential use of the investigated system for low-temperature magnetic refrigeration.

Large field-induced magnetocaloric effect and magnetoresistance in ErNiSi

Large magnetocaloric effect (MCE) and magnetoresistance (MR) together with negligible hysteresis loss have been observed in ErNiSi compound, which undergoes metamagnetic transition at low temperatures. Magnetization, heat capacity, and resistivity measurements confirm the metamagnetic transition. Both MCE and MR follow H2 dependence in the paramagnetic regime. The maximum value of isothermal entropy change (ΔSM) and MR for a field change of 50 kOe are found to be 19.1 J/kg K and ∼34%, respectively. Large MCE with negligible magnetic hysteresis loss could make this material promising for low temperature magnetic refrigeration.

Magnetic and magnetocaloric properties of rare earth intermetallic compounds HoCo2−xNix (x=0.75 and 1.25)

Magnetic and magnetocaloric properties of polycrystalline rare earth intermetallic compounds HoCo2−xNix (x=0.75 and 1.25) have been investigated. Both HoCo1.25Ni0.75 and HoCo0.75Ni1.25 compounds crystallize in MgCu2 type, cubic Laves phase structure (space group Fd3¯m, no. 227) and order ferromagnetically at ~40K and ~36K (TC) respectively. Field dependent magnetization at 5K shows soft ferromagnetic behavior. The saturation magnetization value is about 8.5μB/f.u. for both compounds. Magnetocaloric effect in HoCo2-xNix (x=0.75 and 1.25) compounds has been evaluated in terms of isothermal magnetic entropy change (ΔSm) that peaks around TC with maximum values of about −16.7J/kgK and −15.2J/kgK, respectively, for a field change of 70kOe. Substitution of Ni at the Co-site of HoCo2 broadens the magnetic transition and enhances relative cooling power which makes these materials suitable for low temperature magnetic refrigeration applications.

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 and magnetocaloric properties of equiatomic alloys RAl (R = Ho and Er)

Magnetic and magnetocaloric properties of binary equiatomic alloys RAl (R=Ho and Er) are investigated in this work. HoAl compound undergoes antiferromagnetic (AFM)–ferromagnetic (FM) transition at T1=13K, and FM-paramagnetic (PM) transition at the Curie temperature TC=20K, with temperature increasing. ErAl compound exhibits AFM-PM transition at the Néel temperature TN=9K. The maximal values of magnetic entropy change (ΔSM) are −22.5Jkg−1K−1 for HoAl and −16.4Jkg−1K−1 for ErAl for a magnetic field change of 0–5T. The values of refrigerant capacity (RC) are 379.5Jkg−1 and 259.7Jkg−1 for HoAl and ErAl respectively. The large magnetocaloric effect makes RAl (R=Ho and Er) compounds promising candidates for low-temperature magnetic refrigerants.

Large magnetocaloric effect and critical behavior in Sm0.09Ca0.91MnO3 electron-doped nanomanganite

The magnetic properties and magnetocaloric effect (MCE) in electron-doped Sm0.09Ca0.91MnO3 nanomanganite have been investigated in detail by magnetization and heat capacity measurements. The maximum magnetic entropy change and the relative cooling power (RCP) are found to be, respectively, and for a 7 T magnetic field change along with a negligible hysteresis loss, making of this material a promising candidate for magnetic refrigeration at low temperature. The maximum value of occurs close to the Curie temperature . The values of and RCP are comparable to a few hole-doped manganite. To investigate the nature of the paramagnetic-to-ferromagnetic phase transition, critical exponent study has been carried out. Based on the modified Arrott plot, we have determined the values of critical parameters ( and δ) and conclusively shown that Sm0.09Ca0.91MnO3 has nearly mean-field–like long-range interaction. The calculated values of critical exponents not only obey the scaling hypothesis, but also corroborate the results obtained employing the Kouvel-Fisher method. The re-scaled magnetic entropy change curves for different applied magnetic fields collapse into a single master curve for this electron-doped manganite indicating clearly a second-order magnetic phase transition. Such noticeably large at low magnetic field makes this material a potential candidate for low-temperature magnetic refrigeration.