Search

There is an urgent demand for the development of new resource-saving and high-efficiency cryogenic refrigeration technologies against the historical backdrop of increasing scarcity of resources and energy. Magnetic refrigeration technology based on the magnetocaloric effect (MCE) of magnetic materials is a promising approach to address helium resource constraints and improve energy efficiency. Here, a brilliant cryogenic magnetic refrigerant with a large low-field MCE and excellent refrigeration performance is presented. Benefiting from the enhanced ferromagnetism and low saturation magnetic field, the peaks of magnetic entropy change, refrigeration capacity, and adiabatic temperature change of Eu(Ti,Nb,Zr)O3 compounds reach 19.6 J·kg−1·K−1, 87.6 J·kg−1, and 5.5 K, respectively, for a field change of 0−1 T. Magnetic refrigeration experiments on a Gifford‒McMahon (GM)/magnetic hybrid refrigerator further demonstrated that EuTi0.8375Nb0.0625Zr0.1O3 is an excellent magnetic refrigerant operating near the liquid helium temperature. An appropriate amount of this magnetic refrigerant can significantly improve the refrigeration performance of the hybrid refrigerator. The cooling power in hybrid refrigeration mode is improved by a maximum of 52% over that in pure GM/HoCu2 mode at 4.2 K and 0.5 Hz. In addition, the cooling efficiency at 4.2 K is more than 40% greater than that of the pure GM/HoCu2 refrigerator.

Abstract Hysteresis is an inherent property of first-order transition materials that poses challenges for solid-state refrigeration applications. Extensive research has been conducted, but the intrinsic origins of hysteresis remain poorly understood. Here, we report a study of the kinetic origin of hysteresis and the enhanced barocaloric effect (BCE) in MnCoGe-based alloys with ~2% nonmagnetic In atoms. First-principles calculations demonstrate that substituting In atoms at Ge sites rather than Co sites results in a lower energy barrier, indicating a narrower hysteresis for the former. Combining neutron powder diffraction (NPD) with magnetic and calorimetric measurements completely verified the theoretical prediction. Electron local function (ELF) calculations further reveal the atomic coordination origin of regulated hysteresis due to weaker Co–Ge bonds when In atoms replace Ge, which is opposite to Co sites. Moreover, we experimentally investigate the BCE and find that although MnCo(Ge0.98In0.02) has a lower barocaloric entropy change ΔSP than does Mn(Co0.98In0.02)Ge, the reversible ΔSrev of the former is advantageous owing to a smaller hysteresis. The maximum ΔSrev of MnCo(Ge0.98In0.02) is 1.7 times greater than that of Mn(Co0.98In0.02)Ge. These results reveal the atomic-scale mechanism regulating hysteresis and provide insights into tailoring the functional properties of novel caloric refrigeration materials.

Abstract Plastic crystals as barocaloric materials exhibit the large entropy change rivalling freon, however, the limited pressure-sensitivity and large hysteresis of phase transition hinder the colossal barocaloric effect accomplished reversibly at low pressure. Here we report reversible colossal barocaloric effect at low pressure in two-dimensional van-der-Waals alkylammonium halides. Via introducing long carbon chains in ammonium halide plastic crystals, two-dimensional structure forms in (CH3–(CH2)n-1)2NH2X (X: halogen element) with weak interlayer van-der-Waals force, which dictates interlayer expansion as large as 13% and consequently volume change as much as 12% during phase transition. Such anisotropic expansion provides sufficient space for carbon chains to undergo dramatic conformation disordering, which induces colossal entropy change with large pressure-sensitivity and small hysteresis. The record reversible colossal barocaloric effect with entropy change ΔSr ~ 400 J kg−1 K−1 at 0.08 GPa and adiabatic temperature change ΔTr ~ 11 K at 0.1 GPa highlights the design of novel barocaloric materials by engineering the dimensionality of plastic crystals.

Objective:. This study was performed to explore the possible changes of the serum levels of the cytokines including interleukin 1α (IL-1 α), chemokine monocyte chemotactic protein 1 (also known as chemokine [C-C motif] ligand 2 [CCL2]), and C-X-C motif chemokine ligand 2 (CXCL2) in patients with pemphigus. Methods:. The expression levels of IL-1 α, CCL2, and CXCL2 in the serum of 57 patients with pemphigus PV (including 42 patients in progressive stage and 15 patients in remission stage) and 31 healthy controls were examined by enzyme-linked immunosorbent assay. The indepent-samples t-test was used to compare the two groups. One-way analysis of variance was used for multiple-group comparisons, and the post-hoc least significant difference test was used to detect differences among multiple groups. Results:. The serum expression levels of CCL2 and IL-1a were all significantly higher in the patients in progressive stage than in the controls ([2.69 ± 0.23] ng/mL vs. [2.55 ± 0.28] ng/mL, P = 0.043; [0.62 ± 0.27] ng/mL vs. [0.48 ± 0.23] ng/mL, P = 0.038, respectively). In addition, the serum expression level of CXCL2 was significantly higher in patients in progressive stage than in in the remission stage ([61.70 ± 46.38] ng/mL vs. [24.97 ± 18.46] ng/mL, P = 0.037). Sex, disease classification, disease severity, treatment, and mucosal involvement had no significant influence on the expression of IL-1 α, CCL2, or CXCL2 in the serum of patients groups and controls (all P > 0.05). Conclusion:. IL-1 α, CCL2, and CXCL2 are heavily involved in the occurrence and development of pemphigus and may be related to the activity of the disease.

Nanocrystalline RCo5 (R = Ce, La0.35Ce0.65, and misch-metal noted as MM) ribbons with hexagonal crystal structure and an average grain size of 5 nm have been prepared via a one-step melt-spinning technique. Coercivity as high as 13.0, 13.8, and 10.9 kOe has been obtained at 300 K for the CeCo5, La0.35Ce0.65Co5, and MMCo5 ribbons, respectively. High thermal stability is also achieved as shown by the high coercivity of 9.3 kOe, 10.2 kOe, and 8.8 kOe at 400 K for CeCo5, La0.35Ce0.65Co5, and MMCo5 ribbons, respectively. The coercivity mechanism is studied by magnetization analysis and microstructural observations. The nanocrystalline grains promote a strong exchange interaction, as indicated by the positive δM and the relatively high remanence ratio (∼0.8). In addition, the temperature dependence of coercivity of RCo5 ribbons shows the low coercivity temperature coefficient of −0.2% to −0.25%/K.

The multicaloric and coupled caloric effect of metamagnetic shape memory alloy Ni50Mn35In15 driven by hydrostatic pressure and magnetic field has been systematically investigated. The existence of pressure significantly changes the relationship between the magnetic volume coupling coefficient and temperature. Thermodynamic analysis indicates that the magnetocaloric effect at a certain pressure is equivalent to the magnetocaloric effect at ambient pressure adjusted by the coupled caloric effect (ΔScp). This theoretical result is verified by magnetic measurements under various pressures for the Ni50Mn35In15 with the inverse magnetocaloric effect. When a pressure of 0.995 GPa is applied, the peak value of entropy change can be as high as |ΔS| ∼ 25.7 J kg−1 K−1 upon a magnetic field change of 5–0 T, which increases by 8% compared to that of ambient pressure though the magnetization change (ΔM) across martensitic transition reduces 20% owing to the shift of the transition to higher temperature by 30 K. Detailed analysis indicates that the coupled caloric effect involving the strengthened magnetostructural coupling under pressure is responsible for the enhanced entropy change. The quantitative analysis of cross coupling term driven by dual fields reveals the essence of regulated magnetocaloric effect by pressure, which will be helpful for designing new materials based on the magnetostructural coupling strength.

Complicated magnetic phase transitions and Large magnetocaloric effects (MCEs) in RCoGe (R=Tb, Dy) compounds have been reported in this paper. Results show that the TbCoGe compounds have a magnetic phase transition from antiferromagnetic to paramagnetic (AFM-PM) at TN∼16 K, which is close to the value reported by neutron diffraction. The DyCoGe compound undergoes complicated phase changes from 2 K up to 300 K. The peak at 10 K displays a phase transition from antiferromagnetic to ferromagnetic (AFM-FM). In particular, a significant ferromagnetic to paramagnetic (FM-PM) phase transition was found at the temperature as high as 175 K and the cusp becomes more abrupt with the magnetic field increasing from 0.01 T to 0.1 T. The maximum value of magnetic entropy change of TbCoGe and DyCoGe compounds achieve 14.5 J/kg K and 11.5 J/kg K respectively for a field change of 0-5 T. Additionally, the correspondingly considerable refrigerant capacity value of 260 J/kg and 242 J/kg are also obtained respectively, suggesting that both TbCoGe and DyCoGe compounds could be considered as good candidates for low temperature magnetic refrigerant.

Materials with zero thermal expansion (ZTE) or precisely tailored thermal expansion are in urgent demand of modern industries. However, the overwhelming majority of materials show positive thermal expansion. To develop ZTE or negative thermal expansion (NTE) materials as compensators has become an important challenge. Here, we present the evidence for the realization of ultra-low thermal expansion in Mn–Co–Ge–In particles. The bulk with the Ni2In-type hexagonal structure undergoes giant NTE owing to a martensitic magnetostructural transition. The major finding is that the thermal expansion behavior can be totally controlled by modulating the crystallinity degree and phase transition from atomic scale. Self-compensation effect leads to ultra-low thermal expansion with a linear expansion coefficient as small as +0.68 × 10−6/K over a wide temperature range around room temperature. The present study opens an avenue to reach ZTE particularly from the large class of giant NTE materials based on phase transition.

The electric field dependent high-temperature small-polaron hopping conduction was investigated in patterned Pr0.7(Ca0.6Sr0.4)0.3MnO3 strips. The small-polaronic activation energy EA and the carrier localization were found to decrease with the reduction of the strip size. Meanwhile, a similar dependence on the strip size was also obtained for the calculated small-polaron coupling constants, which could be related to the strain relaxation in strips. These results indicate that the spatial confinement prefers to delocalize the carrier and reduce the electron-phonon interaction. Furthermore, opposite variation trends of EA under negative and positive electric field were found in the strips with small size, which could be attributed to the enhancement of polarization effect induced by the reduction of strip size.

The magnetic entropy change and resistivity measurements of LaFe11.375Al1.625 compound are discussed. Near constant magnetic entropy change in a wide temperature range from ~140 K to 210 K was observed in LaFe11.375Al1.625 due to the two closely spaced magnetic transitions at T(sub O) (~140 K) and T(sub N) (~181 K).

Magnetic properties and magnetocaloric effects (MCEs) have been investigated in hydrogenated La0.5Pr0.5Fe11.4Si1.6Hx (x=0, 0.9, and 1.6) compounds. It is found that the Curie temperature TC can be tuned from 189 to 317 K by adjusting hydrogen content from 0 to 1.6. It is attractive that both thermal and magnetic hysteresis are remarkably reduced because of the weakness of the itinerant-electron metamagnetic transition after hydrogenation, while the large magnetic entropy change is retained. The maximal hysteresis loss at TC decreases from 17.8 to 2.3 J/kg as x increases from 0 to 1.6. For the samples with x=0, 0.9, and 1.6, the maximal values of -ΔS are 26.3, 24.1, and 22.1 J/kg K at TC, with efficient refrigeration capacities of 463, 366, and 351 J/kg for a field change of 0–5 T, respectively. Large reversible MCE and small hysteresis with considerable value of refrigeration capacity indicate the potentiality of La0.5Pr0.5Fe11.4Si1.6Hx hydrides as a candidate magnetic refrigerant around room temperature. [ABSTRACT FROM AUTHOR]

Several studies are conducted to explain the magnetic properties, as well as the magnetoelectric properties of the hydrogenated [La.sub.0.5][Pr.sub.0.5][Fe.sub.11.4][Si.sub.1.6]Hx compounds. The various transitions that reduce the thermal, as well as magnetic hysteresis in these compounds are also discussed.

The various effects of B-addition on the hysteresis losses and the magnetic entropy changes taking place in the La[(Fe.Si).sub.13] compounds are discussed. B-doped compounds are shown to exhibit no hysteric losses.

Several magnetization measurements are conducted to explain the magnetic properties and the magnetocaloric effects observed in the antiferromagnetic ErTiSi compounds. These compounds are shown to be extremely beneficial for magnetic refrigeration applications.

Magnetic hysteresis loss and refrigerant capacity of the Na[Zn.sub.13]-type [La.sub.0.5][Pr.sub.0.5][Fe.sub.11.5-x][Co.sub.x][Si.sub.1.5] compounds are examined. Although the magnetic entropy change has decreased with increasing Co concentration, the hysteresis loss at [T.sub.C] also reduces because an increase in Co content can weaken the iterant electron metamagnetic transition.

The effect of Nd and Co substitution on magnetic entropy changes and hysteresis losses is examined for the cubic Na[Zn.sub.13]-type La[Fe.sub.13]-type La[Fe.sub.13-x][Si.sub.x] compounds. The Co-doped Na[Zn.sub.13]-type LaNdFeSi compounds might be a suitable candidate for magnetic refrigerant near room temperature.

The effects of substitution of Cu and Fe for Cd in Cd[Cr.sub.2][S.sub.4] on magnetic properties and magnetic entropy changes are examined. The maximum values of magnetic entropy change have suggested a potential of the sulfospinel as a magnetic refrigerant in the corresponding temperature range.

Effects of interstitial C atoms on the magnetic properties, magnetic transition and magnetic entropy changes, of LaFe11.5Si1.5 are discussed. The T(sub c) of LaFe11.5Si1.5C(sub y) carbides increases monotonously with increasing carbon concentration.

The textured Pr2Fe14B nanoflakes were produced by surfactant-assisted ball milling (SABM). Single phase tetragonal structure was characterized for the samples before and after SABM by X-ray diffraction (XRD). The thickness and length of the as-milled flakes are mainly in the range of 50-150 nm and 0.5-2μm, respectively. For the field-aligned Pr2Fe14B nanoflakes, the out-of-plane texture (the easy magnetization direction (EMD) along the c-axis) is indicated from the increasing (00l) peaks in the XRD patterns. SEM image demonstrates that the EMD is parallel to flaky surface, which is different from the RCo5 (R=rare earth) system with EMD perpendicular to the surface. We propose a hypothesis that the easy glide planes are related with the area of crystal planes. In addition, a large coercivity Hc=3.9 kOe is observed in the Pr2Fe14B flakes with strong texture. [ABSTRACT FROM AUTHOR]

The effect of the milling time on the structure, morphology, coercivity, and remanence ratio of textured PrCo5 nanoflakes produced by low power surfactant-assisted ball milling (SABM) was investigated. The X-ray powder diffraction (XRD) patterns indicate that the SABM PrCo5 samples are all CaCu5-type hexagonal structure. The average grain size is smaller than 10 nm when the SABM time is equal to or longer than 5.5 h. The thickness of nanoflakes is mainly in the range of 50-100 nm while the length is 0.5-5 μm when the SABM time reaches 8 h. For the field-aligned PrCo5 nanoflakes, the out-of-plane texture is indicated from the increasing (0 0 l) peaks in the XRD patterns, and the easy magnetization direction is perpendicular to the flake surface. The strong texture of PrCo5 nanoflakes leads to a large coercivity Hc (7.8 kOe) and obvious anisotropic magnetic behaviors for the aligned samples. [ABSTRACT FROM AUTHOR]

Magnetic entropy change (delta S) of a single crystal Ni(sub 50.1)Mn(sub 20.7)Ga(sub 29.6) alloy under different applied fields is investigated near the martensitic-austenitic structural transition temperature of 219 K. The phenomenon of the considerable magnetic entropy change under the relatively low applied field of 0.8 T and the easy adjustment of the martensitic-austenitic transition temperature indicate that Ni-Mn-Ga single crystal materials may have a possibility for practical applications as magnetic refrigerants.

The effect of the B-addition on magnetic entropy change ΔSM and hysteresis loss in La(Fe,Si)13 is studied. The maximal values of ΔSM for LaFe11.9Si1.1, LaFe11.5B0.4Si1.1, LaFe11.5Si1.5, and LaFe11.0B0.5Si1.5 are found to be 27.0, 26.1, 23.7, and 21.2 J/kg K at Curie temperature TC for a field change in 0-5 T, respectively. The maximal hysteresis losses around TC are 43 and 21 J/kg for LaFe11.9Si1.1 and LaFe11.5Si1.5, respectively, while almost no magnetic hysteresis is observed for the B-doped compounds. Our result reveals that a large ΔSM and a small hysteresis loss can be simultaneously achieved in NaZn13-type La(Fe,Si)13 compounds by the addition of B. [ABSTRACT FROM AUTHOR]

The electric field dependent high-temperature small-polaron hopping conduction was investigated in patterned Pr0.7(Ca0.6Sr0.4)0.3MnO3 strips. The small-polaronic activation energy EA and the carrier localization were found to decrease with the reduction of the strip size. Meanwhile, a similar dependence on the strip size was also obtained for the calculated small-polaron coupling constants, which could be related to the strain relaxation in strips. These results indicate that the spatial confinement prefers to delocalize the carrier and reduce the electronphonon interaction. Furthermore, opposite variation trends of EA under negative and positive electric field were found in the strips with small size, which could be attributed to the enhancement of polarization effect induced by the reduction of strip size. [ABSTRACT FROM AUTHOR]

Nd2Fe14B films with easy magnetization axis perpendicular to the film plane were grown onto Tabuffered piezoelectric (011)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) substrates using a magnetron sputtering technique. The film retains good permanent magnetic properties, with coercivities up to 1.4 T and spin reorientation near 150 K. Our investigations demonstrated that the converse piezoelectric effect generated by an electric field across the PMN-PT substrate can rotate the angle of spin reorientation of the Nd2Fe14B films, resulting in a considerable manipulation of magnetization by the electric field at temperatures below 150 K. The ratio of magnetization change reaches 30% in a magnetic field of 2 T when an electric field of 6 kV/cm is applied at 30 K. With increasing temperature, the electric field-induced tunability of magnetization decreases. These observations of permanent magnetic properties and electrically controlled magnetization effects make the Nd2Fe14B/PMN-PT heterostructure attractive for exploring multifunctional magnetic/electric devices. [ABSTRACT FROM AUTHOR]

We investigated the epitaxial strain effect on the small-polaron hopping conduction properties in Pr0.7(Ca,Sr)0.3MnO3 (PCSMO) films. An increase in the carrier localization, as evidenced by the enhancement of the small-polaron activation energy EA in the high temperature region, was obtained by increasing the epitaxial lattice strain in either the tensile or compressive strained film. Furthermore, it was found that the magnitude of EA, and thus the carrier localization, strongly depends on the sign of the lattice strain, which explains the diverse percolative transport behaviors in PCSMO films with different types of strains. Meanwhile, similar dependencies on the strain of the films were also obtained for the electron-phonon interaction, characterized by the calculated small-polaron coupling constant. Our results reveal that the type of lattice strain plays a crucial role in determining the degree of localization of charge carriers and the electron-phonon coupling strength, which is important for understanding the lattice strain-induced various novel properties related to phase separation and percolation behaviors. [ABSTRACT FROM AUTHOR]

MnCoGe-based compounds undergo a giant negative thermal expansion (NTE) during the martensitic structural transition from Ni2In-type hexagonal to TiNiSi-type orthorhombic structure. High-resolution neutron diffraction experiments revealed that the expansion of unit cell volume can be as large as ΔV/V ~ 3.9%. The optimized compositions with concurrent magnetic and structural transitions have been studied for magnetocaloric effect. However, these materials have not been considered as NTE materials partially due to the limited temperature window of phase transition. The as-prepared MnCoGe-based compounds are quite brittle and naturally collapse into powders. By using a few percents (3-4%) of epoxy to bond the powders, we introduced residual stress in the bonded samples and thus realized the broadening of structural transition by utilizing the specific characteristics of lattice softening enforced by the stress. As a result, giant NTE (not only the linear NTE coefficient α but also the operation-temperature window) has been achieved. For example, the average .. as much as -51.5 x 10(-6)/K with an operating temperature window as wide as 210 K from 122 to 332 K has been observed in a bonded MnCo0.98Cr0.02Ge compound. Moreover, in the region between 250 and 305 K near room temperature, the α value (-119 x 10-6/K) remains nearly independent of temperature. Such an excellent performance exceeds that of most other materials reported previously, suggesting it can potentially be used as a NTE material, particularly for compensating the materials with large positive thermal expansions. [ABSTRACT FROM AUTHOR]

Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (∼ -17.5 K) and positive colossal electroresistance (∼11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems. [ABSTRACT FROM AUTHOR]

Magnetic properties and magnetocaloric effects (MCEs) of the Dy3Co compound are studied. Two successive magnetic transitions: the antiferromagnetic (AFM)-to-AFM transition at T AF=29 K and the AFM-to-paramagnetic (PM) transition with increasing temperature at the Néel temperature T N=44 K are observed. Dy3Co undergoes a field-induced metamagnetic transition from the AFM to the ferromagnetic (FM) state below T N, giving rise to a large MCE. The maximal value of magnetic entropy change Δ S m is −13.9 J/kg K with a refrigerant capacity (RC) of 498 J/kg around T N for a field change of 0–5 T. A sign change of MCE in Dy3Co with magnetic field and temperature is observed near the critical field where the metamagnetic transition occurs. [ABSTRACT FROM AUTHOR]