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Magnetocaloric refrigeration is a solid-state cooling approach that promises high energy efficiency and low environmental impact. It remains uncompetitive with conventional vapor-compression technologies due to lack of high-performing materials that exhibit large magnetocaloric effects in low magnetic fields. Here we report a game-changing enhancement of the magnetocaloric response in a transition-metal-based Ni–Co–Mn–Ti. Mechanically and chemically stable rapidly solidified ribbons exhibit magnetic entropy changes as high as ∼ 27 J⋅kg−1K−1 for a moderate field change of 2 T, comparable to or larger than the best known materials for near-room temperature applications. The ribbons can be easily manufactured in large quantities and the transition temperature can be adjusted by varying Co concentration. Image 1 [ABSTRACT FROM AUTHOR]

Abstract We investigate the electrical transport and dielectric properties of the nanocrystalline BaCo 0.9 Mn 0.1 O 3-δ under 2H- and 12H-type hexagonal phases. Temperature dependent electrical transport properties under 2H- and 12H-type phases show semiconducting-like behavior above the magnetic transition. The numerical value of electrical resistivity of the 12H-type phase at low temperature is 10-fold higher than the 2H-type counterpart, following the trend of structural stacking sequence. The 12H-type phase exhibits rarely known characteristics of ferromagnetic-insulator. The conduction mechanism under both phases is studied using variable range and small polaron hopping conduction mechanism. The 12H-phase shows large magnetoresistance (∼60%) under an application of 5 T of magnetic field at 50 K. The relation between magnetization and electrical resistivity around the magnetic ordering temperature is studied. The relation has been used to correlate the magnetic entropy change derived by magnetization and electrical resistivity measurements. Temperature dependence and magnetic field induced dielectric permittivity of the 2H- and 12H-type hexagonal phases is studied around the magnetic ordering temperature. Both phases exhibit dielectric suppression by magnetic ordering. The field dependence dielectric behavior shows magnetocapacitance value of ∼4% for 2H-phase and ∼94% for 12H-phase at their magnetic ordering temperature under external magnetic field of 5 T. The existence of intrinsic magneto-dielectric coupling is studied under the framework of Ginzburg-Landau theory for ferroelectromagnet. The origin of extrinsic magneto-dielectric contribution is justified using combinational effect of large negative magnetoresistance and Maxwell-Wagner effect. The magnetic and electrical transport properties of the nanocrystalline BaCo 0.9 Mn 0.1 O 3-δ compound are also studied using density of states. Nanocrystalline BaCo 0.9 Mn 0.1 O 3-δ sample shows novel magnetic field-induced effect on the magnetic, electric and dielectric properties around the same temperature window which could be utilized for multi-functional applications. Highlights • Electrical transport and dielectric properties of nanocrystalline BaCo 0.9 Mn 0.1 O 3-δ. • Relation between magnetic and electrical transport properties. • Study of physical properties using density of states (DOS) plots. • Magnetoresistance and magnetocapacitance properties. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The MnNiGe 1−x Ce x (x = 0.05, 0.10 and 0.15) melt-spun ribbons were synthesized by arc melting. • The crystal structure of MnNiGe 1-x Ce x is measured by room-temperature/ in situ synchrotrons XRD. • The phase transition temperature of MnNiGe 1-x Ce x is impacted by Ce doping concentration. Abstract The MnNiGe 1−x Ce x (x = 0.05, 0.10 and 0.15) melt-spun ribbon flakes were obtained using a melt spinner system in a high purity Argon environment. The crystal structure of the samples was measured by room temperature XRD and in situ synchrotron XRD. The magnetic properties were investigated by PPMS. The results indicated after introducing Ce, the magnetic phase transition (AFM/FM) and structural phase transition (hexagonal/orthorhombic) happened simultaneously in MnNiGe 1−x Ce x , resulted in an enhanced entropy change over the pure phase transition (PM/FM) in MnNiGe. This research showed that partial substitution of Ge with Ce can effectively decrease the Curie temperature of the hexagonal phase and increase the entropy change. This paper proposed an effective way to tune the magneto-structural phase transition temperature. [ABSTRACT FROM AUTHOR]

Abstract The structure, magnetic transition and magnetocaloric properties of half-Heusler CoMnSn 1-x Cu x alloy have been investigated. X-ray diffraction reveals that a main phase of hexagonal structure was obtained in alloys, and there is no obvious secondary phase observed in the less doped samples. The impurity phases appear only when the Cu doping level is high, and the amount of impurity phases is less than 0.7 mol.% in the sample x = 0.10. The substitution of Cu for Sn is found to decrease in c/a lattice parameter and cell volume. ZFC and FC measurements show that a magnetic transition from ferromagnetic to paramagnetic phase occurs around 150 K in CoMnSn 1-x Cu x alloy, and the magnetization and Curie temperature of samples can be tuned by the Cu content, in which the magnetization of alloys decreases with the increasing Cu content, while Curie temperature increases by 13 K. The maximum of magnetic entropy change (ΔS M) in a magnetic field change of 5 T is found to be 17.4(2) J/(kg·K) with a large refrigerating capacity of 230.3(8) J/kg for x = 0.02, revealing that CoMnSn 1-x Cu x alloy with the second-order magnetic transition can provide a considerable magnetocaloric effect at a low cost, which suggests a promising candidate for magnetic refrigeration materials. Highlights • A hexagonal structure was obtained in half-Heusler CoMnSn 1-x Cu x alloys. • Magnetization and Curie temperature of alloys can be tuned by the Cu content. • The alloys exhibit a large magnetic entropy change without thermal hysteresis. • Refrigerating capacity of CoMnSn 1-x Cu x alloy reaches 230.4 J/kg under ΔB = 5 T. [ABSTRACT FROM AUTHOR]

Abstract It is demonstrated that alloying additions of Ga and Ge enable tuning of the magnetocaloric response of the intermetallic boride AlFe 2 B 2. Samples of nominal chemical composition Al 1.2-x M x Fe 2 B 2 (M = Ga, Ge; x ≤ 0.30) were synthesized via suction casting (arc-melting and vacuum drawing into cylindrical copper molds) and subsequent heat treatment (annealed to 1373 K for 72 h). The saturation magnetization (M s), Curie temperature (T c) and specific heat capacity (C p) of the samples all increase with increased Ga and/or Ge additions. Relative to the unmodified parent AlFe 2 B 2 compound, a larger than two-fold improvement in the magnetic entropy change (Δ S (μ 0 H app = 2 T) = 6.5 J kg−1K−1) and adiabatic temperature change (ΔT ad (μ 0 H app = 2 T) = 2.2 K) was observed at 305 K in a sample of composition Al 1.1 Ga 0.05 Ge 0.05 Fe 2 B 2. The enhanced magnetocaloric response of the Al 1.2-x (Ga,Ge) x Fe 2 B 2 system is ascribed to a complex amalgamation of chemical bonding and electronic effects that arise due to Fe and Al antisite defects within the AlFe 2 B 2 lattice. Overall, these results provide insight of both fundamental and applied relevance concerning pathways for maximizing the magnetocaloric potential of AlFe 2 B 2 for potential energy-related applications near room temperature. Graphical abstract Image 1 Highlights • Addition of Ga/Ge enables tuning of the magnetocaloric effect (MCE) in AlFe 2 B 2. • The magnetization of Al 1.2-x (Ga/Ge) x Fe 2 B 2 alloys increase with Ga/Ge content (x). • Over two-fold improvement in MCE was noted in the Al 1.1 Ga 0.05 Ge 0.05 Fe 2 B 2 sample. • Enhanced MCE is ascribed primarily to intrinsic factors (mainly antisite defects). • Results provide guidelines for tailoring the magnetocaloric potential of AlFe 2 B 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • TbMn 2 Si 2-x Ge x exhibit large entropy change accompanying two successive phase transitions at T C1 and T C2. • Neutron diffraction investigations have established the formation of a Fmc-ii + F(Tb) between T C1 and T C2. • Existence of Fmc-ii + F(Tb) magnetic cell leads to a pronounced anomalies in the heat capacity. • Different responses of T C1 and T C2 to external field related to Fmc-ii + F(Tb) is highly unusual. The lack of magnetic refrigeration (MR) materials with high magnetocaloric effect (MCE) and large relative cooling power (RCP) in the temperature range required for hydrogen liquefaction (20 K–77 K) is a bottleneck for practical applications of MR cooling systems. The present investigation of TbMn 2 Si 2-x Ge x compounds (x = 0.1, 0.2) by variable temperature neutron and synchrotron X-ray diffraction, magnetization and heat capacity measurements, establish that substitution of Si with Ge in TbMn 2 Si 2 leads to a significant enlargement of the unit cell and modification of the magnetic properties. Two consecutive ferromagnetic first-order transitions occur below 77 K with the third transition from paramagnetism to a collinear antiferromagnetic state being determined around 500 K. The resultant plateau-like MCE with large RCP below 77 K in these designed compounds offers scope for application for hydrogen liquefaction. Detailed neutron investigation confirm that four magnetic states exist within the temperature range 5 K to 500 K, with two successive first-order magnetic transitions below 77 K responsible for the large MCE. Our specific heat studies provide evidence of strong contributions from the nuclear specific heat and the corresponding nuclear specific heat coefficients of A = 430 ± 50 mJ mol−1 K and A = 418 ± 60 mJ mol−1 K have been determined for TbMn 2 Si 2-x Ge x with x = 0.1 and x = 0.2, respectively. The overlapping entropy curves near these successive transitions lead to a plateau-like magnetothermal effect as well as a large reversible MCE for both samples (e.g. ΔS M max = 14.0 J/kg K and ΔT max = 7.6 K; RCP = 379 J/kg for TbMn 2 Si 1.9 Ge 0.1 for an applied field of 5 T) indicating that the material can operate over a wide temperature range – particularly for hydrogen liquefaction. [ABSTRACT FROM AUTHOR]

• The samples crystallize in the rhombohedral structure with R-3c space group. • All samples exhibit a second order transition. • Our samples can be considered as a potential material for magnetic refrigeration. During this study, we were conducted to analyze the properties of structural, magnetic, magnetocaloric, electrical resistivity and magnetoresistance (by applying magnetic fields of zero, 2 and 5T) of ceramics La 0.6 Ce 0.05 Ba 0.35 Mn 1-x Ru x O 3 (0 ≤ x ≤ 0.2). These samples are prepared by solid-state reaction. The compounds have simple rhombohedral structure R-3c space group. Arrot curves display that all materials exhibit a second-order magnetic transition from ferromagnetic to paramagnetic order. All the manganites synthesized show a maximum variation in magnetic entropy (|ΔSM|) with values between 6.2 J/kg.K for x = 0 and 3.4 J/kg.K for x = 0.2. In addition, the relative cooling power (RCP) values are very important (160 J/kg for x = 0 to 248 J/kg for x = 0.2). Environment-friendly compounds applied in the domestic refrigeration. The samples La 0.6 Ce 0.05 Ba 0.35 Mn 1-x Ru x O 3 (0 ≤ x ≤ 0.1) show a transition from ferromagnetic-metal (FM) to paramagnetic-insulator (MI). Sample La 0.6 Ce 0.05 Ba 0.35 Mn 0.8 Ru 0.2 O 3 exhibits semiconductor behavior over the entire temperature range. The metallic conduction is due to the diffusion of electrons (by the phonons and the grain boundaries) while the semiconducting behavior is due to the attendance of polarons. The curves of the compounds (0 ≤ x ≤ 0.1) in the metallic region (T < Tp), have been fitted to the equation ρ = α T 2 + β T 5 + 1 (γ + δ T 1 / 2 ) . For the high temperature, the semiconductor region was fitted by the small polaron hopping model (ASPH) and by the variable hopping range model (VRH). The electrical resistivity behavior indicates that the substitution of Ru3+ ions weakened the double exchange process and improved the Jahn-Teller effect. Studies of magnetoresistance (MR) under 2 and 5 T magnetic field show two kinds of contribution: one is intrinsic MR and the other is extrinsic MR. [ABSTRACT FROM AUTHOR]

Single crystals are highly desirable to study intrinsic properties of phase transitions, unfortunately due to an embrittlement at the transformation, (Mn,Fe) 2 (P,Si) studies were so far limited to polycrystalline samples. Here, we report the growth of (Mn,Fe) 2 (P,Si) single crystals which can be cycled across their first-order ferromagnetic transition. In single crystals with optimized composition, detailed magnetization measurements reveal a ferromagnetic transition whose shape is significantly different from polycrystalline samples, with unusual discontinuous magnetization steps induced by temperature or magnetic field leading to a stair-like transition. In contrast to the "virgin effect" of (Mn,Fe) 2 (P,Si) samples, this behavior is reproducible. This unique magnetic response of some (Mn,Fe) 2 (P,Si) crystals can be correlated to a microstructure very different from that of the bulk and preserving the clamping/release role played by strains and stresses at the ferro-paramagnetic transformation. On top of offering more details on how the first-order magnetic transition develops in time, space and as a function of the driving parameter, which is of importance for designing functional magnetocaloric materials, the growth of cyclable crystals opens new possibilities for future experiments. [Display omitted] • growth of (Mn,Fe) 2 (P,Si) crystals cyclable across the ferromagnetic transition. • significantly enlarged thermal hysteresis in crystals compared to the bulk. • successive and reproducible magnetization steps at the ferromagnetic transition. • strains/stresses are responsible for an irregular development of the transition. [ABSTRACT FROM AUTHOR]

In this study, we investigate the magnetic and magnetocaloric properties of nanostructured La 0.6 Sr 0.4 CoO 3 (LSC) samples synthesized under confinement conditions within porous templates. Using this method, we obtained de-agglomerated nanoparticles, which provide us with the feasibility of applying them in nanoparticle films that can be tailored to intricate geometries. We specifically explored the impact of pore size of the template on key parameters including saturation magnetization (M S), Curie temperature (T C), maximum entropy change (ΔS), and relative cooling power (RCP). Our findings reveal enhancements in those quantities, that are likely to be related with the nanostructure of the samples, indicating the potential of nanostructured LSC as an active material for magnetic refrigeration devices. Our alternative approach of synthesizing magnetocaloric materials under confinement conditions presents an exciting prospect for future research and development in the field. • For the first time we investigated the magnetocaloric properties of nanostructured tubes of La 0.6 Sr 0.4 CoO 3 perovskites. • The Curie temperature, saturation magnetization and coercive filed is affected by changing the morphology on the samples. • A favorable impact on the magnetocaloric effect can be achieved by nanostructuring La 0.6 Sr 0.4 CoO 3 perovskites. [ABSTRACT FROM AUTHOR]

LaFe 13−x Si x H z alloys are promising candidates for room temperature magnetic refrigeration, but their brittle behaviour hinders their shaping into magnetocaloric devices. Metal bonding of LaFe 13−x Si x H z particles has been performed to overcome this issue, but the fabrication processes reported so far involve the exposure of LaFe 13−x Si x H z particles to temperatures where dehydrogenation occurs, which deteriorates their magnetocaloric properties. This work proposes two processing routes (P1 and P2) which were carried out entirely at room temperature, hence avoiding dehydrogenation. Route P1 consisted of binding LaFe 13−x Si x H z particles with Sn, while in route P2 two binders were combined: Sn and Cu. Final average porosities were equal to 12.8 % (P1) and 12.1 % (P2), which are comparable to what has been reported for hot processed composites, and differential scanning calorimetry analyses indicated that dehydrogenation did not occur during processing, an improvement in comparison to hot processing. Complementarily, the mechanical behaviour of the composites was investigated via Weibull analysis. Characteristic strengths of 49.9 MPa (P1) and 60.7 MPa (P2) were found under uniaxial compression, showing that the combination of Cu and Sn as binders promoted higher strength. Weibull moduli of 10.9 (P1) and 8.8 (P2) were identified, which are greater than what has been previously reported for a bulk alloy, indicating that embedding LaFe 13−x Si x H z particles in a metallic matrix led to a less brittle-like behaviour. [Display omitted] • Room temperature processing La-Fe-Si-H powders to avoid hydrogen losses. • Final porosity of composites similar to achieved by hot processes. • Weibull's analysis used to investigate mechanical behavior of the compounds. • Metal bonding lead to major mechanical strength and reliability of composites. [ABSTRACT FROM AUTHOR]

• Ferrimagnetic transition temperature (T c) gets reduced from 555 (x = 0.0) to 545 K (x = 1.0). • Low temperature M−T curves show spin reorientation, magnetic compensation and paraprocess transition (T B). • - Δ S M is enhanced from 3.92 (x = 0.4) to 4.30 (x = 0.8) J / k g K at 5 T magnetic field. • The measured samples exhibit both normal and inverse magneto caloric effect. • Relative cooling power for x = 0.4 and 0.8 sample is 364.6 and 313.0 J / k g , respectively. • Positive slope in Arrott plots indicate second-order phase transition. The D y 1 - x H o x 3 F e 5 O 12 (Ho-DyIG) with x = 0.0 to 1.0 garnet samples are prepared by solid-state reaction route by sintering them at 1200 °C for 24 hours followed by calcination. The samples have simple cubic structure with Ia 3 ¯ d space group. The lattice constant is obtained from the Rietveld refinement technique and is found to be decreased from 12.4181 Å to 12.3858 Å with Ho doping. All the samples exhibit ferrimagnetic behavior below their transition temperature of 555 K (x = 0.0) to 545 K x = 1.0 . This drop in transition temperature is attributed to the dilution of F e a - O - F e d networks. All the samples show magnetic compensation because of the strong anisotropy induced at lower temperatures. In addition, we have also observed spin reorientation in all the samples of Ho-DyIG series. We have performed magnetocaloric measurements for x = 0.4 and 0.8 samples and observed that the magnetic entropy is improved from 3.92 to 4.30 J / k g K when measured at a maximum applied field of 5 T around their respective Belov tranistion temperature i.e. T B. We have seen both normal and inverse magnetocaloric effects in these samples. To test the extent of magnetic refrigeration capacity, we have calculated the Relative Cooling Power, which comes out to be 364.6 J / k g for x = 0.4 and 313.0 J / k g for x = 0.8 samples at 5 T magnetic field. The Arrott plots are also investigated and they have positive slope suggesting the presence of second-order phase transition in our samples. [ABSTRACT FROM AUTHOR]

We investigated the anisotropic magnetic, electrical transport, and heat capacity of Eu 4 Ga 8 Ge 16 single crystals. Magnetization measurements with temperature and magnetic field revealed a complex behavior. Specifically, we observed anisotropic metamagnetic transitions at low magnetic field, and inverse hysteresis at high magnetic fields. These phenomena can be attributed to a Heisenberg ferromagnetic spin chain aligned along the a-axis. Additionally, this ferromagnetic behavior is interspersed with antiferromagnetic interactions between adjacent Heisenberg spin chains. We also noticed an anomalous increase in electrical resistivity at low temperature under magnetic fields, as well as different temperature-exponents of ρ(T) depending on crystal directions, which are attributed to the anisotropic scattering of carriers due to anisotropic magnetic interactions. We also evaluated the magnetocaloric effect and found a substantial magnetic entropy change than those of type-I Eu-based clathrates. The high entropy change (-Δ S M = 13.5 J kg−1 K−1) and adiabatic temperature difference (Δ T ad = 7.8 K) near Néel temperature T N = 7.9 K reveal that the Heisenberg spin chain system might be advantageous for inducing a larger magnetic entropy change. Furthermore, we measured the hydrogen storage capacity of Eu 4 Ga 8 Ge 16 as a multifunctional property because the zeolite-like cage structure can be a good candidate for hydrogen storage applications. Although the hydrogen storage capacity is considerably lower than that of the leading-edge materials, the hydrogen storage capacity can be improved further when we control the Eu-deficiency to place the hydrogen molecule at the cage site, because the hydrogen molecules reside at the (Ga,Ge) framework not in the cage site for fully occupied Eu atomic chain compounds. Hence, Eu 4 Ga 8 Ge 16 emerges as a versatile substrate for engineering multifunctional energy materials, excelling in both low-temperature magnetocaloric effects and hydrogen storage potential. • Unconventional magnetic and electrical transport properties of Eu 4 Ga 8 Ge 16 single crystals. • High spin entropy change and adiabatic temperature difference near Neel temperature. • Hydrogen storage properties of the compound. • Quasi-1D Heisenberg ferromagnetic spin chains with antiferromagnetic alignment. • Multi-functional properties of the zeolite cage quasi-1D spin structure in Eu 4 Ga 8 Ge 16 compound. [ABSTRACT FROM AUTHOR]

This review of the current state of magnetocalorics is focused on materials exhibiting a giant magnetocaloric response near room temperature. To be economically viable for industrial applications and mass production, materials should have desired useful properties at a reasonable cost and should be safe for humans and the environment during manufacturing, handling, operational use, and after disposal. The discovery of novel materials is followed by a gradual improvement of properties by compositional adjustment and thermal or mechanical treatment. Consequently, with time, good materials become inferior to the best. There are several known classes of inexpensive materials with a giant magnetocaloric effect, and the search continues.

The magnetic and magnetocaloric effects of potassium-substituted La0.8−xKxBa0.05Sr0.15MnO3 (0 ≤ x ≤ 0.20) manganite were explored. The samples in polycrystalline form were synthesized by the sol–gel method, with a final sintering temperature of 1100 °C. Powder X-ray diffraction (XRD) patterns refined by Rietveld refinement show that all samples crystallized in rhombohedral structure with R-3c space group. The unit cell volume of the samples decreases with increasing potassium concentration. In addition, small changes in average bond length and bond angle are also observed in the samples. Scanning electron microscope (SEM) images reveal that the largest average grain size was observed for x = 0.10. Field-cooled (FC) magnetization measurements show that the Curie temperature ( T C ) of the samples increases from 320 K for x = 0 to 360 K for x = 0.2. The largest magnetocaloric (MCE) effect, which is represented by maximum magnetic entropy change (− Δ S M , M A X ), reaches its greatest value for the x = 0.10 sample. The monotonous increase in T C suggests that TC is mainly governed by the ferromagnetic coupling between Mn ions induced by the changes on average bond length and bond angle. The obtained − Δ S M , M A X value suggests that MCE property is more sensitive to Zener theory of double exchange, which is strongly related to the Mn3+/Mn4+ ratio of the samples.

Currently, magnetocaloric refrigeration technologies are emerging as ecofriendly and more energy-efficient alternatives to conventional expansion-compression systems. However, major challenges remain. A particular concern is the mechanical properties of magnetocaloric materials, namely, their fatigue under cycling and difficulty in processing and shaping. Nevertheless, in the past few years, using multistimuli thermodynamic cycles with multicaloric refrigerants has led to higher heat-pumping efficiencies. To address simultaneously the challenges and develop a multicaloric material, in this work, we have prepared magnetocaloric-based flexible composite mats composed of micrometric electroactive (EA) polyvinylidene fluoride (PVDF) fibers with embedded magnetocaloric/strictive La(Fe,Si) 13 particles by the simple and cost-effective electrospinning technique. The composite's structural characterization, using X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, and measurements of the local-scale piezoresponse, revealed a cubic NaZn 13 -type structure of the La(Fe,Si) 13 phase and the formation of the dominant polar β-phase of the PVDF polymer. The PVDF-La(Fe,Si) 13 composite showed an enhancement of the longitudinal piezoelectric coefficient (effective d 33 ) (-11.01 pm/V) compared with the single PVDF fiber matrix (-9.36 pm/V). The main magnetic properties of La(Fe,Si) 13 powder were retained in the PVDF-La(Fe,Si) 13 composite, including its giant magnetocaloric effect. By retaining the unique magnetic properties of La(Fe,Si) 13 embedded in the electroactive piezoelectric polymer fiber mats, we have designed a flexible, easily shapeable, and multifunctional composite enabling its potential application in multicaloric heat-pumping devices and other sensing and actuating devices.

Highlights • A novel concept of the rare-earth-free electromagnetic field source is proposed. • The new concept introduces the magnetic energy recovery. • The device was designed, numerically analysed and experimentally validated. • A comparative analysis of different types of magnetic-field-sources was conducted. • The results reveal the new concept can strongly outperform existing electromagnets. Abstract This article reports on the novel resistive electromagnetic field source with the magnetic energy recovery, which enables the use of the static magnetocaloric regenerator. Most of the existing prototype magnetocaloric devices that operate near room temperature, use magnetic field sources consisting of permanent magnets. The alternating of the magnetic field that is required for the thermodynamic cycle often comes from the rotation of magnets over the refrigerant, that is, an active magnetocaloric regenerator (AMR). Such systems require moving parts and a motor drive, both of which cause additional costs and reduced energy efficiency. Further restrictions in existing devices result from the speed of the magnetisation/ demagnetisation process, which is, in addition to efficient heat transfer, crucial for the compactness of the device. Another drawback is that the instant change of the magnetic field is not feasible, regardless of the principle of movement. Permanent-magnet assemblies based on neodymium are also constrained by the use of this rare-earth-material. Therefore, a number of global research activities relate to the optimization of permanent-magnet-based magnetic field sources. However, ohmic loss, the active cooling of magnets, and considerable energy consumption are the reasons why another type of magnetic field source, that is, the electromagnet, was generally avoided by the magnetocaloric community. This article presents a novel and unique approach that enables substantially improved energy efficiency and applicable operation of rare-earth-free and static electromagnetic field sources, by implementing for the first time the magnetic energy recovery for magnetic refrigeration and heat pumping. To prove the advantages of such a system, a large number of numerical simulations, as well as an experimental proof, were conducted. A comparative analysis was made for the evaluation of the energy efficiency of the proposed novel system vs an example of the existing rotating-magnet assembly. The results of this study reveal that this new type of electromagnetic field sources provides a number of different and important advantages that can lead to new frontiers in research. However, the energy efficiency is still lower than that of the comparable rotating-magnet assembly. [ABSTRACT FROM AUTHOR]

A series of rare-earth-doped Ni43-xRxMn46Sn11 (x = 0, 1 and R = Pr, Gd, Ho, Er) alloys was fabricated by arc melting, and their structural, magnetic, and magnetocaloric properties were studied through room temperature X-ray diffraction (XRD), differential scanning calorimetry, and magnetization measurements. Analysis of XRD data reveal that the alloys crystallize in the cubic L21 austenite phase structure as the major phase with a small trace of martensitic phase (MP). The martensitic transition temperature (TM) shifts to consecutive higher temperatures with the substitution of Pr, Gd, Ho, and Er. A drastic shift in TM by ~60 K relative to the parent compound (TM = 195 K) was found for Ni42PrMn46Sn11. Large values of magnetic entropy changes (ΔSM) of 32 (Pr), 28 (Gd), and 25 J · kg-1 · K-1 (Ho) were obtained at TM for ΔH = 50 kOe. A maximum value of the refrigeration capacity of ~250 J · kg-1 was obtained in the vicinity of TM for ΔH = 50 kOe for the Ho-doped compound. A large exchange bias effect with HEB ~ 1.1 kOe at 10 K was observed for the Pr-doped compound in its MP. [ABSTRACT FROM AUTHOR]

Double-perovskite oxides Sri>98 Nda.02FeMoO6 and Srx. 96 Nd0.04 FeMo(_)6 were prepared by sol-gel method. X-ray diffraction analyses suggest that all the samples are single phase and belong to 14/m space group. With Nd doping, the Rietveld refinement measurements show that the order of Fe/Mo decreased. The magnetic hysteresis curves and the magnetization-temperature curves of these compounds were measured using a vibrating sample magnetometer. Magnetic hysteresis curves and field-cooled magnetization curves indicate that all the compounds have good ferromagnetic properties. H/M-M2 curves analyses indicate a second-order magnetic transition. With Nd doping, Curie temperature and magnetic moment of the cell decreases. M - T curves under different external magnetic field indicate that the blocking temperature shift to lower values with increasing applied magnetic field. [ABSTRACT FROM AUTHOR]

Abstract The polycrystalline La 0.67 Sr 0.33 MnO 3.01 sample was synthesized by standard solid state technique. Crystal structure of sample belongs to rhombohedral system with space group R 3 − c. The parameters are a = 0.55003(2) and c = 1.33753(4) nm for indexing in hexagonal system and a ′ = 0.54689 nm and α = 60.38° for indexing in rhombohedral system. In order to obviously reveal the magnetic interaction we study the critical behavior by the modified Arrott plot, the Kouvel-Fisher method and the critical isotherm technique. Three main critical exponents, β , γ and δ , are derived from different three methods mentioned above. The three critical exponents obey the Widom relation and are able to collapse the different isothermal magnetization data into two branches below and above T C based on the single scaling equation M (H , ε) = ε β f ± (H / ε β + γ ). The critical exponents, β and γ , are on the verge of the theoretical prediction of a mean-field model, implying the existence of long-range magnetic interaction with magnetic exchange distance decaying as J(r) ≈ r −4.57. The exponent n in the power relation Δ S m ∝ H n dependence of temperature increases with temperature decreasing and approaches to 1 well below T C and increases with temperature increasing and approaches to 2 well above T C. Near T C the n = 0.669 is very close to 2/3. These data support that the magnetic interaction can assign to mean-field model. The RCP increases with applied magnetic field and is about 40 J/kg under 1.2 T applied field. Graphical abstract Scale plot with m2 vs h/m below and above T C using critical exponents determined from KF method. Image Highlights • The Curie temperature of La 0.67 Sr 0.33 MnO 3 compound is 394 K. • The critical exponents, β , γ and δ are 0.588, 1.116 and 3.196, respectively. • The magnetic interaction is attributed to long range interaction. • At near T C the n = 0.669 is very close to 2/3. • The RCP is about 40 J/kg under 1.2 T applied field. [ABSTRACT FROM AUTHOR]

Highlights • Investigation of the needed improvement in the properties of magnetocaloric materials. • The requirements for non-magnetic properties are also discussed. • Comparison between the existing refrigerators and simulated magnetic ones. • For demanding conditions and compact designs better materials are needed. Abstract A primary motivation underlying the research on room-temperature magnetic refrigeration is reaching energy efficiency levels beyond what is achievable with vapor-compression technology. However, the goal of building commercially viable magnetic refrigeration systems with high performance and competitive price has not been achieved yet. One of the obstacles to reach this goal is the inadequate properties of the currently existing magnetocaloric materials. In this article, the needed improvements in the properties of the magnetocaloric materials are investigated. Two existing vapor-compression refrigerators are used as reference for the required performance, and magnetic refrigerators are simulated using a numerical model. Apart from the requirements such as uniformity of transition temperature for each layer, small increment in transition temperature in adjacent layers, and mechanical strength of the materials, the study shows that for the investigated cases materials with adiabatic entropy change 2.35 times larger than the existing materials are needed to outperform vapor-compression systems. [ABSTRACT FROM AUTHOR]

Caloric refrigeration is an emerging class of cooling technologies based on caloric effects detected in ferro-caloric solid-state materials. Depending of the nature of the driving field, it is possible distinguishing four main caloric refrigerations: magnetocaloric, electrocaloric, elastocaloric and barocaloric. Therefore, caloric refrigeration is based on solid-state materials, unlike vapor compression, nowadays still the most diffused cooling technique, whom employs fluids as refrigerants. Solid-state materials do not provide a direct contribution in global warming, since they do not disperse in the atmosphere, but only an indirect impact is registered when they are employed as refrigerants in cooling systems. On the other side, a vapor compression plant is characterized by both direct and indirect contributions to global warming. The main parameter to evaluate global warming impact and carbon-dioxide emissions coming out from a cooler is the Total Environmental Warming Impact (TEWI) index, which accounts both the direct and indirect contributions produced. In this paper a numerical ?TEWI analysis is presented, comparing the environmental impact of a caloric refrigerator, operating with different caloric materials, with the one of a vapor compression cooler working with HFC134a. [ABSTRACT FROM AUTHOR]

Magnetic cooling systems near room temperature have attracted attention as an attractive, “green,” thermal management technology, offering high energy efficiency and environmental friendliness. There is an urgent need for low-cost, easy-to-manufacture magnetocaloric materials for such applications. We report the magnetocaloric properties of low-cost, high-relative-cooling-power (RCP) Fe75–xMnxAl25 ($12.5 \le x \le 25$) alloys with tunable Curie temperatures. A second-order magnetic phase transition, with negligible magnetic and thermal hysteresis, was observed. Fe60Mn15Al25 and Fe57.5Mn17.5Al25 buttons exhibited high values of RCP, i.e., 395 and $430\,\,\text {J}\cdot \text {kg}^{-1}$ , respectively, and Curie temperatures near room temperature. Universal scaling behavior and local exponent analyses of the thermodynamic data were performed. The low cost, easy availability, and established manufacturing technology are additional advantages of these alloys. [ABSTRACT FROM AUTHOR]

Abstract We studied the magnetic and magnetocaloric properties of (La, A)MnO 3 (A = divalent metal) compounds on basis of the double-exchange Kubo-Ohata model considering magnetoelastic interactions. The adequacy of the calculations is demonstrated by comparison with experimental magnetization curves for the La 0.69 Pb 0.31 MnO 3 and La 0.75 Ca 0.25 MnO 3 compounds. For the case of divalent admixture La 2/3 (Ca 1-x Sr x) 1/3 MnO 3 we calculated successfully the isothermal magnetocaloric potential for this series of compounds. Additionally, we showed a correlation between the compressibility and the η -parameter which defines the order of the transition. Highlights • A thermodynamic route to study the magnetocaloric effect in manganites. • Application of the Kubo-Ohata exchange model considering the magnetoelastic term. • Implementation of the model with the Zeeman term in the Gibbs free energy. [ABSTRACT FROM AUTHOR]

Abstract Both magnetic transition and magnetocaloric properties of LaFe 11.6 Si 1.4 doped with boron (B) and carbon (C) were investigated. Experimental data showed that nearly pure τ 1 phase was obtained in LaFe 11.6 Si 1.4 , LaFe 11.6 Si 1.4 B 0.06 and LaFe 11.6 Si 1.4 C 0.06 alloys after annealing at 1373 K for 100 h. All annealed samples underwent a first-order magnetic transition. B doping decreased the magnetic transition temperature from 192 K to 188 K, whereas C doping increased to 206 K. In combination with X-ray diffraction results, the density-functional theory was used to reconstruct the unit-cell in order to understand the magnetic transition behavior. The results suggested that almost all B atoms occupy 96 i FeII/Si substitutional site, and all C atoms prefer 24 d interstitial site in the present given conditions. The annealed samples possessed the maximum magnetic entropy changes higher than 20 J/(kg⋅K) under a magnetic field change of 3 T, and their effective refrigeration capacities reached 200 J/kg. Highlights • Doping effects of boron and carbon on La−Fe−Si compounds were investigated. • Density-functional theory was used to reconstruct the crystallographic unit-cell. • The occupation information of boron and carbon in La−Fe−Si was clarified. [ABSTRACT FROM AUTHOR]

Magnetic transitional behaviors and the magnetocaloric effect of the intermetallic compound Pr7Pd3 have been studied. A second-order metamagnetic transition between ferromagnetic and paramagnetic states was observed with a Curie temperature (TC) of 14.9 K. The paramagnetic Curie temperature (휃p) and the effective magnetic moment (μeff) were investigated and determined to be 5.1 K and 3.43 μB/Pr, respectively. A reversible magnetocaloric effect was observed in this compound originated from the magnetic phase transition. For a magnetic field change of 0-5 T, the maximum magnetic entropy change − ΔSM reached 5.5 J kg− 1 K− 1, and the corresponding value of refrigerant capacity was estimated to be about 65 J kg− 1 with no thermal and field hysteresis loss. [ABSTRACT FROM AUTHOR]

Conventional magnetometry is irreplaceable in evaluating bulk magnetization of materials over broad temperature and field ranges. The technique is also effective in quantifying hysteresis that may be associated with magnetic and structural phase transitions that occur during the magnetizing/demagnetizing cycling, and the derived magnetic field-induced isothermal entropy change – one of the most important properties in the field of magnetocalorics. Both systematic and random errors present during the measurements of magnetization, however, may lead to erroneous conclusions. Using two well-known materials – elemental Gd and intermetallic Gd 5 Si 2 Ge 2 as examples, we consider best practices in performing reliable and rapid magnetization measurements for proper characterization of magnetocaloric properties. [ABSTRACT FROM AUTHOR]

The crystal structure, magnetic transitional behaviors and magnetocaloric effect were investigated in Nd 6 Fe 13 Pd compound. The results show that Nd 6 Fe 13 Pd crystallizes in the tetragonal Nd 6 Fe 13 Si-type structure (space group I 4/ mcm ) with the lattice parameters a = b = 8.0765 Å and c = 22.3747 Å and two magnetic transitions from the ferromagnetic to the antiferromagnetic states with T tr  = 173 K and from the antiferromagnetic to the paramagnetic states with the Néel temperature of 369 K occurred in the Nd 6 Fe 13 Pd compound. The magnetic transition between the ferromagnetic and the antiferromagnetic states can be induced by either changing temperature or applying a magnetic field with very small thermal and magnetic hystereses and the transition temperature is very sensitive to the applied field. The experimental results indicate a broad working temperature span and negative magnetic entropy changes around T tr  = 173 K. For a magnetic field change of 2 T, the maximum magnetic entropy change −Δ S M reaches to 4.4 J kg −1  K −1 with the corresponding refrigeration capability of about 125 J kg −1 . [ABSTRACT FROM AUTHOR]

The critical behavior and magnetocaloric effects of the monoclinic Cr 5 Te 8 single crystal have been studied by using magnetization measurements. Experimental results show that the paramagnetic (PM) to ferromagnetic (FM) phase transition is a second-order phase transition at T c = 222 K. The detailed critical behavior analysis indicates that the values of critical exponents β , γ , and δ determined by the modified Arrott plots, the Kouvel-Fisher method as well as the critical isotherm analysis agree well with each other and fulfill the Widom scaling law. The critical exponents are close to those expected for the three-dimensional Ising model and the ferromagnetic interaction is at the boundary between long-range type and short-range one. In addition, the magnetocaloric property of monoclinic Cr 5 Te 8 is consistent with the analysis of critical behavior. [ABSTRACT FROM AUTHOR]

The structural, magnetic and magnetocaloric properties of the antiperovskite materials M n 3 C u N 1 − x C x have been studied. Substituting N with C increases the temperature of the magnetostructural transition between a paramagnetic cubic high temperature phase and a ferrimagnetic tetragonal low temperature phase. Furthermore, the first order character of the phase transition is retained upon substitution with a hysteresis below 2 K for all compositions. The magnetostructural transition gives rise to giant magnetocaloric effects in a tunable 30 K temperature range with a maximum entropy change of 11.8 J/Kkg at a 2 T field change, making these compounds promising for low temperature magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

We have investigated the magnetocaloric effects and critical behaviors of Eu 2 NiMnO 6 and Dy 2 NiMnO 6 double perovskite oxides. For a magnetic field varying from 0 to 7 T, the maximum values of the magnetic entropy change ( | Δ S M max | ) reach 4.0 J/kg K and 5.2 J/kg K, and the relative refrigeration capacity ( RCP ) values are 241.5 J/kg and 385.1 J/kg for Eu 2 NiMnO 6 and Dy 2 NiMnO 6 , respectively. The relatively high values of | Δ S M | and RCP suggest that these double perovskite oxides can be used as candidates of magnetic refrigerants working in a wide temperature range. Various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis are used to estimate the critical exponents ( β , γ and δ ) as well as T C for Eu 2 NiMnO 6 . These critical exponents not only obey the Widom scaling relation δ = 1 + γ / β , but also fulfill the scaling equation M ( H , ε ) = ε β f ± ( H / ε β + γ ) where ε = ( T – T C )/ T C , f + ( T  >  T C ) and f - ( T  <  T C ) are the regular analytic functions. Therefore, the deduced critical exponents are reasonably accurate. Moreover, temperature variation in effective critical exponents resemble with those for disordered ferromagnet, which matches with the Griffiths-like phase behavior observed from inverse magnetic susceptibility just above T C . [ABSTRACT FROM AUTHOR]

Microstructures of magnetocaloric Ni-Mn-In-based Heusler alloys, Ni 50.2 Mn 35.0 In 14.8 and Ni 46.1 Mn 37.9 Fe 3.0 In 13.0, were studied to understand the origin of a large difference in thermal hysteresis in these two alloys. In-situ transmission electron microscopy (TEM) observation showed that the Fe containing sample with a large hysteresis shows a discontinuous phase transition due to the existence of nano-scale Fe-rich bcc phase, along with Fe-lean B2 and L2 1 phases in the austenite state. The Fe-free sample with a low hysteresis shows a uniform phase transition from martensite to austenite initiated by the nucleation of austenite at the twin boundaries. Ni segregation was found at the twin boundaries of the low hysteresis sample that is considered to facilitate the nucleation of the austenite. The phase transition progresses by the growth of the nucleated austenite to the neighboring twins. 5M and 7M modulated martensites in the low hysteresis sample give rise to a slight difference in the phase transition temperatures in the twin bands contributing to the small hysteresis of 4.4 K in the Fe-free sample. Based on these results, we conclude that to minimize the thermal hysteresis of the Ni-Mn-In based magnetocaloric compounds, one of the key factors is to achieve a uniform composition and crystal structure in the alloy. [ABSTRACT FROM AUTHOR]

In this study, we have expanded our previous work on the Gd 2 (Co 3-x Si x ) solid solution to form the family of R 2 ( T 3-x Si x ) compounds with a wide range of the rare earth metals (Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er) by variation of the composition and, where necessary, the transition element (Co and Ni). We report the crystallographic and the magnetic properties of this La 2 Ni 3 -type series. The R 2 Co 3-x Si x compounds with R = Pr, Nd, Sm and Gd, undergo ferro- or ferrimagnetic transitions at T C ranging from 64 K (Nd) to 338 K (Gd) and the R 2 Ni 3-x Si x phases with R = Gd-Er display ferromagnetic order below T C from 96 K (Gd) to 7 K (Er). [ABSTRACT FROM AUTHOR]

In this work, we report the structural and magnetic properties of La 0.75 Ca 0.25 MnO 3 nanoparticles synthesized by the sol-gel route. Rietvield refinement of X-ray powder diffraction confirms that our sample is single phase and crystallizes in orthorhombic system with Pnma space group. The facts that effective magnetic moment is large and the inverse susceptibility deviates from the Curie Weiss lawn indicate the presence of Griffiths-like cluster phase. The critical exponents have been estimated using different techniques such as modified Arrott plot, Kouvel-Fisher plot and critical isotherm technique. The critical exponents values of La 0.75 Ca 0.25 MnO 3 are very close to those found out by the mean-field model, and this can be explained by the existence of a long-range interactions between spins in this system. These results were in good agreement with those obtained using the critical exponents of magnetic entropy change. The self-consistency and reliability of the critical exponent was verified by the Widom scaling law and the universal scaling hypothesis. Using the Harris criterion, we deduced that the disorder is relevant in our case. The maximum magnetic entropy change (ΔS M ) calculated from the M-H measurements is 3.47 J/kg K under an external field change of 5 T. The ΔS M - T curves collapsed onto a single master curve regardless of the composition and the applied field, confirming the magnetic ordering is of second order nature. The obtained result was compared to ones calculated based on the Arrott plot and a good concordance is observed. Moreover, the spontaneous magnetization obtained from the entropy change is in excellent agreement with that deduced by classically extrapolation the Arrott curves. This result confirms the validity of the estimation of the spontaneous magnetization using the magnetic entropy change. [ABSTRACT FROM AUTHOR]

• Different electro-permanent magnetic structures designed. • Extensive multi-parametric numerical analyses performed. • Energy efficiency of designed electro-permanent magnetic structures evaluated. • Future guidelines for highly energy efficient and high-frequency magnetic field sources for magnetic energy conversion discussed and highlighted. We present the results of a comprehensive study of the design, numerical analyses and experimental validation of various electro-permanent magnetic structures that can be used in magnetocaloric refrigeration. Most magnetic field sources currently used in conceptual magnetic cooling devices require moving parts, which produce noise, vibrations and require maintenance. Furthermore, the operating frequency of such magnetic structures is relatively low and limited by aspects of the mechanical construction. Unlike any magnetic structure currently used in a magnetocaloric refrigeration device, the presented structure consists of a hybrid assembly of an electromagnet and a permanent magnet. We report on how different configurations of permanent magnets and the windings of electromagnets, including the air gaps, affect the energy efficiency, the input power and the total mass of the magnetic field source. Some guidelines for future research and the development of electro-permanent magnetic field sources for magnetocaloric refrigeration and heat pumps are presented, supported by information on how such structures can enable higher operating frequencies that could increase the compactness of future magnetocaloric devices. [ABSTRACT FROM AUTHOR]

The relation between the microstructure and the magnetic properties of Fe 2 P-type (Mn,Fe) 2 (P,Si,B) based materials has been systematically investigated by changing the annealing temperature and time. X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy measurements show that the alloys contain the main Fe 2 P-type phase and two impurity phases of (Fe,Mn) 5 Si 3 -type and Fe 2 MnSi-type. Boron appears to facilitate the formation of the Fe 2 P-type phase during the arc-melting progress. Upon increasing the annealing temperatures from 1123 to 1423 K, the Curie temperature ( T C ) decreases from 302.0 to 270.5 K in the Mn 1.15 Fe 0.85 P 0.55 Si 0.45 alloys and the magnetic-entropy change (Δ S M ) increases linearly with annealing temperature. For the Mn 1.15 Fe 0.85 P 0.52 Si 0.45 B 0.03 alloys annealed at 1423 K for different times, T C decreases from 263.8 and 232.8 K with increasing annealing time and Δ S M reaches a maximum value after annealing for 48 h. The differences in the annealing temperature and time influence the Si content in the Fe 2 P-type phase of the alloys and determine T C , the thermal hysteresis and the magneto-elastic transition. [ABSTRACT FROM AUTHOR]

Future advancements in magnetocaloric refrigeration/heat pumping technologies depend on the discovery of new materials that demonstrate large, tunable magnetocaloric effects (MCEs) in the vicinity of coupled magnetic and structural phase transitions that occur reversibly with minimum hysteresis. With this in mind, we investigate phase transitions, microstructure, magnetic, thermal, magnetocaloric, and transport properties of (Gd 5-x Sc x )Si 1.8 Ge 2.2 compounds. Replacement of magnetic Gd with non-magnetic Sc in Gd 5-x Sc x Si 1.8 Ge 2.2 increases the ferromagnetic to paramagnetic first order phase transition temperature, T C , with only a minor reduction in MCE when x ≤ 0.2. We also demonstrate that hydrostatic pressure further increases T C and reduces the hysteresis of the first order phase transition in Gd 4.8 Sc 0.2 Si 1.8 Ge 2.2 from 7 to 4 K. Temperature-dependent x-ray powder diffraction study of Gd 4.8 Sc 0.2 Si 1.8 Ge 2.2 confirms the monoclinic ↔ orthorhombic structural transformation at T C , in agreement with magnetic, calorimetric, and electrical transport measurements. In addition to the substantial magnetocaloric effect, a large magnetoresistance of ∼20% is also observed in Gd 4.8 Sc 0.2 Si 1.8 Ge 2.2 for ΔH = 50 kOe in the vicinity of the magnetostructural transition. In a drastic reversal of the initial doping behavior further additions of Sc (x > 0.2) suppress formation of the monoclinic phase, change the nature of the transition from first-to second-order, and reduce both the transition temperature and magnetocaloric effect. [ABSTRACT FROM AUTHOR]

Films are of particular interest for magnetocaloric refrigeration as they allow for a fast heat exchange. Here we report on metamagnetic epitaxial Ni–Mn–Ga–Co films, where a reduction of thermal hysteresis to 50% during several tens of temperature cycles is observed. This reduction occurs by an increase of the martensitic start temperature and thus can be attributed to a facilitated nucleation of martensite. Two mechanisms for reduction of hysteresis are identified: 1) delamination, which reduces constraints from the rigid substrate and 2) the formation of defects, which reduces the nucleation barrier. The detailed analysis and interpretation of microstructure before and after cycling gives a detailed understanding of the nucleation and delamination process. [ABSTRACT FROM AUTHOR]

A systematic study of structural transformation, magnetism and magnetic entropy change in the vicinity of structural and magnetic transformation has been performed in the NiMnSb by substituting Sb with a large amount of Al. This substitution enhanced the transformation temperature close to room temperature and also made it less sensitive to the variation in composition. Alloys exhibited conventional and inverse magnetocaloric effects due to the Curie and magnetostructural transformation respectively. The inverse magnetocaloric effects were less compared to those reported in pure Sb system, but it showed a large value of conventional magnetocaloric effect with the added advantage of insensitivity to the compositional variation. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration is considered as an alternative to conventional gas-compression-expansion cooling techniques. While the physical properties of magnetocaloric materials have been studied extensively, the question of how to process and shape these materials into active magnetic regenerator (AMR) heat exchangers for application in magnetocaloric cooling devices is less explored. Packed beds made from gas atomized spherical particles offer attractive shaping options to realize an AMR. In this work, we show that X-ray computed tomography (XCT) allows for non-destructive testing of the packed bed magnetic regenerators, including 3D visualization of the internal bed structure, measurement of the particles’ packing density and homogeneity, detection of defects, cracks and interfaces between the layers with different transition temperatures. In this way, XCT can help to understand structural details of fabricated magnetocaloric regenerators and their influence on the performance in a cooling device. [ABSTRACT FROM AUTHOR]

The isothermal evolution of magnetization under different magnetic fields, described by an equation of state, not only defines de entropy change Δ S ( T ) (magnetocaloric effect) but also the cooling power (area enclosed by the Δ S ( T ) curve). In fact, the area under the M T 0 ( H ) curve limited by the initial ( H i ) and final ( H f ) fields equals the area under the Δ S ( T ) curve above T > T 0 for the same field range. This “sum rule” has been used to compare magnetocaloric curves for a number of materials. We based this study in the prediction that M T 0 ( H ) contains all the information to the establishment of the cooling power above T 0 over the whole range of considered magnetic fields. To perform a check, we studied here some magnetic systems described by different equations of state including that around the transition region (power law). We show results of theoretical calculations in GdAl 2 -like ferromagnetic material with equation of state in the framework of Brillouin and Oguchi models. An intricate phenomenological equation of state for polycrystalline NdAl 2 under hydrostatic pressure is also used to validate the sum-rule. [ABSTRACT FROM AUTHOR]

The orthorhombic Pr 0.8 Na 0.2−x K x MnO 3 (x = 0.10 and 0.15) manganites are prepared by using the solid state reaction at high temperatures. The critical exponents (β, γ, δ) are investigated through various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis based on the data of the magnetic measurements recorded around the Curie temperature. The critical exponents are derived from the magnetization data using the Kouvel-Fisher method, are found to be β = 0.32(4) and γ = 1.29(2) at T C ~ 123 K for x = 0.10 and β = 0.31(1) and γ = 1.25(2) at T C ~ 133 K for x = 0.15. The critical exponent values obtained for both samples are comparable to the values predicted by the 3D-Ising model, and have also been verified by the scaling equation of state. Such results demonstrate the existence of ferromagnetic short-range order in our materials. The magnetic entropy changes of polycrystalline samples with a second-order phase transition are investigated. A large magnetic entropy change deduced from isothermal magnetization curves, is observed in our samples with a peak centered on their respective Curie temperatures (T C ). The field dependence of the magnetic entropy changes are analyzed, which show power law dependence Δ S max ≈ a ( µ 0 H ) n at transition temperature. The values of n obey to the Curie Weiss law above the transition temperature. It is shown that for the investigated materials, the magnetic entropy change follow a master curve behaviour. The rescaled magnetic entropy change curves for different applied fields collapse onto a single curve for both samples. [ABSTRACT FROM AUTHOR]

Thermomagnetic energy harvesting technology has not received significant attention despite great potential for generating electricity from low thermal gradient near room temperature. This review summarizes the findings reported in literature covering the broad topical areas within thermomagnetic energy harvesting and provides perspective on the potential applications of this technology. The information has been organized chronologically in order to provide systematic understanding of the concepts and evolution of the device designs. Both, active and passive types of thermomagnetic energy harvesters have been included in the paper. The selection of suitable thermomagnetic material is key towards achieving an efficient energy generation device. Therefore, various material compositions have been discussed and their thermomagnetic behavior has been elucidated to provide guidance for their implementation in future devices. [ABSTRACT FROM AUTHOR]

Magnetic and magnetocaloric properties, as well as the phase diagrams of a ferromagnetic ternary alloy system have been studied. A detailed comparison of two different methods, namely the effective field theory (EFT), and Monte Carlo (MC) simulations has been provided. Our numerical data show that the general qualitative picture presented by two methods are in a good agreement with each other. In terms of the magnetocaloric properties, our results yield that it is possible to design magnetic materials with a variety of working temperatures and magnetocaloric properties (such as large Δ S M and q values) by manipulating the magnetic phase transition via tuning the compositional factor (i.e. the mixing ratio of sublattice ions). The observed magnetocaloric effect has been found to be a direct one with Δ S M < 0 associated with a second order phase transition. [ABSTRACT FROM AUTHOR]

In the present work, we report the outstanding magneto-elastic and magneto-caloric properties of a Tb-Co binary amorphous alloy. The glass forming ability (GFA) of Tb-Co binary alloys was studied and the best glass former was obtained near the eutectic point of the binary alloys. The magnetic properties of the eutectic Tb 62.5 Co 37.5 amorphous alloy were measured, and it was found that the Tb 62.5 Co 37.5 amorphous ribbons exhibited excellent magneto-elastic properties (the magnetostriction of nearly 470 ppm at 50 K under 5 T) and magneto-caloric properties (the peak magnetic entropy change of 9.3 Jkg −1 K −1 at 92.5 K under 5 T). The mechanism for the improved GFA, magneto-caloric effect (MCE) and magneto-elastic properties of the Tb 62.5 Co 37.5 amorphous ribbons was analyzed. [ABSTRACT FROM AUTHOR]