Textured magnetocaloric materials offer a cost-effective alternative to single crystals while retaining magnetic anisotropy required for rotational magnetic refrigeration. In this work, a textured DyNiAl intermetallic compound was prepared by directional solidification during arc melting and systematically investigated for low-temperature magnetic refrigeration. Structural characterization confirmed texturing along the c-axis of the main phase identified as DyNiAl, which crystallizes in a hexagonal structure with space group P-62m. Magnetic and heat-capacity measurements revealed pronounced magnetic anisotropy and magnetic transitions at approximately 14 K and 32 K. The compound exhibited magnetocaloric effects below and above 14 K, respectively, with the maximum response near 32 K. A maximum adiabatic temperature change of 10.6 K was obtained for a field change of 0–14 T, while the maximum magnetic entropy change reached ∼18 J/kgK at 5 T for the magnetic field applied along the texture axis. Direct measurements also revealed a rotating magnetocaloric effect of 0.7 K at 1.8 T. These results demonstrate that textured DyNiAl exhibits magnetocaloric properties comparable to those of single crystals while benefiting from simpler and more cost-effective processing, making it a promising candidate for conventional and rotational magnetic refrigeration in the hydrogen liquefaction temperature range.

The critical behavior around ferromagnetic-paramagnetic phase transition of polycrystalline Tb1-xHoxNi2 solid solutions (x = 0.25, 0.5, 0.75) was investigated using magnetization measurements in a magnetic field range of 0-5 T. The critical exponents obtained using the Kouvel-Fisher modified Arrott plot methods and the Widom scaling relation are consistent. The tricritical and 3D-Ising models adequately describe the samples, likely due to Ho substitution affecting the critical parameters. The spin interactions indicate long-range character in all studied compositions. Critical parameter analysis shows that the magnetic transition temperature decreases with the increasing Ho content, from 29.3 K for Tb0.75Ho0.25Ni2 to 17.1 K for Tb0.25Ho0.75Ni2. For the Tb0.5Ho0.5Ni2, direct measurements of adiabatic temperature change near the Curie temperature were performed in magnetic fields up to 14 T. The maximum Delta T-ad reaches similar to 11 K near 26.3 K for mu(0)Delta H = 14 T. These results are compared with TbNi2 and HoNi2 and analyzed within the Landau theory of second-order phase transitions. To demonstrate application potential, composite materials based on Tb1-xHoxNi2 (x = 0.25-0.75) were proposed. Optimal molar ratios of Tb0.75Ho0.25Ni2, Tb0.5Ho0.5Ni2, and Tb0.25Ho0.75Ni2 were theoretically determined. The composites exhibit a nearly constant calculated magnetic entropy changes, similar to 3.4 J/kg K for mu(0)Delta H = 1 T and similar to 6.3 J/kg K for mu(0)Delta H = 2 T over a wide temperature range of 18-30 K. These results indicate that the proposed composites are promising candidates for use as refrigerants in low-temperature magnetic refrigerators.

Magnetic refrigeration (MR) driven by the magnetocaloric effect (MCE) is an emerging as a viable and ecofriendly alternative to traditional cooling technology. However, realizing its practical application requires overcoming the gap between current MCE material performance and the demands of practical implementation. The intriguing MCE properties of rare-earth double perovskite oxides make them strong contenders for cooling applications at cryogenic temperatures. Ho2FeMnO6 synthesized using sol-gel method crystallizes in the monoclinic crystal structure belonging to the space group of P21/n. The magnetic phase transition was observed at 8.5 K. The Arrott plot indicates that the compounds undergo a second-order phase transition. Under the applied magnetic field of 5 T, the maximum magnetic entropy change (-Delta Sm) and the relative cooling power (RCP) for Ho2FeMnO6 were found to be 10.2 J/kg. K and 242 J/kg, respectively. Employing a quantitative approach facilitates precise and systematic evaluation of the magnetocaloric properties of rare earth double perovskites under cryogenic conditions. Additionally, the ground-state electronic structure and magnetic properties of Ho2FeMnO6 were investigated using the DFT + U formalism within the simplified Dudarev approach, which predicts the compound to exhibit semiconducting behavior.

The magnetic and magnetocaloric properties of gaudefroyite minerals were studied. The magnetocaloric effect was investigated by direct and indirect methods in the temperature range 4.2-40 K and magnetic field up to 10 T. The magnetization was measured in a low magnetic field (200 Oe) with zero-field cooled and field cooling protocol and previous observation of typical spin glass behavior was confirmed. The giant magnetic entropy changes with anisotropic behavior and maximums |Delta Delta Sm|= m |= 17 J kg- 1 K-1 (H||c) at 18 K and |Delta Sm|= Delta S m |= 20 J kg- 1 K-1 (H||ab) at 12 K at an applied magnetic field 10 T were observed. The direct measurements of the magnetocaloric effect demonstrated the maximum of adiabatic temperature changes of Delta T ad = 11 K at a magnetic field change of 10 T (H||ab) at 11.5 K. Obtained values of magnetocaloric parameters for the mineral of gaudefroyite are comparable to promising materials for magnetic crycooling technologies (for example, hydrogen (LH2) 2 ) liquefaction) and have an advantage for the absence of rare-earth elements in the gaudefroyite.

As is known, rare-earth metals (REMs) are promising magnetocaloric materials. The magnitude of the magnetocaloric effect (MCE) of REMs significantly depends on their purity. This paper presents results of studies of the magnetic and magnetocaloric properties of sublimed dysprosium, prepared in the course of the present study, with an emphasis on its impurity and structure perfection. The comprehensive analysis of the chemical composition of sublimed dysprosium, which was performed for the first time by atom probe tomography, showed that the metal corresponds to high-purity rare-earth metals (3N+). The MCE effect was studied using direct measurements of the adiabatic temperature change (ΔTad) in pulsed (up to 50 T) and steady (up to 14 T) magnetic fields. The studies of the MCE of polycrystalline sublimed Dy by direct method showed that the high ΔTad value for sublimed Dy are comparable with that for magnetic fields of 5 T. The vacuum sublimation, which is more economical and technologically advanced in contrast to single crystal growing, can be used to create magnetocaloric REM-based materials with high MCE values.

We present here a detailed study on the magnetic and magnetocaloric (MC) behaviors of a perovskite/hausmannite composite material of LYCMO/Mn3O4, where LYCMO (La0.5Y0.1Ca0.4MnO3) is a primary phase of 95 wt %. The analysis of M(T) data indicates a coexistence of ferromagnetic-paramagnetic transitions associated with LYCMO and Mn3O4 at about 56 and 43 K, respectively. Critical-behavior analyses have proved the composite exhibiting a second-order phase transition at magnetic fields H <= 10 kOe, with critical exponents beta= 0.347 and gamma = 1.167 characteristic of 3D-Heisenberg and 3D-Ising ferromagnets, respectively. At higher fields, it tends to exhibit crossover behaviors of first-/second-order transitions. As analyzing the MC effect upon isothermal M(H) data, we have found the maximum magnetic-entropy change of -3.1 J/kg & sdot;K, and the relative refrigerant capacity (RCP) of -150 J/kg for H = 30 kOe, which are higher than those obtained for other oxides in the same temperature and applied-magnetic ranges. With the absence of hysteresis loop and large RCP value, this material can be used in magnetic-cooling devices working at temperatures T = 40-85 K to liquefy nitrogen.

The Δ T ad values are high and reach their maximum within a narrow temperature range below 20 K. This indicates that Dy 1− x Er x Ni 2 solid solutions may be a viable option for refrigerants in magnetic cryocoolers suitable for hydrogen liquefaction.

Many exciting effects resulting from the coupling of magnetic sublattice with a magnetic field, may be exposed by changing the field. One such phenomenon is the magnetocaloric effect, which is characterized by the absorption or emission of heat in response to changes in the external magnetic field. Magnetic refrigeration based on the magnetocaloric effect has emerged as an attractive alternative to conventional cooling technology that relies on gas compression and expansion. It is not only more efficient and environmentally friendly, but it can also be implemented across a broad temperature range, from ultra-low to a few hundred Kelvin temperatures. One of the areas where magnetic cooling can have a significant impact is hydrogen liquefaction. Hydrogen is one of the most promising candidates for clean energy sources, but it must be liquefied to facilitate storage and transportation, which requires cooling it down to similar to 20 K. The ideal magnetic refrigerant should exhibit consistent magnetocaloric properties across the entire operating temperature range of a cooler. This paper presents novel three-layer composite magnetic refrigerants that provide a uniform magnetocaloric response over a 30 K temperature range. The selected initial HoNi2, DyNi2, and TbNi2 magnetic intermetallic compounds with a Laves phase structure exhibit large magnetocaloric properties in the temperature range of 13-37 K. The composite composition of 23.56 wt% HoNi2 + 18.21 wt% DyNi2 + 58.23 wt% TbNi2 optimized for 2 T magnetic field change, was determined through numerical approach. The composites are manufactured using spark plasma sintering (SPS) and innovative high-isostatic-pressure (HIP) synthesis. The results of isothermal entropy change derived from magnetization data for a 2 T magnetic field change indicated 4.7 J/kgK (47.2 mJ/cm(3)K) and 4.4 J/kgK (44.2 mJ/cm(3)K) in the temperature range of approx. 13-42 K for composites after SPS and SPS + HIP processes, respectively. Despite the sample subjected to HIP showing slightly lower results, the entropy change is nearly uniform over the 30 K temperature range due to enhanced atomic diffusion between neighboring compounds, as confirmed by microscopic studies. Such a uniform magnetocaloric response in similar to 30-K temperature range has never been observed before in layered refrigerants. By utilizing the innovative high-isostatic-pressure synthesis technique, we have paved the way to high-performing magnetic composite materials that can be used in cryogenic magnetic coolers operating over a broad temperature span, expanding the possibilities of what can be achieved and laying the foundation for cost-effective, clean hydrogen energy.

Experimental and analytical studies were carried out on the magnetocaloric effect (MCE) in the rare-earth alloy of the Laves phase DyAl2, which has the second-order magnetic phase transition (PT) in the region of cryogenic temperatures. The measurements are carried out using an extraction magnetic calorimeter with a Bitter electromagnet. A polycrystalline DyAl2 sample was synthesized followed by heat treatment. X-ray diffraction and elemental chemical analyzes are provided. The magnetization of the sample was measured in magnetic fields up to 13.5 T. Calculations of the entropy changes of the magnetic subsystem z S mag are provided. Measurements of the MCEs z T- effect in adiabatic and z Q- effect in quasi-isothermal conditions were carried out. The MCE investigated by direct method in the temperature range of 15-110 K and magnetic field up to 14 T. It was found that the maximum of the adiabatic MCE in the region of the Curie temperature of the DyAl2 alloy under adiabatic magnetization in a magnetic field of 14 T is z T = 12.94 K. The obtained values are well approximated by the z T similar to zH2/3, The maximum value of the quasi-isothermal MCE is z Q = 3.1 kJ/kg. The value corresponds to the maximum of the entropy change of the magnetic subsystem z S mag = 32.3 J/ (kg*K). The influence of thermal contact resistance (TCR) on the results of measuring the MCE under quasi-isothermal conditions is assessed.

In this paper, we discuss the magnetic behavior and magnetocaloric effect of lithium erbium tetraphosphate (LiErP4O12) single crystal in the temperature range 2-85 K under magnetic fields up to 50 kOe. Detailed investigation of the temperature-dependent magnetization M(T) proves an existence of magnetic ordering below T-m, which has been estimated as a minimum in the dM/dT vs. T dependence. Above T-m, LiErP4O12 possesses paramagnetic behavior and its magnetic susceptibility follows the Curie-Weiss law giving a higher value of the effective magnetic moment of Er3+ compared to the theoretical one. This could be due to the Kramers spin degeneracy and the Stark structure of multiplets. Under an applied field H = 50 kOe, the maximum value of the magnetic-entropy change at 2 K reaches about 15 J/kgK, corresponding to a relative-cooling-power value of similar to 343 J/kg. Assessments of the magnetic ordering exponent n and N(T, H) data prove LiErP4O12 exhibiting short-range magnetic order. Due to the absence of magnetic hysteresis and large magnetocaloric response, we believe that LiErP4O12 could be a promising candidate for magnetic-cooling applications in liquefying hydrogen and He-3 isotope.

This work presents the results of a comparative analysis of the thermal, magnetic, magnetocaloric and magnetostrictive properties of the Dy0.42Ho0.42Tb0.16Co2, Dy0.5Ho0.5Co2 and TbCo2 compounds. All studied compounds have the MgCu2-type Laves phase structure at room temperature. Dy0.5Ho0.5Co2 and TbCo2 demonstrate first- and second-order transitions from a paramagnetic state to a magnetically ordered one, respectively. Special attention is given to determining the order of magnetic phase transition in a multicomponent compound with three rare earth elements (Tb, Dy and Ho). Features of the magnetocaloric effect and magnetostriction of (Tb,Dy,Ho)Co-2 compounds have been studied in magnetic fields up to 14 T and in wide temperature range (4.2 - 300 K). The joint manifestation of significant magnetocaloric and magnetovolume effects at the Curie temperature can be useful for a variety of technical applications.

Hydrogen is quickly becoming a desired type of fuel, however, the energy and cost required for liquefaction using today's cooling technology is excessively high. Magnetic cooling based on the magnetocaloric effect is an energy -efficient and environmentally friendly alternative to commonly used vapor compression, but improvements in refrigerants are crucial for this technology to succeed. Polycrystalline Er1-xHoxNi2 (x = 0.25, 0.5, 0.75) Laves-phase solid solutions obtained by the arc-melting method have been investigated due to their potential for low-temperature refrigerants. Er0.75Ho0.25Ni2 and Er0.5Ho0.5Ni2 crystallize in cubic Laves phase superstructure (space group F-43 m), while Er0.25Ho0.75Ni2, similarly to the initial ErNi2 and HoNi2 binary compounds, crystallizes with the formation of the regular cubic C15 structure (space group Fd-3 m). To evaluate how the structure affects magnetic and magnetocaloric properties, studies in a wide magnetic field range, up to 14 T, were conducted. Measurements show all samples obey the second-order magnetic phase transition from ferromagnetic to para-magnetic state, and their Curie temperatures increase with increasing Ho content from 8 K for Er0.75Ho0.25Ni2 to 12.3 K for Er0.25Ho0.75Ni2. At higher temperatures, all solid solutions are Curie-Weiss paramagnets. However, it has been observed that the formation of the superstructure with lower translational symmetry seems to affect magnetic moments and magnetic entropy values. Er0.25Ho0.75Ni2, with the regular cubic C15 structure, showed the highest entropy changes of 43.5 J/kgK around 12 K, while Er0.75Ho0.25Ni2 and Er0.5Ho0.5Ni2, with cubic superstructure, provided similar to 30 % lower results of 30.3 and 35.1 J/kgK, around 8 and 10 K, respectively, for magnetic field change of 14 T. Nevertheless, relatively large and reversible values of magnetic entropy prove that these compounds can be promising candidates for magnetic cooling operating within the low-temperature range needed for hydrogen liquefaction.

State of research in the study of magnetocaloric materials based on rare-earth metals that are promising for application in the technology of low-temperature magnetic cooling is reviewed. Physical principles and characteristics of the magnetocaloric effect in materials based on rare-earth metals with low-temperature magnetic phase transitions are presented.

We report a detailed study on the magnetic behaviors and magnetocaloric (MC) effect of a single crystal of lithium samarium tetraphosphate, LiSm(PO3)4. The analyses of temperature-dependent magnetization data have revealed magnetic ordering established with decreasing temperature below Tp, where Tp is the minimum of a dM/dT vs. T curve and varies as a linear function of the applied field H. The Curie temperature has been extrapolated from Tp(H) data, as H → 0, to be about 0.51 K. The establishment of magnetic-ordering causes a substantial change in the heat capacity Cp. Above Tp, the crystal exhibits paramagnetic behavior. Using the Curie-Weiss (CW) law and Arrott plots, we have found the crystal to have a CW temperature θCW ≈ -36 K, and short-range magnetic order associated with a coexistence of antiferromagnetic and ferromagnetic interactions ascribed to the couplings of magnetic dipoles and octupoles at the Γ7 and Γ8 states. An assessment of the MC effect has shown increases in value of the absolute magnetic-entropy change (|ΔSm|) and adiabatic-temperature change (ΔTad) when lowering the temperature to 2 K, and increasing the magnetic-field H magnitude. Around 2 K, the maximum value of |ΔSm| is about 3.6 J kg-1 K-1 for the field H = 50 kOe, and ΔTad is about 5.8 K for H = 20 kOe, with the relative cooling power (RCP) of ∼82.5 J kg-1. In spite of a low MC effect in comparison to Li(Gd,Tb,Ho)(PO3)4, the absence of magnetic hysteresis reflects that LiSm(PO3)4 is also a candidate for low-temperature MC applications below 25 K.

Here, we investigated polycrystalline pseudo-binary (Ho,Er)Ni-2 intermetallic compound. Its magnetic and thermodynamic properties were extensively studied over a wide field range, which enables to define and describe high-field regularities of magnetocaloric effect. The isothermal magnetic entropy change and relative cooling power were estimated based on magnetization measurements. The magnetocaloric parameters obtained for the temperatures from the phase transition range are discussed in the framework of the mean-field theory for the second-order phase transitions. Precise experimental characterization of the magnetic properties of the (Ho,Er)Ni-2 intermetallic compound was also performed. Composite with optimum proportions of the individual parent and Ho0.5Er0.5Ni2 compounds were theoretically determined.

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni44.4Mn36.2Sn14.9Cu4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆Tad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T0 = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones.

In this paper, the results of heat capacity measurements performed on the polycrystalline Tb1-xErxNi2 intermetallic compounds with x = 0.25, 0.5 and 0.75 are presented. The Debye temperatures and lattice contributions as well as the magnetic part of the heat capacity were determined and analyzed. The heat capacity measurements reveal that the substitution of Tb atoms for Er atoms leads to a linear reduction of the Curie temperatures in the investigated compounds. The ordering temperatures decrease from 28.3 K for Tb0.25Er0.75Ni2 to 12.9 K for Tb0.75Er0.25Ni2. Heat capacity measurements enabled us to calculate with good approximation the isothermal magnetic entropy ΔSmag and adiabatic temperature changes ΔTad for Tb1-xErxNi2, for the magnetic field value equal to 1 T and 2 T. The optimal molar ratios of individual Tb0.75Er0.25Ni2, Tb0.5Er0.5Ni2 and Tb0.25Er0.75Ni2 components in the final composite were theoretically determined. According to the obtained results, the investigated composites make promising candidates that can find their application as an active body in a magnetic refrigerator performing an Ericsson cycle at low temperatures. Moreover, for the Tb0.5Er0.5Ni2 compound, direct measurements of adiabatic temperature change in the vicinity of the Curie temperature in the magnetic field up to 14 T were performed. The obtained high-field results are compared to the data for the parent TbNi2 and ErNi2 compounds, and their magnetocaloric properties near the Curie temperature are analyzed in the framework of the Landau theory for the second-order phase transitions.

To date, significant efforts have been put into searching for materials with advanced magnetocaloric properties which show promise as refrigerants and permit realization of efficient cooling. The present study, by an example of Ho1-xErxNi2, develops the concept of magnetocaloric efficiency in the rare-earth Laves-phase compounds. Based on the magneto-thermodynamic properties, their potentiality as components of magnetocaloric composites is illustrated. The determined regularities in the behaviour of the heat capacity, magnetic entropy change, and adiabatic temperature change of the system substantiate reaching high magnetocaloric potentials in a desired temperature range. For the Ho1-xErxNi2 solid solutions, we simulate optimal molar ratios and construct the composites used in magnetic refrigerators performing an Ericsson cycle at low temperatures. The tailored magnetocaloric characteristics are designed and efficient procedures for their manufacturing are developed. Our calculations based on the real empirical data are very promising and open avenue to further experimental studies. Systems showing large magnetocaloric effect (MCE) at low temperatures are of importance due to their potential utilization in refrigeration for gas liquefaction.

The magnetocaloric effect (MCE) in samples of the Gd2In compound has been studied by the direct method in temperature range of 4–240 K in magnetic fields of Bitter coil up to 14 T. The maximum detected value of the inverse MCE at cryogenic temperatures in the 1st-order metamagnetic phase transition (PT) is ∆Tad =  − 0.5 K at T0 = 45 K in the field of 1.8 T. The MCE in this temperature range changes sign with increasing of the magnetic field up to 5 T, and the direct MCE is observed with further increasing of the field. The kinetic arrest of the 1st-order metamagnetic PT is observed on the temperature dependence of magnetization in the steady magnetic field of 5 T. The direct MCE in the Curie temperature Tc = 200 K increases with increasing of the magnetic field, and the effect maximum shifts to higher temperatures. The maximum detected value of the direct MCE is ∆Tad = 7.8 K at T0 = 215 K in the field of 14 T.

To date, significant efforts have been put into searching for materials with advanced magnetocaloric properties which show promise as refrigerants and permit realization of efficient cooling. The present study, by an example of Ho 1−x Er x Ni 2 , develops the concept of magnetocaloric efficiency in the rare-earth Laves-phase compounds. Based on the magneto-thermodynamic properties, their potentiality as components of magnetocaloric composites is illustrated. The determined regularities in the behaviour of the heat capacity, magnetic entropy change, and adiabatic temperature change of the system substantiate reaching high magnetocaloric potentials in a desired temperature range. For the Ho 1−x Er x Ni 2 solid solutions, we simulate optimal molar ratios and construct the composites used in magnetic refrigerators performing an Ericsson cycle at low temperatures. The tailored magnetocaloric characteristics are designed and efficient procedures for their manufacturing are developed. Our calculations based on the real empirical data are very promising and open avenue to further experimental studies. Systems showing large magnetocaloric effect (MCE) at low temperatures are of importance due to their potential utilization in refrigeration for gas liquefaction.