Multilayer caloric regenerators with tailored transition temperatures offer a promising strategy to overcome the limited temperature span of single material caloric heating and cooling systems. However, existing optimization approaches typically rely on predefined transition temperature profiles and incur high computational cost, limiting their scalability and generality. Here, we present a generalized and computationally efficient algorithm that iteratively refines the transition temperature distribution of multilayer regenerators without requiring predefined profiles. The method supports multiple design objectives, including maximum cooling capacity, maximum coefficient of performance, and minimum levelized cost of heat, through objective functions formulated within a reduced order material model. Validation across three magnetocaloric devices spanning room temperature cooling to cryogenic hydrogen liquefaction shows that optimal transition temperature distributions consistently evolve into asymmetric sigmoid shapes, yielding 10% to 50% improvements in cooling capacity compared with conventional linear distributions. For a five-layer regenerator, the proposed approach reduces computational time by 77.4% relative to a gradient based method while maintaining equivalent optimization accuracy. These results establish a scalable optimization framework for multilayer caloric regenerators and provide new insight into the coupling between material transition temperatures, device architecture, and thermal performance.

Magnetic refrigeration at cryogenic temperatures represents a promising cleaner-production approach to reduce the energy intensity of hydrogen liquefaction. Experimental development of cryogenic active magnetic regenerators (AMRs) has been limited by the scarcity of magnetocaloric materials (MCMs), complex fluid-solid interactions, and the challenges of scaling up laboratory prototypes. Here, we present HyDRA, the largest hydrogen liquefaction AMR test bench to date, designed to achieve large temperature spans while using minimal MCM and supporting scalable regenerator geometries. Using holmium as the MCM, a maximum temperature span of 16.5 K at 9 T was achieved, representing the highest value reported for a single-layer cryogenic AMR. Internal temperature measurements reveal phase-shifted profiles caused by helium compressibility, providing new insight into fluid-solid thermal interactions under cryogenic conditions. The test bench enables adaptive optimization of flow and operating parameters, achieving high thermal efficiency with minimal parasitic losses. This scalable, material-efficient platform establishes a foundation for cleaner, lower-energy hydrogen liquefaction technologies.

We report here on the development of the first CE certified commercial magnetic beverage cooler, marking a decisive breakthrough from decades of laboratory prototypes to fully market ready magnetic refrigerators operating in supermarkets. Using a unified optimization framework that integrates experimental insights from both component level and system level testing, this work captures the complex interplay from which several critical design knobs emerge. By prioritizing plug-in coefficient of performance (COP) over thermodynamic COP, the optimized configuration achieved a specific cooling capacity of 131 W/kg, a plug-in COP of 1, and a second law efficiency of 5.4 % at a 15 K temperature span. A temperature span of 28.5 K was realized through a cascade multi stage active magnetic regeneration system using Gd under 0.8 T, underscoring the potential of Curie temperature tailoring for future freezer applications. Full plug-in power consumption was addressed, delivering an 80 % reduction in total power draw and lowering noise levels to 57.8 dB through streamlined component design. The successful commercialization including months-long supermarket deployment at a stable 6 degrees C, advanced the technology readiness level from TRL 6 to TRL 9.

We have investigated NdCo2-xNix cubic Laves compounds with 0 <= x <= 1 using neutron diffraction and bulk magnetization measurements to study the influence of partial Ni substitutions of Co on the phase transitions and the magnetocaloric effect (MCE). Upon cooling, NdCo2 undergoes a cubic-to-tetragonal transition at 100 K and a tetragonal-to-orthorhombic transition at 42 K. The transitions are associated with long-range ferromagnetic ordering of the magnetic moments along the c axis and spin reorientation into the ab plane, respectively. Both transitions shift to lower temperatures as the Ni content x increases. For x >= 0.5, the orthorhombic phase is suppressed. Additionally, there was a reduction in the magnetic moment upon increasing the Ni substitution of Co. The MCE was determined both indirectly and directly, with good agreement between the methods. NdCo2 exhibits an adiabatic temperature change of 6.3 K for a field of 20 T, which is decreased to 4.9 K for NdCoNi for the same field strength due to the reduced magnetic moment upon Ni substitution.

Abstract Disorder is generally expected to destabilize quantum disordered systems such as quantum spin liquids (QSLs), yet some frustrated magnets appear to evade this tendency. We report low temperature thermodynamic, magnetometric, and muon spin relaxation measurements on single crystals of the triangular-lattice compound Ba4Nb0.8Ir3.2O12, where substantial Ir/Nb site mixing introduces chemical randomness. No signatures of long-range order or spin freezing are observed down to 20 mK. Instead, the specific heat follows a T 2 dependence and the muon relaxation rate remains temperature-independent at low temperatures. This behavior is consistent with low-energy excitations characteristic of a quantum disordered system with linearly dispersing modes. Density-functional calculations reveal preferential Nb/Ir site arrangement and site-selective Ir magnetism that preserve two-dimensional magnetic frustration despite structural disorder. These results demonstrate a correlated magnetic ground state that remains quantum disordered even in the presence of pronounced chemical randomness, pointing to a mechanism for disorder-resilient quantum magnetism in a 5d triangular-lattice iridate.

Cryogenic magnetic refrigeration becomes more and more important nowadays, especially for the liquefaction of gases such as hydrogen. In this study, we have synthesized La1−zCez(Fe0.88−yMnySi0.12)13 samples and investigated their magnetic and magnetocaloric properties in order to assess their potential for cryogenic applications. By adjusting the Mn and Ce content and adding excess rare-earth elements, the first-order ferromagnetic transition was lowered from 200 to 40 K and the adiabatic temperature change of the samples was measured directly using pulsed magnetic fields. The sample with the lowest transition temperature still showed a significant adiabatic temperature change in magnetic fields up to 10 T, with an increasingly stronger first-order transition observed in samples with higher Ce substitution. In addition, we synthesized spherical powder with diameters between 20 and 120 μm using ultrasonic atomization while maintaining the magnetic transition, which is a promising starting material for future additive manufacturing of magnetocaloric materials.

The magnetocaloric effect (MCE) offers a promising alternative for environmentally friendly cooling technologies, particularly at cryogenic temperatures. However, overestimating material capabilities can lead to misguided research efforts and hinder technological progress. Metamagnetic materials undergoing a transition from an antiferromagnetic to a ferromagnetic state are often predicted to exhibit a strong inverse MCE at cryogenic temperatures based on magnetization measurements. This assumption is critically assessed here using Tb 3 Ni as a case study. By employing a simple model and comparing results across various measurement techniques, it is demonstrated that the predicted inverse MCE does not exist. Specific‐heat data reveal no evidence of this effect, while direct Δ T ad pulsed‐magnetic‐field measurements indicate significant heating caused by dissipative effects linked to hysteresis. Furthermore, total‐entropy calculations derived from magnetization data violate the second law of thermodynamics, clearly ruling out the existence of an inverse MCE. These findings underscore the necessity of complementary experimental approaches and a precise understanding of the transitions to accurately characterize magnetocaloric materials and identify suitable candidates for cryogenic magnetic refrigeration.

Ni-Co-Mn-Ti all-d Heusler alloys are attracting considerable attention for solid-state caloric cooling applications due to their promising combination of excellent caloric and mechanical properties. Here, we report on the maximum attainable magnetocaloric effect in Ni 37 Co 13 Mn 34.5 Ti 15.5 , which shows a first-order magnetostructural martensitic transformation around room temperature. Heat capacity measurements reveal a giant transition entropy change of 43.5 J(kgK)-1 and are utilized to estimate the magnetocaloric effect as well as the magnetic fields required to saturate it in isothermal and adiabatic conditions. Confirming the results based on this approach, we achieve maximum isothermal entropy changes and directly measured adiabatic temperature changes of 37.8 J(kgK)-1 and -20.2 K, respectively. Thus, the herein reported maximum attainable magnetocaloric effect outperforms classical Ni-Mn-based Heusler alloys, such as Ni(-Co)-Mn-In. Especially the saturated adiabatic temperature change surpasses all previously published values of magnetic field-induced first-order phase transitions measured around room temperature in pulsed magnetic fields in recent years. Thereby, we demonstrate that Ni(-Co)-Mn-Ti Heusler alloys are particularly suitable for the application of sufficiently large external stimuli to fully induce the phase transition and exploit their intrinsically large caloric effect.

The magnetocaloric effect enables magnetic refrigeration and plays an important role for cooling at cryogenic temperatures, which is essential for emergent technologies such as hydrogen liquefaction and quantum computing. Here, we study the origin of the low-temperature magnetocaloric effect in multiferroic hexagonal manganites. By conducting direct adiabatic temperature measurements in pulsed magnetic fields exceeding 20 T on different RMnO3 systems with varying magnetic 4f-moments (i.e., R = Y, Ho, Er, and Tm), we demonstrate significant magnetic-field-driven reversible temperature changes, ΔTad. Our data show that the effect is predominantly driven by the rare-earth magnetism, scaling with the effective magnetic moment of the R atom. The largest reversible temperature change is observed in HoMnO3 with ΔTad of up to 20.1 K, whereas the effect is largely suppressed in YMnO3. Our findings demonstrate the importance of the 4f-magnetism for the magnetocaloric effect in hexagonal manganites, which is expected to be relevant for other magnetic oxide systems and their optimization for refrigeration applications at cryogenic temperature. Magnetic refrigeration at cryogenic temperatures is crucial for technologies like hydrogen liquefaction and quantum computing. Here, the authors investigate multiferroic hexagonal manganites, revealing that rare-earth magnetism drives significant reversible temperature changes, up to 20.1 K for HoMnO3, suggesting potential optimization for other magnetic oxide systems in cryogenic refrigeration.

Large magnetocaloric effects can be observed in materials with first-order magneto-structural phase transition. However, materials with large thermal hysteresis show a reduced effect in moderate fields (∼2 T) because the external field is insufficient to induce a fully reversible transformation. The hysteresis can be overcome or even exploited by applying a second external stimulus. A multi-stimuli test bench has been built to demonstrate the multicaloric effect in FeRh alloy using a pulsed magnetic field up to 9 T and a uniaxial stress of up to 700 MPa. A cyclic multicaloric effect of ±2.5 K could be observed for a sequential application of a pulsed field of 3 T and a uniaxial stress of 700 MPa. The interplay among external field strength, thermal hysteresis, and the transition width enables the use of pulsed magnetic fields and allows a decoupling of the applied magnetic field and the heat transfer process in the multi-stimuli cycle.

The magnetocaloric effect (MCE) offers a promising alternative for environmentally friendly cooling technologies, particularly at cryogenic temperatures. However, overestimating material capabilities can lead to misguided research efforts and hinder technological progress. Metamagnetic materials undergoing a transition from an antiferromagnetic to a ferromagnetic state are often predicted to exhibit a strong inverse MCE at cryogenic temperatures based on magnetization measurements. This assumption is critically assessed here using Tb3Ni as a case study. By employing a simple model and comparing results across various measurement techniques, it is demonstrated that the predicted inverse MCE does not exist. Specific-heat data reveal no evidence of this effect, while direct Delta Tad pulsed-magnetic-field measurements indicate significant heating caused by dissipative effects linked to hysteresis. Furthermore, total-entropy calculations derived from magnetization data violate the second law of thermodynamics, clearly ruling out the existence of an inverse MCE. These findings underscore the necessity of complementary experimental approaches and a precise understanding of the transitions to accurately characterize magnetocaloric materials and identify suitable candidates for cryogenic magnetic refrigeration.

Spin crossover (SCO) complexes have been shown to exhibit giant mechanocaloric effects. Due to the change of magnetization at the spin crossover transition, they are also expected to show magnetocaloric effects. However, experimental studies on the magnetocaloric properties in SCOs are scarce. Here, we have studied the magnetocaloric response in the SCO complex [Fe(L)2](BF4)2, [L = 2,6-di(pyrazol-1-yl)pyridine] using pulsed magnetic fields. We show that applying a magnetic field can induce a partial transformation from the low spin to the high spin state. We directly measure the adiabatic temperature change of the transformation for different initial sample temperatures and magnetic fields and compare them with calculations using the Clausius–Clapeyron equation. While we found a large change in entropy of 70 J kg−1 K−1 at 50 T, the corresponding temperature change of 1.5 K is small due to the weak dependence of the transformation temperature on the magnetic field. Our study enhances the knowledge of caloric effects in SCO complexes, which so far have mainly focused on mechanocaloric studies.

Magnetic refrigeration (MR) offers a sustainable and emission-free solution to the prevalent heat-pumping systems used worldwide. Typically, it utilizes the magnetocaloric effect (MCE) to achieve cooling by changing the external magnetic field intensity. However, an alternative approach involves maintaining a fixed field intensity while manipulating its orientation to induce temperature changes, in an effect known as the rotating MCE (RMCE). While the RMCE has been extensively studied in materials with magnetocrystalline anisotropy, its investigation in polycrystalline magnetocaloric samples with asymmetric shapes has been lacking until recently. In this case, the RMCE is induced by the demagnetizing effect, which becomes more pronounced in high aspect-ratio sample geometries exhibiting different effective demagnetizing factors at different orientations, such as in films. In this work, we characterize the conventional and rotational MCE of 40 mu m-thick gadolinium films through magnetization and direct temperature measurements. The maximum adiabatic temperature change achieved under a 1 T magnetic field was 2.05 K when the film was oriented in plane with the field and 1.25 K when the film was perpendicular to the magnetic field, corresponding to an adiabatic temperature difference of around 0.8 K which may be induced through magnetic field rotation. Additionally, the maximum adiabatic temperature change upon rotation is shown to exhibit a non-monotonous behavior with field intensity, displaying a peak value for field intensities of around 0.8 T. The high aspect ratio of the Gd film has been demonstrated to considerably enhance the intensity of demagnetizing field-based RMCE compared to bulk samples, paving the way for future research in this emerging field of MR cooling.

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) has been recognized as an environmentally benign and energy-efficient cooling technology. Exploring suitable magnetocaloric materials is a crucial prerequisite for practical MR applications. We have herein provided a systematic investigation of the crystal structure, microstructure, electronic structure, magnetic phase transition, critical behavior, and MCE of the GdCoC compound featuring excellent cryogenic magnetocaloric performance by means of experimental determination and theoretical calculation. The GdCoC compound is crystallized in a simple layered tetragonal crystal structure with a P42/mmc space group and undergoes two successive ferromagnetic (FM) transitions along with a low-temperature weak antiferromagnetic (AFM) transition under low magnetic fields. Density functional theory calculations confirms the FM coupling of the Gd and Co intra-sublattice interactions, whereas AFM coupling for their inter-sublattice interaction. The magnetic transitions are merged in to one under high magnetic fields which has been confirmed to be second-order type and its critical behavior can be understood in the framework of tri-critical mean-field model, whereas the low-temperature weak AFM transition is belonging to the first-order type. The excellent magnetocaloric performance of the GdCoC compound was identified by the parameters of magnetic entropy change, adiabatic temperature change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, which are superior to most of the well-known magnetocaloric materials with similar working temperatures, making it attractive for practical cryogenic MR applications.

AbstractMagnetic refrigeration, which utilizes the magnetocaloric effect, can provide a viable alternative to the ubiquitous vapor compression or Joule-Thompson expansion methods of refrigeration. For applications such as hydrogen gas liquefaction, the development of magnetocaloric materials that perform well in moderate magnetic fields without using rare-earth elements is highly desirable. Here we present a thorough investigation of the structural and magnetocaloric properties of a novel layered organic-inorganic hybrid coordination polymer Co4(OH)6(SO4)2[enH2] (enH2 = ethylenediammonium). Heat capacity, magnetometry and direct adiabatic temperature change measurements using pulsed magnetic fields reveal a field-dependent ferromagnetic second-order phase transition at 10 K <$${T}_{C}$$ T C < 15 K. Near the hydrogen liquefaction temperature and in a magnetic field change of 1 T, a large maximum value of the magnetic entropy change, $$\Delta {S}_{M}^{{Pk}}$$ Δ S M P k = − 6.31 J kg−1 K−1, and an adiabatic temperature change, $$\Delta {T}_{{{\rm{ad}}}}$$ Δ T ad = 1.98 K, are observed. These values are exceptional for rare-earth-free materials and competitive with many rare-earth-containing alloys that have been proposed for magnetic cooling around the hydrogen liquefaction range.

The low efficiency of conventional liquefaction technologies based on the Joule-Thomson expansion makes liquid hydrogen currently not attractive enough for large-scale energy-related technologies that are important for the transition to a carbon-neutral society. Magnetocaloric hydrogen liquefaction has great potential to achieve higher efficiency and is therefore a crucial enabler for affordable liquid hydrogen. Cost-effective magnetocaloric materials with large magnetic entropy and adiabatic temperature changes in the temperature range of 77 $\sim$ 20 K under commercially practicable magnetic fields are the foundation for the success of magnetocaloric hydrogen liquefaction. Heavy rare-earth-based magnetocaloric intermetallic compounds generally show excellent magnetocaloric performances, but the heavy rare-earth elements (Gd, Tb, Dy, Ho, Er, and Tm) are highly critical in resources. Yttrium and light rare-earth elements (La, Ce, Pr, and Nd) are relatively abundant, but their alloys generally show less excellent magnetocaloric properties. A dilemma appears: higher performance or lower criticality? In this review, we study how cryogenic temperature influences magnetocaloric performance by first reviewing heavy rare-earth-based intermetallic compounds. Next, we look at light rare-earth-based, "mixed" rare-earth-based, and Gd-based intermetallic compounds with the nature of the phase transition order taken into consideration, and summarize ways to resolve the dilemma.

The heavy rare-earth-based Laves phases are well-studied intermetallic materials that stand out for their remarkably high magnetocaloric effects, particularly at cryogenic temperatures. In this study, we present the findings of our comprehensive investigation of cobalt Laves phases RCo2 with R standing for erbium, holmium, dysprosium, and terbium. This includes the determination of the magnetocaloric effect by indirect methods using calorimetric and magnetization data. Furthermore, for the first time in these materials, we directly measured the adiabatic temperature change at high magnetic fields up to 20 T. The largest Delta Tad value of 17 K, we obtained for ErCo2. Because the order of the transition significantly impacts the efficiency of thermodynamic cycles, we have also focused on determining the transition order in these materials. This was done through the application of established methods and a recently proposed quantitative criterion including the value of the local exponent n. Further, we compare our results with other materials using a straightforward material-based figure of merit - the temperature-averaged entropy change (TEC). Our results demonstrate the great potential of these materials for applications such as for magnetic hydrogen liquefaction.

The magnetocaloric effect enables magnetic refrigeration and plays an important role for cooling at cryogenic temperatures, which is essential for emergent technologies such as hydrogen liquefaction and quantum computing. Here, we study the magnetocaloric effect in multiferroic hexagonal manganites by conducting direct adiabatic temperature measurements in pulsed magnetic fields exceeding 20 T. Data gained on polycrystalline HoMnO3, ErMnO3, TmMnO3, and YMnO3 demonstrate a direct correlation between the magnetic 4f-moments and the measured adiabatic temperature change. In HoMnO3, i.e., the system with the largest magnetic 4f-moments, significant temperature changes, ΔTad, of up to 20.1 K are observed, whereas the effect is largely suppressed in YMnO3. Our systematic investigations show the importance of the rare-earth magnetism for the magnetocaloric effect in multiferroic hexagonal manganites at cryogenic temperatures, reaching about 64 for gadolinium at room temperature.

The excellent magnetic entropy change ($\Delta S_T$) in the temperature range of 20 $\sim$ 77 K due to the first-order phase transition makes $Pr_2In$ an intriguing candidate for magnetocaloric hydrogen liquefaction. As an equally important magnetocaloric parameter, the adiabatic temperature change ($\Delta T_{ad}$) of $Pr_2In$ associated with the first-order phase transition has not yet been reported. In this work, the $\Delta T_{ad}$ of $Pr_2In$ is obtained from heat capacity measurements: 2 K in fields of 2 T and 4.3 K in fields of 5 T. While demonstrating a $\Delta T_{ad}$ that is not as impressive as its remarkable $\Delta S_T$, $Pr_2In$ exhibits an unusual low Debye temperature ($T_D$) of around 110 K. Based on these two observations, an approach that combines the mean-field and Debye models is developed to study the correlation between $\Delta T_{ad}$ and $T_D$. The role of $T_D$ in achieving large $\Delta T_{ad}$ is revealed: materials with higher $T_D$ tend to exhibit larger $\Delta T_{ad}$, particularly in the cryogenic temperature range. This discovery explains the absence of an outstanding $\Delta T_{ad}$ in $Pr_2In$ and can serve as a tool for designing or searching materials with both a large $\Delta S_T$ and a $\Delta T_{ad}$.

Magnetic refrigeration based on the principle of the magnetocaloric effect (MCE) in magnetic solids has been considered as a prospective cooling technology. Exploring suitable magnetocaloric materials (MCMs) is a vital prerequisite for practical applications. Herein, an excellent cryogenic MCM-the B-site-ordered Gd2CuTiO6 double perovskite (DP) oxide-which exhibits the largest MCE among known Gd-based DP oxides, is identified. Such enhanced cryogenic MCE in the Gd2CuTiO6 DP oxide likely stems from the exchange interaction effect between Gd-4f and Cu-3d magnetic sublattices. Under a magnetic field change of 0-7 T, the maximum magnetic entropy change (-Delta STmax) of the Gd2CuTiO6 DP oxide reaches 51.4 J kg(-1) K-1 (378.2 mJ cm(-3) K-1), which is much larger than that of the commercialized magnetic refrigerant Gd(3)Ga5O(12), which is 38.3 J kg(-1 )K(-1) (271.2 mJ cm(-3 )K(-1)), and it is also superior to most of the recently reported benchmarked cryogenic MCMs, indicating the possibility for practical applications. This work also provides a productive route for future cryogenic MCM design by harnessing 4f-3d exchange interactions.