A groundbreaking advancement in magnetic refrigeration technology has emerged from an international collaboration of leading research institutions, including Japan’s National Institute for Materials Science (NIMS), Kyoto Institute of Technology, and Germany’s Technical University of Darmstadt. This team has developed a pioneering materials design strategy that achieves an unprecedented synergy between a giant magnetocaloric effect and remarkable cycling stability, overcoming a long-standing dilemma in magnetic cooling materials. Their work demonstrates that precise manipulation of covalent bonding within the unit cell of intermetallic compounds can fundamentally reshape the energy landscape surrounding phase transitions, leading to elimination of hysteresis-related energy losses. Published in Advanced Materials on December 18, 2025, this breakthrough heralds a new era for environmentally sustainable, energy-efficient magnetic refrigeration systems.
Traditional vapor-compression refrigeration technologies, ubiquitous in air conditioners, refrigerators, and freezers, have faced severe criticism due to their reliance on refrigerants with high global warming potential. Magnetic refrigeration offers a compelling alternative, utilizing magnetocaloric materials whose temperature changes when subjected to alternating magnetic fields, thereby eliminating the need for harmful chemical refrigerants. However, the field’s progress has been hampered by a fundamental tradeoff: materials that exhibit a large magnetocaloric cooling effect typically suffer from irreversible hysteresis losses, leading to rapid degradation over repeated thermal cycles. On the other hand, magnetocaloric materials engineered for durability generally exhibit diminished cooling performance. This inherent compromise has thwarted efforts to realize practical magnetic cooling devices with superior efficiency and longevity.
The research team’s innovative materials design approach targets this impasse by finely tuning the covalent bonding environment within intermetallic crystals. Their case study focused on the gadolinium-germanium compound Gd₅Ge₄, a well-known magnetic refrigerant displaying a strong magnetocaloric response coupled to a coupled magnetic-structural phase transition. When exposed to a magnetic field, the unpaired electron spins of Gd align, raising the material’s temperature through an adiabatic process. This magnetic ordering triggers a concomitant structural change, characterized by significant shifts in lattice parameters and interatomic distances, particularly between germanium atoms that connect structural slabs within the material. These atomic-scale distortions produce hysteresis, manifesting as energy losses that degrade refrigerated cooling upon cycling.
To overcome these challenges, the team employed a strategic chemical substitution, partially replacing germanium atoms with tin. This carefully controlled substitution modulates the covalent character of the bonds connecting the slabs, reducing the extent of geometric rearrangements during the phase transition. The result is a flattened energy landscape around the transition point, which suppresses hysteresis and its associated losses. Such precise bond chemistry control stabilizes the crystal lattice framework during repeated magnetization and demagnetization cycles, enabling durable performance without sacrificing the magnitude of the cooling effect.
Experimental validation of this design strategy revealed remarkable performance improvements. The partially substituted Gd₅(Ge₁₋ₓSnₓ)₄ compound exhibited a reversible adiabatic temperature change that more than doubled, increasing from approximately 3.8 K to 8 K under cycling conditions. This enhancement marks a significant leap forward in magnetic refrigerant functionality, as it combines both an intensified magnetocaloric response and enhanced cyclic stability. These features are crucial for translating laboratory-scale discoveries into reproducible, long-lasting refrigeration devices suitable for commercial and industrial deployment.
From a fundamental perspective, this research sheds light on the crucial interplay between electronic bonding, crystal structure, and magnetic order in determining magnetocaloric properties. By controlling covalent bonding networks, the energy barrier associated with the structural phase transition can be tuned, effectively minimizing irreversibility. This concept challenges conventional wisdom which often viewed magnetic and structural transitions as inseparable and difficult to decouple, offering a new paradigm for materials design across related fields such as spintronics and solid-state cooling technologies.
The implications of this research extend beyond room-temperature cooling applications. Given that the developed magnetocaloric materials operate effectively at cryogenic temperatures, they are highly promising candidates for next-generation hydrogen liquefaction technologies. The need for low-environmental-impact liquefaction methods is rapidly increasing alongside global efforts to adopt hydrogen as a clean energy carrier. The ability of this material system to deliver large cooling effects reliably under cyclic operation could significantly improve energy efficiency in hydrogen liquefiers, reducing carbon footprints associated with fuel production and storage.
Looking forward, the team envisions expanding the bond chemistry tuning approach to a broader class of intermetallic compounds, potentially unlocking magnetocaloric systems with customizable characteristics tailored for diverse cooling and gas liquefaction challenges. Integrating advanced characterization techniques such as synchrotron X-ray diffraction and neutron scattering, alongside computational modeling, will facilitate accelerated discovery and optimization. This strategy holds promise for the creation of an entirely new generation of magnetic refrigerants that combine energy efficiency, long-term stability, and reduced reliance on problematic refrigerants.
This research was enabled by extensive interdisciplinary collaboration, harnessing expertise in materials science, crystallography, magnetism, and chemical physics. Contributions came from senior researchers and emerging scientists across multiple prestigious institutions, supported by multiple international funding agencies including Japan’s JSPS and JST as well as Germany’s DFG. Such collective efforts exemplify the increasingly global nature of frontline scientific innovation, where cross-border knowledge exchange accelerates solutions for pressing technological and environmental challenges.
Beyond magnetic refrigeration, the concept of controlling covalent bonds to tune energy landscapes around phase transitions represents a versatile design principle. Analogous challenges encountered in thermoelectric materials, shape-memory alloys, and battery electrode materials could also potentially benefit from similar chemical engineering approaches. This could open exciting cross-disciplinary avenues towards materials with finely tuned phase stability and durability, enabling more efficient energy conversion and storage technologies essential for a sustainable future.
In summary, this landmark study demonstrates that precise atomic-scale control of bonding within magnetocaloric materials can decisively break the historical tradeoff between cooling efficacy and cyclic durability. Such achievements unlock new horizons for magnetic cooling technology as a powerful, environmentally friendly alternative to conventional refrigeration. By enabling large temperature swings without hysteresis losses, this approach paves the way for robust, energy-saving devices with transformative potential for everyday climate control, hydrogen energy infrastructure, and beyond.
Subject of Research:
Magnetic cooling materials; intermetallic compounds; magnetocaloric effect; covalent bonding; phase transition tuning.
Article Title:
Control of Covalent Bond Enables Efficient Magnetic Cooling
News Publication Date:
December 18, 2025
Web References:
DOI: 10.1002/adma.202514295
Image Credits:
Tang Xin, National Institute for Materials Science; Sepehri Navid Hossein Sepehri-Amin, National Institute for Materials Science; Tadakatsu Ohkubo, National Institute for Materials Science; Yoshio Miura, Kyoto Institute of Technology; Shintaro Kobayashi, Japan Synchrotron Radiation Research Institute; Takuo Ohkochi, University of Hyogo; Konstantin Skokov, Technical University of Darmstadt
Keywords
Magnetocaloric effect, magnetic refrigeration, Gd₅Ge₄, covalent bond tuning, hysteresis elimination, energy-efficient cooling, cryogenic temperature, hydrogen liquefaction, phase transition control, intermetallic compounds, cyclic stability, sustainable refrigeration.
