Magnetic refrigeration has long been discussed as a potential alternative to vapor compression cooling, but materials limitations have slowed its development. A new study led by Professor Oliver Gutfleisch and Dr. Xin Tang at Technische Universität Darmstadt, working in collaboration with researchers from the National Institute for Materials Science in Japan and other international partners, presents a materials strategy that addresses one of the field’s most persistent barriers. Their work, published in Advanced Materials, focuses on improving both the efficiency and durability of magnetocaloric compounds through targeted atomic scale modification.
Tang, X., Miura, Y., Terada, N., Xiao, E., Kobayashi, S., Döring, A., Tadano, T., Martin‐Cid, A., Ohkochi, T., Kawaguchi, S., Matsushita, Y., Ohkubo, T., Nakamura, T., Skokov, K., Gutfleisch, O., Hono, K., & Sepehri‐Amin, H. (2026). Control of Covalent Bond Enables Efficient Magnetic Cooling. Advanced Materials, 38(7). https://doi.org/10.1002/adma.202514295
Magnetic refrigeration relies on the magnetocaloric effect, a phenomenon in which certain materials change temperature when exposed to a magnetic field. When the field is applied, magnetic moments align and the material heats up. When the field is removed, it cools. In principle, this allows cooling cycles without conventional chemical refrigerants. In practice, however, materials that exhibit strong temperature changes often undergo structural phase transitions that introduce hysteresis. These irreversible energy losses reduce efficiency and lead to performance degradation under repeated cycling. Materials that avoid hysteresis typically deliver weaker cooling performance, creating a long standing trade off between stability and effectiveness.
The research team focused on the intermetallic compound Gd5Ge4, composed of gadolinium and germanium, which is known for its significant magnetocaloric response at cryogenic temperatures. Earlier studies showed that during magnetic phase transitions, structural rearrangements occur between atomic slabs within the material. Changes in bond lengths between germanium atoms contribute directly to hysteresis and gradual degradation during operation. Rather than suppressing the magnetic transition itself, the researchers targeted the bonding environment that drives structural instability.
By partially substituting germanium with tin, the team modified the covalent bonding characteristics that connect structural slabs. This substitution stabilizes inter slab distances during magnetic transitions, reducing the structural strain responsible for irreversible losses. The approach demonstrates how small adjustments in chemical composition can moderate mechanical distortion without compromising the magnetic response. It reframes the problem as one of bond engineering rather than simply magnetic optimization.
Experimental results show that the modified material maintains stable performance under repeated cycling while substantially improving its reversible temperature change. The reversible adiabatic temperature change increased from approximately 3.8 degrees Celsius to 8 degrees Celsius. At the same time, hysteresis losses were significantly reduced. Doubling the reversible temperature span while preserving structural stability represents a meaningful advance for magnetocaloric materials research, particularly given the historical difficulty of improving both metrics simultaneously.
The optimized compound operates in a cryogenic temperature range between roughly minus 233 degrees Celsius and minus 113 degrees Celsius. While this range does not target domestic refrigeration, it aligns with industrial gas liquefaction processes. Liquefying hydrogen, nitrogen, and natural gas requires substantial energy input, and improvements in cooling efficiency could have system level implications for emerging hydrogen infrastructure and low carbon fuel supply chains. Several international research groups have been exploring magnetocaloric materials for cryogenic applications, and this study contributes a materials design principle that may be applicable beyond gadolinium based systems.
Commercial implementation will depend on additional engineering considerations, including magnetic field generation, thermal management integration, and material cost. Rare earth elements such as gadolinium introduce supply chain and economic constraints that must be evaluated alongside performance metrics. Nevertheless, the study highlights how controlling covalent bonding can reduce hysteresis without sacrificing magnetocaloric strength, a strategy that may inform future development of alternative compounds.
Magnetic refrigeration has progressed incrementally over the past two decades, often constrained by the same materials limitations. This work does not resolve all system level challenges, but it addresses a central barrier with measurable improvement. For engineers working at the intersection of materials science and energy systems, the findings reinforce the importance of atomic scale design in resolving macroscopic performance trade offs. As industrial cooling and hydrogen technologies continue to evolve, advances in magnetocaloric materials may find their first large scale role in cryogenic infrastructure rather than household appliances.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
