Conventional cryogenic cooling used in medical MRI and related systems relies heavily on liquid helium and rare earth elements, which face supply instability and concerns over long term resource depletion. Holmium, a key element in many existing regenerator materials, has an annual production of only about 100 tons and reserves that are unevenly distributed globally. With demand for cryogenic cooling expected to rise, researchers have been seeking alternative materials and mechanisms that remove this dependence on rare resources while maintaining practical performance.
The joint NIMS and KOSEN Oshima College team focused on regenerator materials for mechanical coolers of the Gifford McMahon (GM) type, which can operate without liquid helium. They designed and tested a regenerator material that uses only abundant elements, demonstrating that it can cool to cryogenic temperatures while delivering performance comparable to conventional rare earth based materials. The composition, described as CuFe0.98Al0.02O2 (CFAO), avoids rare earth metals entirely and instead exploits a magnetic phenomenon to achieve high specific heat at low temperatures.
The key physical mechanism at work in the new material is magnetic frustration, a property found in some magnetic systems with a triangular lattice crystal structure where spins cannot simultaneously satisfy all mutual interactions. In such lattices, the spin orientations remain difficult to fully align until the system reaches cryogenic temperatures, which creates enhanced magnetic entropy and high specific heat in the low temperature regime. By harnessing this frustrated spin state in a transition metal oxide made from copper, iron and aluminum, the researchers achieved cryogenic specific heat behavior previously associated mainly with rare earth based compounds.
Experimental measurements revealed that the rare earth free regenerator material exhibits high specific heat at cryogenic temperatures despite being based on transition metals rather than rare earth elements. Its cooling capacity was shown to be comparable to that of lead, which was used in GM coolers in the 1960s, and to holmium based compounds such as HoCu2 that have dominated the field since the 1990s. This marks the first time a magnetic regenerator material without rare earth elements has reached performance levels considered practical for real world cooler applications.
Beyond matching performance, the new material offers advantages in sustainability and environmental impact because it is composed only of widely available elements. The use of copper, iron and aluminum reduces exposure to supply disruptions and price volatility associated with rare earth mining and processing. As a result, the technology could underpin a new generation of cryogenic cooling systems that are more robust against resource constraints and better aligned with long term environmental and economic goals.
The team highlights that this development directly addresses concerns over the limited availability of liquid helium as well as rare earth elements used in current regenerator designs. By decoupling cryogenic cooling performance from these constrained resources, the material could help stabilize the supply chain for critical medical and quantum technologies. In particular, MRI scanners and quantum computing hardware, both of which are expected to see continued growth in deployment, stand to benefit from more sustainable cooling solutions.
The project brought together expertise from NIMS and the National Institute of Technology (KOSEN), Oshima College under the Japan Science and Technology Agency (JST) Adaptable and Seamless Technology Transfer Program through Target driven R and D (A STEP). The research, titled "Innovative Cryogenic Cooling Material Using Spin Frustration from Abundant Elements," was led by principal investigator Noriki Terada and involved researchers Hiroaki Mamiya and Akiko Saito of the Green Magnetic Materials Group and Research Center for Magnetic and Spintronic Materials at NIMS, along with Professor Shinji Masuyama at KOSEN Oshima College. The results were published online in the journal Scientific Reports on December 22, 2025.
Looking ahead, the researchers see strong potential for applying the abundant element regenerator material in commercial GM coolers used for MRI systems and emerging quantum computing platforms. They note that the combination of high cryogenic specific heat, absence of rare earth elements and use of abundant resources positions the material as a promising candidate for large scale deployment. Further development is expected to focus on integrating the material into practical cryocooler designs, optimizing manufacturing processes and validating long term operational stability under real world conditions.
Research Report:Innovative Cryogenic Cooling Material Using Spin Frustration from Abundant Elements
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