Rare-earth-free regenerator materials for enhanced 4-K cryocooler performance

Abstract Cryogenic cooling, a vital technology in magnetic resonance imaging and quantum computing, depends on scarce helium and heavy rare-earth elements. The increasing demand for this technology highlights the urgent need for alternative materials to reduce this reliance. Although frustration-based delafossite CuFe 1– x Al x O 2 has recently been discovered to enable cryogenic-temperature refrigeration without rare-earth elements, its cooling capacity near 4 K remains inferior to that of the benchmark rare-earth material HoCu 2 . To address this limitation, this paper reports the design and performance of a novel, entirely non-rare-earth regenerator material for 4-K Gifford–McMahon cryocoolers. We investigated MnNb 2– x Ta x O 6 , a non-rare-earth frustrated magnet exhibiting a large specific heat around 4 K, as a potential cryogenic regenerator and combined it with CuFe 1– x Al x O 2 . Cooling tests revealed that, by exploiting the complementary specific-heat peaks of the two constituents, the cooling capacity of the combined material at 4.2 K increases by approximately 40% compared with that of CuFe 1– x Al x O 2 alone. Numerical simulations also proved that the large enhancement is caused by intrinsic material contributions. Our results show that rare-earth-free materials can match the performance of higher than 70% of the benchmark HoCu 2 material in the key 4.2 K regime, opening a viable route to sustainable, high-performance cryogenic temperature refrigeration without critical elements.