PI: Ganesh Balasubramanian

University: Lehigh University

Cryogenic helium gas regenerators have critical applications in medicine, scientific research, and quantum information sciences. A typical regenerator bed employs erbium nickel alloy (Er3Ni) in the lowest temperature zone because of its notable specific heat below 10 K governed by the pronounced magnetic energy states, while lead (Pb) is used for intermediate temperatures of about 15 K to 50 K. However, U.S. manufacturers are facing challenges with the supply of rare-earth alloys, as well as in identifying environmentally friendly alternatives to Pb. A promising and, as yet, untapped strategy for new regenerator materials lies with the examination of heat capacity of multicomponent alloys, where several elements (four or more) are typically mixed in equimolar or near-equimolar concentrations. These complex concentrated alloys, often referred to as high-entropy alloys (HEAs), are a relatively new class of materials that have attracted intense research interest worldwide over the last decade due to their unique material properties. Unlike conventional alloys that contain a single base element, HEAs are concentrated solid-solutions generally consisting of multiple principal elements in significant proportions. The overarching goal of the proposed research is to test and potentially adopt the multicomponent strategy to pave the way for a new generation of cryocoolers with higher efficiencies and greater refrigeration capacities. In pursuit of this goal, the research objective of this proposal is to understand and exploit the contribution of magnetic energy states towards specific heat capacity of multicomponent alloys. To realize this objective, the research tasks will involve quantifying the effect of the ferro and paramagnetic states to the specific heat capacity of magnetic multicomponent alloys relative to the electronic and phonon contributions. The initial selection of materials will be guided by compositions such as CoOsReRu and EuTe alloys, which have demonstrated high specific heat around 20 K.