Regenerator performance below 4 K in Tm-based bulk metallic glasses

The main obstacle for reaching low temperatures below 4 K using cryocoolers was the inefficiency of the regenerator materials. We report that large volumetric specific heat below 4 K in a wide temperature range has been obtained in Tm-based bulk metallic glasses, and the peak temperature of specific heat peak is tunable. We show that the amorphization of rare-earth based crystalline alloys and the lower magnetic transition temperature of spin glass behavior in the glasses result in the specific heat anomaly below 4 K. The large and tunable specific heat anomaly below 4 K indicates the potential regenerator performance of the glassy materials for sub-4 K cryocoolers.