Exploration of the rare-earth cobalt nickel-based magnetocaloric materials for hydrogen liquefaction

Magnetic refrigeration based on the magnetocaloric effect (MCE) of magnetic solids has been considered as an emerging technology for hydrogen liquefaction. However, the lack of high-performance materials has slowed the development of any practical applications. Here, we present a family of rare-earth cobalt nickel-based magnetocaloric materials, namely Dy_1-xHo_xCoNi and Ho_1-xEr_xCoNi compounds, and systematically investigated their structural and magnetic properties as well as the MCE and magnetocaloric performance. All of these compounds crystallize in the C15-type Laves-phase structure and undergo typical second-order magnetic phase transition (MPT). The change in magnetism and the MPT temperature for the Dy_1-xHo_xCoNi and Ho_1-xEr_xCoNi compounds originate from the exchange interactions between nearest-neighbor RE³⁺ ion pairs. No hysteresis magnetocaloric effect was achieved, and the MPT temperature of these compounds could be tuned from the liquefaction temperature of nitrogen (∼77 K) to hydrogen (∼20 K) by adjusting the ratio of rare-earth elements. This study's findings indicate that the Dy_1-xHo_xCoNi and Ho_1-xEr_xCoNi compounds are of potential for practical magnetic refrigeration applications in the field of hydrogen liquefaction.