Wide temperature span and giant refrigeration capacity magnetic refrigeration materials for hydrogen liquefaction

Based on theoretical calculations and experiments, the crystal structure, electronic structure, magnetism, and magnetocaloric effect (MCE) of the Ho₅B₂C₅ compound have been systematically investigated. The Ho₅B₂C₅ compound with a typical metallic nature was found to crystallize in a tetragonal structure belonging to space group P4/ncc (No. 130), and its magnetic ground state was identified as ferromagnetic (FM) ordering based on theoretical and experimental results. Additionally, a second-order magnetic phase transition from FM to paramagnetic around approximately 27 K was observed in the Ho₅B₂C₅ compound, resulting in a large MCE. Under varying magnetic fields ( Δ H ) from 0 to 7 T, the maximum magnetic entropy change ( − Δ S M max ), refrigeration capacity (RC), and δ TFWHM are 21.3 J/kg K, 1001.6 J/kg, and 60.2 K (a wide temperature range from 15.2 to 75.4 K), respectively. The outstanding MCE performance of the Ho₅B₂C₅ compound is expected to facilitate the progress of magnetic refrigeration for hydrogen liquefaction.