Enhanced low-field magnetocaloric effect induced by Co doping in RCu_2–xCo_x (R = Er, Ho) compounds for liquid hydrogen

Hydrogen, as a clean energy carrier, requires liquefaction at 20–77 K, a process that is energy-intensive and traditionally dependent on conventional refrigeration methods. Magnetocaloric refrigeration offers a promising alternative, especially when using permanent magnets as the magnetic field source, which can significantly simplify system design and reduce operational costs. Designing magnetocaloric materials with magnetic ordering temperatures within the hydrogen liquefaction range and exhibiting superior magnetocaloric effects under low magnetic fields is essential for advancing sustainable energy technologies. This study presents an in-depth investigation of the enhanced low-field magnetocaloric effect (MCE) in RCu_2−xCo_x (R = rare-earth) compounds. The results indicate that Co doping significantly modifies orbital hybridization and magnetic properties, which in turn improves the MCE under low fields. Experimental data confirm that Co-doped compounds show MCE performance at low fields. For instance, under a varying magnetic field of 0–2 T, the volumetric magnetic entropy change of the ErCu_1.75Co_0.25 compound reaches 0.12 J⋅cm⁻³⋅K⁻¹. First-principles calculations provide further insights into the electronic density of states and magnetic exchange interactions, clarifying the mechanisms behind the enhanced MCE.