Crystal structure, magnetic phase transition and magnetocaloric effect in Fe2Hf1-xTax (x = 0.20–0.24) alloys

Fe₂(Hf,Ta) Laves phase alloys have attracted significant attention as promising magnetocaloric materials due to their rare-earth-free composition, tunable magnetoelastic transition temperatures in the cryogenic range, and low thermal hysteresis. This study investigates the magnetoelastic transition and magnetocaloric effect in high-Ta-content Fe₂Hf_1-xTa_x alloys (x = 0.20, 0.21, 0.22, 0.23, 0.235, and 0.24). With increasing Ta content (0.20 ≤ x ≤ 0.23), the lattice parameters systematically decrease while the magnetic transition temperature shifts correspondingly from 170 K to approximately 70 K, covering the liquefaction temperature zones of natural gas. Distinct first-order magnetic phase transitions are observed at x  = 0.20 and 0.22, terminating at the critical composition of x  = 0.23. Notably, the x  = 0.22 alloy exhibits a high magnetic entropy change of 2.44 J/(kg·K) at 84 K under a magnetic field change of 2 T.