Fig. 1. Comparison between conventional ferromagnet and antiferromagnet with a metamagnetic phase transition in entropy−temperature diagram.

a Thermal variation of magnetic entropy change in typical magnetic fields (H) from H/J = 0 to H/J = 5.0 (where J is the ferromagnetic exchange constant) for ferromagnetic cases simulated in a previous theoretical study in ref. ³⁰. The temperature is normalized to the Curie temperature T_C. b Schematic illustration of magnetic refrigeration (MR) cycle for the case of antiferromagnetic (AFM) material that shows a metamagnetic phase transition. Magnetic fields are represented by zero field μ₀H = 0 and finite fields H₁ < H₂ < H₃ < H₄ < H₅. For the AFM case in b, the metamagnetic phase transition occurs over a small magnetic field change, ΔH = ∣H₂ − H₃∣, during the MR cycle A′ → B′ → C′ → A′.