Multiphase critical point type phase boundary induced superior magnetocaloric properties in ferromagnetic Tb_1-xGd_xCo₂ alloys

In this work, we report an exotic combination of magnetic entropy change (ΔS_M =4.56 Jkg^-1K⁻¹), refrigerant capacity (RC=190.6 J kg⁻¹) and adiabatic temperature change (ΔT_ad=6.8 K) for varying magnetic fields (ΔH) from 0 to 5 T, with near-zero hysteresis loss at the critical point of multiphase coexistence of rhombohedral, cubic and tetragonal phases at x=0.9 in Tb_1−xGd_xCo₂ alloys. Additionally, the ΔS_M curves cover a broad temperature range of 42 K. Further analysis demonstrates that the excellent magnetocaloric performance observed at the multiphase coexistence point stems from the flattening free energy, which provides minimal energy barriers, enabling magnetic spins to switch between different crystal symmetries.