The lack of magnetic refrigeration (MR) materials with high magnetocaloric effect (MCE) and large relative cooling power (RCP) in the temperature range required for hydrogen liquefaction (20 K–77 K) is a bottleneck for practical applications of MR cooling systems. The present investigation of TbMn₂Si_2-xGe_x compounds (x = 0.1, 0.2) by variable temperature neutron and synchrotron X-ray diffraction, magnetization and heat capacity measurements, establish that substitution of Si with Ge in TbMn₂Si₂ leads to a significant enlargement of the unit cell and modification of the magnetic properties. Two consecutive ferromagnetic first-order transitions occur below 77 K with the third transition from paramagnetism to a collinear antiferromagnetic state being determined around 500 K. The resultant plateau-like MCE with large RCP below 77 K in these designed compounds offers scope for application for hydrogen liquefaction. Detailed neutron investigation confirm that four magnetic states exist within the temperature range 5 K to 500 K, with two successive first-order magnetic transitions below 77 K responsible for the large MCE. Our specific heat studies provide evidence of strong contributions from the nuclear specific heat and the corresponding nuclear specific heat coefficients of A = 430 ± 50 mJ mol⁻¹ K and A = 418 ± 60 mJ mol⁻¹ K have been determined for TbMn₂Si_2-xGe_x with x = 0.1 and x = 0.2, respectively. The overlapping entropy curves near these successive transitions lead to a plateau-like magnetothermal effect as well as a large reversible MCE for both samples (e.g. ΔS_M^max = 14.0 J/kg K and ΔT_max = 7.6 K; RCP = 379 J/kg for TbMn₂Si_1.9Ge_0.1 for an applied field of 5 T) indicating that the material can operate over a wide temperature range – particularly for hydrogen liquefaction.

在氢气液化所需的温度范围（20 K-77 K）内缺乏具有高磁热效应（MCE）和大相对冷却功率（RCP）的磁制冷（MR）材料是MR冷却系统实际应用的瓶颈。目前通过变温中子和同步加速器X射线衍射、磁化强度和热容测量对TbMn ₂ Si _2-x Ge _{x化合物（x = 0.1, 0.2）进行研究，确定用Ge取代TbMn 2} Si ₂中的Si会导致晶胞的显着增大和磁性能的改变。在 77 K 以下发生两个连续的铁磁一级转变，并在 500 K 左右确定从顺磁性到共线反铁磁状态的第三次转变。在这些设计的化合物中，所得的具有大 RCP 的平台状 MCE 低于 77 K，为氢的应用提供了范围液化。详细的中子研究证实，在 5 K 至 500 K 的温度范围内存在四种磁态，其中两个连续的一阶磁转变在 77 K 以下导致了大的 MCE。我们的比热研究提供了核比热的强烈贡献的证据，并且 已确定 TbMn ₂ Si的相应核比热系数A  = 430 ± 50 mJ mol ^-1 K 和A  = 418 ± 60 mJ mol ^{-1 K} _2-x Ge _x，其中 x = 0.1 和 x = 0.2。这些连续转变附近的重叠熵曲线导致了类似平台的磁热效应以及两个样品的大可逆 MCE（例如 ΔS _M ^max  = 14.0 J/kg K 和 ΔT _max  = 7.6 K；RCP = 379 J/kg对于 TbMn ₂ Si _1.9 Ge _0.1（适用于 5 T 的应用场），表明该材料可以在很宽的温度范围内工作 - 特别是对于氢液化。