Complex magnetic interactions and large inverse magnetocaloric effect in TbSi and TbSi_0.6Ge_0.4

We aim to investigate correlations between physical behaviors and crystal structure of TbSi and TbSi_0.6Ge_0.4 compounds through comprehensive analysis of magnetization, specific heat, and temperature-dependent x-ray diffraction (XRD) measurements. Despite their distinct crystal structures (FeB-type Pnma for TbSi and CrB-type Cmcm for TbSi_0.6Ge_0.4), both samples exhibit similar temperature and magnetic field-dependent magnetization behaviors. Each sample displays two antiferromagnetic (AFM) transitions, consistent with previous studies [1, 2], as well as metamagnetic behavior. Moreover, both samples exhibit a significant inverse magnetocaloric effect, with magnetic entropy change (∆S_M­) of 9.6 J/Kg-K for TbSi and 11.6 J/Kg-K for TbSi_0.6Ge_0.4 at µ₀∆H=7T. Remarkably, the temperature-dependent ∆S_M­ for the TbSi_0.6Ge_0.4 sample reveals the appearance of two additional minima at higher magnetic fields, indicating the emergence of field-induced ferromagnetic (FM) coupling, which is further supported by the evolution of the additional peaks in the specific heat curves at elevated magnetic fields. Additionally, our temperature-dependent XRD measurements unveil anisotropic thermal expansion of the unit cell in both samples, while combined XRD and magnetization data highlight the critical role of the 3^rd and 4^th nearest neighbor Tb-Tb interactions in governing low- and high-temperature AFM coupling in both samples.