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

We present a comprehensive investigation of the electronic structure, magnetization, specific heat, and crystallography of TbSi (FeB structure type) and TbSi_0.6Ge_0.4 (CrB structure type) compounds. Both TbSi and TbSi_0.6Ge_0.4 exhibit two antiferromagnetic (AFM) transitions at T_ N1≈ 58 K and 57 K, and T_ N2≈ 36 K and 44 K, respectively, along with an onset of weak metamagnetic-like transition around 6 T between T_ N1 and T_ N2. High-resolution specific heat (C_ P) measurements show the second- and first-order nature of the magnetic transition at T_ N1 and T_ N2, respectively, for both samples. However, in the case of TbSi, the low-temperature (LT) AFM to high-temperature (HT) AFM transition takes place via an additional AFM phase at the intermediate temperature (IT), where both LT to IT AFM and IT to HT AFM phase transitions exhibit a first-order nature. Both TbSi and TbSi_0.6Ge_0.4 manifest significant magnetic entropy changes (Δ S_ M) of 9.6 and 11.6 J/kg-K, respectively, for Δμ_0H=7 T, at T_ N2. The HT AFM phase of TbSi_0.6Ge_0.4 is found to be more susceptible to the external magnetic field, causing a significant broadening in the peaks of Δ S_ M curves at higher magnetic fields. Temperature and field-dependent specific heat data have been utilized to construct the complex H-T phase diagram of these compounds. Furthermore, temperature-dependent x-ray diffraction measurements demonstrate substantial magnetostriction and anisotropic thermal expansion of the unit cell in both samples.