Evolution of physical and magnetic properties of La rich La 1−x Tb x Mn 2 Si 2 (x = 0, 0.1 and 0.225) compounds is studied using temperature and field dependent dc magnetization, electrical transport, and heat capacity measurements. LaMn 2 Si 2 undergoes a paramagnetic to antiferromagnetic ordering at T N ~ 400 K and a long range ferromagnetic ordering below T C ~ 308 K. However, the substitution of Tb at La site results in the contraction of unit cell as well as decrease in the Mn-Mn spacing, which leads to an additional antiferromagnetic phase below T N ~ 87 K and 257 K for La 0.9 Tb 0.1 Mn 2 Si 2 and La 0.775 Tb 0.225 Mn 2 Si 2 , respectively. Using magnetization isotherm results, we have constructed an H-T phase diagram for x = 0.225 and have found the coexistence of this additional antiferromagnetic phase with ferromagnetic phase. The phase coexistence at x ~ 0.225 is further analysed using magnetoresistance (MR) and magnetocaloric effect (MCE) studies and a reasonable correlation is established between MCE and MR. In order to analyse the nature of the magnetic transition at T C , a universal master curve is constructed by rescaling the magnetic entropy curves. Low temperature neutron diffraction measurements performed on the polycrystalline samples revealed a canted ferromagnetic structure for x ~ 0.1 and a canted antiferromagnetic structure for x ~ 0.225.

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