In this study, we investigated the optical, magnetic, and electrical transport properties of Si_1-xMn_x (0.1 < x < 0.9) single crystals grown by the vertical Bridgman method. The alloys with a Mn concentration of up to 64% demonstrated weak ferromagnetic ordering around TC = 30 K. The Si_0.25Mn_0.75 and Si_0.18Mn_0.82 alloys showed weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, as confirmed by magnetization, neutron diffraction, and transport studies.