Mn films of similar to 50 nm has been deposited by electron beam evaporation technique on cleaned and etched Si [(1 0 0), 8-10 Omega cm] substrates to realize a Mn/Si interfacial structures. The structures have been irradiated from energetic (similar to 100 MeV) ion beam from Mn side. The irradiated and unirradiated structures have been characterized from atomic force microscopy, X-ray diffractometry, magnetic force microscopy, and vibrating sample magnetometer facilities. It has been found that surface/interfacial granular silicide phases (of Mn(x)Si(y)) are formed before and after the irradiation with a irradiation induced modifications of surface morphology and magnetic property. The surface/interface roughness has been found to increase on the irradiation from the atomic force microscopy data. The magnetic property on the irradiation shows an interesting and significant feature of an increased coercivity and a ferromagnetic like behavior in the Mn-Si structure. The observed increased coercivity has been related to the increased roughness on the irradiation. The ferromagnetism after the irradiation is a curious phenomenon which seems due to the formation of Mn-C-Si compound from the carbon dissolved in silicon. (C) 2010 Elsevier B.V. All rights reserved.