In this work we report on swift heavy ion irradiation induced nano granular magnetic metallic Fe5Si3 silicide phase formation due to strong interfacial intermixing in Fe/Si bilayer samples. The bilayer samples have been irradiated with swift (100 MeV) heavy (Fe-56(7+)) ions having a fluence of 1 x 10(14) ions cm (2). It has been found that swift heavy ion causes strong irradiation induced interfacial intermixing and forms nano granular magnetic metallic Fe5Si3 silicide in Fe/Si bilayer samples, which shows strong uniform magnetic interaction and interacting magnetic particle behaviour at room temperature (RT). (C) 2008 Elsevier B. V. All rights reserved.