We report here on changes in magnetism and microstructure when implanting, at 92 or 300 K, up to 5 x 10(15) Au26+-ions cm(-2) of 350 MeV into Fe-nat(45 nm)/Fe-57(20 nm)/Si trilayers. This choice of ions and energy allowed to test the irradiation effects in the regime of pure electronic stopping. The samples were analysed before and after irradiation by Rutherford back-scattering spectroscopy, X-ray diffraction, conversion electron Mossbauer spectroscopy, and magneto-optical Kerr effect. Up to 1 x 10(15) ions cm(-2), there was interface broadening at a mixing rate of Delta o(2)/Phi = 55(5) nm(4), followed by full Fe-Si inter-diffusion. The Mossbauer spectra revealed fractions of alpha-Fe and amorphous ferromagnetic and paramagnetic iron silicides, but no crystalline Fe-Si phase. The magnetic remanence in the as-deposited Fe-layer showed small components of uniaxial and four-fold magnetization. For increasing ion fluence, the component with four-fold symmetry grew at the expense of the uniaxial component. For the highest fluences, an isotropic magnetization was found. (c) 2005 Elsevier B.V. All rights reserved.