On the structure and magnetism of Ni/Si and Fe/Si bilayers irradiated with 350-MeV Au ions

Modifications of Ni/Si and Fe/Si bilayers induced by swift heavy ions were studied in the regime of pure electronic stopping. Polycrystalline films, 65-75 nm thick, were deposited via electron evaporation (Ni) or pulsed laser deposition (Fe) onto Si wafers and irradiated at ≤300 K with 350-MeV Au26+ ions to fluences of up to 5 x 1015 ions/cm2. The samples were analyzed by Rutherford backscattering spectroscopy, X-ray diffraction and the magneto-optical Kerr effect. In the Fe/Si samples, a 20 nm 57Fe layer was interlayed between natFe and Si in order to monitor interface mixing and phase formation by means of Moessbauer spectroscopy. In both systems, a high mixing rate of ∼60 nm4 was found, correlated with relaxation of the as-deposited stress and uniaxial magnetic anisotropy. At higher fluences, full interdiffusion gives rise to amorphous silicide phases, build-up of stress and loss of magnetic texture