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 × 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.