Interface mixing and phase transformations in Xe-ion-irradiated Co/Fe bilayers

Bilayers of polycrystalline Co(37 nm)/Fe(37 nm) were deposited onto Si wafers via electron-gun evaporation and irradiated at room temperature with 200 keV Xe+ ions to fluences of 5x1014-1x1016/cm2. The magneto-optical Kerr effect, Rutherford backscattering spectroscopy and x-ray diffraction were used to characterize the magnetization and microstructure of the films. Xe fluences of up to 5x1015 ions/cm2 were found to induce a four-fold magnetic anisotropy in the originally isotropic films, as a consequence of the phase transformation of hexagonal Co to face-centered-cubic Co caused by ion irradiation. Xe fluences exceeding 7x1015 ions/cm2 produced a uniaxial magnetic texture, which is explained by strong Co/Fe interface mixing and possibly ion-induced formation of CoFe grains at the interface