Irradiation effects at the Ni/Fe interface

Layered thin film samples of 100 nm 56Fe/3 nm 57Fe/43 nm Ni (coating) or 100 nm 56Fe/3 nm 57Fe/63 nm Ni (coating) have been irradiated with 100 keV Ar+ or 200 keV Kr2+ ions, respectively, at doses up to 6x1016 ions/cm2. In order to study the effects of irradiation at the Ni/Fe interface, the samples have been analyzed before and after ion bombardment by means of Rutherford backscattering spectrometry, conversion electron Moessbauer spectroscopy, and nuclear reaction analysis. For the first time the resonant 58Ni(p, γ)59Cu reaction at Ep=1424 keV has been used to obtain Ni concentration depth profiles at a Ni/Fe interface. Three distinct Fe-Ni phases have been identified by their hyperfine field in the ion beam mixed region after irradiation: a solid solution of Ni in bcc α-Fe, an fcc Fe-Ni alloy (possibly either Ni3Fe or Fe0.64Ni0.36 invar alloy), and a nonmagnetic Fe-rich fcc Fe (γ-Fe) phase. The mixing efficiency for fcc Fe-Ni phase formation and for Ni migration into the Fe-rich region as a function of dose has been determined quantitatively indicating that Kr2+ is more effective than Ar+, as expected, and that saturation occurs at higher Ar+ doses. (orig.)