Atomic mixing induced by swift heavy ion irradiation of Fe/Zr multilayers

The mechanism of ion induced mixing and phase change was studied for Fe/Zr multilayers, and specifically for the case of swift heavy ions giving rise to a very large electronic excitation of the target. The multilayers had a modulation of 7.6nm and an overall composition Fe69Zr31. The Zr layers were amorphous whereas the Fe ones were crystalline (bcc) with a very strong(1 1 0) texture in the growth direction. The phase transformation and the composition changes were analysed using the structural and magnetic properties of the Fe component by means of a detailed analysis of the X-ray diffraction profiles and with the aid of backscattering Mossbauer spectroscopy. A complete mixing was observed at a fluence of 10(13) U/cm(2). Both phenomena. the dose dependence of the ion beam mixed amorphous non-magnetic phase and the quantitative evolution of the crystalline iron layer thickness, suggest that mixing occurs in a two-stage process. At an initial stage, an anisotropic diffusion of iron atoms in the amorphous zirconium layers takes place along the interface. while subsequent ion bombardment leads to a generalised transformation through the whole of the Fe layer. Finally, the implications of these observations are discussed in comparison to the plastic deformation phenomena reported for amorphous alloys. (C) 1999 Elsevier Science B.V. All rights reserved.