Defect production efficiency in Fe 60Co 40 thin films irradiated with swift heavy ions

Abstract

The damage production in Fe 60Co 40 thin films has been studied at liquid nitrogen temperature during low energy (15–360 keV He +, Ne +, Ar +, Xe +) and high energy ion irradiations (445 MeV Ag ions, 186 MeV and 40 MeV N ions). The irradiated films are polycrystalline with a very small grain size of 5–8 nm are in an initially chemically disordered state. Elastic collisions occurring during low temperature ion irradiations induce displacement cascades and this Frenkel pair creation results in an electrical resistivity increase of the alloy. In situ electrical resistivity measurements have allowed the experiment determination of the damage production. It is shown that the radiation damage produced by low energy ions and 40–186 MeV N ions are well explained by elastic collisions effects only. Moreover, a reduced defect production efficiency is observed in the case of energetic displacement cascades in agreement with previous experimental results obtained in thin pure metals and also with recent molecular dynamic computer simulations. On the other hand, an important defect production efficiency increase is observed in the case of a 445 MeV Ag ion irradiation where the slowing down of the ions occurs mainly via inelastic collisions. This result is discussed by comparison with previous experimental data demonstrating that an additional contribution to the classical defect production by elastic collisions exists in some metals above a given electronic stopping power threshold.