Magnetisation and magnetic anisotropy of ion beam synthesised iron nitride

Abstract

We report the effects of implantation-induced-sputtering in determining the true magnetisation of iron nitrides formed by nitrogen implantation into iron films and the changes subsequently observed in their magnetic anisotropy. Iron thin films (40 nm) capped with gold layers were synthesized by ion beam sputtering. Nitrogen was implanted onto the thin film to a dose of 7 × 1016 cm−2. Dynamic ion–solid interaction simulations calculate the average nitrogen concentration within the iron thin films to be 13 at.%. Ion beam analysis was used to evaluate the composition and depth profile of the thin films before and after implantation. Cross-sectional transmission electron microscopy helped in identifying the implantation induced effects at the surface and interface of the thin film structure. Magnetisation measurements show that nitrogen implantation enhances the magnetisation of thin films and reduces their in-plane magnetic anisotropy. High resolution TEM and magnetisation results suggest formation of α’/α”-Fe16N2 with large magnetic moments and perpendicular magnetic anisotropy. The enhancement in magnetisation of the thin film with and without considering the sputtering losses is determined to be 15% and 5%, respectively. Our review of literature shows that underestimating the sputtering losses from implantation leads to reporting of inconsistent and reduced magnetic moments for Fe16N2.