Ion irradiation of Co/Pt multilayer films

This article describes a microstructural and magnetic investigation of the modification of Co/Pt multilayer films by Ar ion irradiation which results in a change of the orientation of the magnetization from perpendicular to the film plane to the in-plane direction. Transmission electron microscopy observation confirms the general structure of the as-deposited samples and correlates with the x-ray reflectivity measurements in showing the eventual mixing of the layers and a large increase in grain size caused by the irradiation. TRIM (transport of ions in matter) calculations show that large numbers of recoils are placed outside the individual layers and in the adjacent layers on irradiation. This signifies considerable roughening of the interfaces and mixing in the multilayer structure. Magnetic measurements and magnetic force microscopy observations confirm the decrease of perpendicular anisotropy and the changes of the magnetization direction from the perpendicular direction to an in-plane direction after irradiation.