Controlling the Magnetic Properties of Cr-Implanted Co/Pt Multilayer Films Using Ion Irradiation for Planar Patterned Media

We have investigated the modification of the microstructure and magnetic properties of Co/Pt multilayer films with various layer structures using ion beam irradiation. Cr/[Co/Pt] multilayer films prepared by a magnetron sputtering deposition on a surface oxidized Si substrate were irradiated by 30 keV Kr⁺ ion beam with various ion doses from 1×10¹⁴ to 5×10¹⁵ ions/cm². The modifications of magnetic properties and microstructures due to Kr⁺ ion irradiation depended on Co/Pt layer structures. The as-prepared [Co(0.4 nm)/Pt(0.45 nm)]15 multilayer films were confirmed to exhibit the square shaped M-H loop and the perpendicular easy axis with a saturation magnetization of 620 emu/cc and coercivity of 1.1 kOe. After the irradiation with ion dose of 5×10¹⁵ ions/cm², the easy axis changes from perpendicular to in-plane direction. The coercivity and saturation magnetization decrease down to 2% and 13% of its original values, respectively. The decrease of coercivity and saturation magnetization is due to the implantation of the Cr atom in the top most layers into Co/Pt multilayer films caused by Kr⁺ ion irradiation, as confirmed from Auger electron spectroscopy (AES) depth profiles.