Selective Modification of Magnetic Properties of $Co_1$ /Au/$Co_2$/Au Multilayers by He Ion Bombardment

We show that in a $[Co_1//Au//Co_2//Au]_4$ multilayer, where $Co_{1(2)}$ denote Co layers of different thicknesses, a 10 keV He-ion bombardment with a 6×$10^{14}$ ions $cm^{-2}$ dose leads to changes of the easy direction from out-of-plane to in-plane in the thicker Co layers ($t_{Co2}$ = 1 nm) while the perpendicular anisotropy of the thinner Co layers ($t_{Co1}$ = 0.6 nm) is preserved. The investigated multilayers were obtained by sputtering and the thickness of the Au layers ($t_{Au}$ = 4 nm) ensured that a direct coupling between the Co layers (through pinholes) and Ruderman-Kittel-Kasuya-Yosida-like interactions were negligible.