Effect of ion irradiation on the structural and magnetic properties of sputtered CoPt alloy

We are interested in studying thin layers of CoPt alloy prepared by co-deposition sputtering. The CoPt layers are deposited on a MgO(001) substrate with a Pt(001) buffer layer. We obtain a layer with the L10 tetragonal structure, ordered in the growth direction. This equiatomic L10 phase is a “natural” multilayer which consists in a stacking along the (001) direction of pure Co and pure Pt monolayers. In this case, we get an easy magnetization direction perpendicular to the layer plane, which is the required configuration for the perpendicular magneto-optic recording. The order state of these thin films has been modified locally by a low energy ion irradiation. The structural and magnetic properties have changed jointly: with a 40-keV energy and a 4×1016-ions/cm2 flux, the chemical order decreases (the long-range-order (LRO) parameter changed from S=0.80 to S=0.50), the coercive field diminished from 0.090 T down to 0.052 T. Such results show that it is possible to locally change the magnetization easy axis, which is promising for applications.