Perpendicular magnetic anisotropy of CoPt/AlN multilayer

CoPt/AlN multilayer films have been prepared by a two-facing-target magnetron sputtering apparatus at room temperature. The thickness of AlN layer was fixed to 20nm, and the thickness of CoPt layer was varied from 1 to 8 nm. It is found that all as-deposited film show in-plane magnetic anisotropy After vacuum annealing at 400 degrees C for 3h CoPt/AlN films with CoPt thickness below 4nm show perpendicular magnetic anisotropy Among these annealed films, the one with CoPt thickness of 2nm exhibits clearly uniaxial magnetic anisotropy. Cross-section TEM observation has proved that the CoPt layers have {111} preferred orientation, while the AN layers have (001) preferred orientation. We believe that for the CoPt/AlN multilayer film to show perpendicular magnetic anisotropy, it is important that the CoPt layers are coherent with thee neighboring AlN layers.