Roles of L1₀ ordering in controlling the magnetic anisotropy and coercivity of (111)-oriented CoPt ultrathin continuous layers in CoPt/AlN multilayer films

Chemical ordering of (111)-oriented CoPt ultrathin continuous layers in CoPt/AlN multilayer structure has been investigated. It is found that upon thermal annealing at 600 C, CoPt layers undergo ordering transformation even when the CoPt layers are as thin as 2 nm. The degree of ordering increases with increasing the layer thickness. For the 600 C annealed CoPt/AlN multilayer film with 2 nm thick CoPt layers, due to the ordering, out-of-plane coercivity is increased to 3330 Oe, while large perpendicular magnetic anisotropy constant of 8.1 × 10⁶ erg/cm³ is exhibited. These coercivity and anisotropy energy are appropriate for the practical use as magnetic recording media. It is clear that for such a structure, ordering transformation does not impair the perpendicular magnetic anisotropy induced by the interface and magnetoelastic effects. The easy axis of magnetization still lies in the layer normal direction, i.e., [111] direction, although for L1₀ structure it is supposed to lie in the [001] direction. But L1₀ ordering does contribute to the enhancement of coercivity.