Roles of interface roughness and internal stress in magnetic anisotropy of CoPt/AlN multilayer films

Magnetic anisotropy of CoPt/AlN multilayer films has been studied by systematically varying the nominal thickness of CoPt layers, tCoPt (1–10 nm), and the annealing temperature, Ta (300–500 °C). The as-deposited films show in-plane magnetic anisotropy in the full range of tCoPt, whereas the annealed films show perpendicular magnetic anisotropy (PMA) within small tCoPt but change to in-plane magnetic anisotropy when tCoPt is over a certain thickness. The critical thickness for such anisotropic transformations increases as the Ta increases. The maximum PMA obtained in this work is 1.13 × 107 erg cm−3. The interface roughness was analyzed by cross-sectional high-resolution electron microscopy and X-ray reflectivity using an abrupt interface model with a Debye exponent shape. The internal stress was analyzed by X-ray diffraction using an equal biaxial stress model. The results show that the CoPt/AlN interface roughness decreases from 0.385 nm to 0.158 nm and the internal stress increases from −2.36 GPa (compressive) to 1.73 GPa (tensile), as the Ta increases to 500 °C. The roles of the interface roughness and the internal stress in the magnetic anisotropy of CoPt/AlN multilayer films are studied.