Perpendicular magnetic anisotropy of CoPt–AlN composite film with nano-fiber structure

Abstract

Co–Pt–AlN films were prepared by sputtering a Co–Pt–Al composite target in Ar+N₂ atmosphere. Upon thermal annealing at elevated temperatures, fcc CoPt and a-AlN are formed in the films as phases separated from one other. Both phases develop as fiber-like columnar grains vertical to the substrate and with their lateral size less than 10 nm. Because of the shape anisotropy of the magnetic fiber grains the CoPt–AlN film shows a perpendicular magnetic anisotropy at a thickness equal to or larger than about 25 nm while the Co–TiN [6] and CoPt–TiO₂ [11] films do not unless their thicknesses reach 50 and 100 nm, respectively. This suggests that both the shape anisotropy of the CoPt magnetic fiber grains and their mutual separation in an a-AlN medium work more effectively in the formation with the perpendicular magnetic anisotropy. Such a perpendicular magnetic anisotropy of the CoPt–AlN film associated with the nano-scale feature makes it a very promising candidate for future recording media with ultra-high area density .