Effect of topological bumpy surface underlayer on compositionally modulated atomic layer stacking for high K_u Co₈₀Pt₂₀ film with closed-packed orientation

Recently, closed-packed orientation CoPt-based alloys with oxides granular films have been studied as a candidate for the first generation microwave assisted magnetic recording (MAMR) media^1-2). For granular films, it is well known that the CoPt magnetic grains grown on a bumpy surface underlayer have a columnar structure and separated with oxides at the grain boundaries. To increase thermal stability of the grains, the enhancement of uniaxial magneto-crystalline anisotropy (K_u) of the grains is indispensable. In general, to further increase K_u of a CoPt-based alloy grains, increasing the spin-orbital interaction is thought to be effective. One way to achieve this is by forming a compositionally modulated atomic layer stacking structure^3-4). In this structure in-plane-disordered atomic layers of each composition are aligned parallelly to the substrate normal. Therefore, the authors consider the realization of such structure on a bumpy surface underlayer will be a big challenge. In this paper, we will discuss about the effect of the bumpy surface including surface roughness and grain size of the underlayer on compositionally modulated atomic layer stacking of overlying Co₈₀Pt₂₀ film in relation with K_u.