Formation of Ultra-High-Density Ferromagnetic Column Arrays Beyond 1 Tera/inch² Using Porous Alumina Template

Abstract

The formation of ultra-high-density ferromagnetic column arrays beyond 1 Tera/inch² was investigatedusing porous alumina films formed on Si substrate. It was empirically known that a pitch of nanohole array shrunk with a reduction of anodic voltage. We carried out anodic oxidation of sputtered Al film at the anodic voltage below 10V, and found that the density of the nanohole arraysincreased significantly with a reduction of the anodic voltage.and reached 1.5 Tera/inch² when the anodic voltage was 5.0 V. We also succeeded in the electro-plating of Co column array in these fine holes.The Co column arrays formed by electroplating in the nanoholes were polycrystalline. and showed perpendicular magnetic anisotropy when their aspect ratio was larger than 3. The coercive field of Co columns tended to increase with a reduction of the hole diameter, which was confirmed by micromagnetic simulation based on the LLG equations. These results strongly suggest that ferromagnetic nano column arrays buried in porous alumina film on substrate have a high potential for application to a future ultra-high density magnetic recording media.