The effect of oxygen gas pressure on Ba-ferrite sputtered films for perpendicular magnetic recording media

Barium ferrite (BaM) sputtered films with a small c-axis dispersion angle, Δθ₅₀, and smooth surface are needed for ultra-high-density perpendicular recording. These properties, which depend strongly on oxygen partial pressure, P_O2, during sputtering, were studied experimentally. In the low-P_O2 region (below 0.003 mTorr at total P (P_Ar+P_O2) of 3.7 mTorr), a spinel phase was formed and exhibited a rough surface with large grain. In the mid-P_O2 (0.003-0.2 mTorr) and high-P_O2 (0.3-3.7 mTorr) regions, a mixed spinel and a BaM single phase were formed, respectively. The films deposited at high P_O2 exhibited large perpendicular anisotropy and consisted of needle-like particles, while those deposited at medium P_O2 exhibited perpendicular anisotropy of about 1.0 kOe. The H_k⊥ of these films was about 10 kOe, and they had a very smooth surface and small Δθ₅₀