Influence of Ar pressure on morphology and recording characteristics of hybrid sputtered magnetic disks

Hybrid sputtered magnetic disks of the type Cr/Co₈₀Ni ₂₀ and Cr/Co_62.5Ni₃₀Cr_7.5 on Al/Ni-P substrates were prepared at Ar pressures of 5×10^-4 to 5×10^-2 mbar. From low to high Ar pressure, the morphology of the layer system changes drastically from a dense structure to a structure characterized by separated columns. The relative density of the metallic part of the layer decreases by 40 vol.% and the surface of the columns is oxidized by contact with air, creating a high O content of 20 at.% in the Cr layer and 6 at.% in the magnetic layer. As a consequence, the rectangular hysteresis loop, typical for longitudinally magnetized thin films, changes to a shape which is typical for pigmented media. Recording tests give constant values for resolution and D₅₀ (20-21.5 kfci). The signal level decreases by 50% with increasing Ar pressure, whereas the S/N ratio is drastically improved from 22 dB to 32 dB. The low S/N ratio of layers prepared at low Ar pressure is a consequence of strong exchange interaction between the closely packed magnetic crystallites, which creates high modulation noise. At high Ar pressure these interactions are blocked due to the columnar structure of the layer