Noise dependence on the thickness of plated disks

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Abstract
Noise is as important a system performance determinant as signal, and yet in many recording system designs it is ignored in the erroneous pursuit of maximizing output signal regardless of the associated media noise. The dominant noise in thin metallic films used in high recording density applications is modulation noise, arising from the zig-zag magnetization pattern in the transition regions, which in turn may arise from strong exchange coupling between the crystallites of the film. In this study we investigated the dependence of the signal, the noise, and the signal-to-noise ratio in chemically deposited thin films as a function of their thickness which was varied from 0.02 to 0.16 μm, while the magnetic parameters of the films varied only in a narrow range (Hc: 480–580 Oe; SQ: ∼0.7; Ms=138 emu/g, and SFD: 0.06–0.13). The low density signal output increases monotonically with thickness in this range. The high density output (15–20 KFCI) shows a pronounced peak at a thickness of 0.05–0.07 μm. The peak modulation noise was found to increase with thickness, from a low value of 3 μV (RMS) to a high value of 13 μV (over 12 dB). Consequently, the high density signal-to-noise ratio of these films decreases monotonically with increasing thickness. The implications of these results on the optimization of thin-film media for high recording density applications are discussed.

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