A smoothed underlayer surface produces a low level of disk noise in unrecorded disks and a high level of recording noise generated by recording marks. To achieve high S/N disks, the recording noise must be suppressed. By investigating the domain wall motion, we examined the origin of the high recording noise and studied ways of reducing it. When a flat underlayer was used, we found that the high recording noise was caused by irregular domain shapes that resulted from the decrease in the number of domain-wall-pinning sites. A possible cause of the irregular domain shapes is the smaller coercivity of Fe-rich disks and the larger contracting force acting on the domain wall in Tb-rich disks. When we deposited an improved TbFeCo film at a higher Ar pressure in order to create more wall-pinning sites, the recording noise was suppressed at about 4 dB in TM-rich disks, while the disk noise remained low.

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