| 摘要 |
A polishing composition includes at least water, alumina and a sol product derived from an aluminum salt. A magnetic recording disk substrate polished with the polishing composition suppresses formation of roll-off on the outer peripheral portion thereof, has a high-quality mirror-finished surface with few pits, nodules and scratches, and enables a distance between it and a magnetic head to be small, thereby making it possible to the recording density.
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