Substrate for magnetic recording medium, magnetic recording medium, hard disk drive

Abstract

The present invention provides a substrate for a magnetic recording medium in which bulges are not easily formed on a surface thereof by a physical impact in a size for a 2.5-inch type hard disk drive, and a width of displacement caused by fluttering is small. The substrate for a magnetic recording medium includes an Al alloy substrate and a Ni alloy plating film formed on a surface of the Al alloy substrate, has a diameter of 54 to 70 mm, and a disk shape having a hole whose inner diameter ranges from 19 to 26 mm in the center thereof. The Al alloy substrate has a Young's modulus (E) of 74 GPa or more, a density (ρ) of 2.75 g/cm3 or less, and a ratio (E/ρ) of 27 or more between the Young's modulus (E) and the density (ρ). The Ni alloy plating film has a thickness of 4 to 7 μm, and when an indentation is formed by pressing a diamond indentor whose tip has a square pyramid shape against a surface of the Ni alloy plating film with a test force of 0.49 N for 10 seconds in a vertical direction, an average height of bulges generated around the indentation ranges from 10 to 50 nm.

Dependencies are inferred from the claim text.