Substrate for magnetic disk and magnetic disk
A magnetic-disk glass substrate capable of suppressing turbulence of air flow in a vicinity of an outer circumferential side edge portion of the magnetic disk and suppressing disk flutter is provided. This magnetic-disk glass substrate includes a pair of main surfaces, a side wall surface formed on an outer circumferential side edge surface, and chamfered surfaces interposed between the side wall surface and the main surfaces, respectively. The side wall surface has a roundness of 1.5 μm or less. A difference in radius between an inscribed circle and a circumcircle of a plurality of outlines of the side wall surface at a plurality of positions that include a central position of the magnetic-disk glass substrate in a thickness direction and are different from each other in the thickness direction is 5 μm or less.
1. An annular substrate used as an original for a magnetic-disk substrate comprising:
a pair of main surfaces;
a side wall surface formed at an outer circumferential side edge portion; and
chamfered surfaces interposed between the side wall surface and the main surfaces, respectively,
a thickness of the annular substrate being 0.635 mm or less,
the side wall surface having a roundness of 1.5 μm or less,
when, in the side wall surface, three outlines in a circumferential direction of the side wall surface, which include an outline at a center position of a thickness of the substrate and outlines at two positions that are spaced apart from the center position in opposite directions along a thickness direction by a predetermined distance, are obtained, and when an inscribed circle and a circumcircle of each of the three outlines are obtained, a difference in radius between a smallest inscribed circle and a largest circumcircle being 5 μm or less, and
when positions spaced apart from the center position in the opposite directions along the thickness direction by 200 μm exist on the side wall surface, the predetermined distance being 200 μm, and when positions spaced apart from the center position in the opposite directions of the thickness direction by 200 μm do not exist on the side wall surface, the predetermined distance being 100 μm.
2. The annular substrate according to claim 1 , wherein
outlines in the circumferential direction are obtained at two positions on the side wall surface on an outer circumferential side spaced apart by 200 pin in the thickness direction, and a middle point between centers of two least square circles determined from the outlines is referred to as middle point A,
outlines in the circumferential direction are obtained at positions that are located at centers of the two chamfered surfaces on the outer circumferential side in the thickness direction, and among centers of least square circles determined from the outlines, a center determined from one chamfered surface is referred to as center B, and a center determined from the other chamfered surface is referred to as center C, and
a sum of a distance between the middle point A and the center B and a distance between the middle point A and the center C is 1 μm or less.
3. The annular substrate according to claim 1 , wherein
the difference in radius between the inscribed circle and the circumcircle is 3 μm or less.
4. The annular substrate according to claim 1 , wherein
a thickness of the annular substrate is 0.500 mm or less.
5. A method for manufacturing a magnetic-disk substrate, the method comprising:
polishing at least the main surfaces of the annular substrate according to claim 1 .
6. A method for manufacturing a magnetic disk, the method comprising:
forming at least a magnetic layer on a main surface of the magnetic-disk substrate obtained from the method according to claim 5 .
7. A magnetic-disk substrate comprising:
a pair of main surfaces;
a side wall surface formed at an outer circumferential side edge portion; and
chamfered surfaces interposed between the side wall surface and the main surfaces, respectively,
a thickness of the magnetic-disk substrate being 0.635 mm or less,
the side wall surface having a roundness of 1.5 μm or less,
when, in the side wall surface, three outlines in a circumferential direction of the side wall surface, which include an outline at a center position of a thickness of the substrate and outlines at two positions that are spaced apart from the center position in opposite directions along a thickness direction by a predetermined distance, are obtained, and when an inscribed circle and a circumcircle of each of the three outlines are obtained, a difference in radius between a smallest inscribed circle and a largest circumcircle being 5 μm or less, and
when positions spaced apart from the center position in the opposite directions along the thickness direction by 200 μm exist on the side wall surface, the predetermined distance being 200 μm, and when positions spaced apart from the center position in the opposite directions of the thickness direction by 200 μm do not exist on the side wall surface, the predetermined distance being 100 pun.
8. The magnetic-disk substrate according to claim 7 , wherein
outlines in the circumferential direction are obtained at two positions on the side wall surface on an outer circumferential side spaced apart by 200 μm in the thickness direction, and a middle point between centers of two least square circles determined from the outlines is referred to as middle point A,
outlines in the circumferential direction are obtained at positions that are located at centers of the two chamfered surfaces on the outer circumferential side in the thickness direction, and among centers of least square circles determined from the outlines, a center determined from one chamfered surface is referred to as center B, and a center determined from the other chamfered surface is referred to as center C, and
a sum of a distance between the middle point A and the center B and a distance between the middle point A and the center C is 1 μm or less.
9. The magnetic-disk substrate according to claim 7 , wherein
the difference in radius between the inscribed circle and the circumcircle is 3 μm or less.
10. The magnetic-disk substrate according to claim 7 ,
wherein a thickness of the magnetic-disk substrate is 0.500 mm or less.
11. The magnetic-disk substrate according to claim 7 , wherein
the magnetic-disk substrate is used as a magnetic disk substrate for a shingle write system or a magnetic disk for energy-assisted magnetic recording system.
12. A magnetic disk comprising:
at least magnetic layers on the main surfaces of the magnetic-disk substrate according to claim 7 .
13. A magnetic disk in which at least a magnetic layer is formed on a main surface of the magnetic-disk substrate according to claim 8 .
14. A magnetic disk in which at least a magnetic layer is fanned on a main surface of the magnetic-disk substrate according to claim 9 .
15. A magnetic disk in which at least a magnetic layer is formed on a main surface of the magnetic-disk substrate according to claim 10 .
16. A magnetic disk in which at least a magnetic layer is formed on a main surface of the magnetic-disk substrate according to claim 11 .
17. A hard disk drive comprising:
the magnetic disk according to claim 12 .
18. A hard disk drive comprising:
the magnetic disk according to claim 14 .
19. A hard disk drive comprising:
the magnetic disk according to claim IS.
20. A hard disk drive comprising:
the magnetic disk according to claim 16 .