US 12,131,763 B2
Magnetic recording medium
Noboru Sekiguchi, Miyagi (JP); and Minoru Yamaga, Miyagi (JP)
Assigned to Sony Group Corporation, Tokyo (JP)
Filed by Sony Group Corporation, Tokyo (JP)
Filed on May 23, 2023, as Appl. No. 18/200,913.
Application 18/200,913 is a continuation of application No. 16/651,542, granted, now 11,676,631, previously published as PCT/JP2019/038990, filed on Oct. 2, 2019.
Claims priority of application No. 2019-151589 (JP), filed on Aug. 21, 2019.
Prior Publication US 2023/0343365 A1, Oct. 26, 2023
This patent is subject to a terminal disclaimer.
Int. Cl. G11B 5/714 (2006.01); G11B 5/592 (2006.01); G11B 5/706 (2006.01); G11B 5/78 (2006.01)
CPC G11B 5/714 (2013.01) [G11B 5/5928 (2013.01); G11B 5/70678 (2013.01); G11B 5/78 (2013.01)] 19 Claims
OG exemplary drawing
 
1. A magnetic recording medium, comprising:
a substrate;
an underlayer disposed on the substrate; and
a magnetic layer disposed on the underlayer,
wherein the substrate includes a polyester,
the magnetic recording medium includes a lubricant,
the magnetic layer has a surface including a plurality of holes,
an arithmetic average roughness Ra of the surface of the magnetic layer is 2.5 nm or less,
a BET specific surface area of the magnetic recording medium measured in a state where the magnetic recording medium has been washed and dried is 3.5 m2/g or more and 7.0 m2/g or less,
a squareness ratio of the magnetic layer in a longitudinal direction is 35% or less,
an average thickness of the magnetic layer is 80 nm or less,
an average thickness of the magnetic recording medium is 5.6 μm or less,
a servo pattern is recorded on the magnetic layer and a statistical value σSW indicating a non-linearity of the servo pattern is 24 nm or less, and
the statistical value σSW is defined by:

OG Complex Work Unit Math
where WIP(f) is a displacement difference during actual drive and df is a wave number interval,
wherein a friction coefficient ratio (μB/μA) between a dynamic friction coefficient μA between the surface of the magnetic layer and a magnetic head when tension applied to the magnetic recording medium is 1.2 N, and a dynamic friction coefficient up between the surface of the magnetic layer and the magnetic head when tension applied to the magnetic recording medium is 0.4 N is 1.0 or more and 2.0 or less.