The magnetic tape includes a non-magnetic support; and a magnetic layer including ferromagnetic powder and a binding agent on the non-magnetic support, in which the magnetic layer includes one or more components selected from the group consisting of fatty acid and fatty acid amide, a C—H derived C concentration calculated from a C—H peak area ratio of C1s spectra obtained by X-ray photoelectron spectroscopic analysis performed on a surface of the magnetic layer at a photoelectron take-off angle of 10 degrees is equal to or greater than 45 atom %, and an absolute value ΔN of a difference between a refractive index Nxy measured regarding an in-plane direction of the magnetic layer and a refractive index Nz measured regarding a thickness direction of the magnetic layer is 0.25 to 0.40.

The magnetic tape includes a non-magnetic support; and a magnetic layer including ferromagnetic powder and a binding agent on the non-magnetic support, in which the magnetic layer includes one or more components selected from the group consisting of fatty acid and fatty acid amide, a C—H derived C concentration calculated from a C—H peak area ratio of C1s spectra obtained by X-ray photoelectron spectroscopic analysis performed on a surface of the magnetic layer at a photoelectron take-off angle of 10 degrees is equal to or greater than 45 atom %, and an absolute value ΔN of a difference between a refractive index Nxy measured regarding an in-plane direction of the magnetic layer and a refractive index Nz measured regarding a thickness direction of the magnetic layer is 0.25 to 0.40.

A magnetic-disk substrate has a pair of main surfaces and arithmetic average roughnesses Ra of the main surfaces are each 0.11 nm or less. Also, in surface unevenness of the main surfaces, an average area of regions occupied by a plurality of protrusions having a height of 0.1 [nm] or more from an average plane of the surface unevenness is 25 [nm.sup.2/protrusion] or less. The arithmetic average roughness Ra and the surface unevenness are measured using an atomic force microscope with a probe having a probe tip provided with a carbon nanofiber rod-shaped member.

A magnetic-disk substrate has a pair of main surfaces and arithmetic average roughnesses Ra of the main surfaces are each 0.11 nm or less. Also, in surface unevenness of the main surfaces, an average area of regions occupied by a plurality of protrusions having a height of 0.1 [nm] or more from an average plane of the surface unevenness is 25 [nm.sup.2/protrusion] or less. The arithmetic average roughness Ra and the surface unevenness are measured using an atomic force microscope with a probe having a probe tip provided with a carbon nanofiber rod-shaped member.

A magnetic-disk glass substrate contains an alkaline earth metal component as a glass composition and includes a pair of main surfaces, and an outer circumferential side edge surface that is a mirror surface. The outer circumferential side edge surface includes a surface having a roughness percentage of 40% or more and 68% or less when a bearing ratio of a roughness cross-sectional area is 50% in a bearing ratio curve of roughness cross-sectional areas obtained when a surface roughness of the outer circumferential side edge surface obtained after the outer circumferential side edge surface is etched by 2.5 μm is measured. A glass transition point of the glass composition that constitutes the magnetic-disk glass substrate is 700° C. or more. The glass composition that constitutes the magnetic-disk glass substrate is alkali-free glass.

A magnetic-disk glass substrate contains an alkaline earth metal component as a glass composition and includes a pair of main surfaces, and an outer circumferential side edge surface that is a mirror surface. The outer circumferential side edge surface includes a surface having a roughness percentage of 40% or more and 68% or less when a bearing ratio of a roughness cross-sectional area is 50% in a bearing ratio curve of roughness cross-sectional areas obtained when a surface roughness of the outer circumferential side edge surface obtained after the outer circumferential side edge surface is etched by 2.5 μm is measured. A glass transition point of the glass composition that constitutes the magnetic-disk glass substrate is 700° C. or more. The glass composition that constitutes the magnetic-disk glass substrate is alkali-free glass.

This fluorine-containing ether compound is represented by formula (1) shown below.

R.sup.1—CH.sub.2—R.sup.2—CH.sub.2—R.sup.3  (1)

In formula (1), R.sup.2 is a perfluoropolyether chain represented by a formula (2) shown below. R.sup.1 is a terminal group that is bonded to R.sup.2 via a CH.sub.2 group, and is represented by a formula (3) shown below. R.sup.3 is bonded to R.sup.2 via a CH.sub.2 group, is a terminal group having at least one hydroxyl group, and may be the same as, or different from, R.sup.1.

—(CF.sub.2).sub.p-1—O—((CF.sub.2).sub.pO).sub.q—(CF.sub.2).sub.p-1—  (2)

In formula (2), p represents an integer of 2 to 3, and q indicates the average polymerization degree and is a number within a range from 1 to 20.

—O(CH.sub.2—CH(OH)—CH.sub.2—O).sub.2—CH.sub.2—(CH.sub.2).sub.n,—OH  (3)

In formula (3), n represents an integer of 1 to 8.

A method for manufacturing a ring-shaped glass spacer to be arranged in contact with a magnetic disk in a hard disk drive device includes processing for forming a film on the surface of a glass spacer main body, which is the base of the glass spacer. In the processing, the film is formed by passing the glass spacer main body through a location where the components of the film are in a spray state while an outer circumferential edge surface of the glass spacer main body is being rotated in a circumferential direction thereof.

According to an embodiment, a manufacturing method includes: estimating a distribution of an initial value of a clearance of a magnetic head on a first recording surface; and recording first spiral signals on the first recording surface while controlling a clearance using the distribution of the initial value of the estimated clearance. The manufacturing method includes measuring a distribution of an initial value of a clearance of a magnetic head on a second recording surface under positioning control using the first spiral signals recorded on the first recording surface. The manufacturing method includes recording the first spiral signals on the second recording surface while controlling a clearance using the distribution of the initial value of the measured clearance of the magnetic head on the second recording surface. The manufacturing method includes recording the second spiral signals on a third recording surface under positioning control using the first spiral signals recorded on the second recording surface.

According to an embodiment, a manufacturing method includes: estimating a distribution of an initial value of a clearance of a magnetic head on a first recording surface; and recording first spiral signals on the first recording surface while controlling a clearance using the distribution of the initial value of the estimated clearance. The manufacturing method includes measuring a distribution of an initial value of a clearance of a magnetic head on a second recording surface under positioning control using the first spiral signals recorded on the first recording surface. The manufacturing method includes recording the first spiral signals on the second recording surface while controlling a clearance using the distribution of the initial value of the measured clearance of the magnetic head on the second recording surface. The manufacturing method includes recording the second spiral signals on a third recording surface under positioning control using the first spiral signals recorded on the second recording surface.