A magnetic-disk glass substrate containing an alkaline earth metal component as a glass composition includes an edge surface that is a mirror surface, and has a roughness percentage of 40% or more 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 edge surface obtained after the edge surface is etched by 2.5 m is measured.

A magnetic recording medium includes a non-magnetic substrate, a soft magnetic underlayer, an orientation control layer, a perpendicular magnetic layer, and a protective layer arranged in this order. The perpendicular magnetic layer includes a first magnetic layer and a second magnetic layer from the non-magnetic substrate side in this order. The second magnetic layer contains a magnetic grain and provided farthest from the non-magnetic substrate. The first magnetic layer has a granular structure that contains an oxide in a grain boundary. The second magnetic layer has a granular structure that contains a carbide of an element contained in the magnetic grain in a grain boundary.

A magnetic recording medium includes a non-magnetic substrate, a soft magnetic underlayer, an orientation control layer, a perpendicular magnetic layer, and a protective layer arranged in this order. The perpendicular magnetic layer includes a first magnetic layer and a second magnetic layer from the non-magnetic substrate side in this order. The second magnetic layer contains a magnetic grain and provided farthest from the non-magnetic substrate. The first magnetic layer has a granular structure that contains an oxide in a grain boundary. The second magnetic layer has a granular structure that contains a nitride of an element contained in the magnetic grain in a grain boundary.

A data storage medium having a seed structure formed of a first seed layer comprising a nickel alloy NiY, where Y is an element selected from Al, B, Fe, Nb, W, and Co, and a second seed layer represented by NiWAX, where A is an element selected from Al, B, Fe, Nb, and Co, and X is either B, Si, Ti, Nb, V, Cr, Ru, or an oxide, with the second seed layer being disposed on the first seed layer; and a magnetic recording layer above the seed structure. In addition, a method for manufacturing a data storage medium containing the aforementioned seed structure is also disclosed.

A magnetic recording medium has a recording surface having an average surface roughness SRa of 3.0 ?m or less, the number of projections having a height of 7.5 nm or more included in a unit region (where the unit region is a square region with each side having a length of 30 ?m) of the recording surface is 256 or more, and the number of projections having a height of 15 nm or more included in the unit region of the recording surface is 0 or more and 104 or less.

A magnetic recording medium has a recording surface having an average surface roughness SRa of 3.0 ?m or less, the number of projections having a height of 7.5 nm or more included in a unit region (where the unit region is a square region with each side having a length of 30 ?m) of the recording surface is 256 or more, and the number of projections having a height of 15 nm or more included in the unit region of the recording surface is 0 or more and 104 or less.

Methods and media structures are provided for increasing writability and reducing unintentional erasure of perpendicular magnetic recording media. Variable permeability is controlled within a thin soft underlayer (SUL) structure, independent of bulk SUL material properties such as magnetic moment (B.sub.s) and magnetic anisotropy (Hk). Media with an improved combination of easier writability on the recorded track and difficult erasure off-track (between tracks and on neighboring tracks) is achieved, in part, by an unbalanced antiferromagnetically coupled (AFC) SUL structure. A permeability gradient is established within the soft underlayer with layers having different values of permeability and magnetic thickness (B.sub.s*t). In an aspect, a first SUL layer includes a high permeability region and an overlying low permeability region. A second layer antiferromagnetically couples the first layer to a low permeability third SUL layer. The present invention may be utilized with high density perpendicular recording media requiring carefully balanced magnetic properties.

According to one embodiment, a magnetic recording medium includes: a substrate; and a magnetic recording layer structure formed above the substrate. The magnetic recording layer structure includes five or more magnetic recording layers and four or more nonmagnetic exchange coupling layers, where the magnetic recording layers and the nonmagnetic exchange coupling layers are arranged in an alternating pattern, and where the magnetic recording layers are separated from each other by least one of the nonmagnetic exchange coupling layers. The magnetic recording layer positioned closest to the substrate has each of the following: an average magnetic grain pitch of about 8.3 nm or less, a magnetic anisotropy field (H.sub.k) value of greater than or equal to about 20 kOe, and a thickness that is about 40% of a total thickness of the magnetic recording layer structure.

According to one embodiment, a magnetic recording medium with high magnetic recording characteristics and improved corrosion resistance is obtained. The magnetic recording medium includes a substrate, an orientation control layer provided on the substrate and made from a Ni alloy or an Ag alloy, a nonmagnetic seed layer provided to be in contact with the orientation control layer, a perpendicular magnetic recording layer containing Fe or Co and Pt as main components. The nonmagnetic seed layer is formed of Ag particles, Ge grain boundaries and a compound X, and the compound X is selected from an oxide, nitride or carbide of aluminum, titanium, chromium, silicon and tantalum and also distributed in both the Ag particles and Ge grain boundaries.

A recording medium having improved signal-to-noise ratio (SNR) capabilities includes dual cap layers over the recording layer, where the Curie temperature of the first cap layer over the recording layer is greater than the Curie temperature of the recording layer, and the Curie temperature of the second cap layer over the first cap layer is greater than the Curie temperature of the first cap layer. The first cap layer may be composed of a magnetically hard material, such as L1.sub.0 CoPt, where the second cap layer may be composed of a magnetically soft material, such as Co. Such a medium is particularly useful in the context of heat-assisted magnetic recording (HAMR).