In a magnetic recording medium, an average thickness t.sub.T is t.sub.T5.5 m, a dimensional variation w in a width direction to tension change in a longitudinal direction is 650 ppm/Nw, and a rate of shrinkage in the longitudinal direction is 0.08% or less.

The magnetic recording medium includes a non-magnetic support; and a magnetic layer including a ferromagnetic powder and a binding agent on the non-magnetic support, in which the magnetic layer further includes a compound including one or more partial structures selected from the group consisting of a partial structure represented by Formula 1 and a partial structure represented by Formula 2, and a polyalkyleneimine chain. A magnetic recording and reproducing apparatus including this magnetic recording medium. A composition for a magnetic recording medium including a ferromagnetic powder and the compound. L.sup.1 in Formula 1 and L.sup.2 in Formula 2 each independently represent a divalent linking group, Z.sup.1 in Formula 1 and Z.sup.2 in Formula 2 each independently represent a monovalent group represented by OM or a monovalent group represented by O.sup.A.sup.+, M represents a hydrogen atom or an alkali metal atom, and A.sup.+ represents an ammonium cation.

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The magnetic tape includes a magnetic layer having ferromagnetic powder and a binder on a non-magnetic support, in which the magnetic layer includes a timing-based servo pattern, the ferromagnetic powder is ferromagnetic hexagonal ferrite powder having an activation volume equal to or smaller than 1,600 nm.sup.3, and an edge shape of the timing-based servo pattern specified by a magnetic force microscope observation is a shape in which a difference (l.sub.99.9l.sub.0.1) between a value l.sub.99.9 of a cumulative frequency function of 99.9% of a position deviation width from an ideal shape in a longitudinal direction of the magnetic tape and a value l.sub.0.1 of the cumulative frequency function of 0.1% thereof is equal to or smaller than 180 nm.

The magnetic recording medium includes: a non-magnetic support; and a magnetic layer including a ferromagnetic powder and a binding agent on the non-magnetic support, in which the magnetic layer further includes a compound including a polyalkyleneimine chain and a vinyl polymer chain. The composition for a magnetic recording medium includes: ferromagnetic powder; and a compound including a polyalkyleneimine chain and a vinyl polymer chain.

The magnetic tape includes a magnetic layer having ferromagnetic powder and a binder on a non-magnetic support, in which the magnetic layer includes a timing-based servo pattern, the ferromagnetic powder is ferromagnetic hexagonal ferrite powder having an activation volume equal to or smaller than 1,600 nm.sup.3, and an edge shape of the timing-based servo pattern specified by a magnetic force microscope observation is a shape in which a difference (l.sub.99.9l.sub.0.1) between a value l.sub.99.9 of a cumulative frequency function of 99.9% of a position deviation width from an ideal shape in a longitudinal direction of the magnetic tape and a value l.sub.0.1 of the cumulative frequency function of 0.1% thereof is equal to or smaller than 180 nm.

Provided is a magnetic tape in which the total thickness of the non-magnetic layer and the magnetic layer is equal to or smaller than 0.60 m, the magnetic layer includes ferromagnetic hexagonal ferrite powder and an abrasive, a percentage of a plan view maximum area of the abrasive confirmed in a region having a size of 4.3 m6.3 m of the surface of the magnetic layer by plane observation using a scanning electron microscope, with respect to the total area of the region is equal to or greater than 0.02% and less than 0.06%, and a tilt cos 0 of the ferromagnetic hexagonal ferrite powder with respect to a surface of the magnetic layer acquired by cross section observation performed by using a scanning transmission electron microscope is 0.85 to 1.00.

According to one embodiment, a magnetic recording medium includes: a substrate; an underlayer positioned above the substrate; a magnetic recording layer positioned above the underlayer; and a plurality of conductive polymers dispersed within the substrate, the underlayer, the magnetic recording layer, the substrate and the underlayer, the substrate and the magnetic recording layer, the underlayer and the magnetic recording layer, or the underlayer, the magnetic recording layer, and the substrate. In addition, the conductive polymers are dispersed such that a concentration of the conductive polymers has a gradient in a single one of the layers in a thickness direction.

According to one embodiment, a magnetic recording medium includes a substrate, an underlayer positioned above the substrate, a magnetic recording layer positioned above the underlayer, and a plurality of conductive polymers dispersed within at least one of the substrate, the underlayer and the magnetic recording layer.

A magnetic recording medium is a tape-shaped magnetic recording medium and includes: a base; and a magnetic layer. An average thickness of the magnetic recording medium is 5.30 m or less. The magnetic layer contains a chlorine atom and a nitrogen atom, an atomic concentration ratio (A2/A1) of a maximum chlorine atomic concentration A1 obtained by measuring a chlorine atomic concentration of the magnetic layer in a thickness direction of the magnetic layer and a maximum nitrogen atomic concentration A2 obtained by measuring a nitrogen atomic concentration of the magnetic layer in the thickness direction of the magnetic layer is 0.50 or more and 0.75 or less. An average value of a protruding peak height Rpk of a surface of the magnetic layer is 2.10 nm or less.