A heat-assisted magnetic recording medium includes a substrate, an underlayer, and a magnetic layer including an alloy having a L1.sub.0 crystal structure and first and second layers, arranged in this order. Each of the first and second layers has a granular structure including C, SiO.sub.2, and BN at grain boundaries. Vol % of the grain boundaries in each of the first and second layers is 25 to 45 vol %. Vol % of C in the first layer is 5 to 22 vol %, and a volume ratio of SiO.sub.2 with respect to BN in each of the first and second layers is 0.25 to 3.5. Vol % of SiO.sub.2 in the second layer is greater than that of the first layer by 5 vol % or more. Vol % of BN in the second layer is smaller than that in the first layer by 2 vol % or more.

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 has a nonmagnetic layer containing nonmagnetic powder and binder on a nonmagnetic support and a magnetic layer containing ferromagnetic powder and binder on the nonmagnetic layer, wherein a fatty acid ester is contained in at least the magnetic layer, the ferromagnetic powder is ferromagnetic hexagonal ferrite powder, the ferromagnetic hexagonal ferrite powder has a crystallite volume as determined by X-ray diffraction analysis ranges from 1,000 nm.sup.3 to 2,400 nm.sup.3, and a ratio of the crystallite size D.sub.x(107) obtained from a diffraction peak of a (107) plane to a particle size in a direction of an easy axis of magnetization D.sub.TEM as determined by observation with a transmission electron microscope, D.sub.x(107)/D.sub.TEM, is greater than or equal to 1.1, and SFD in a longitudinal direction of the magnetic tape as calculated with Equation 1: SFD=SFD.sub.25 C.SFD.sub.190 C., ranges from 0.50 to 1.60.

A magnetic tape device includes a magnetic tape; and a reproducing head, in which the reproducing head is a Tunneling Magnetoresistive (TMR) head, the center line average surface roughness Ra measured regarding the surface of the magnetic layer of the magnetic tape is equal to or smaller than 2.0 nm, the logarithmic decrement acquired by a pendulum viscoelasticity test performed regarding the surface of the magnetic layer is equal to or smaller than 0.050, and the ratio (Sdc/Sac) of an average area Sdc of a magnetic cluster of the magnetic tape in a DC demagnetization state and an average area Sac of a magnetic cluster of the magnetic tape in an AC demagnetization state measured with a magnetic force microscope is 0.80 to 1.30.

The magnetic tape device includes a Tunneling Magnetoresistive (TMR) head as a reproducing head; and a magnetic tape which includes a non-magnetic support, and a magnetic layer including ferromagnetic hexagonal ferrite powder and a binding agent on the non-magnetic support, an XRD intensity ratio (Int(110)/Int(114)) of a hexagonal ferrite crystal structure obtained by an X-ray diffraction analysis of the magnetic layer by using an In-Plane method is 0.5 to 4.0, a vertical direction squareness ratio of the magnetic tape is 0.65 to 1.00, a center line average surface roughness Ra measured regarding a surface of the magnetic layer is equal to or smaller than 2.0 nm, and a logarithmic decrement acquired by a pendulum viscoelasticity test performed regarding the surface of the magnetic layer is equal to or smaller than 0.050.

The magnetic tape has a nonmagnetic layer containing nonmagnetic powder and binder on a nonmagnetic support, and a magnetic layer containing ferromagnetic powder and binder on the nonmagnetic layer; wherein the combined thickness of the nonmagnetic layer and the magnetic layer is less than or equal to 0.60 m, the coefficient of friction as measured on the base portion of the surface of the magnetic layer is less than or equal to 0.35, at least the magnetic layer contains one or more components selected from the group consisting of a fatty acid and a fatty acid amide, and a CH derived carbon, C, concentration calculated from a CH peak area ratio in a C1s spectrum obtained by X-ray photoelectron spectroscopy conducted at a photoelectron take-off angle of 10 degrees on the surface of the magnetic layer is greater than or equal to 45 atom %.

A magnetic tape includes a non-magnetic support; and a magnetic layer including ferromagnetic powder and a binding agent on the non-magnetic support. The center line average surface roughness Ra measured regarding the surface of the magnetic layer is less than or equal to 1.8 nm. The logarithmic decrement acquired by a pendulum viscoelasticity test performed regarding the surface of the magnetic layer is less than or equal to 0.050, and the contact angle with respect to 1-bromonaphthalene measured regarding the surface of the magnetic layer is 45.0 to 55.0.

A magnetic tape includes a non-magnetic support; and a magnetic layer including ferromagnetic powder and a binding agent on the non-magnetic support. The center line average surface roughness Ra measured regarding the surface of the magnetic layer is less than or equal to 1.8 nm. The logarithmic decrement acquired by a pendulum viscoelasticity test performed regarding the surface of the magnetic layer is less than or equal to 0.050. The ferromagnetic powder is ferromagnetic hexagonal ferrite powder, the magnetic layer includes an abrasive, and the tilt cos of the ferromagnetic hexagonal ferrite powder with respect to the surface of the magnetic layer acquired by cross section observation performed using a scanning transmission electron microscope is 0.85 to 1.00.

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.

An object is to provide a magnetic recording medium excellent in an electromagnetic conversion characteristic and traveling performance.

The present technology provides a magnetic recording medium including a magnetic layer containing a magnetic powder, the magnetic recording medium having an average magnetic cluster size of 1850 nm.sup.2 or less, the average magnetic cluster size measured on the basis of an MFM image of a surface on a side of the magnetic layer, the magnetic layer containing first particles having conductivity and second particles having a Mohs hardness of 7 or more, in which protrusions are formed by the first particles and protrusions are formed by the second particles on the surface on the side of the magnetic layer, and a ratio (H.sub.1/H.sub.2) of an average height H.sub.1 of the protrusions formed by the first particles to an average height H.sub.2 of the protrusions formed by the second particles is 2.00 or less.