A magnetic recording medium that can exhibit good traveling performance during use is provided. This magnetic recording medium is a tape-shaped magnetic recording medium, and includes a substrate, a base layer disposed on the substrate, and a magnetic layer disposed on the base layer. On the surface of the magnetic layer, recesses having a depth of 20% or more of the average thickness of the magnetic layer are formed at a ratio of 20 or more and 200 or less per 1600 μm.sup.2. On the surface of the magnetic layer, a logarithmic decay rate determined by a pendulum viscoelasticity test at a temperature of 10° C. or higher and 45° C. or lower is 0.025 or more and 0.040 or less. A difference between a maximum value of the logarithmic decay rate and a minimum value of the logarithmic decay rate is 0 or more and 0.020 or less. The squareness ratio in the perpendicular direction is 65% or more. The average thickness of the magnetic layer is 80 nm or less. The average thickness of the magnetic recording medium is 5.6 μm or less.

A non-metallic media substrate includes a disc-shaped substrate body having at least one media storage surface on a face thereof. The substrate body has a center opening having an inner diameter and an outer diameter surface, and the substrate body has a thickness. The substrate further includes an annular groove at the outer diameter of the media substrate, the annular groove having chamfered edges and an internal concavity extending toward the inner diameter.

A substrate for a magnetic disk has a disk shape. The substrate has a diameter D of 85 mm or more and a thickness T of 0.6 mm or less. When an impact is applied to the substrate under conditions of 70 (G) and 2 (msec) in a normal direction of main surfaces of the substrate in a state in which an inner circumferential end portion of the substrate is fixed, the maximum amplitude of vibration in a thickness direction of an outer circumferential end portion of the substrate is 0.25 mm or less, the substrate is a non-magnetic metal substrate, and regarding the Young's modulus E and the thickness T of the substrate, a value of E.Math.T.sup.3 is 3 to 18 (GPa.Math.mm.sup.3).

A substrate for a magnetic disk includes a substrate main body having two main surfaces and an outer circumferential edge surface, and a film that is an alloy film containing Ni and P and provided on a surface of the substrate main body. A disk shape of the substrate main body has an outer diameter of 90 mm or more. A thickness T of the substrate that includes film thicknesses of sections of the film provided on the main surfaces is 0.520 mm or less. A total thickness D mm, which is a sum of the film thicknesses of the sections of the film on the main surfaces and the thickness T mm satisfy D≥0.0082/T−0.0015. A surface roughness maximum height Rz of the film provided on the outer circumferential edge surface is smaller than that of the substrate main body at the outer circumferential edge surface.

A magnetic recording medium that can exhibit good traveling performance during use is provided. This magnetic recording medium is a tape-shaped magnetic recording medium, and includes a substrate including a polyester as a main component, a base layer disposed on the substrate, a magnetic layer disposed on the base layer, and a back layer disposed on a side of the substrate opposite to the base layer. A surface of the back layer opposite to the substrate has a kurtosis of 2.0 or more. On a surface of the magnetic layer, recesses having a depth of 20% or more of the average thickness of the magnetic layer are formed at a ratio of 10 or more and 200 or less per 1600 μm.sup.2. A surface of the magnetic layer has arithmetic average roughness Ra of 2.5 nm or less. The entire magnetic recording medium has a BET specific surface area of 3.5 m.sup.2/g or more in a state where the lubricant has been removed from the magnetic recording medium and the magnetic recording medium has been dried.

A magnetic recording medium that can exhibit good traveling performance during use is provided. This magnetic recording medium is a tape-shaped magnetic recording medium, and includes a substrate, a base layer disposed on the substrate, and a magnetic layer disposed on the base layer. On the surface of the magnetic layer, recesses having a depth of 20% or more of the average thickness of the magnetic layer are formed at a ratio of 20 or more and 200 or less per 1600 μm.sup.2. On the surface of the magnetic layer, a logarithmic decay rate determined by a pendulum viscoelasticity test at a temperature of 10° C. or higher and 45° C. or lower is 0.025 or more and 0.035 or less. A difference between a maximum value of the logarithmic decay rate and a minimum value of the logarithmic decay rate is 0 or more and 0.020 or less. The squareness ratio in the perpendicular direction is 65% or more. The average thickness of the magnetic layer is 80 nm or less. The average thickness of the magnetic recording medium is 5.6 μm or less.

A substrate for a magnetic disk includes a substrate main body having two main surfaces, and a film that is provided on the main surfaces and is made of a material having a loss factor of 0.01 or more. The substrate for a magnetic disk including the film has a thickness T of 0.700 mm or less, and a thickness D [mm] of the film provided on the main surfaces and the thickness T [mm] of the substrate for a magnetic disk including the film satisfy a relationship D≥0.0082/T−0.0015.

A disk-shaped substrate for a magnetic disk has a diameter D of 85 mm or more and a thickness T of 0.6 mm or less, and a material of the substrate has a Young's modulus E of 90 GPa or more.

A fluorine-containing ether compound represented by R.sup.1R.sup.2CH.sub.2R.sup.3CH.sub.2R.sup.4R.sup.5 is provided. (R.sup.3 is a perfluoropolyether chain; R.sup.1 and R.sup.5 are each independently any one of an alkyl group that may have a substituent, an organic group having at least one double bond or at least one triple bond, and a hydrogen atom; and R.sup.2CH.sub.2R.sup.3 is represented by Formula (2), and R.sup.3CH.sub.2R.sup.4 is represented by Formula (3))

-[A]-[B]OCH.sub.2R.sup.3 (2)

R.sup.3CH.sub.2O[C]-[D]- (3)

([A] is represented by Formula (4), [B] is represented by Formula (5), [C] is represented by Formula (6), [D] is represented by Formula (7), and in the formula, a and b are integers of 0 to 2, c is an integer of 2 to 5, d and f are integers of 0 to 2, and e is an integer of 2 to 5, and at least one of b and d in the formula is 1 or more)

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A magnetic recording medium substrate is provided in which a NiP type plating film is formed on a surface of an aluminum alloy substrate that includes Si in a range of 9.5 mass % or more and 11.0 mass % or less, Mn in a rage of 0.45 mass % or more and 0.90 mass % or less, Zn in a range of 0.32 mass % or more and 0.38 mass % or less, Sr in a range of 0.01 mass % or more and 0.05 mass % or less. In the alloy structure of the aluminum alloy substrate, an average particle diameter of Si particles is 2 m or less, the film thickness of the NiP type plating film is 7 m or more. An outer diameter of the magnetic recording medium substrate is 53 mm or more, the thickness is 0.9 mm or less, and the Young's modulus is 79 GPa or more.