Provided are a magnetic tape including: a non-magnetic support; and a magnetic layer including ferromagnetic powder and a binding agent on the non-magnetic support, in which a total thickness of the magnetic tape is equal to or smaller than 5.30 μm, the magnetic layer has a servo pattern, a center line average surface roughness Ra measured on a surface of the magnetic layer is equal to or smaller than 1.8 nm, and an absolute value ΔN of a difference between a refractive index Nxy of the magnetic layer, measured in an in-plane direction and a refractive index Nz of the magnetic layer, measured in a thickness direction is 0.25 to 0.40, a magnetic tape cartridge and a magnetic tape apparatus including this magnetic tape, a magnetic tape cartridge and a magnetic tape apparatus including this magnetic tape.

A magnetic recording medium is provided and includes a layer structure including a magnetic layer, a non-magnetic layer, and a base layer in order, in which an average thickness t.sub.T of the magnetic recording medium is 4.0 μm≤t.sub.T≤5.3 μm, a dimensional variation Δw in a width direction of the magnetic recording medium to tension change in a longitudinal direction of the magnetic recording medium is 680 ppm/N≤Δw≤2000 ppm/N , and an average thickness t.sub.n of the non-magnetic layer is t.sub.n≤1.0 μm.

A magnetic recording medium is provided and includes a layer structure including a magnetic layer, a non-magnetic layer, and a base layer in order, in which an average thickness t.sub.T of the magnetic recording medium is 4.0 μm≤t.sub.T≤5.3 μm, a dimensional variation Δw in a width direction of the magnetic recording medium to tension change in a longitudinal direction of the magnetic recording medium is 680 ppm/N≤Δw≤2000 ppm/N , and an average thickness t.sub.n of the non-magnetic layer is t.sub.n≤1.0 μm.

A magnetic tape device, in which a magnetic tape is caused to run between a winding reel and a cartridge reel in a state where a tension is applied in a longitudinal direction of the magnetic tape and a maximum value of the tension is 0.50 N or more, and the magnetic tape after running in a state where the tension is applied is caused to be wound around the cartridge reel by applying a tension of 0.40 N or less in the longitudinal direction of the magnetic tape, and an adhesive strength of the magnetic layer of the magnetic tape is 1.0 N or more, and an adhesive strength of the back coating layer is 1.0 N or more.

The average thickness t.sub.T of a magnetic recording medium meets the requirement that t.sub.T≤5.5 [μm], and the dimensional change amount Δw in the width direction of the magnetic recording medium with respect to the tension change in the longitudinal direction of the magnetic recording medium meets the requirement that 700 ppm/N≤Δw.

The average thickness t.sub.T of a magnetic recording medium meets the requirement that t.sub.T≤5.5 [μm], and the dimensional change amount Δw in the width direction of the magnetic recording medium with respect to the tension change in the longitudinal direction of the magnetic recording medium meets the requirement that 700 ppm/N≤Δw.

In a magnetic recording medium, an average thickness t.sub.T is t.sub.T≤5.5 μm, a dimensional variation Δw in a width direction to tension change in a longitudinal direction is 650 ppm/N≤Δw, and a rate of shrinkage in the longitudinal direction is 0.08% or less.

In a magnetic recording medium, an average thickness t.sub.T is t.sub.T≤5.5 μm, a dimensional variation Δw in a width direction to tension change in a longitudinal direction is 650 ppm/N≤Δw, and a rate of shrinkage in the longitudinal direction is 0.08% or less.

A magnetic tape device, in which a magnetic tape is caused to run between a winding reel and a cartridge reel in a state where a tension is applied in a longitudinal direction of the magnetic tape and a maximum value of the tension is 0.50 N or more, the magnetic tape after running in a state where the tension is applied is caused to be wound around the cartridge reel by applying a tension of 0.40 N or less in the longitudinal direction, and a number distribution A of equivalent circle diameters of a plurality of bright areas and a number distribution B of equivalent circle diameters of a plurality of dark areas in a binarized image of a secondary electron image obtained by imaging a surface of the magnetic layer of the magnetic tape with a scanning electron microscope satisfy predetermined number distributions, respectively.

An optical recording medium includes a plurality of information signal layers. The plurality of information signal layers include a recording layer having a first surface that faces a light irradiation surface and a second surface on the side opposite to the first surface, a first dielectric layer that is provided on the side of the first surface, and a second dielectric layer that is provided on the side of the second surface. The second dielectric layer provided in the information signal layer positioned on the innermost side when viewed from the light irradiation surface contains indium oxide and tin oxide. The recording layer provided in the information signal layer positioned on the innermost side when viewed from the light irradiation surface contains an oxide of a metal MA, an oxide of a metal MB, an oxide of a metal MD, and an oxide of a metal ME, the metal MA is at least one selected from the group consisting of Mn and Ni, the metal MB is at least one selected from the group consisting of W, Mo, Zr and Ta, the metal MD is at least one selected from the group consisting of Cu and Ag, the metal ME is Nb, the contents of the metal MA, the metal MB and the metal ME satisfy the relationship of 0.30≤a.sub.1/(b.sub.1+e.sub.1)≤0.41 (where, a.sub.1: atomic ratio [atomic %] of the metal MA with respect to a total amount of the metal MA, the metal MB, the metal MD and the metal ME, b.sub.1: atomic ratio [atomic %] of the metal MB with respect to a total amount of the metal MA, the metal MB, the metal MD and the metal ME, and e.sub.1: atomic ratio [atomic %] of the metal ME with respect to a total amount of the metal MA, the metal MB, the metal MD and the metal ME), and the atomic ratio e.sub.1 of the metal ME with respect to a total amount of the metal MA, the metal MB, the metal MD and the metal ME is 5 atomic % or more and 18 atomic % or less.