A magnetic tape device. The angle θ formed by the axis of the element array of the magnetic head with respect to a width direction of the magnetic tape is changed during running of the magnetic tape in the magnetic tape device. The magnetic tape satisfies Equation 1: TDSage+TDSenv−TC≤0.10 μm. In Equation 1, the TDSage is a maximum value of an absolute value of a difference between a servo band spacing obtained before storage for 24 hours in a predetermined environment and a servo band spacing obtained after the storage. TDSenv is a value calculated by multiplying a difference between a maximum value and a minimum value of servo band spacings obtained in each of five predetermined environments by ½, and TC is a value calculated by TC=L{cos (θ.sub.initial−Δθ)−cos (θ.sub.initial+Δθ)}.

A magnetic tape device. The angle θ formed by the axis of the element array of the magnetic head with respect to a width direction of the magnetic tape is changed during running of the magnetic tape in the magnetic tape device. In a case where a maximum value of an absolute value of a difference between a servo band spacing obtained before storage in a predetermined environment and a servo band spacing obtained after storage in the environment for a storage time T is defined as A, and T is set to a plurality of predetermined times, a medium life calculated by a linear function of A and a logarithm log.sub.e T of T, that are derived from a value of A and a value of the logarithm log.sub.e T of T obtained for each T is 5 years or longer.

A substrate for a magnetic disk includes a substrate main body having two main surfaces and an outer circumferential edge surface that has a side wall surface and chamfered surfaces, 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 the film provided on the main surfaces is 0.520 mm or less. A total thickness D mm of the film on the main surfaces and the thickness T mm satisfy D≥0.0082/T−0.0015. A film thickness of the film on the outer circumferential edge surface is larger than a film thickness of the film on the main surfaces, and is 150% or less of the film thickness of the film on the main surfaces.

A magnetic recording medium is a tape-shaped magnetic recording medium that has a recording layer including an ε-iron oxide particle. An area ratio R.sub.low (=(S.sub.low/S.sub.total)×100) of a total area S.sub.total of an SFD curve of the recording layer in a perpendicular direction and an area S.sub.low of the SFD curve in which a coercivity Hc is in a range from −500 [Oe]≤Hc≤500 [Oe] is equal to or less than 5.5%.

An ionic liquid comprising: a cation (or conjugate acid), wherein the cation (or conjugate acid) is represented by General Formula (A) below or General Formula (B) below or General Formula (C) or General Formula (D) below or General Formula (E) below: ##STR00001## wherein R.sub.1 represents CH.sub.2CH.sub.2(CF.sub.2).sub.nCF.sub.3, where n is an integer ranging from 0 to 7, or an alkyl chain CH.sub.3, or CH.sub.2OH, or CH.sub.2CH.sub.2OH; R.sub.2 represents CH.sub.2CH.sub.2(CF.sub.2).sub.nCF.sub.3, where n is an integer ranging from 0 to 7, or a hydrogen atom H, or CH.sub.2OH, or CH.sub.2CH.sub.2OH; and R.sub.3 represents CH.sub.2CH.sub.2(CF.sub.2).sub.nCF.sub.3, where n is an integer ranging from 0 to 7.

A substrate for a magnetic disk includes a substrate main body having two main surfaces and an outer circumferential edge surface that has a side wall surface and chamfered surfaces, 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 the film provided on the main surfaces is 0.520 mm or less. A total thickness D mm of the film on the main surfaces and the thickness T mm satisfy D≥0.0082/T−0.0015. A film thickness of the film on the outer circumferential edge surface is larger than a film thickness of the film on the main surfaces, and is 150% or less of the film thickness of the film on the main surfaces.

A magnetic tape device. The angle θ formed by the axis of the element array of the magnetic head with respect to a width direction of the magnetic tape is changed during running of the magnetic tape in the magnetic tape device. The magnetic tape satisfies Equation 1: TDSage+TDSenv−TC≤0.10 μm. In Equation 1, the TDSage is a maximum value of an absolute value of a difference between a servo band spacing obtained before storage for 24 hours in a predetermined environment and a servo band spacing obtained after the storage. TDSenv is a value calculated by multiplying a difference between a maximum value and a minimum value of servo band spacings obtained in each of five predetermined environments by ½, and TC is a value calculated by TC=L{cos (θ.sub.initial−Δθ)−cos (θ.sub.initial+Δθ)}.

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 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 data storage drive includes a magnetic recording media comprising a ferroelectric layer between a bottom electrode layer and a top electrode layer. An applied voltage to the ferroelectric layer generates a strain that is transferred to a ferromagnetic recording layer formed proximate to the ferroelectric layer. The change in strain transferred to the recording layer changes the magnetic properties of the recording layer. A voltage can be selectively applied to all or part of the ferroelectric layer to place the ferromagnetic recording layer in a low coercivity state to assist in writing data. Voltage-assisted magnetic recording (VAMR) is provided based upon control of a magnetic recording media comprising a ferroelectric layer between a bottom electrode layer and a top electrode layer.