A lubricant, which includes an ionic liquid including a conjugate base and a conjugate acid, wherein the conjugate acid is represented by General Formula (A) below, and wherein a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less,

##STR00001##

where, in General Formula (A), R.sub.1, R.sub.2, and R.sub.3 are each independently a group including a hydrocarbon group, with the proviso that at least one of the hydrocarbon groups in R.sub.1, R.sub.2, and R.sub.3 is a straight-chain hydrocarbon group having 6 or greater carbon atoms.

A lubricant, which includes an ionic liquid including a conjugate base and a conjugate acid, wherein the conjugate acid is represented by General Formula (A) below, and wherein a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less,

##STR00001##

where, in General Formula (A), R.sub.1, R.sub.2, and R.sub.3 are each independently a group including a hydrocarbon group, with the proviso that at least one of the hydrocarbon groups in R.sub.1, R.sub.2, and R.sub.3 is a straight-chain hydrocarbon group having 6 or greater carbon atoms.

The fluorine-containing ether compound is represented by the following formula (1): R.sup.1—R.sup.2—CH.sub.2—R.sup.3—CH.sub.2—R.sup.4. In the formula (1), R.sup.1 is represented by the following formula (2), R.sup.2 is represented by the following formula (3), R.sup.3 is a perfluoropolyether chain, and R.sup.4 is an organic end group different from R.sup.1—R.sup.2— and contains two or three polar groups, wherein each polar group is bonded to a different carbon atom, and the carbon atoms to which the polar groups are bonded are bonded to one another via a linking group containing a carbon atom to which the polar group is not bonded. In the formula (2), R.sup.5 is an alkoxy group selected from the group consisting of a methoxy, an ethoxy and a propoxy group. In the formula (3), w is 2 or 3.

##STR00001##

The fluorine-containing ether compound is represented by the following formula (1): R.sup.1-R.sup.2—CH.sub.2—R.sup.3—CH.sub.2—R.sup.4. In the formula (1), R.sup.1 is represented by the following formula (2), R.sup.2 is represented by the following formula (3), R.sup.3 is a perfluoropolyether chain, and R.sup.4 is an organic end group different from R.sup.1-R.sup.2- and contains two or three polar groups, wherein each polar group is bonded to a different carbon atom, and the carbon atoms to which the polar groups are bonded are bonded to one another via a linking group containing a carbon atom to which the polar group is not bonded. In the formula (2), r is 1 to 3. In the formula (3), w is 2 or 3.

##STR00001##

A magnetic recording medium includes a long-shaped base substrate having flexibility, a soft magnetic layer, and a magnetic recording layer. A squareness ratio in a longitudinal direction of the base substrate is equal to or less than a squareness ratio in a short-side direction of the base substrate. The squareness ratio in the longitudinal direction of the base substrate is 30% or less.

The magnetic tape has a magnetic layer containing ferromagnetic powder and binder on one surface of a nonmagnetic support and has a backcoat layer containing nonmagnetic powder and binder on the other surface thereof, wherein the thickness of the backcoat layer is less than or equal to 0.20 μm, the contact angle for 1-bromonaphthalene that is measured on the surface of the backcoat layer falls within a range of 10.0° to 30.0°, and the contact angle for 1-bromonaphthalene that is measured on the surface of the magnetic layer falls within a range of 45.0° to 55.0°.

The magnetic tape has a magnetic layer containing ferromagnetic powder and binder on one surface of a nonmagnetic support and has a backcoat layer containing nonmagnetic powder and binder on the other surface thereof, wherein the thickness of the backcoat layer is less than or equal to 0.20 μm, the contact angle for 1-bromonaphthalene that is measured on the surface of the backcoat layer falls within a range of 10.0° to 30.0°, and the contact angle for 1-bromonaphthalene that is measured on the surface of the magnetic layer falls within a range of 45.0° to 55.0°.

A fluorine-containing ether compound represented by Formula (1) is provided.
R.sup.1—R.sup.2—CH.sub.2—R.sup.3—CH.sub.2—R.sup.4—R.sup.5   (1)
(In Formula (1), R.sup.1 and R.sup.5 each represents a group having a heterocyclic ring and may be the same as or different from each other, R.sup.2 and R.sup.4 each represents a divalent linking group having a polar group and play be the same as or different from each other, and R.sup.3 represents a perfluoropolyether chain.)

Provided is a compound which has heat resistance and decomposition resistance and with which a monomolecular film having a reduced thickness can be obtained. A fluoropolyether compound in accordance with an aspect of the present invention is represented by R.sup.1—C.sub.6H.sub.4O—CH.sub.2CH(OH)CH.sub.2OCH.sub.2—R.sup.2—CH.sub.2—O—CH.sub.2CH(OH)CH.sub.2—OC.sub.6H.sub.4—R.sup.1 where R.sup.1 is a hydrogen atom, an alkoxy group having 1 to 4 carbon atoms, an amino group, or an amide group, R.sup.2 is —CF.sub.2O(CF.sub.2CF.sub.2O).sub.xCF.sub.2—, and x is a real number of 1 to 35.

Provided is a compound with which a lubricant having excellent adhesion to a magnetic disk, particularly to a protective layer can be provided. A perfluoropolyether compound in accordance with one aspect of this invention has a structure in which two perfluoropolyethers are bonded to each other through an aliphatic ether, the aliphatic ether including a carbon atom to which a primary alcohol is bonded.