A lubricant including an ionic liquid including a conjugate base and a conjugate acid, wherein the conjugate acid includes a group including a hydroxyl group and a group including a straight-chain hydrocarbon group having 6 or greater carbon atoms, and a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less.

A lubricant including: an ionic liquid, which includes a conjugate acid (B.sup.+) and a conjugate base (X.sup.), and is protic, wherein the ionic liquid is represented by the following general formula (1), and wherein the conjugate base is a conjugate base of sulfonic acid, a conjugate base of sulfonimide, or a conjugate base of trisulfonylmethide: ##STR00001##
where R.sup.1 and R.sup.2 each represent a hydrogen atom or R.sup.1 and R.sup.2 form a benzene ring together with carbon atoms to which R.sup.1 and R.sup.2 are bonded, R.sup.3 represents a to straight-chain hydrocarbon group having 10 or more carbon atoms, and R.sup.4 represents a hydrogen atom or a hydrocarbon group in the general formula (1).

There is provided a fluorine-containing ether compound represented by the following formula. R.sup.1R.sup.2CH.sub.2R.sup.3CH.sub.2OCH.sub.2CH(OH)CH.sub.2OCH.sub.2R.sup.3CH.sub.2R.sup.4R.sup.5 (in the formula, R.sup.3 represents a perfluoropolyether chain; R.sup.2 and R.sup.4 represent a divalent linking group having a polar group and may be the same or different from each other; R.sup.1 and R.sup.5 represent a terminal group bonded to an oxygen atom of R.sup.2 or R.sup.4 and may be the same or different from each other; and at least one of R.sup.1 and R.sup.5 is an organic group having 1 to 8 carbon atoms and at least one of hydrogens included in the organic group is substituted by a cyano group).

The magnetic recording medium includes a non-magnetic support, and a magnetic layer including a ferromagnetic powder. An anisotropic magnetic field Hk is 12 kOe or more, a center line average roughness Ra of the surface of the magnetic recording medium on the magnetic layer side is 1.2 nm or less, and a ratio ?r of a contact angle ?2 with respect to 1-bromonaphthalene, measured on a surface on the magnetic layer side after a 1,1,1,2,2,3,4,5,5,5-decafluoropentane immersion, to a contact angle ?1 with respect to 1-bromonaphthalene, measured on the surface on the magnetic layer side before the 1,1,1,2,2,3,4,5,5,5-decafluoropentane immersion is 0.95 or less.

There is provided a magnetic recording medium in which a contact angle with water, which is measured on a surface of the magnetic layer, is 96 degrees or more, a fluorine concentration F obtained by X-ray photoelectron spectroscopy performed on the surface of the magnetic layer at a photoelectron take-off angle of 10 degrees is 1.0 at % or more and less than 5.0 at %, and ?C calculated by Equation ?C=C.sub.before?C.sub.after is 10.0 at % or more and 30.0 at % or less. The C.sub.before is a CH derived carbon concentration calculated from a CH peak surface area ratio in C1s spectra obtained by the X-ray photoelectron spectroscopy performed on the surface of the magnetic layer at the photoelectron take-off angle of 10 degrees before a methanol extraction treatment, and the C.sub.after is a CH derived carbon concentration after the methanol extraction treatment.

A lubricating agent including an ionic liquid formed from a Bronsted acid (HX) and a Bronsted base (B), wherein the Bronsted base has a linear hydrocarbon group having 10 or more carbon atoms and the difference between the pKa value of the Bronsted acid in water and the pKa value of the Bronsted base in water is 12 or more.

A lubricating agent including an ionic liquid formed from a Bronsted acid (HX) and a Bronsted base (B), wherein the Bronsted base has a linear hydrocarbon group having 10 or more carbon atoms and the difference between the pKa value of the Bronsted acid in water and the pKa value of the Bronsted base in water is 12 or more.

A fluorine-containing ether compound represented by the following formula (1) is provided.
R.sup.2CH.sub.2R.sup.1CH.sub.2OCH.sub.2CH(OH)(CH.sub.2).sub.nCH(OH)CH.sub.2OCH.sub.2R.sup.1CH.sub.2R.sup.2(1)
(in the formula (1), n is an integer of 2 to 6, R.sup.1 is a perfluoropolyether chain, R.sup.2 is OCH.sub.2CH(OH)CH.sub.2O(CH.sub.2).sub.mOH (m in the formula is an integer of 2 to 4)).

A lubricant including an ionic liquid, which includes a conjugate acid (B.sup.+) and a conjugate base (X.sup.), and is protic, wherein the conjugate acid includes a straight-chain hydrocarbon group having 10 or more carbon atoms, and wherein the conjugate base is represented by the following general formula (1): ##STR00001##
where n is an integer of from 0 to 6 in the general formula (1).

A lubricant including: an ionic liquid, which includes a conjugate acid (B.sup.+) and a conjugate base (X.sup.), and is protic, wherein the ionic liquid is represented by the following general formula (1), and wherein the conjugate base is a conjugate base of sulfonic acid, a conjugate base of sulfonimide, or a conjugate base of trisulfonylmethide:

##STR00001##

where R.sup.1 and R.sup.2 each represent a hydrogen atom or R.sup.1 and R.sup.2 form a benzene ring together with carbon atoms to which R.sup.1 and R.sup.2 are bonded, R.sup.3 represents a to straight-chain hydrocarbon group having 10 or more carbon atoms, and R.sup.4 represents a hydrogen atom or a hydrocarbon group in the general formula (1).