A lubricant which includes an ionic liquid including a conjugate acid and a conjugate base having 2 or more anions in a molecule of the conjugate base, wherein the conjugate acid has a group including a straight-chain hydrocarbon group having 6 or more 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 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 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): ##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, and R.sup.3 represents a straight-chain hydrocarbon group having 10 or more carbon atoms 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): ##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, and R.sup.3 represents a straight-chain hydrocarbon group having 10 or more carbon atoms in the general formula (1).

A lubricant for a magnetic recording medium including an ionic liquid including a Bronsted acid and a Bronsted base that is primary amine as constituents of the ionic liquid, wherein the Bronsted acid includes a fluorine-containing chain, the Bronsted base includes a fluorine-containing chain that is a perfluoroalkyl chain or a perfluoropolyether chain, wherein the fluorine-containing chain in the Bronsted acid is a perfluoropolyether chain or the fluorine-containing chain in the Bronsted base is the perfluoropolyether chain, or the fluorine-containing chain in the Bronsted acid is the perfluoropolyether chain and the fluorine-containing chain in the Bronsted base is the perfluoropolyether chain, and a number average molecular weight of the fluorine-containing chain in the Bronsted acid is 1,500 or less.

A lubricant for a magnetic recording medium including an ionic liquid including a Bronsted acid and a Bronsted base that is primary amine as constituents of the ionic liquid, wherein the Bronsted acid includes a fluorine-containing chain, the Bronsted base includes a fluorine-containing chain that is a perfluoroalkyl chain or a perfluoropolyether chain, wherein the fluorine-containing chain in the Bronsted acid is a perfluoropolyether chain or the fluorine-containing chain in the Bronsted base is the perfluoropolyether chain, or the fluorine-containing chain in the Bronsted acid is the perfluoropolyether chain and the fluorine-containing chain in the Bronsted base is the perfluoropolyether chain, and a number average molecular weight of the fluorine-containing chain in the Bronsted acid is 1,500 or less.

A lubricant, which includes an ionic liquid including a conjugate base and a conjugate acid including 2 or more cations in a molecule of the conjugate acid, wherein the conjugate acid includes a monovalent group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and an acid that is a source of the conjugate base has a pKa in acetonitrile of 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):

##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, and R.sup.3 represents a straight-chain hydrocarbon group having 10 or more carbon atoms 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):

##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, and R.sup.3 represents a straight-chain hydrocarbon group having 10 or more carbon atoms in the general formula (1).