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).

Provided is a fluorine-containing ether compound represented by the following formula. R.sup.1OR.sup.2CH.sub.2R.sup.3CH.sub.2R.sup.4OR.sup.5 (R.sup.3 represents a perfluoropolyether chain, R.sup.2 and R.sup.4 represent a divalent linking group having one or more polar groups, R.sup.1 and R.sup.5 represent Formula (2), Formula (3), or a hydrogen atom, and at least one of R.sup.1 or R.sup.5 is represented by Formula (2) or (3), in Formula (2), X.sup.1 represents an alkylene group having 1 to 30 carbon atoms, and Y and Z represent an aliphatic group having 1 to 30 carbon atoms, in Formula (3), X.sup.2 represents an alkylene group having 1 to 30 carbon atoms, and A and B represent an aliphatic group having 1 to 30 carbon atoms.)

##STR00001##

This fluorine-containing ether compound is a fluorine-containing ether compound represented by the following formula:

R.sup.1CH.sub.2R.sup.2(CH.sub.2OCH.sub.2CR.sup.3R.sup.4CH.sub.2OCH.sub.2R.sup.2).sub.zCH.sub.2R.sup.5

(z represents 1 or 2. R.sup.2 is a perfluoropolyether chain. R.sup.1 and R.sup.5 are terminal groups having 1 to 50 carbon atoms and having at least one polar group. R.sup.3 and R.sup.4 may be the same as or different from each other, and are organic groups which do not include a secondary hydroxy group and a tertiary hydroxy group, include one primary hydroxy group, and have 1 to 5 carbon atoms bonded to a tetrasubstituted carbon atom. The organic group may include an ether oxygen atom between the carbon atoms, and a bonding terminal to the tetrasubstituted carbon atom may be an ether oxygen atom.)

A fluorine-containing ether compound represented by the following formula: R.sup.1R.sup.2CH.sub.2R.sup.3[CH.sub.2R.sup.4CH.sub.2R.sup.3].sub.xCH.sub.2R.sup.5R.sup.6 (R.sup.1 and R.sup.6 are an organic group having 1 to 50 carbon atoms; R.sup.2 is Formula (2-1) or (2-2); R.sup.5 is Formula (2-3) or (2-4); R.sup.3 is a perfluoropolyether chain; R.sup.4 is Formula (3-1) or (3-2); and x is 0 to 2).

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An object is to provide a lubricant whose heat resistance and adhesion to a magnetic disk are further improved, a multimerized fluoropolyether compound which is for realizing the lubricant, and a magnetic disk for which the lubricant and the fluoropolyether compound are used. The object is attained by linking two perfluoropolyether group-containing groups with a linking group having the following structure:

##STR00001##

In the formula, i is an integer of 1 to 10, and R.sup.5 and R.sup.6 are each independently a hydrocarbon group having 1 to 10 carbon atoms and may each independently contain a polar group and/or an ether bond formed by substitution of at least one carbon atom in the hydrocarbon group with an oxygen atom.