Abstract: A synthetic lubricant comprising a compound represented by the following general formula (I): ##STR1## wherein Rf and Rf' represent a fluorine-containing polyoxyalkylene group, X and X' a polar group, Y of one or more selected from the group consisting of methylane, ethylene, propylene, oxygen, ketone, imino, sulfon and sulfur or no atom or group, and n an integer of 0 to 5, and a magnetic recording medium coated with this lubricant.

Abstract: A synthetic lubricant comprising a compound represented by the following general formula (I): ##STR1## wherein Rf and Rf' represent a fluorine-containing polyoxyalkylene group, X and X' a polar group, Y of one or more selected from the group consisting of methylene, ethylene, propylene, oxygen, ketone, imino, sulfon and sulfur or no atom or group, and n an integer of 0 to 5, and a magnetic recording medium coated with this lubricant.

Abstract: A synthetic lubricant for lubricating a thin film containing a phosphonitrile ester obtained by cyclic polymerization or ring opening polymerization and represented by the following general formula (I): ##STR1## wherein n represents 3 to 10, and Rf and Rf' represent one or two groups selected from the following groups: ##STR2## wherein l represents 3 to 250, m 1 to 250, and Y one selected from the group consisting of F--, CF.sub.3 --, C.sub.2 F.sub.5 --, CF.sub.3 O--, C.sub.2 F.sub.5 O-- and C.sub.3 F.sub.7 O--; and a magnetic recording medium coated with this lubricant.