A lubricant adheres to a magnetic recording medium via at least one of chemisorption or bonding, and contains a perfluorinated polyether attached to or terminated with a functional group that is phosphonic acid, silanol or carboxylic acid, and may be:

R.sub.1R.sub.fR.sub.1 where R.sub.f is CF.sub.2O(CF.sub.2CF.sub.2CF.sub.2CF.sub.2O).sub.n, CF.sub.2O(CF.sub.2CF.sub.2CF.sub.2O).sub.nCF.sub.2, CF.sub.2O[CF(CF.sub.3)CF.sub.2O].sub.nCF.sub.2, CF.sub.2O(CF.sub.2CF.sub.2O).sub.m(CF.sub.2O).sub.nCF.sub.2, CF.sub.2O(CF.sub.2CF.sub.2O).sub.nCF.sub.2, n, m is from 1 to 100 and R.sub.1 is the functional group. A lubricant is formed from a multiple ether segments according to formula:

Re.sup.1Rb.sup.1-Ri-Rc-Ri-Rb.sup.2Re.sup.2; where Rc includes perfluoroalkyl ether, Rb.sup.1 and Rb.sup.2 are, independently, a sidechain segment including a perfluoroalkyl ether, optional Ri independently is a divalent linking segment including a functional group including elements from periodic table Group 13-17, and of Re.sup.1 and Re.sup.2 are phosphonic acid, silanol or carboxylic acid. Lubricant synthesis includes reacting a perfluorinated polyether with a halogenated functional group, selected from phosphonic acid, silanol or carboxylic acid.

This vibration damping device (10) includes a magnetorheological fluid composition in a cylinder (12). The magnetorheological fluid composition includes magnetic particles; a dispersant having the magnetic particles dispersed therein; and a friction modifier. The friction modifier is an ester-based additive having a hydrocarbon chain having 14 to 22 carbon atoms, preferably an alkyl chain or an alkenyl chain. The content of the friction modifier is 0.1 to 5 mass %.

The present invention provides a magnetic viscous fluid and a mechanical device with both improved drag force during excitation and improved rubber-resistant properties. The magnetic viscous fluid comprises a magnetic particle and base oil, wherein the base oil comprises ester base oil and non-polar base oil, and a non-polarity index of the base oil is in the range of 10 to 45.

This vibration damping device (10) includes a magnetorheological fluid composition in a cylinder (12). The magnetorheological fluid composition includes magnetic particles; a dispersant having the magnetic particles dispersed therein; and a friction modifier. The friction modifier is an amine-based additive having a hydrocarbon chain having 14 to 22 carbon atoms, preferably an alkyl chain or an alkenyl chain. The content of the friction modifier is 0.1 to 5 mass %.

The present invention provides a magnetic viscous fluid and a mechanical device with both improved drag force during excitation and improved rubber-resistant properties. The magnetic viscous fluid comprises a magnetic particle and base oil, wherein the base oil comprises ester base oil and non-polar base oil, and a non-polarity index of the base oil is in the range of 10 to 45.

The present invention provides a magnetic viscous fluid comprising a magnetic particle, base oil, an inorganic cation exchanger with a siloxane bond, and silicone oil. A difference AB between a solubility parameter A of the base oil and a solubility parameter B of the silicone oil is 1.3 (cal/cm.sup.3).sup.1/2 or more.