A magnetic recording medium includes a layer structure including a magnetic layer, a base layer, and a back layer in this order, in which an average thickness t.sub.T is t.sub.T≤5.5 μm, a dimensional variation Δw in a width direction to tension change in a longitudinal direction is 660 ppm/N≤Δw, and a surface roughness R.sub.abe of the base layer on a side of the back layer is 4.2 nm≤R.sub.abe≤8.5 nm.

Low-profile thermally stable lubricants for data storage devices are provided based on multi-dentate molecular designs. One such lubricant comprises perfluoroalkyl ether segments, a divalent linking segment, and anchoring functional groups attachable to, or engageable with, a protective overcoat of a magnetic recording medium. The lubricants can be used in conjunction with a magnetic recording medium and/or a magnetic data storage system.

The magnetic tape includes a non-magnetic support, and a magnetic layer including a ferromagnetic powder. A fluorine-containing compound is included in a portion on the non-magnetic support on a magnetic layer side, and a ratio θr of a water contact angle measured on a surface of the magnetic layer after sliding on a magnetic head to a water contact angle measured on the surface of the magnetic layer before sliding on the magnetic head is 0.70 or more.

The fluorine-containing ether compound is represented by the following formula (1): R.sup.1—R.sup.2—CH.sub.2—R.sup.3—CH.sub.2—R.sup.4. In the formula (1), R.sup.1 is represented by the following formula (2), R.sup.2 is represented by the following formula (3), R.sup.3 is a perfluoropolyether chain, and R.sup.4 is an organic end group different from R.sup.1—R.sup.2— and contains two or three polar groups, wherein each polar group is bonded to a different carbon atom, and the carbon atoms to which the polar groups are bonded are bonded to one another via a linking group containing a carbon atom to which the polar group is not bonded. In the formula (2), r is 1 to 3. In the formula (3), w is 2 or 3. ##STR00001##

The invention provides a fullerene compound; a lubricant that is for a magnetic recording medium and that contains the fullerene compound; and a magnetic recording medium. The fullerene compound is an ionic liquid that is represented by general formula (1) and is formed from a Bronsted acid (H.sub.n1X) and a Bronsted base ([R.sub.2R.sub.3)N—].sub.m1—R.sub.1); wherein one of the Brønsted acid and the Broønsted base contains a group having a fullerene; and the other contains a perfluoroalkyl chain. ##STR00001##

The fluorine-containing ether compound is represented by the following formula (1): R.sup.1-R.sup.2—CH.sub.2—R.sup.3—CH.sub.2—R.sup.4. In the formula (1), R.sup.1 is represented by the following formula (2), R.sup.2 is represented by the following formula (3), R.sup.3 is a perfluoropolyether chain, and R.sup.4 is an organic end group different from R.sup.1-R.sup.2- and contains two or three polar groups, wherein each polar group is bonded to a different carbon atom, and the carbon atoms to which the polar groups are bonded are bonded to one another via a linking group containing a carbon atom to which the polar group is not bonded. In the formula (2), r is 1 to 3. In the formula (3), w is 2 or 3.

##STR00001##

A magnetic recording medium includes a long-shaped base substrate having flexibility, a soft magnetic layer, and a magnetic recording layer. A squareness ratio in a longitudinal direction of the base substrate is equal to or less than a squareness ratio in a short-side direction of the base substrate. The squareness ratio in the longitudinal direction of the base substrate is 30% or less.

A magnetic recording cartridge is provided and including a magnetic recording medium, wherein an average thickness of the magnetic recording medium t.sub.T is 3.5 μm≤t.sub.T≤5.6 μm, a dimensional change amount Δw in a width direction of the magnetic recording medium with respect to a tension change in a longitudinal direction of the magnetic recording medium is 700 ppm/N≤Δw≤20000 ppm, the magnetic recording medium is accommodated in a state of being wound around the reel in the cartridge case and (a servo track width on an inner side of winding of the magnetic recording medium)−(a servo track width on an outer side of winding of the magnetic recording medium)>0 is satisfied, and a squareness ratio measured in a vertical direction of the magnetic recording medium is 65% or more.

The present application provides binary azeotrope or azeotrope-like compositions comprising perfluoroheptene and an additional component, wherein the additional component is present in the composition in an amount effective to form an azeotrope composition or azeotrope-like composition with the perfluoroheptene. Methods of using the compositions provided herein in cleaning and carrier fluid applications are also provided.

A fluorine-containing ether compound represented by the following formula (1) is provided.

R.sup.2—CH.sub.2—R.sup.1—CH.sub.2OCH.sub.2CH(OH)—(CH.sub.2).sub.n—CH(OH)CH.sub.2OCH.sub.2—R.sup.1—CH.sub.2—R.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)).