Abstract: A magnetic disk has optical servo grooves formed at specified intervals along data tracks so that variations in reflected light of light applied to the grooves are detected so as to allow a magnetic head to perform tracking servo. A level difference between a regenerative signal and a fundamental wave of modulation noise during reads of data recorded on the data tracks (4A, 4B) is set to 28 dB or more. Thus, comb-shaped modulation in a regenerative signal due to optical servo grooves is reduced so that output drop of the regenerative signal is suppressed and deterioration of window margin and the like is lessened.

Abstract: A magnetic disc cartridge comprising a cartridge case, a magnetic disc housed rotatably in the cartridge case, and a liner, which serves as a cleaning sheet, secured on the inner surface of the cartridge case, characterized in that the magnetic disc has a magnetic layer containing a ferromagnetic metal powder, a reinforcing powder, whose content is defined in the range of from 5 to 40% by weight, and a fatty acid ester with a melting point of 0.degree. C. or lower, and that at least the disc side surface layer of the cleaning sheet, which is brought into sliding contact directly with the magnetic layer, is almost entirely composed of rayon fiber, such that the magnetic disc cartridge of the present invention can provide a highly reliable magnetic disc cartridge having a magnetic disc which is excellent in durability and substantially error free.

Abstract: A magnetic recording medium suitable for high density recording having improved erasing characteristics is produced by a method comprising the steps of forming an under coat layer containing an electrically conductive material on at least one surface of a substrate, applying a magnetic paint containing hexagonal system ferrite magnetic powder on the under coat layer and drying the applied magnetic paint to form a magnetic layer having a thickness of not larger than 0.7 .mu.m.

Abstract: A magnetic recording medium improved in durability over a wide range of temperature which comprises a substrate and a magnetic layer comprising magnetic powder and a resinous binder formed on the substrate, characterized in that the magnetic layer further comprises a monovalent alcohol ester of a fatty acid and a straight chain saturated fatty acid ester of not less than 28 carbon atoms in a weight proportion of 99:1 to 1:99 in a combined amount of 0.1 to 20 percent by weight based on the weight of the magnetic powder.

Abstract: A magnetic recording disc having a high durability and good electromagnetic conversion characteristics which comprises a non-magnetic support and a magnetic layer provided on at least one surface of the support, wherein the magnetic layer comprises magnetic powder, a resinous binder, polishing particles and a lubricating agent, characterized in that the polishing particles have a Mohs' scale of hardness of not less than 7 and an average particle size of 0.25 r to 0.75 r (r being the thickness (.mu.m) of the magnetic layer) and the lubricating agent is a fatty acid ester having a melting point of not higher than 10.degree. C.

Abstract: A magnetic recording medium improved in durability at an elevated temperature which comprises a substrate and a magnetic layer comprising magnetic powder and a resinous binder formed on the substrate, characterized in that the magnetic layer further comprises an ester of a polyvalent alcohol with a fatty acid in an amount of 0.01 to 40 parts by weight to one part by weight of the magnetic powder.

Abstract: A magnetic recording disc having a high durability and being rotatively driven with small starting torque which comprises a non-magnetic support and a magnetic layer provided on at least one surface of the support, the magnetic layer comprising magnetic powder, a resinous binder, (a) an ester of an unsaturated fatty acid of 8 to 18 carbon atoms with a monovalent or polyvalent, saturated or unsaturated alcohol of not more than 18 carbon atoms optionally substituted with at least one alkoxy group having not more than 8 carbon atoms and (b) a fatty acid ester of the formula: ##STR1## wherein R.sub.1 is a saturated or unsaturated aliphatic hydrocarbon group having 8 to 18 carbon atoms, R.sub.2 is an alkyl group having not more than 18 carbon atoms and n is an integer of 1 or more, the combined amount of the unsaturated fatty acid ester (a) and the fatty acid ester (b) being not less than 5 parts by weight to 100 parts by weight of the magnetic powder.

Abstract: A magnetic disc comprising a non-magnetic substrate, an undercoat coated on the surfaces of the substrate and a magnetic layer containing magnetic powder dispersed in a binder coated on the undercoat, characterized in that the undercoat has a thickness of from 0.5 to 10.0 .mu.m and such a porosity that a lubricant is contained therein in an amount of from 30 to 200 mg/cm.sup.3, which provides good surface lubricity and improved durability.