Metallic thin film magnetic recording medium having a hard protective layer

Claim 1

A ferromagnetic recording medium comprising: (A) a non-magnetic substrate; (B) a magnetic layer on said substrate comprising a cobalt/chromium alloy having an atomic ratio of cobalt to chromium between about 75/25 and 90/10, the cobalt of which is all metallic cobalt; (C) a bonding layer, between about 40 and 300 Angstroms thick, on the magnetic layer of part (B) comprising reaction products of cobalt and chromium selected from the group consisting of oxides, nitrides and carbides of cobalt and chromium and combinations of such oxides, nitrides and carbides, said bonding layer providing a surface which is completely oxidized, nitrides and or carburized and having a substantial absence of metallic cobalt and chronium; and (D) a lubricant layer on the bonding layer of part (C), said lubricant comprising a primer layer and a perfluoropolyether having the formula Q(R.sub.f).sub.k C.sub.a F.sub.2a --Z wherein Q comprises a polymerizable terminally unsaturated group attached to R f , which represents a plurality of randomly distributed perfluoroalkylene oxide repeating units which may be branched or straight chain structures represented by the formula --C a F 2a O-- in which a of each unit is independently an integer of 1 to 4, k is the number of such units having a value of from 1 to 300 such that the segment R f has a number average molecular weight of 500 to 20,000 and Z is selected from --OC a F 2a+1 and Q, there being no layer in between the bonding layer and the lubricant layer.