Patent ID: 7291409

Claim:
A magnetic recording medium comprising a non-magnetic support, at least one primer layer formed on one surface of the non-magnetic support, comprising a non-magnetic powder and a binder resin, at least one magnetic layer formed on the primer layer, comprising a magnetic powder and a binder resin, and a back layer formed on the other surface of the non-magnetic support, wherein the magnetic powder contained in an uppermost layer of the magnetic layer is a magnetic powder of substantially spherical or ellipsoidal particles comprising a rare earth element, iron and optionally at least one other transition metal, and has a number average particle size of 5 to 50 nm and an average axis ratio of 1 to 2, and the total thickness of the magnetic recording medium is less than 6 μm, wherein said uppermost magnetic layer has a product of a residual magnetic flux density (Br) and a thickness of 0.0018 μTm to 0.05 μTm, wherein said magnetic powder particles in said uppermost magnetic layer comprise an outer layer part and a core part, wherein the rare earth element is present primarily in the outer layer part, and the core part comprises a Fe 16 N 2 phase and optionally at least one transition metal other than iron, and wherein said magnetic powder particles have a saturation magnetization of 79.6–159.2 emu/g.