1. Field of the Invention
The present invention relates to a high-density magnetic recording medium, and in particular, to a magnetic recording medium whose recorded signals are reproduced in a system using a magneto-resistive head (MR head) or a giant magneto-resistive head (GMR head).
2. Description of Related Art
In the field of video tape recorders and the like, a so-called metal thin film type magnetic recording medium has been recently proposed to enhance image quality and increase recording density. In a metal thin film type magnetic recording medium, various types of magnetic materials such as a metal magnetic material, a Co—Ni alloy, a Co—Cr alloy and a Co—CoO metal oxide or the like may be evaporated onto a non-magnetic substrate by a vacuum thin film forming technique to form a magnetic layer. Such a metal thin film type magnetic recording medium has been put into practical use as, for example, a metal evaporated tape for high-band 8 mm video tape recorders, digital video tape recorders and the like.
A metal thin film type magnetic recording medium is superior in coercivity and squareness ratio, and since its magnetic layer can be formed extremely thin, a metal thin film type magnetic recording medium is superior in electromagnetic conversion characteristics at short wavelengths, with extremely small recording demagnetization and thickness loss upon reproduction. Moreover, unlike so-called coated type magnetic recording media, whose magnetic layer is formed of a magnetic coating in which a magnetic powder is dispersed in a binder, because a binder, which is a non-magnetic material, is not mixed in the magnetic layer, a metal thin film type magnetic recording medium has various advantages such as being able to increase the filling density of fine ferromagnetic metal particles and so forth.
Moreover, with an increased demand for magnetic recording media, such as magnetic tapes, as data streamers, a higher recording density is being demanded of magnetic recording media. Furthermore, as magnetic heads used for reproducing recorded information, magneto-resistive heads (MR heads) are beginning to see more frequent application in place of conventional inductive heads.
Since MR heads are capable of sensitively detecting an extremely small leakage flux from a magnetic layer, they are effective in achieving improvements in recording density.
Since MR heads have an upper detection limit at which its sensitivity to leakage flux saturates, and MR heads are incapable of detecting a leakage flux beyond the design thereof, in a recording medium whose recorded signals are reproduced with MR heads, its magnetic layer is required to be made thinner for purposes of optimization.
Moreover, in magnetic recording tape systems in general, when the degradation in the magnetization of a tape reaches or exceeds 16%, the amount of degradation becomes too large for sufficient reproduction signals to be obtained. Thus, such systems are designed with the assumption that the degradation in the amount of magnetization of a tape is 15% or less.