Cobalt-alloy-based thin-film magnetic recording media have been increasingly used in the manufacturing of hard disks for read/write operations in computers. Thin-film magnetic recording media are typically prepared by sputtering a thin magnetic film, or the so-called magnetic recording layer, on a substrate, which is typically a textured aluminum or NiP substrate. A chromium- or chromium-alloy-based underlayer is typically provided which is sandwiched between the cobalt-alloy-based magnetic layer and the aluminum or NiP substrate. After the cobalt-alloy-based magnetic layer is sputtered on the chromium underlayer, a protective overcoat layer, which typically comprises a carbon overcoat, is then applied over the magnetic layer, also by sputtering.
A number of cobalt-alloy-based alloys have been developed and used as magnetic recording films for preparing the thin-film magnetic recording media. For example, U.S. Pat. No. 4,888,514 discloses a thin film magnetic recording disk containing a cobalt-nickel magnetic recording layer sputtered over a chromium underlayer. The magnetic disks prepared using the cobalt-nickel film were reported to exhibit a coercivity of 650 Oersteds (Oe), and a loop squareness ratio greater than 0.9.
Coercivity is defined as the magnetic field required to reduce the remanence magnetic flux to 0, i.e., the magnetic field required to erase a stored bit of information. A higher coercivity allows adjacent recorded bits to be placed more closed together in a medium without mutual cancellation. Thus a higher coercivity is preferred for high density disks. Loop squareness is defined as the ratio of coercivity to the magnetic saturation field. As the saturation field becomes smaller, approaching the coercivity, it would take less field strength to write to the medium. This ratio is typically referred to as an overwrite ratio, i.e., the ratio of the old signal residual to the new signal. A small overwrite ratio indicates good writability, and is thus preferred.
A number of cobalt-nickel and cobalt-nickel-chromium alloys based magnetic layers have been developed. They are disclosed in, for example, U.S. Pat. Nos. 4,833,044, 4,816,127, and 4,735,840. In an attempt to improve the performance of cobalt-alloy-based magnetic hard disks, a four-component cobalt-alloy-based magnetic layer was develop containing 70-80 atom percent cobalt, 10-20 atom percent chromium, 3-20 atom percent platinum, and 2-10 atom percent tantalum. This magnetic recording medium, which was disclosed in U.S. Pat. No. 5,049,451, exhibited a coercivity of less than 2,000 Oe.
In light of the increasing need for larger capacity hard disks, it is always desirable to develop new magnetic media which would provide improved read/write properties. Preferably, the magnetic recording media would exhibit a coercivity greater than 2,000 Oe and can be used for making hard disks with a capacity of at least 2 GB.