The present invention relates to magnetic recording media, such as thin film magnetic recording disks, and to a method of manufacturing the media. The invention has particular applicability to high areal density magnetic recording media exhibiting low noise, low signal modulation, high overwrite and narrow pulse width.
The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanance (Mr), coercivity squareness (S*), medium noise, i.e., signal-to-noise ratio (SNR), and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
The linear recording density can be increased by increasing the Hr of the magnetic recording medium while decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise in thin films is a dominant factor restricting increased recording density of high density magnetic hard disk drives, and is attributed primarily to inhomogeneous grain size and intergranular exchange and magnetostatic couplings. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
There are other basic characteristics of magnetic recording media, aside from SNR, which are indicative of recording performance, such as half-amplitude pulse width (PW5O), overwrite (OW), and modulation level. A wide PW50 indicates that adjacent bits are crowded together resulting in interference which limits the linear packing density of bits in a given track and, hence, reduces packing density in a given area thereby eliminating the recording capacity of the magnetic recording medium. Accordingly, a narrow PW5O is desirable for high areal recording density.
OW is a measure of the ability of the magnetic recording medium to accommodate overwriting of existing data. In other words, OW is a measure of what remains of a first signal after a second signal, e.g., at a different frequency, has been written over it on the medium. OW is considered low or poor when a significant amount of the first signal remains.
It is extremely difficult to obtain optimum performance from a magnetic recording medium by optimizing each of the PW50, OW, SNR and modulation level, as these performance criteria are interrelated and tend to be offsetting. For example, if coercivity (Hc) is increased to obtain a narrower PW50, OW is typically adversely impacted, as increasing Hc typically degrades OW. A thinner medium having a lower Mr x thickness (Mrt) yields a narrower PW50 and better OW; however, the medium signal is usually reduced as well, which might pose difficulty in recording system design since the fraction of electronic noise of the system increases. Increasing the squareness of the hysteresis loop contributes to a narrower PW50 and better OW; however, noise may increase due to intergranular exchange coupling and magnetostatic interaction. Thus, a formidable challenge is present in optimizing magnetic performance in terms of PW50, OW, SNR and modulation level.
It is recognized that the magnetic properties, such as Hr, Mr, S* and SNR, which are critical to the performance of a magnetic alloy film, depend primarily upon the microstructure of the magnetic layer which, in turn, is influenced by the underlying layers, such as the underlayer. It is also recognized that underlayers having a fine grain structure are highly desirable, particularly for growing fine grains of hexagonal close packed (HCP) Co alloys deposited thereon.
It has been reported that nickel-aluminum (NiAl) films exhibit a grain size which is smaller than similarly deposited Cr films, which are the underlayer of choice in conventional magnetic recording media. Li-Lien Lee et al., xe2x80x9cNiAl Underlayers For CoCrTa Magnetic Thin Filmsxe2x80x9d, IEEE Transactions on Magnetics, Vol. 30, No. 6, pp. 3951-3953, 1994. Accordingly, NiAl thin films are potential candidates as underlayers for magnetic recording media for high density longitudinal magnetic recording. However, it was found that the coercivity of a magnetic recording medium comprising a NiAl underlayer is too low for high density recording, e.g. about 2,000 Oersteds (Oe). The use of a NiAl underlayer is also disclosed by C. A. Ross et al., xe2x80x9cThe Role Of NiAl Underlayers In Longitudinal Recording Mediaxe2x80x9d, J. Appl. Phys. 81(a), P.4369, 1997.
In order to increase Hr, magnetic alloys containing platinum (Pt), such as Coxe2x80x94Crxe2x80x94Ptxe2x80x94tantalum (Ta) alloys have been employed. Although Pt enhances film Hr, it was found that Pt also increases media noise. Accordingly, it has become increasingly difficult to achieve high areal recording density while simultaneously achieving high SNR and high Hr.
In U.S. Pat. No. 6,010,795, issued to Chen et al., a magnetic recording medium is disclosed comprising a surface oxidized seed layer, e.g. NiP, and sequentially deposited thereon a Cr-containing sub-underlayer, a NiAl or iron aluminum (FeAl) sub-underlayer, a Cr-containing intermediate layer and a magnetic layer.
Kitakami et al., in U.S. Pat. No. 5,543,221, disclose a magnetic recording medium comprising a non-magnetic intermediate layer interposed between a recording layer and a soft magnetic layer, which intermediate layer can contain ruthenium or an alloy, oxide or nitride thereof. Shiroishi et al., in U.S. Pat. No. 4,833,020, disclose a magnetic recording medium comprising a composite underlayer which contain ruthenium and aluminum. Honda et al., in U.S. Pat. No. 4,722,869, disclose a magnetic recording medium containing a columnar crystal grain size control layer on the substrate which can contain ruthenium. Asada et al., in U.S. Pat. No. 4,743,491, disclose a perpendicular magnetic recording medium comprising an electrically conductive underlayer which can contain ruthenium and aluminum. Japanese Patent No. J""63187-416-A discloses a magnetic recording medium comprising a composite underlayer, containing a lower layer and an upper layer which can contain ruthenium.
There exists a need for high areal density magnetic recording media exhibiting high magnetic properties and high SNR. There also exists a need for magnetic recording media exhibiting a narrow PW50, high OW, high SNR and low signal modulation.
An advantage of the present invention is a magnetic recording medium for high areal recording density exhibiting a narrow PW50, high OW, high SNR and low signal modulation.
Another advantage of the present invention is a method of manufacturing a magnetic recording medium suitable for high areal recording density and exhibiting a narrow PW50, high OW, high SNR and low signal modulation.
Additional advantages and features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following only to be learned from the practice of the present invention. The advantages of the present invention maybe realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved by a magnetic recording medium comprising a non-magnetic substrate; a nickel-aluminum-ruthenium (NiAlRu) alloy seedlayer on the substrate; an underlayer on the seedlayer; and a magnetic layer on the underlayer.
Another aspect of the present invention is a method of manufacturing a magnetic recording medium, the method comprising sputter depositing a nickel-aluminum-ruthenium (NiAlRu) alloy seedlayer on a non-magnetic substrate; depositing an underlayer containing chromium or a chromium alloy on the seedlayer; and depositing a cobalt alloy magnetic layer on the underlayer.
Embodiments of the present invention include sputter depositing a NiAlRu alloy seedlayer on a non-magnetic substrate, such as an aluminum-magnesium substrate, or a glass or glass ceramic substrate, depositing chromium or a chromium alloy underlayer, such as a chromium-molybdenum underlayer, and depositing a cobalt-chromium magnetic alloy, such as a cobalt-chromium-platinum-tantalum-niobium alloy. Embodiments of the present invention further include depositing the NiAlRu seedlayer at a thickness of about 10 521  to about 2,000 xc3x85, the seedlayer comprising about 40 to about 50 at. % nickel, about 45 to about 55 at. % aluminum and greater than about 0.1 to about 10 at. % ruthenium.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.