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Perpendicular Granular Recording Medium With Superior Thermal Stability and Corrosion Resistance Disclosure Number: IPCOM000013704D
Original Publication Date: 2002-May-02
Included in the Prior Art Database: 2003-Jun-18

Publishing Venue



Disclosed is a perpendicular medium structure capped with a thin layer of Pt, which improves the thermal stability and the corrosion resistance of the magnetic medium. Magnetic recording at ultra-high bit densities requires high Hc, small medium thickness, and small magnetic spacing. However, as the medium thickness decreases, the magnetization becomes thermally unstable owing to thermally activated magnetization processes. And also, the thinning of overcoat to reduce the magnetic spacing would decrease the corrosion resistance.Perpendicular media are expected to offer a number of advantages in terms of stability of bit patterns recorded at ultra-high bit densities because the demagnetizing fields in these media stabilize adjacent transitions at high bit densities. Ideally, the SNR and resolution can be improved by decreasing the thickness of perpendicular media. However, the demagnetizing field at the top surface also increases with decreasing medium thickness. Conventional granular perpendicular media are vulnerable to demagnetization and thermal decay at low bit densities, because strong demagnetizing fields exist at the center of large bit cells. The center of such bit cells has been reported to undergo severe demagnetization and thermal instability in granular perpendicular media . This invention provides a method and describes materials and processes to achieve the improved thermal stability and corrosion resistance without SNR degradation. Figure 1 shows the structure of a novel magnetic recording medium. This composite medium consists of a Pt layer with hetero epitaxy on top of a granular perpendicular magnetic host layer. We use a carbon top layer and lubricant for the protection of contacts with a recording head. Without the carbon layer, the Pt would act like a cathode with a large reactive area. This could potentially accelerate the corrosion of Co at pinhole sites. We have discovered that the Pt layer with hetero epitaxy and the interface between the granular host layer and the Pt layer influence the magnetic property of the host granular perpendicular layer. Consequently, the Pt and interface layers increase Hc and squareness (S Mr/Ms) of the host granular layer owing to the increase of exchange magnetic coupling. The larger Hc, Hcr, and S stabilize the magnetization of the host grains and prevent reverse magnetic domain that would normally occur because of large demagnetization fields and imperfections in the granular magnetic host layer. We prepared the perpendicular medium consisting of a CoCr10Pt20 host layer of 25 nm and a Pt layer. The crystal structure of the medium was determined by X-ray diffraction (XRD). The effect of the Pt layer on the interplanar spacing, d , of the h.c.p. Co (002) planes is shown in Fig. 2. The 0.19 change of d-spacing in C-axis indicates that the Pt and the interface layers can influence the magnetic property and the crystal orientation of the host granular perpendicular layer. The magnetic properties were measured with SQUID magnetometer and Kerr instrument. The Hc Hcr and S dependences on the Pt thickness for the composite medium are shown in Figs. 3 and 4, respectively. The Hc and S values increase by 10% and 12%, respectively, for the medium with 2 nm of Pt. To further confirm the effect of Pt layer and the interface layer, we have measured the Mr decay for the composite medium by SQUID. Medium A is a composite medium with 2 nm of Pt over 25 nm of CoCr10Pt20 layer, which was sputter-deposited on a glass disk with NiAl and Ti underlayers. A reference granular medium (B) that has the same structure but lack the