Effect of medium thickness on the signal-to-noise ratio of perpendicular media

The effect of the medium thickness of Co-Cr and Co-Cr-Pt perpendicular media on the signal-to-noise ratio (S/N) was investigated by using two different types of merged magnetoresistive (MR) heads. Two types of medium were employed in this measurement: Cr-rich Co/sub 72/-Cr/sub 28/ and (Co/sub 72/Cr/sub 28/)/sub 78/Pt/sub 22/ which have high-anisotropy field (H/sub k/). The write demagnetization increased when a shorter write gap was used. The high SM value for the Cr-rich Co-Cr medium does not decrease even for a large medium thickness of 100-300 nm; however, the SM of the Co-Cr-Pt medium decreases with increasing thickness. To obtain a high SM value, two types of medium can be used. One is a Co-Cr-Pt medium whose thickness is less than 50 nm, and the other is a Cr-rich Co-Cr medium whose thickness is sufficient for thermal stability. The Cr-rich Co-Cr medium, which shows a high S/N for a large medium thickness of over 100 nm, will contribute to the thermal stability of magnetic bits at future high recording densities of 10 Gbits/in/sup 2/ and beyond.