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 Co72Cr28 and (Co72Cr28)(78)Pt-22 which have high-anisotropy field (Hr). The write demagnetization increased when a shorter write gap was used, The high S/N value for the Cr-rich Co-Cr medium does not decrease even for a large medium thickness of 100-300 nm; however, the S/N of the Co-Cr-Pt medium decreases with increasing thickness. To obtain a high S/N 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, mill contribute to the thermal stability of magnetic bits at future high recording densities of 10 Gbits/in(2) and beyond.