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)78Pt22 which have high-anisotropy field (Hk). 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 uf 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/m2 and beyond.
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