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C 23 The CoPtCr-SiO2 medium shows great potential for high-density perpendicular magnetic recording, as it displays excellent signal-to-noise ratio (SNR) characteristics together with high thermal stability. However, significant bit percolation, involving a partial combination with the neighboring magnetic bits, has been observed at a high linear recording density, and has been shown to degrade the magnetic-recording patterns. On the other hand, it is known that the magnetic cluster size is a significant factor limiting the linear recording. Therefore, in this paper, we have investigated the relationship between magnetic cluster size and the recording bit length at which bit percolation begins to occur in a CoPtCr-SiO2 perpendicular magnetic-recording medium to the range of 1500 kfci. According to our experiments using perpendicular recording media with four types of recording layers, which determine the magnetic properties, high-resolution magnetic-force microscopy patterns indicate that the bit length at which percolation begins to occur is almost the same as the magnetic cluster size. These results suggest that the bit length with percolation, which determines the limit of the recording density, can be improved by decreasing the magnetic cluster size of the medium. Bit-Percolation Studies on CoPtCr-SiO2 Perpendicular Magnetic-Recording Media