Low-Noise Co-Cr Perpendicular Medium with High Cr Content

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Abstract
We investigated the noise reduction mechanism of a Cr-rich Co72Cr28 perpendicular magnetic recording medium. By increasing the Cr content from 22 at% to 28 at%, the signal-to-noise ratio at a recording density of 70 kFCI was increased from 25 dB to 31 dB. The medium noise was reduced more than the magnetic parameters, such as MS and HC⊥. When the average crystalline diameter of the media increases, the medium noise of the Cr 28 at% medium does not increase, whereas that of a Cr 22 at% medium increases. Analysis of a medium with a Ti under-layer shows that the Δθ50 does not have any significant effect on the medium noise. To analyze the noise of these media, we introduced ΔM⊥ measurement method that takes account of the demagnetization field. The ΔM⊥ value is related to the medium noise. The relation is different from that of longitudinal medium. Analysis of the minor loops showed that the Cr 28 at% medium has low noise due to its highly stable dc-erased state. MFM observation for 4-μm-wide dc-erased tracks confirmed the mechanism for smaller reversed magnetic domains in a Cr 28 at% medium than in a Cr 22 at% medium. This mechanism contributes to the low noise of the Cr-rich Co-Cr single-layer perpendicular medium.

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