Magnetic properties, recording performance, and thermal stability of CoTb amorphous/CoCrPt granular composite media are discussed. Thermal stability at low recording density of the composite media with CoCrPtB improves significantly as CoTb thickness increases, in accord with the increase of loop squareness, M r/M s. The media having CoTb thickness of more than 6 nm show almost no signal decay. Moreover, the signal-to-medium-noise ratio, SNR, improves with increasing CoTb thickness up to 6 nm. CoTb(6 nm)/CoCrPtB(20 nm) medium shows the best SNR performance under the present experimental conditions with no thermal decay. Media noise of the composite media with CoCrPt increases super linearly from ∼300 kfci, which is caused by the percolation of the recorded bits, probably due to the strong exchange coupling in the CoTb layer. The media with CoCrPtB shows less media noise than that with CoCrPt, and the super-linear increase of this media noise starts at ∼400 kfci which is higher than that of the media with CoCrPt. It is thought that the well-segregated grain structure of CoCrPtB layer, having the enhanced and fine distribution of M s, reduces the magnetic cluster size effectively, resulting in the reduction of the media noise.
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