Recording performance of double-layered perpendicular recording media with an antiferromagnetic layer

For a double-layered perpendicular media having an antiferromagnetic layer, it has been reported that increasing the exchange bias field H_ex is effective to reduce spike noise generated from the domain walls of the soft magnetic underlayer (SUL). In this study, a high exchange-coupling energy J_ex of 0.345 erg/cm² was obtained by using the combination of a NiFeB underlayer and a CoFeNiB enhancement layer. By investigating the effects of H_ex on the recording performance, it was revealed that increasing H_ex caused the writability of a head to deteriorate. However, reducing the nonmagnetic interlayer thickness, which reduces the magnetic spacing between the head and the SUL, could minimize the deterioration in writability. In addition, when the writability was unaffected by H_ex, the signal-to-media-noise ratio was improved by the effect of SUL domain noise reduction.