Analysis of overwrite spectrum in perpendicular magnetic recording

In the overwrite process, overwrite noise is caused by both incomplete erasure of the old magnetization data (non-saturated overwrite recording) and the modulation of the write magnetic field by the old magnetization. The overwrite modulation of the post-recording signal is caused by easy/hard transition shifts on the pre-recorded signal. From theoretical analysis, it was indicated that the frequency components generated from easy/hard transitions appear only around the even harmonics of the post-recording signal as the sideband having odd harmonics of the pre-recorded signal, while non-saturated overwrite spectrum is characterized by the sideband around the odd harmonics of the post-recording signal. The dominant source of overwrite noise was experimentally distinguished by the locations of the frequency components of the reproduced overwriting signal. The change from non-saturated overwrite to a modulated one was observed with increasing the overwrite head current.