Analysis of Adjacent Track Erasure for the HAMR Media

Abstract

Writing tracks narrowly spaced in the crosstrack direction appears to increase the User Areal Density (UAD), but can lead to erasure of the adjacent tracks. This phenomena is called Adjacent Track Erasure (ATE). Our research aims to establish the numerical extent of ATE and introduce efforts to reduce this ATE for different HAMR media. This research can help increase the HAMR storage density by making HAMR media resistant to ATE. The ATE in HAMR is limited to tracks immediately adjacent to the track being overwritten [1]. For a single write, we have previously found that the optimum track spacing between these tracks to maximize the UAD for a noise free reader is 70% of the heat spot FWHM [2]. By implementing micromagnetic simulations, we find the single layer FePt media is more susceptible to ATE as its thickness decreases. The 3nm-6nm high temperature Thermal ECC media [3] has a slightly higher ATE susceptibility compared to the 9nm single layer FePt media. In contrast the 3nm-6nm low temperature Thermal ECC media [4] has a significantly higher ATE susceptibility (Table 1). To reduce the ATE, we change the applied field angle and introduce exchange coupling between grains of the media. The single layer FePt media ATE is impervious to the applied field angle although the ATE reduces as the field angle reduces for the high temperature Thermal ECC media. The ATE reduces for the single layer FePt media and the high temperature Thermal media with optimized exchange coupling (IGC) values. The ATE for the single layer FePt and high temperature Thermal ECC media using these optimization techniques is shown in Fig. 2. Both these optimization techniques however do not sufficiently improve the ATE susceptibility for the low temperature Thermal ECC media. We believe the ATE is proportional to the thermal stability factor at a temperature just below the write temperature. This hypothesis correctly predicts the ATE in the single layer FePt media assuming coherent rotation. For Thermal ECC media, other mathematical techniques that capture incoherent rotation can be used to verify this hypothesis.