High Track Pitch Capability for HAMR Recording

Differences in the areal density capability limits for heat-assisted magnetic recording (HAMR) and conventional perpendicular magnetic recording (PMR) are explored using spinstand measurements and micromagnetic modeling. The written track curvature and the transition width are measured with a special technique that mitigates cross-track averaging effects due to finite read sensor width. Tracks written with HAMR heads are shown to have more curvature compared with those written with modern PMR writers. Both broadening and transition curvatures are present cross track, that can be described reasonably well using Landau-Lifshitz-Gilbert modeling and indicates the effective gradient profile dominates. However, as we get to the track edge, we see disagreement between the model and the experiment, which is not currently reconciled. The curvature and broadening effects appear to challenge not only the downtrack bit resolution during readback, but also the cross-track written width with increased linear density. We discuss different near field transducer (NFT) designs, and comparing narrow versus wide thermal profile NFT designs, we can see that track pitch appears to weakly optimize to a maximal cross-track gradient point. Experimental measurements of constant bit error rate for different linear and track densities indicate a significant opportunity for high track density recording using HAMR. The difference appears to be related to the ability for HAMR to address high track pitches with a minimal increase in risk of adjacent track interference compared with PMR. We revise NFT head-to-media spacing requirements when we attempt to account for interference effects.