Heat-assisted magnetic recording (HAMR) is the next generation hard disk drive technology that enables continued and significant areal density growth. There are currently two common architectures for the layout of tracks in hard disk drives: conventional magnetic recording (CMR) and shingled magnetic recording (SMR). In CMR, any track can be written at any time and neighboring tracks do not intentionally overlap. In SMR, the tracks are written sequentially in bands with the tracks intentionally overlapping like shingles on a roof. In this paper, we introduce a novel track layout, interlaced magnetic recording (IMR), and apply it to a HAMR recording system. With heat-assisted IMR, we observed a 31% increase in areal density over HAMR CMR whereas in a HAMR SMR architecture, we observed a 27% increase in areal density over HAMR CMR.
Heat Assisted Magnetic Recording (HAMR) is the next generation hard disk drive technology which enables continued and significant areal density growth [1]. As the track pitch continues to scale down, the HAMR reader must continue to scale. The scalability of the current reader technology is greatly challenged at high track densities [2]-[3]. With significant growth in areal density, the reader width must reduce with high signal to noise ratio (SNR) to avoid side reading from adjacent tracks. Typically, there is a tradeoff between reader width and SNR [4]-[5]. For HAMR areal density to continue to scale, innovations to enable reader width reduction without SNR degradation are necessary. Traditional reader head media spacing (HMS) reduction and reader width scaling may not be enough to improve the reader resolution for high track pitches. In this paper, we compare the areal density capability (ADC) of HAMR Conventional Magnetic Recording (CMR) and HAMR Shingled Magnetic Recording (SMR) at various reader clearances with integrated HAMR readers and cross tested (CT) narrow high SNR readers.
Differences in the areal-density capability limits for heat-assisted magnetic recording (HAMR) and conventional perpendicular magnetic recording (PMR) are explored using spinstand measurements, drive footprinting, and micromagnetic modeling. The written track curvature is measured with a special technique that mitigates the cross-track averaging effects due to a finite read sensor width. Tracks written with HAMR heads are shown to have more curvatures compared with those written with modern PMR writers. Mitigation of written track curvature is demonstrated with two different HAMR writer designs. The curvature effect appears to challenge not only the downtrack bit resolution during readback, but also the cross-track written width with increased linear density (LD). Experimental measurements of a constant bit error rate for different LDs and track densities (TDs) indicate a significant opportunity for high TD 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.
This study aims to investigate the impact that factors such as skew, radius, and transition curvature have on areal density capability in heat-assisted magnetic recording hard disk drives. We explore a “ballistic seek” approach for capturing in-situ scan line images of the magnetization footprint on the recording media, and extract parametric results of recording characteristics such as transition curvature. We take full advantage of the significantly improved cycle time to apply a statistical treatment to relatively large samples of experimental curvature data to evaluate measurement capability. Quantitative analysis of factors that impact transition curvature reveals an asymmetry in the curvature profile that is strongly correlated to skew angle. Another less obvious skew-related effect is an overall decrease in curvature as skew angle increases. Using conventional perpendicular magnetic recording as the reference case, we characterize areal density capability as a function of recording position.
Finite-size scaling is utilized to study the erasure mechanism in heat-assisted magnetic recording (HAMR). Predicted scaling equations are evaluated both numerically and experimentally by using the write current-assist percentage (WCAP) method. The method estimates the erasing temperature of an external magnetic field by writing and erasing magnetization patterns at different frequencies. In particular, WCAP modeling shows that the Curie temperature scales according to the time scale that the recording grain is exposed to the elevated temperature. The deviation of the erase temperature from T c for different values of the applied field is also used to estimate the scaling behavior of the anisotropy field H k and the critical exponent β. In addition, the Stoner-Wohlfarth model is shown to be an accurate approximation for field angle dependence of the erasing process for the FePt media. Faster roll-off in the effective field is observed at small angles for the thermal ECC media.
The dependence of CoPt stabilization properties on surface topography and seedlayer thickness has been investigated. The coercivity degrades drastically without a Cr seed, showing a dependence upon surface angle. Using the resulting data wafer level sensor structures are micromagnetic simulated. Poor seedlayer coverage on the junction edge yields open transfer curve loops and degraded sensor response.
We present results from a high-density giant magnetoresistive magnetic recording reader using exchange bias stabilization. This novel reader design approach reduces the amount of parasitic resistance, as the sense current is not delivered through high resistivity permanent magnets. Heads were demonstrated to deliver areal densities in excess of 24 Gb/inch/sup 2/. The electrical performance of these heads, in particular, amplitude sensitivity, microtrack profiles and areal density capability are presented. Reader film properties and manufacturability of this approach are discussed in detail.
Recording curvature in magnetic data-storage technology has long been one of the significant challenges impacting on recording performance. Despite curvature occurrence in the conventional recording techniques such as perpendicular magnetic recording (PMR), heat-assisted magnetic recording (HAMR) is demonstrated to induce much more severe curvature than PMR. HAMR curvature could cause poor bit error rate and limits the maximum areal density capacity. Here we have theoretically predicted and demonstrated various approaches for curvature reduction from the aspect of either altering the near-field transducer head design or recording medium design. Optical and thermal modeling have indicated that by utilizing a crown-shape peg to change the thermal source profile and compensate for thermal expansion and rounding effect, it could potentially improve curvature figure of merit (FOM) and achieve curvature reduction by ~45%. In terms of the recording media design, by altering the heat sink and internal layer media material or geometry, it could also achieve curvature cancellation of ~40% with increased thermal gradient. The combined approach from both HAMR head and media perspectives with balanced recording FOMs, could potentially realize significant curvature reduction to be of similar or better recording curvature level to PMR.
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