A spin-stand level Dynamic Read-back Microscopy (DRM) technique (first described in [1]) offers versatility, ease of use and full compatibility with standard media parametrics testing. We designed and implemented a DRM tester based on a LeCroy DDA5005 oscilloscope and a Guzik spin-stand. High resolution and stability was achieved primarily by using servo and on-disk recorded data trigger. Data recording and imaging is made by a commercial magneto-resistive head with variable scanning (flying) height. Fig. 1 shows a DRM image of a 900kfci square-wave pattern on a perpendicular magnetic recording (PMR) medium [2]. (Higher densities can actually be resolved but with lower contrast and the image is modulated by the magnetic clusters.) The read gap is ～70nm and a down-track resolution <30nm is readily achieved. The magnetic read width is ～0.12μm which presumably reduces resolution along the cross-track direction. However, fine magnetic cluster features under 50nm can also be resolved outside the track. Within the track, the magnetic domains are broken by stable recorded transitions that are narrower than the average cluster size. Using a DRM, we investigated the effect of magnetic exchange coupling on side erasure of CoCrPt-SiO PMR media. Exchange was controlled by varying the oxygen partial pressure PO{sub}2 during deposition. Figs. 2 and 3 show tracks after a progressive edge-trimming from the both sides using a low DC-negative erase current. For a high-exchange medium A (PO{sub}2=0.37mTorr), the original rectangular recorded bit magnetization shape becomes trapezoidal after a 40% squeeze (Fig. 2). As a DC field was used, rise time effects can be excluded. The transitions seem intact so reversal is occurring mostly at the middle of the bits where the demagnetizing field is the highest. With a shielded-pole head, the side fringing fields at the gap are at an angle relative to the track direction which may explain the "squeezed" bit shape. Fig. 3 shows that the low-exchange medium B (PO{sub}2=0.75mTorr), is significantly more robust to aggressive side erasure. We have also looked at the effect of phase on track side erasure. Fig. 4 shows a middle track trimmed from each side by a pattern 180° out of phase on medium B. This phase difference results in maximal side erasure efficiency with a clearly defined erase band. More results on media with a wide range of PO{sub}2 (0.37 to 0.75mTorr) will be reported in the paper.
展开▼
