To explore recording head challenges for perpendicular recording at 200 Gb/in/sup 2/ and beyond, the design, fabrication and performance of narrow track dual-element heads were studied using an ABS trailing shield writer design and a conventional CIP-GMR reader design. Parametric recording tests of these heads on low noise CoCrPt/SUL media show that, with the trailing shield design, good writability and low disk transition jitter around 2.5 nm were achieved at narrow write trackwidths down to 120 nm. In addition, peak-to-peak signal amplitudes around 1 mV and T/sub 50/ widths around 28 nm were also achieved at read trackwidths around 60 nm. The areal density potential of these heads was studied using a PRML channel at /spl sim/50 MB/s data rate. Results show linear densities around 1000 Kbpi at ontrack byte error rates of 10/sup -4/, and track densities around 200-240 ktpi using a criterion of 15% offtrack to trackpitch ratio. In all, areal densities of 210-230 Gb/in/sup 2/ were achieved with these head and disk components.

High-resolution magnetic force microscopy (hrMFM) has been used to investigate the write characteristics of forward and reverse flying heads on perpendicular recording media with soft underlayers. hrMFM has the advantage that it provides much better resolution than the read element of a head, particularly in the cross-track direction. Using a quantitative analysis method, many parameters, such as transition position jitter, transition width and signal-to-noise ratio are estimated from the hrMFM image. Furthermore, these parameters, which can also be measured using a spinstand, are compared to the micromagnetic properties of the transitions, such as track curvature, transition width and the local noise associated with transitions. The results give insights into the recording physics and, in particular, in the write process of shielded and un-shielded write heads in perpendicular recording.

A study has been conducted on the characteristics of the reversal dynamics for a perpendicular recording system consisting of a pole head, a recording layer, and a soft under layer (SUL) using time-resolved Kerr microscopy. It was found that the local step response as well as the 2-D magnetization distribution of the SUL in the pole area during reversal depend on the initial magnetization state of the recording layer. This phenomenon can cause pattern-dependent nonlinear timing shifts of the write process. The precessional frequency of the SUL response also differs for the two initial states. In the 2-D time-slices of the magnetization reversal we find evidence for the generation of spin wave modes which can limit the achievable data rate.

Adjacent-track interference (ATI) in a dual-layer perpendicular recording system arises during both writing and reading. During writing, the stray fields from the write head can cause side writing and side erasure. A dc-erase method using media with a low nucleation field is used to identify the extent and polarity of these fields. In media with a strong anisotropy in the soft underlayer (SUL), experimental results reveal that the fields causing ATI have a strong cross-track asymmetry due to interactions between the writing flux and the magnetization of the SUL. On readback, cross-track amplitude profiles taken at long wavelengths show a distinctive "side bump" predominantly on just one side of the track profile. This asymmetry is again found to be associated with the magnetization in the SUL. A theoretical study yields expressions for the lateral extent of the side reading and a critical bit length at which side reading becomes significant. Both of these are consistent with experimental observations. The onset of side erasure during writing is further equated with the time-dependent nucleation field of the medium. Theoretical arguments on thermal decay in the presence of external and demagnetizing field indicate that the threshold for ATI-associated side erasure is expected to follow a time dependence similar to Sharrock's formula for dynamic coercivity.

A cross-track noise profile measurement is developed for identifying the source of adjacent-track interference (ATI) fields in perpendicular recording systems. The noise amplitude as a function of cross-track position and write current clearly delineates the extent, magnitude, and polarity of stray fields under different portions of the head. Experimentally obtained stray field strength relative to writing field is in good agreement with finite element modeling. For given head and disk components, the composite picture of noise amplitude for both writing field and stray fields as a function of write current also provides a way of selecting an optimal write current with respect to the medium dynamic coercivity, saturation, and ATI threshold. Further investigation on the asymmetries in the noise profiles have led to two interesting discoveries. The first is an asymmetry in ATI field that can be attributed to the polarity of the radially oriented magnetization in the soft underlayer. The second is an artifact associated with the change in read head sensitivity around track edges due to fields from the dc-erased hard recording layer.