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Abstract
Several issues related to the optimization of write heads and media for ultra high density and data rate magnetic recording are analyzed in this thesis.
On the writing side, the tapered neck pole with a very small throat height has been suggested for ultra-high density perpendicular recording. An optimal write-pole design must fit the following criteria. (1) The down-track field and field gradient must be sufficiently large to write high anisotropy (HK) media with sharp transitions. (2) The off-track field must decrease very quickly to avoid erasure of neighboring tracks. (3) The remanent field should be small enough to prevent overwrite of the previous written data. (4) The switching speed must be 0.2–0.5 ns for high data rate recording (>1Gbit/s). (5) The skew effect should be limited, or a solution found for small skew angle. Our micromagnetic simulations show that by utilizing a tapered neck pole with a very small throat height optimizes these conditions and therefore is a good candidate for ultra-high density perpendicular recording.
On the media side, tilted perpendicular (TP) recording has been proposed as an effective method for ultra-high density and ultra-high data rate magnetic recording. The central design includes a medium anisotropy direction tilted at a certain angle, optimally about 45°, with respect to the perpendicular direction. The main effect is that a medium with much higher anisotropy can be utilized as compared to conventional perpendicular (CP) recording. For a given thermal stability criterion, a much smaller medium grain diameter can be utilized. Both analytical and numerical analyses show that at a fixed density, there is approximately a 10 dB gain in SNR for TP media vs. CP media. TP recording allows for a higher data rate than CP recording, due to enhanced reversal torque. TP recording also provides a narrower erase band and therefore a larger track density due to increased grain energy stability at the track edges. The specific analyses at the 1 Tbit/in2 density point will be presented, including the effects of inter-granular exchange and anisotropy distributions.
A simple energy surface model has been developed, combined with micromagnetic simulations, to analyze the damped gyro-magnetic switching phenomena in a single domain particle. We show that for small damping and a fast applied field rise time, the switching field can be lower than the Stoner-Wohlfarth (S-W) value. The minimum switching field, depending on both the damping and the initial magnetization configuration, can in fact be well below the S-W value. For a small applied field angle, the switching time decreases with decreasing field magnitude up to a limit approximately equal to HK. For a large applied field angle, the switching time is fast and does not depend on the system damping. These results are consistent with both micromagnetic simulations and experimental data. The results suggest that a reduced applied field can be utilized for ultra high density (low reverse field to write on high HK media) and ultra high data rate (fast switching) magnetic recording applications, such as Magnetic Random Access Memory (MRAM), tilted and conventional perpendicular recording.
