Search

Thermal decay in magnetic recording media increases with time, consequently decreasing the signal-to-noise ratio. A recently developed scaling technique, based on the equivalence of time and temperature within micromagnetics, has been used to predict bit decay over long time scales. An ideal square-wave field is used to record bits in thin film magnetic recording media. Comparison of bit thermal stability for longitudinal and perpendicular thin film media with similar KuV/kT is carried out at recording densities from 50 to 400 Gbit/in.2. Bit decay in a Co/Pd superlattice film at ∼100 Gbit/in.2 is also studied.

A scaling technique is developed to predict micromagnetic properties of magnetic materials subject to thermal fluctuations over long time scales. This theory, based on the equivalence of time and temperature for thermally activated processes, is tested by predicting hysteresis loops for two different thin film magnetic recording media. A comparison to directly calculated values and to experimental hysteresis loop results shows that important features such as the coercivity are predicted with less than 1% error.

A micromagnetic model with realistic grain configuration (planar Voronoi cells) is developed to simulate perpendicular magnetic recording media. The model is applied to an experimental Co/Pd superlattice film. The calculated perpendicular hysteresis loop exhibits a coercivity of 6560 Oe, in approximate agreement with the experimental value. It is found that the coercivity is largely invariant to grain irregularity, but the initial switching field depends greatly on grain size uniformity for ideally oriented material. In particular, an assumption of uniform grains produces a knee in the hysteresis loop that is not found with the more realistic Voronoi grains or in experiment.

In this second part of the work, the MAGPAR micromagnetic/finite element model was reused to investigate the physics of the write and erase processes in perpendicular recording. The damping constant needed in the Landav–Lifshitz–Gilbert equation was found by applying the Klaassen nonlinear eddy current damped model and set to be 0.1. Previous work highlighted the fact that domains were formed in the soft magnetic underlayer (SUL) under the writer pole in regions where the field opposes the SUL magnetization direction. The domains participate in flux closure and help a more linear response out of the return pole that enhanced fields with an overshoot and opposite polarity relative to the main pole field. These return pole fields could cause adjacent track erasure and MAGPAR was used to study the physics behind it. Particular attention was given to the analysis of frequency or time dependent effects caused by flux delays from the slow moving SUL domains (between the main and return poles). In contrast, fast...

A comprehensive analysis of the areal density potential of bit-patterned media recording shows that the recording performance is dominated by written-in errors. The statistical fluctuations of the magnetic properties and the locations of the individual bits lead to error probabilities so that some dots are either not recorded at all or cannot be recorded in the time window necessary to ensure synchronized writing. The highest areal densities are obtained with a combination of a pole head, a soft magnetic underlayer, and a storage medium of the composite type. Areal density scenarios of up to 5Tbits∕in.2 are analyzed.

Incomplete magnetization switching may take place between two recorded transitions in perpendicular magnetic recording. These write process issues were studied with a micromagnetic model. The relatively poor effective field from the central part of the perpendicular writer is unable to reverse the media grains properly. Consequently, media dc noise will increase as the incomplete switching becomes more severe. An expression for the effective field heff was proposed to easily discover those cases. The incompletely switched magnetization observed in the static footprint could also be partially transferred into the dynamic write process. The calculated media signal-to-noise ratio on a pseudorandom sequence could be reduced by as much as 3dB (compared to the fully switched case). On the other hand, transition quality does not become worse with a smaller heff. This insensitivity to the transition quality was caused by the magnetostatic field from the opposite magnetization polarity on the other side of the rec...

A readback model is developed to study characteristics of perpendicular recording media with a soft underlayer. The model is applied to an experimental perpendicular recording media represented by Voronoi cells. The readback voltage from this model shows dependence both on the transition length and the fly-height separately. A roll-off curve produced from reading continuous, perfect arctangent transition media is compared to experimental results to obtain the transition length and the fly height. The calculated autocorrelation signal to noise ratio (SNR) from the model with Voronoi grain based media compared to those obtained from a particular example shows cluster forming with areas equal to about three times the grain size. This reduces the media SNR by about 4.7 dB. This readback model therefore allows SNR measurement to be converted to detailed understanding of the media structure.