A two-dimensional, dynamic, micromagnetic model of a thin strip of permalloy is described and used to model the magnetization dynamics of the strip as it is subjected to a transverse step field. The numerical results are compared to experimental data. The experimental precession frequency is matched by varying H k , the longitudinal, uniaxial, magnetocrystalline anisotropy field. The damping is matched by varying ␣, the phenomenological damping parameter in the LLG equation. A good fit to the data was obtained with a single damping constant of ␣ϭ0.013.

A dynamic micromagnetic model which includes gyromagnetic effects (via the Landau–Lifshitz equation) and eddy currents has been developed and applied to the rise time problem in thin film write heads. A cross-section of the part of the head covering the coils is simulated with this model, while the rest of the head is modeled as saturable reluctances. The reluctances do not include eddy currents, but they do include leakage, fringing and saturation, and allow for computation of the deep gap field. This model is used to study the details of the dynamics of the magnetization in the yoke as well as the dependence of rise time on geometric and material parameters. It is found that switching starts at the surfaces of the pole and moves inward in “transition zones.” Also, if rise time is defined as the time it takes the deep gap field to reach 7 kOe, the rise time increases with pole thickness but decreases with saturation magnetization and driving current.

Multiple techniques have been developed and used to characterize the width of a written track in perpendicular recording. This work investigates written tracks using the WPE (write plus erase) test based on writing the main track at a given density and trimming both sides of the track multiple times with another density. The edge of the original track, after each trimming step, is characterized by a narrow band measurement of the read-back signal as a function of cross-track position. The use of a narrow band filter improves the test SNR and helps separate the track into 2 sections: A good region (track center) and a degraded region (track edge). Test and micro-magnetic analysis were used under multiple linear densities for the main track and for the trimming tracks. The results indicate that the WPE value decreases as the density increased between 200 kfci and 1500 kfci. For densities lower than 200 kfci and higher than 1500 kfci, the WPE value does not change significantly. When the main track was fixed at 200 kfci, increasing the trimming density resulted in a higher WPE. Using a micro-magnetic model and spin-stand tests, it is demonstrated that the apparent increase in WPE is caused by a region with opposite polarity at the edge of the main track (in the media) produced by the magneto-static (demagnetization) field generated by the main track. The section with opposite polarity is found to be coherent with the main track. During the read-back process, the field from the opposite polarity region in the media is integrated by the reader (read sensitivity function) and subtracted from the main track signal. The result is a loss in signal at the track edge that yields a larger WPE value. This phenomenon could have a direct impact on shingled recording.

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