James H. Giusti

Micromagnetic study of effect of media intergranular exchange interaction in perpendicular recording

A micromagnetic study is performed for the writing and reading processes in perpendicular recording at high areal densities. In particular, the effect of intergranular exchange interactions in media is examined. Calculations are done for three different values of intergranular exchange coupling. The calculated media hysteresis loops show that the saturation magnetic field increases when exchange becomes weaker. The writer deep gap field is chosen to be equal to the saturation field so that proper overwrite is assured. Modeling shows that the magnetic cluster domain size becomes larger and the readback signal exhibits larger variation at its peaks when exchange constant increases. The variation of readback signal at its peaks in square wave perpendicular recording is primarily due to the variation of bit cell length of written patterns. On the other hand, transition curvature increases when exchange constant decreases. Although on-track isolated pulse width of a differentiated signal is not affected much b...

Exact calculation of demagnetization field in micromagnetic simulation of shielded read heads

In micromagnetic simulation of shielded GMR heads, the self-demagnetizing field is usually calculated under the assumption that the two shields extend to infinity beyond the air bearing surface. Under this assumption, the demagnetization tensor for rectangular cells in free space and the method of images are used to calculate the self-demagnetizing field in the sensor. An unanswered question for this approach is how accurate it is. In this work, the Fourier series method is used to calculate the self-demagnetizing field of the sensor in the shielded environment exactly. Simulation results from this rigorous approach and the common approach are compared for both simple spin valve and synthetic antiferromagnet (SAF) biased spin valve heads. It is shown that the error of the common approach is very small for a SAF spin valve head and can be as large as 10% for a simple spin valve head.

Design Of High Density Dual Stripe MR Heads Using A Thermal Transmission Line Model

A thermal transmission line model is described and used to study the performance of high track density dual stripe magnetoresistive (DSMR) recording heads. The model was calibrated to actual thermal and signal amplitude data by adjusting sensor material properties. Signal sensitivity per unit track width from the preamp are shown to improve by decreasing the sensor thickness. Further improvement with track density is predicted for smaller aspect ratios. For a square active region (aspect ratio =1.0) no degradation in signal sensitivity was seen up to approximately 19 ktpi.

Optimization of PM stabilization for balanced sensitivities and variations of spin valve heads

The control of variations of amplitude and symmetry of synthetic antiferromagnetic spin valve heads becomes increasingly difficult with the shrinking of head sizes. Micromagnetic Monte Carlo simulations were carried out to investigate the correlations between different head parameters and head performance variations. It was found that the head performance variation is strongly correlated with the permanent magnet stabilization strength. In addition, the magnetization orientation of the reference layer in the biasing state varies more from head to head than that of the free layer, when the sizes of the spin valve heads are in the deep-submicron range. The conflict between the head sensitivity and the head performance variation is clearly shown by the modeling results.

Hybrid transmission line-micromagnetic model for MR heads

A hybrid transmission line-micromagnetic model for a shielded MR read head is described. In this model, the magnetostatic potentials and magnetization orientation angles in the magnetic films of a sensor stack satisfy the transmission line and micromagnetic equations. This coupled system of partial differential equations is solved by a finite difference method with nonuniform mesh. The magnetic flux entering the sensor from the media or permanent magnets are calculated by reciprocity. The hybrid model is found to agree closely with a conventional micromagnetic model for magnetization distributions in the sensor.