A Micromagnetic Study of the Effect of Spatial Variations in Damping in Perpendicular Recording Heads

We have used micromagnetic modeling to study the effect of the gyromagnetic damping constant, alpha, on the dynamics of a perpendicular write head. Cases are considered where different regions of the head have different values of alpha, to examine where increased damping might offer benefits in head field rise time. It is found that increasing alpha in the pole region from 0.02 to 0.2 significantly improves both field rise time and amplitude at a drive frequency of 1 Gb/s. Similar increases in the damping of the yoke region and in the soft underlayer (SUL) did not yield nearly as significant improvements in field magnitudes or rise times, but was associated with reduced noise from the SUL. It is also noted for a monopole head design, that a SUL with higher magnetization-thickness product, M_St, is needed to achieve the desired field amplitude as compared to a shielded pole head. An improvement in the gradient of the field is observed for the shielded head design along with a reduction in the field magnitude