Considerations for high data rate recording with thin-film heads

The significance of head inductance and eddy currents in limiting field rise times is discussed. Poor rise times can cause severe distortion and loss of performance at high data rates. A simple reluctance model is developed to explore the relationship between the geometry of a head and its inductance. The model is extended to include the effects of eddy currents, and to allow the frequency-dependent efficiency (hence the field rise time) to be calculated. Based on this rise time, a geometric model is used to calculate the positions of the recorded transitions and the resulting transition-shift distortion. Experimental results at transition separations down to 6 ns reveal a strong write current dependency which is not seen in the model. This dependence is, however, clearly seen in a simple domain wall model which implicitly includes magnetic saturation. Transition shift distortion can be mitigated by the use of precompensation. It is found that it is possible to successfully recover data at 180 Mbit/s using a conventional thin-film head