Delayed relaxation in thin-film heads

The delayed relaxation after writing with a Permalloy thin-film head has been studied experimentally. The phenomenon of delayed relaxation is shown to be caused predominantly by stress-induced relaxation of the flux closure domains along the edges of the thin-film-head yoke. It is necessary for this effect that the composition of the Permalloy yields nonzero magnetostriction. The fairly rapid temperature change directly after write will then trigger irreversible wall displacements which show up as transient noise pulses in the head output. Depending on the actual edge domain relaxation, these transients can have a positive or a negative polarity, or can be bipolarity transients. This thermomechanically triggered irreversible wall-motion process can fairly accurately be modeled as a Poisson process. The model predicts the arrival time distribution, the probability of occurrence for different write currents, and threshold settings reasonably well. This `noise-after-write´ effect can be made smaller by striving for zero magnetostriction and a lower write power dissipation, and to some extent by increasing the thermal conductivity to the slider