Flux reversal time in thin film write heads: A nonlinear system theoretic approach

Large amplitude write currents elicit a nonlinear frequency response from t hin film write heads. Saturation of the yoke structure causes the measured inductance to be a simultaneous function of both frequency and amplitude. D ensity plots are used to study the change in inductance over a two dimensio nal input parameter space comprising ac write current frequency (1 < f < 50 MHz) and dc write current amplitude (0 < I < 60 mA). A simple lumped eleme nt reluctance model representing such coupled behavior is proposed. The mod el extends quasistatic measurements that indicate a quadratic relation betw een the input magneto-motive force and the magnetic flux in the yoke struct ure. The circuit consists of a nonlinear reluctance element, described by a Volterra series, connected in series to a linear inductive element. The su perposition theorem allows an analytic estimation of the flux reversal time for increasing write current amplitudes. A typical thin film write head th at exhibits a quadratic dependence of flux on write current amplitude is an alyzed. The model predicts a 30% decrease in flux reversal time over that p redicted by a linear model as the amplitude of a stepped input write curren t is increased by a factor of 10. (C) 1999 American Institute of Physics. [ S0021-8979(99)09909-0].