Time-Resolved Domain Dynamics in Thin-Film Heads

Abstract

A new magneto-optic imaging technique was used to investigate the dynamics of magnetization response in thin film head yokes. Completed head devices were excited with a sinusoidal current applied to the integrated coils. The amplitude (20 to 40 mA pp) and frequency (1 to 50 MHz) of excitation were chosen to simulate the write process. Pulsed laser illumination permitted stroboscopic observation of domain-wall and flux-flow dynamics with a time-resolution 1imited only by the 5 ns pulse width (FWHM). Results suggest that high-frequency write performance is degraded by two mechanisms not considered previously for thin-film heads: first, 180° walls appear to impede the flux· flow across the plane of the wall, and second, the inhomogeneous rotational magnetization response observed here is known to be much slower than the typically assumed coherent rotation. The effect of NiFe composition on dynamics was also investigated by comparing responses of two heads, one having positive, the other negative magnetostriction, Flux in the head with positive magnetostriction flows in a constricted path along yoke edges, rather than its center, consistent with the signif· icantly lower efficiency measured electrically for this head. © 1990 IEEE