Observation of Magnetic Domains in Thin-Film Heads by Electron Microscopy

Magnetic domains were observed using an image lock-in technique for backscattered electron contrast (type II) with a JEOL 2000FX-II 200 kV electron microscope. A thin film head without a protective layer was excited by applying a 10 mAp-p 100 kHz driving current. Backscattered electrons were synchronously detected by using a diode detector and a lock-in amplifier, and images were acquired digitally using a LINK eXL-II system. The backscattered electrons detected under conditions of changing acceleration voltage revealed a difference in the magnetic domain configurations in the upper and lower parts of the upper pole piece. Since the location of a pair of black and white lines in a synchronous mode indicates the maximum limit of domain wall movement in one driving current period, the observed difference must have been caused by the difference in domain wall movement, that is, the difference in magnetic flux flow. Inversion of the domain configuration between the upper and lower parts was also observed and is one possible cause of noise-after-write.