The micromagnetics of thin-film disk recording tracks

This paper, for the first time, illustrates the details of the recorded tracks of thin film disks written with film heads flying 1600-2600 Å above the disk surfaces. The magnetic medium was a thin film of Fe-Co-Cr alloy with a Mrt of 2.8-2.9×10^-3emu/cm²and a coercivity of 450-490 Oe. Readback signals were carefully taken from the tracks. They were then studied micromagnetically using ferrofluid decoration and Lorentz electron microscopy techniques. The bit pattern was essentially a series of isolated single domains with alternate magnetization along the circumferential direction of the disk. The transition zone consisted of sawtooth shaped, head-on domain walls. Bit shift, readback signal asymmetry, and the amplitude modulation due to overwrite were directly observed on the tracks microscopically. It was concluded that these phenomena could be related to the writability of the head with respect to the media.