Measurement of side-write, -erase and -read behaviour of conventional narrow track disk heads

Narrow-track recording heads suffer from wavelength-dependent side-fringing effects. During writing these manifest themselves in track widening and erasing of neighbouring tracks and during reading in side-fringing response and cross-talk. Side fringing fields have been analyzed theoretically [1] but experimental verification of these phenomena is scarce. Actual track-width, erasing-width and cross-talk have been measured with specially manufactured disk heads with widths ranging from 10-50 μm. Actual track-width was measured as a function of write-current amplitude at low recording-density (no pulse crowding) and as a function of wavelength at optimum write- -current amplitude. The measured track-widening confirms with theory and can be as high as 5 μm at either side of the head at optimum write-current and low pulse-density. Track widening decreases with decreasing wavelength. The distance from the head side at which the head still effectively erases can be as high as 10 μm. In a disk drive this will be the factor that limits the track density. Inter-track read-crosstalk is determined by measuring the displacement curve (i.e. the curve representing the read signal versus position when the head is shifted across its own track at different wavelengths). The curves confirm with theory except for the presence of "side lobes". We intend to report on these measurements in the near future in this Journal.