Measurement of side-write, -erase, and -read behavior 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 neighboring tracks, and during reading in side fringing response and crosstalk. Side fringing fields have been analyzed theoretically but experimental verification of this phenomena is scarce. Measured values of actual track width, erasing width and crosstalk are reported. The measurements have been performed with specially manufactured disk heads with widths ranging from 10-50 μm. One set of heads was constructed similar to the 3330-II heads. Another set was constructed such that they resemble as closely as possible the shape of the theoretical head that is used as a model. Some heads were locally narrowed by laser machining. 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 agrees 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 15μm. 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 as the head is shifted across its own track at different wavelengths). The curves agree with theory except for the presence of "side lobes."