Dependence of readback output on medium thickness in the presence of a permeable underlayer--Part 1: General theory

The readback response of a perpendicular recording system utilizing a medium with a soft magnetic underlayer (SMUL) had been investigated using rigorous two-dimensional theory. The results are as follows. 1) Changes in the medium thickness (with a SMUL) effect radical changes in the wavelength response of the heads. 2) For a thin medium, the effective gap of a ring head becomes twice its geometrical gap. 3) The combination of probe head and medium with SMUL has adequate resolution only if the recording medium thickness is an order of magnitude less than probe thickness. 4) The foregoing combination has a potential advantage over longitudinal recording on conventional thin media with respect to the absolute value of readback output.