Exact calculation method for medium field from a perpendicular medium

An exact calculation method for the medium field from a perpendicular magnetic recording medium with a soft underlayer was derived. The new method utilizes the Fourier series expansion, and the derived equation converges to the equation for the medium without a soft underlayer in the limit of infinite distance between the head surface and the soft underlayer. The new method, when combined with a micromagnetics simulation of the medium and the giant magnetoresistive head, provides a useful tool for the analysis of the read back signals in perpendicular magnetic recording.