Micromagnetics of a soft underlayer

The micromagnetic properties of a soft underlayer in perpendicular media are studied. It is shown that stray fields from a recording layer can substantially modify magnetic properties of soft underlayer material. The degree of modification is determined by the characteristic bit size in the recording layer and by the soft underlayer material magnetic characteristics. It is found that there exists a thin layer within a soft underlayer with reduced permeability. The effects of the presence of such a reduced permeability region within a soft underlayer on both reading and writing processes are discussed.