Effective permeability and imaging of multilayered soft films for perpendicular recording media

Thinner soft magnetic film layers show significant variation of effective permeability with wavenumber or magnetic recording density. When the magnetic material is divided between several equally thick soft layers, the effective permeability of the composite films is reduced, particularly at lower wavenumbers. At lower wavenumbers and low bulk film permeabilities, the imaging factor for soft magnetic multilayered films can be significantly reduced, making writing high coercivity media more difficult. For single pole heads, a two-dimensional analysis of writing on a perpendicular medium shows that these effects become pronounced at bulk film permeabilities less than 10. Effects on recording field gradients are much less.