High-moment FeCo-IrMn exchange-coupled soft underlayers for perpendicular media

Ferromagnetic/antiferromagnetic coupled multilayers provide a unique solution to several problems found with soft underlayers for perpendicular media. Properly designed, they demonstrate outstanding characteristics: a unique single-domain remanent direction, reversible hysteretic behavior over a wide angular range, optimum permeability (mu)~100, and high saturation flux density 4(pi)M/sub s/. Initially, FeTaN-IrMn multilayers were prepared with these characteristics and a target ferromagnetic thickness of 200 nm, but 19 total layers were required and they were thermally unstable. These problems were first overcome by replacing FeTaN with high-anisotropy Fe/sub 10/Co/sub 90/, although 4(pi)M/sub s/ was reduced from ~19 to ~16 kG. Further work, however, revealed that soft anisotropic Fe/sub 65/Co/sub 35/ films with an induced anisotropy field H/sub k/ of 30 Oe and 4(pi)M/sub s/~23 kG could be successfully produced on Cu, NiFe, Ru, Ta-Cu, TaNiFe, or Cu-IrMn underlayers. An optimized structure was found to be glass/Cu(20 nm)/IrMn(10 nm)/[Fe/sub 65/Co/sub 35/(50 nm)/IrMn(10 nm)]/sub 4//Fe/sub 65/Co/sub 35/(25 nm). Furthermore, postannealing will allow the number of layers to be reduced from 11 to 7.