Exchange-coupled CoZrNb/CoSm underlayer for perpendicular recording media

The characteristics and effects of an exchange-coupled CoZrNb/CoSm underlayer for perpendicular recording media are reviewed. A CoSm layer pins CoZrNb domains via exchange coupling resulting from large induced radial anisotropy of the CoSm layer in the disk medium as well as in the CoZrNb layer. The number of CoZrNb domain walls is considerably reduced by the CoSm pinning effect which is effective in both signal stabilization to stray fields and noise reduction. Furthermore, the CoZrNb/CoSm underlayers exhibit high-frequency responses of over 1 GHz in permeability, which also result from their large induced anisotropy. The CoZrNb/CoSm underlayer is expected to enable the practical realization of perpendicular recording in data storage applications requiring high densities and high-speed data rates.