Exchange coupled composite media for perpendicular recording

For conventional perpendicular recording media of saturation magnetization M_S and grain volume V, the ratio of the stabilizing energy barrier ΔE to the switching field H_S is ξ=2ΔE/(M_SH_SV)=1, in contrast to a value of 2 for the case of anisotropy axes tilted at an angle of 45°. This means only half the possible resistance to superparamagnetism is gained; it makes writability a serious problem for high density perpendicular media when a large anisotropy is used to compensate decreased grain size. To address this problem, an exchange coupled composite perpendicular recording media has been proposed that increases ξ by a factor of two, as in 45° tilted media, but reduces some of the difficulties, particularly in fabrication.