Prediction of spike noise based on soft underlayer energy minimization

An energy minimization and balancing approach was adopted to predict the occurrence of spike noise by obtaining estimates of the magnetostatic and total wall energy of a soft underlayer (SUL) for a given configuration of domain walls. We find that single-layer SULs (thicknesses of 100-200 nm) are usually sources of spike noise unless their saturation magnetization is below 70-100 emucc. However, the use of such low-moment SULs is unacceptable in perpendicular recording. One solution that has been advocated is a multilayer SUL structure with C, Ta, etc., interlayers. Our predictions show that the ground state of a 200-nm double-layer FeCoC SUL is completely spike-free.