Determination of intrinsic switching field distributions in perpendicular recording media:: Numerical study of the ΔH(M,ΔM) method

We present a numerical study of the Delta H(M,Delta M) method and its ability to accurately determine intrinsic switching field distributions in interacting granular magnetic materials such as perpendicular recording media. In particular, we study how this methodology fails for large ferromagnetic intergranular interactions, at which point the associated strongly correlated magnetization reversal cannot be properly represented by the mean-field approximation, upon which the Delta H(M,Delta M) method is based. In this study, we use a two-dimensional array of symmetric hysterons that have an intrinsic switching field distribution of standard deviation sigma and ferromagnetic nearest-neighbor interactions J. We find the Delta H(M,Delta M) method to be very accurate for small J/sigma values, while substantial errors develop once the effective exchange field becomes comparable with sigma, corroborating earlier results from micromagnetic simulations. We furthermore demonstrate that this failure is correlated with deviations from data set redundancy, which is a key property of the mean-field approximation. Thus, the Delta H(M,Delta M) method fails in a well defined and quantifiable manner that can be easily assessed from the data sets alone.