Analysis of Magnetic Cluster Size Distributions from AC Erased Noise Spectra

We have developed a method of analysis to estimate magnetic cluster size distributions, including average size and size deviations through spin-stand testing. To statistically analyze the ac-erased magnetization distribution, the autocorrelation functions of the magnetization distributions were derived from readback media noise spectra. The cluster size distributions were quantified from the autocorrelation function by utilizing the undershoot value as well as the zero-crossing shift length. By analyzing a series of capped granular perpendicular media, we observed that the average cluster size increased when the cap layer was thick, while the size deviations decreased. This trend agrees well with the results obtained from the minor loop analysis. This method is useful for developing media because measuring is easy, fast, and can be used for various kinds of recording media under a variety of conditions. The relationship between transition jitter and the average magnetic cluster size revealed that reducing the cluster size distribution while keeping writability high was important to achieve high areal density recording.