Zero field relaxation measurements in magnetic recording media

Thermal relaxation of the magnetization is a critical issue in ultra-high density recording media. The thermal stability is typically characterized by measuring the time dependence of the coercivity or by measuring the magnetization decay as a function of the reverse field after saturation. The relaxation is usually given in terms of a magnetic viscosity coefficient. The viscosity is usually greatest near the coercivity, and for large thermal stability factors, it is usually very small in zero applied field. We have recently reported zero field relaxation (ZFR) measurements in a variety of films, including longitudinal media, perpendicular media, and particulate films The measurements were made in zero field as a function of the initial remanent magnetization obtained after applying a saturation-reverse-zero field sequence.