Universal thermal decay produced by time scaling in magnetic films and recording media

Abstract

The logarithmic relaxation of the magnetisation in recording media under different applied negative fields can collapse onto an universal decay curve, by applying a scaling law based on the fluctuation field Hf, which describes the time-dependent magnetic behaviour in terms of thermal effects. In this work the scaling approach is investigated, in which multiple measurements of thermal decay curves in varying holding fields are scaled via the fluctuation field in order to reproduce the long-time decay of magnetisation. The scaling technique is tested using a numerical model of a granular perpendicular media and then applied to experimental data. Scaling is shown to be successful for systems of multiple layers of soft (Ni) and hard (Co) magnetic materials, coupled by a Pt interlayer and for CoCrPt granular recording media systems. Based on a dataset of decay curves in negative fields, the data lifetime of magnetic recording media can be quantified, this representing an important factor for media design and production.