Ac-bias recording and Preisach diagrams

Abstract

Preisach diagrams can be useful for modeling the magnetic properties of particulate media. On such diagrams, magnetic applied fields are supposed to have a well-determined direction. However, in magnetic recording processes, the applied magnetic fields change both in magnitude and direction. We report an extension of the well-known coherent switching mode for fine particles that makes possible the definition of an effective longitudinal applied field which depends on both longitudinal and transverse components of the externally applied field. The possibilities of Preisach diagrams are explored in the case of reasonably well-aligned particulate media, and a model of ac-biased magnetic recording for such media is presented. It is shown that, knowing the longitudinal and transversal profiles of magnetic head fields and the magnitude of the writing current, it is possible to determine the zones of Preisach diagrams, which correspond to dipoles switched + or −, and the zone corresponding to the unaffected dipoles, which remain in the initial state. The effect of angular dependence of particle switching fields is naturally included, and magnetic remanence in the direction perpendicular to alignment may be obtained whenever the Preisach diagram is also available for that direction.