Magnetic parameter control for high-density quadrivalued MO recording (invited) (abstract)

Abstract

To increase recording density of MO media, several schemes have been proposed. Among them, magnetic multivalued (MMV) recording is one of the most promising methods. We have first realized the quadrivalued MMV media using a field modulation method. Such media is composed of an exchange coupled TbFeCo/PtCo bilayer. By switching the external field in four levels, the separated signal corresponding to the each field is obtained as a four leveled output. For the acutal device application for high-density and high-speed recording, it is necessary to reduce the external field as small as possible. In the previous experiment, about ±900 Oe was necessary to record the whole levels. For such MMV media, the quadrivalued signal response depends on the magnetic characteristics of the TbFeCo/PtCo bilayer, which is so called dual write state. The higher field level on the MMV media is defined by the threshold field of the dual write state. It is found that the threshold field is controllable to tune the magnetic parameter, especially the exchange coupling force between the TbFeCo and PtCo. As a result, the reduction of the recording field less than 350 Oe is realized on a new media. Using such tuned media, high-density quadrivalued recording is experimentally carried out.