(A) Study on grain refinemnet and thermal stability improvement in longitudinal recording meida

Abstract

An increase of areal density can be achieved only if the medium SNR is increased. This requires a magnetically separated smaller grain and a smaller transition width. To reduce transition width, low $M_r t$ is also required in addition to a small grain size. As a result, as a grain size is reduced, energy barrier for magnetization reversal becomes smaller and thus thermal instability of written information is induced. Thus, the combination of SNR and thermal activation of small grains limit the potential areal density of the longitudinal recording media. Thus, this thesis is focused on a study on grain refinement and thermal stability improvement in longitudinal recording media. In the first part, since magnetic properties and microstructure of magnetic layer depend strongly on microstructure of its underlayer, a novel VMn underlayer has been studied to reduce grain size and to improve magnetic properties of magnetic layer. It was found that VMn underlayer had (002) preferred orientation and finer and more uniform grain size compared with pure Cr underlayer. Also, the coercivity of magnetic layer on VMn underlayer was higher than that of magnetic layer on Cr underlayer. Contrary to the grain size of underlayer, however, the grain size of CoCrPt/VMn film was larger than that of CoCrPt/Cr film, due to the diffusion of Mn from VMn underlayer into magnetic layer. To use the fine and uniform grain of VMn underlayer, a CrMo intermediate layer as diffusion barrier layer was inserted at interface between magnetic layer and VMn underlayer. The CoCrPt/CrMo/VMn film showed fine and uniform grain size. The CoCrPt/CrMo/VMn film applied sub-bias voltage showed high coercivity. This implies that CoCrPt/CrMo/VMn type longitudinal media may be a good candidate for high density recording. In second part, the effects of Co or CoCr-alloy interlayer on interlayer exchange coupling and thermal stability of AFC medium have been studied. In case of the conventional AFC medium,...