Activation volume and interaction of metal particulate media

We have investigated the activation volume (Vac) and magnetostatic interaction of metal particulate (MP) media. The activation volume of MP media decreases with the decrease of physical volume (Vphy) of metal particles. The activation volume and the ratio of Vphy/Vac of advanced metal particles are 6×10−24 m3 and 1.5, respectively. It can be predicted that the physical volume of metal particle is about 3×10−24 m3 when the physical volume is equal to the activation volume. This value is agreement with the practical lower limit of physical volume of metal particle predicted by Sharrock. The negative interaction (demagnetization effect) in MP media decreases with low saturation magnetization of the metal particles, a thin magnetic layer, a high orientation of MP media, and a low packing fraction of metal particles in the MP media. The activation volume of the MP media decreased as the negative interactions decreased. In advanced MP media with low Mr·t (Mr=remanent magnetization and t=thickness), the influence of interaction on the activation volume is reduced.