Recent advances in metal particulate recording media: Toward the ultimate particle

The rapid evolution of particulate coatings ensures their continuing dominance in data recording tapes and flexible disks. The leading material is the metal particulate composition, known as MP, The advent of highly sensitive heads (MR and possibly GMR) has made small particle size a high priority in MP development, because the media-limited signal-to-noise ratio depends upon the number of particles per recorded bit. This trend to smaller size will ultimately be limited by insufficient thermal magnetic stability of the particles. An Arrhenius-Neel switching model can be used, together with the dependence of the experimental coercivity N-c on held duration, to determine an effective switching volume. This volume agrees well with the particle volume, as determined by transmission electron microscopy (TEM), for recently developed MP particles, but is somewhat smaller than the TEM volume for earlier ones. The model predicts that the practical lower limit of particle size in current MP technology is about 3 to 4 x 10(-18) cm(3). Volumes can therefore be reduced by 2- to 3-fold from those of the most advanced current particles, and by 6- to 10-fold from those generally used commercially, before approaching the thermal stability limit predicted by the model. This reduction would be expected to give an improvement in signal-to-noise ratio of 8 to 10 dB, relative to current data recording tapes.