Collective thermal fluctuations in nominally "independent" granular recording media: Application to thermal decay

We present initial results of a study of a system of fine magnetic grains w ith resonance interactions. For the case of magnetostatic and exchange inte ractions a general criterion for collective magnetization motion of a pair of grains is derived. Simulations demonstrate a dynamic cluster structure i n both longitudinal and perperndicular recording media. These clusters may significantly reduce thermal degradation of recorded patterns. An indirect interaction between grains through an antiferromagnetic substrate is also d iscussed.