Energy barriers in composite media grains

Thermal stability is critical for magnetic grains in high density recording applications. Composite media grains consisting primarily of a hard and soft layer with intergrain exchange coupling are examined. Here it is shown, as in single domain particles, that power laws, to a good approximation, describe the field dependence of the energy barrier. In general, the power law exponent decreases with increasing relative moment and/or decreasing relative anisotropy of the soft/hard subgrain. Results for a variety of medium parameters as well as grain orientations are given. Index Terms--Coercivity time dependence, magnetic grains, magnetic reversal, multilayer media, perpendicular recording, thermal energy barriers.