The energy barriers in antiferromagnetically coupled media

We study the physics of the energy barriers for magnetization reversal in antiferromagnetically coupled (AFC) media by means of temperature dependent magnetometry as well as modeling. We find that the energy barrier of the lower layer is fairly low, and mainly given by its anisotropy–volume product (KV). This means the lower layer magnetization is actually in thermal equilibrium, but the presence of the interlayer coupling makes the state with AF alignment of both layers thermodynamically so much more probable, that AFC media are thermally stable overall. The model further predicts that for typical values of the exchange coupling constant, the energy barrier of the composite system at zero field is essentially equal to the upper layer KV with the additional energy from the interlayer coupling being only a small perturbation.