Exponential Dependence of Interlayer Exchange Coupling in Fe/MgO(001) Superlattices on Temperature

The interlayer exchange coupling in Fe/MgO(001) superlattices is found to increase exponentially with decreasing temperature. Around 150~K, the field induced response changes from discrete switching, governed by field-driven domain propagation, to a collective rotation of the magnetic layers. This transition is accompanied by a change in the magnetic ground state from 180${}^{\circ }$ (antiferromagnetic) to 90${}^{\circ }$ alignment between adjacent Fe layers. These effects are argued to arise from quantum well states, defined by the total thickness of the samples.