Long-range interlayer exchange coupling in [Fe/MgO]_N (100) superlattices: the impact of the Fe thickness

To explain sequential switching in Fe/MgO superlattices, beyond nearest neighbor interactions need to be included, despite the tunneling mediated interlayer exchange coupling (IEC). Fe/MgO superlattices can be described as coupled quantum wells created by the Fe layers, potentially forming collective electronic states responsible for the long-range nature of the IEC. Previous studies have investigated the influence of the MgO thickness and bilayer repetitions N on the coupling and Fe layer switching. These relate to the barrier width and number of quantum wells, respectively. Here, we further examine the effect of the quantum well extension, in terms of the Fe thickness, on the overall magnetic properties of the superlattices. Using a combination of magneto-optical Kerr effect measurements and polarized neutron reflectometry, we investigate the sequential switching of the individual Fe layers. The coupling strength increases linearly for Fe layer thickness between 12 and 23 Å for MgO barriers of 17 Å. The results shed more light on the physics behind the tunneling mediated coupling Fe/MgO superlattices, highlighting how coupled quantum well states in artificial magnetic structures can affect their mesoscopic magnetic properties.