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A structural and magnetic study of interfacial spin coupling in Fe-MgO ferromagnetic-dielectric thin film composites


Metal-oxide heterostructures that couple ferromagnetic spin polarization and dielectric polarization have received much attention for their potential use in novel spintronics devices, such as spin valves and low power memories. The application of an electric field to a dielectric substrate results in an internal electronic polarization and a reduction in the applied external field, similar to the behavior of a traditional capacitor. It is currently believed that this screening phenomenon unevenly distributes free surface charge between majority- and minority- spin states in the adjacent ferromagnetic layer, creating an interfacial spin polarization.

A model system of Fe-MgO was studied to better understand this mechanism. Early first principles calculations have predicted that the formationof a Fe-O oxide will affect the free electron density at the film-substrate interface. Preliminary transmission electron microscopy (TEM) studies have also confirmed the presence of this oxide in nearly all Fe-MgO films. It may be possible to tune the composition of the oxide and adjust the interfacial defect population to control magnetoelectric coupling. To do so it is necessary to examine both the spatial and magnetic structure of the composite.