Modification of the perpendicular magnetic anisotropy of ultrathin Co films due to the presence of overlayers

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Abstract
In order to understand the effect of interfacial strain on perpendicular magnetic anisotropy (PMA) of ultrathin Co films, ex situ Brillouin light scattering measurements were performed for various overlayer materials. The samples were prepared by molecular beam epitaxy and Cu, Al, and Au were used as overlayer materials. We observed a decrease in PMA of the Co with the Cu and Al overlayers. In addition, we found an unexpected result that the PMA is significantly reduced when an Au overlayer of 35 Å is covered by an extra Al capping layer. The amount of this reduction depends on the thickness of the Al layer. Our results lead us to speculate that misfit strain at the interface between the Al and the Au can be propagated through the Au layer to affect the magnetic properties of Co.