Magnetic superlattices fabricated by monoatomic layer control

Co/Ru superlattices were prepared by monoatomic layer control through the use of molecular beam epitaxy technique. The Co and Ru thicknesses were varied in the range from 1 to 5 ML (ML: monoatomic layer thickness). Coherent layered structures have been confirmed for all the samples by X-ray diffraction. For the Co and Ru thicknesses equal to 1 ML, furthermore, transmission electron microscopy observation shows the formation of an ordered structure with hcp stacking of Co and Ru atomic planes. The magnetization measurements indicate that the effect of direct ferromagnetic contact between Co layers due to bridges is negligible even when the Ru thickness is reduced to 2 ML. Only 1 ML difference in the Co and Ru thicknesses has strong influence on the indirect exchange coupling of Co through Ru. First-principles calculations support the fact that the difference in Ru thickness critically affects the indirect exchange coupling.