Theoretical study of the onset of magnetism in (Fe)x/(Ru)xsuperlattices

The electronic and magnetic structure of (Fe${)}_{\mathit{x}}$/(Ru${)}_{\mathit{x}}$ (x being the number of atomic planes in each layer) hexagonal-close-packed superlattices has been investigated by self-consistent spin-polarized linear-muffin-tin-orbital–atomic-sphere-approximation calculations for x ranging from 1 to 5. It is shown that for x=1 no magnetic order exists due to the strong hybridization between the Fe and Ru atoms. For larger thicknesses several magnetic phases appear, with a ferromagnetic, antiferromagnetic, or ferrimagnetic ordering within each layer. The total energies of these phases are very close to each other, and the ground state depends upon x. Comparison is made with the available experimental results on (Fe${)}_{\mathit{x}}$/(Ru${)}_{\mathit{y}}$ samples grown by molecular-beam epitaxy.