Structure and magnetism in thin films and multilayers of hexagonal ruthenium and iron

Abstract

The results of ab initio calculations for the electronic structure and the magnetic moments of unsupported hexagonal thin Ru and Fe films, bulk Ru and Fe metals, and ${\mathrm{Ru}}_{5}{\mathrm{Fe}}_{5}$ multilayer are presented with the focus on the crystallographic phase stability of the Fe layers. The calculated equilibrium lattice parameters of hcp Ru and Fe solids reproduce accurately the values found experimentally. For Ru/Fe multilayers it is demonstrated that in an Fe part of a multilayer an unusual hexagonal stacking with a distorted bcc-like local environment is more stable than the standard hexagonal close-packed stacking. The same result was obtained in thin Fe films and it is shown to be associated with band structure effects of Fe at the Fermi level. For thin films the ground state lattice parameters and magnetic states of films up to four monolayers were determined by total energy minimization. The faults in hexagonal planes stacking and interdiffusion do not lead to nonmagnetic Fe layers at the interfaces which were observed experimentally.