Interlayer exchange coupling between FeCo and Co ultrathin films through Rh(001) spacers

Abstract

Using spin density functional theory (SDFT) calculations, we have studied the magnetic states, including collinear and noncollinear magnetic interlayer coupling, of ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}$ ultrathin films sandwiching Rh(001) layers. We found very large values for the interlayer exchange coupling (IEC) in $\mathrm{Co}/{\mathrm{Rh}}_{n}/\mathrm{Co}$ or ${(\mathrm{FeCo})}_{m}/{\mathrm{Rh}}_{n}/\mathrm{Co}$ structures as compared to, e.g., Ag or Au spacer layers. The IEC oscillates with the Rh spacer thickness showing a transition between strong antiferromagnetic and ferromagnetic coupling between five- and seven-layer thickness of the Rh film. Moreover, depending on the thickness of the FeCo film, a reorientation transition between in-plane and out-of-plane easy axis was found when spin-orbit coupling is considered in the calculations. This result suggests that, for specific arrangements such as ${(\mathrm{FeCo})}_{2}/{\mathrm{Rh}}_{5}/\mathrm{Co}$ structures, a competition between IEC and magnetic anisotropy of coupled films may result in noncollinear ordering. This possibility was studied with constrained, noncollinear SDFT calculations and the results were mapped onto a classical spin model to explore the richness of spin structures that can arise in these multilayer systems.