Magnetic anisotropy of iron chains embedded in copper

We investigate the magnetic ground states of iron inclusions embedded in fcc copper using first principles calculations. Of main interest are linear monatomic chains of atoms aligned along different directions in a Cu matrix. The method of calculation we employ is the locally selfconsistent multiple scattering (LSMS) real space method for solving the LDA Kohn-Sham-Dirac equation. We have extended our code to perform fully relativistic calculations to enable us to investigate the spin-orbit coupling effects leading to anisotropic and potentially noncollinear ordering of magnetic moments in these systems of iron inclusions in copper. With this approach we find that the magnetocrystalline anisotropy in systems of magnetic iron chains embedded in copper strongly prefers an orientation of the magnetic iron moments perpendicular to the direction of the chain. This competes with the magnetostatic energy of the chains, which is lowest when the moments are aligned parallel to the chain. Our parameter free calculations suggest that, depending on whether the chains of magnetic atoms are embedded in copper along the 100 or 110 directions, the ground state orientation of the magnetic moments on the iron sites can be either parallel or perpendicular to the chain, due to the balance of these competing effects.