Microscopic origin of large perpendicular magnetic anisotropy in an FeIr/MgO system

The FeIr/MgO multilayer system was found to exhibit large interfacial perpendicular magnetic anisotropy (PMA) and voltage-controlled magnetic anisotropy effects. We herein report the x-ray magnetic circular dichroism spectroscopy of both the Fe and Ir absorption edges in the FeIr/MgO system. Although Ir insertion at the Fe/MgO interface increased the PMA energy in the system, the orbital magnetic-moment anisotropy of Fe remained approximately constant. We found significant anisotropy in the orbital magnetic moment but not in the magnetic-dipole Tz term in the Ir atoms. Our experimental and theoretical results demonstrated that the large PMA of FeIr/MgO originates from second-order perturbation of the spin-orbit interaction energy of Ir. Moreover, the energy mainly originates from the spin-conserved virtual excitation process terms from the majority-spin bands of the Ir atoms located in the second atomic layer from MgO.