Strongly enhanced orbital moment by reduced lattice symmetry and varying composition of Fe1-xCox alloy films

We studied tetragonally distorted Fe1-xCox alloy films on Rh(001), which show a strong perpendicular anisotropy in a wide thickness and composition range. Analyzing x-ray magnetic circular dichroism spectra at the L-3,L-2 edges we found a dependence of the Co magnetic orbital moment on the chemical composition of the Fe1-xCox alloy films, with a maximum at x = 0.6. For this composition, we observed an out-of-plane easy axis of magnetization at room temperature for film thickness up to 15 monolayers. Since both the magnetic orbital moment and the anisotropy energy show similar composition dependence, it confirms that both quantities are directly related. Our experiments show that the adjustment of the Fermi level by a proper choice of the alloy composition is decisive for the large magnetic orbital moment and for a large magnetic anisotropy in a tetragonally distorted lattice.