Magnetic properties of ultrathin FexCo(1-x) films on Pt(111)

Abstract

The magnetism of 1-ML-thick films of Fe(x)Co(1−x) on Pt(111) was investigated both experimentally, by x-ray magnetic circular dichroism and magneto-optical Kerr effect measurements, and theoretically, by first-principles electronic structure calculations, as a function of the film chemical composition. The calculated Fe and Co spin moments are only weakly dependent on the composition and close to 3µ(B)/atom and 2µ(B)/atom, respectively. This trend is also seen in the experimental data, except for pure Fe, where an effective spin moment of only Seff=(1.2 ± 0.2) µ(B)/atom was measured. On the other hand, both the orbital moment and the magnetic anisotropy energy show a strong composition dependence with maxima close to the Fe(0.5)Co(0.5) stoichiometry. The experiment, in agreement with theory, gives a maximum magnetic anisotropy energy of 0.5 meV/atom, which is more than 2 orders of magnitude larger than the value observed in bulk bcc FeCo and close to that observed for the L10 phase of FePt. The calculations clearly demonstrate that this composition dependence is the result of a fine tuning in the occupation number of the d(x^2−y^2) and d(xy) orbitals due to the Fe-Co electronic hybridization.