Strongly Enhanced Orbital Moment by Reduced Lattice Symmetry and Varying Composition ofFe1−xCoxAlloy Films

Abstract

We studied tetragonally distorted Fe(1-x)Co(x) 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_(3,2) edges we found a dependence of the Co magnetic orbital moment on the chemical composition of the Fe(1-x)Co(x) 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.

High magnetic moments and anisotropies forFexCo1−xmonolayers on Pt(111)

“…53 and a significantly smaller one for 6-ML-thick FeCo films on Rh͑100͒ close to the equiatomic composition ͑1.8 B ͒. 7 An evident discrepancy between theory and XMCD data exists in the case of pure Fe for which we measured a strongly reduced effective spin moment of S eff = ͑1.2Ϯ 0.2͒ B vs 3.0 B found by theory. The experimental value is also substantially lower than 2.5 B reported in FePt nanoparticles 54,55 and multilayers.…”

“…[5][6][7] Our experimental and theoretical results dem- onstrate an out-of-plane MAE for the FeCo films. However, a clear discrepancy exists for the pure Fe film MAE which is found out of plane in the experiments and predicted in plane by the calculations.…”

“…Until now, large MAE values have been predicted and experimentally observed only in distorted FeCo-bct bulk, respectively, several monolayers thick films. [5][6][7] In a combined experimental and theoretical study we demonstrate that 1-ML-thick Fe x Co 1−x films grown on Pt͑111͒ possess both very large M S and MAE values compared to most ferromagnetic materials.…”

“…Bimetallic alloys represent a viable route to tune both M S and the MAE, as these quantities are strongly influenced by compositional effects and lattice distortions. While the MAE of ferromagnetic transition metals in their cubic structures is on the order of a few tens of eV/ atom, structurally distorted alloys, such as FePt in the L1 0 phase [2][3][4] or bct-FeCo, [5][6][7] may have MAE values close to 1 meV/atom. Moreover, the total magnetic moment can be tuned by choosing the two elements of the alloy.…”

First-principles study of thermodynamical properties of random magnetic overlayers on fcc-Cu(001) substrate

“…There are no experimental data for the present sys-tem to compare with although FeCo-overlayers on various non-magnetic substrates (Cu,Pd,Rh) were studied often with the aim to estimate the magnetic anisotropy energies [4][5][6] . Also, there are no doubts on the importance of a parameter-free approach to estimate T C of imperfect ultrathin magnetic overlayers (see, e.g., a recent review 7 ).…”