Ground-state magnetic properties of CoN clusters on Pd(111): Spin moments, orbital moments, and magnetic anisotropy
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abstract
The ground-state spin moments 〈Sz〉, orbitalmoments 〈Lz〉, and magnetic anisotropy energy (MAE) of CoN clusters deposited on the Pd(111) surface are determined in the framework of a self-consistent, real-space tight-binding method. Two-dimensional CoN/Pd(111) with N≤13 show remarkably large total magnetic moments per Co atom Mz = (2〈Sz〉 %2b 〈Lz〉)IN = (2.4-2.7) μB, which are the result of three physically distinct effects. The first and leading contribution comes, as expected, from the local spin moments 〈Siz〉 at the Co atoms i = 1-N [2〈Siz〉Co ≃ 1.7 μB]. Second, significant spin moments are induced at the Pd atoms i>N close to the Co-Pd interface, which amount to about 20%25 of Mz [2〈Siz〉pd = (0.2-0.3) μB]. Finally, remarkably enhanced orbital magnetic moments 〈Liz〉 are found that are responsible for approximately 20%25 of Mz. In the case of Co atoms, 〈Liz〉Co ≃ (0.3-0.5) μB is almost a factor of 3 larger than the Co-bulk orbital moment, while in Pd atoms 〈Liz〉Pd = (0.02-0.04) μB represents about 10%25 of the total local moment μiz = 2〈Siz〉 %2b 〈Liz〉. The dependence of the orbital moments on the orientation of the magnetization with respect to the cluster structure is quantified. These results and the associated MAEs are analyzed from a local point of view. One- and two-dimensional (2D) CoN are considered in order to investigate the structural dependence of the magnetic behavior. The role of the cluster-surface interactions is discussed by comparison with free cluster calculations. In particular, we observe that the lowest-energy magnetization direction (easy axis) changes from in-plane to off-plane upon deposition of 2D CoN on Pd(111). Cluster-substrate hybridizations are therefore crucial for the magnetoanisotropic behavior of magnetic islands deposited on metallic substrates.
