Ground-state magnetic properties of CoN clusters on Pd(111):: Spin moments, orbital moments, and magnetic anisotropy -: art. no. 094430

The ground-state spin moments [S-z], orbital moments [L-z], and magnetic anisotropy energy (MAE) of Co-N clusters deposited on the Pd(111) surface are determined in the framework of a self-consistent, real-space tight-binding method. Two-dimensional Co-N/Pd(111) with Nless than or equal to13 show remarkably large total magnetic moments per Co atom M-z=(2[S-z]+[L-z])/N=(2.4-2.7)mu(B), which are the result of three physically distinct effects. The first and leading contribution comes, as expected, from the local spin moments [S-iz] at the Co atoms i=1-N [2[S-iz](Co)similar or equal to1.7mu(B)]. Second, significant spin moments are induced at the Pd atoms i>N close to the Co-Pd interface, which amount to about 20% of M-z [2[S-iz](Pd)=(0.2-0.3)mu(B)]. Finally, remarkably enhanced orbital magnetic moments [L-iz] are found that are responsible for approximately 20% of M-z. In the case of Co atoms, [L-iz](Co)similar or equal to(0.3-0.5)mu(B) is almost a factor of 3 larger than the Co-bulk orbital moment, while in Pd atoms [L-iz](Pd)=(0.02-0.04)mu(B) represents about 10% of the total local moment mu(iz)=2[S-iz]+[L-iz]. 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) Co-N 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 Co-N on Pd(111). Cluster-substrate hybridizations are therefore crucial for the magnetoanisotropic behavior of magnetic islands deposited on metallic substrates.