Induced magnetic properties at isolated nonmagnetic atoms (Cd) attached to ferromagnetic Ni surfaces are found to be independent of the local symmetry and dependent on the number of nearest Ni neighbors. This dominance of coordination-number dependence as opposed to local symmetry could be studied on differently oriented surfaces at constant coordination numbers using perturbed angular correlation spectroscopy. Mediated by the localized sd-electron hybridization, the impurities form zero-dimensional magnetic units with their nearest Ni neighbors. We discuss this finding as basic research toward future applications with self-organizing patterned structures.

The magnetic behavior of isolated nonmagnetic probe atoms (Cd) at ferromagnetic Ni surfaces and interfaces have been studied using perturbed angular correlation (PAC) spectroscopy. Atomic resolution is achieved making it possible to distinguish between probe atoms at various surface sites, i.e., in/at terraces, atomic steps, kinks. These different atomic surface sites have differing Ni coordination numbers, (i.e., the number of Ni nearest neighbours). With decreasing coordination number, a continuous nonlinear dependent correlation was found with increasing magnetic hyperfine fields (Bhf). Furthermore, experimental evidence is presented, that the induced s-moments on the Cd isolated impurity is independent of the details of the surface symmetry but essentially determined only by the coordination number. Finally, it has been observed that monolayers of Pd on Ni form large unit cells, which offer selected sites to the Cd impurity. We discuss this finding as basic research towards future applications with self-organizing patterned structures.

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Magnetic properties of impurities at ferromagnetic surfaces and interfaces have been investigated performing Perturbed Angular Correlation (PAC) measurements in the ultra-high vacuum chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN) using different PAC probes. We present the measurements of magnetic hyperfine fields (B hf ) at 111 Cd probe atoms (i) in Pd covered by Ni, (ii) on Pd-decorated Ni surfaces, (iii) and on pure Ni surfaces at a variety of local structures like terraces, steps, kinks. The results yield a deep insight into the interplay of structural surface roughness and magnetic roughness on the atomic scale. Correlating the experimental B hf values with the number of their nearest Ni and Pd neighbours, the coordination number, nonlinear dependences were found. These findings are compared with recent theoretical studies which were prompted by the experiments.