Element-specific magnetism at the atomic scale is important in low-dimensional materials such as thin magnetic films and quantum dots, where interfacial and surface effects can give rise to novel behavior. However, probing magnetism specific to the topmost atomic layer remains a key experimental challenge. Here, we introduce a synchrotron x-ray scanning tunneling spectroscopy approach that enables detection and quantification of surface magnetism via x-ray-excited electron tunneling. By illuminating a scanning tunneling microscope tip-sample junction with circularly polarized x-rays tuned to the Ni $L_{2,3}$ absorption edges, ensemble-averaged and surface atomic-layer x-ray magnetic circular dichroism are simultaneously measured on a $\sim 2.5$-monolayer-thick Ni film grown on a Cu(111) surface. Measurements are performed at substrate temperatures of 90 and 22 K. The results reveal enhanced orbital and spin magnetic moments in the outermost atomic layer as compared to the ensemble-averaged moments of the thin Ni film at both temperatures. This work establishes an experimental method for quantitative, element-specific magnetometry with atomic-layer sensitivity using x-rays.

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• Magnetic order
• Methods in magnetism
• Ferromagnets
• Magnetic systems
• Magnetic thin films
• Scanning tunneling microscopy
• X-ray absorption spectroscopy
• X-ray magnetic circular dichroism