Nanoscale magnetism probed by nuclear resonant scattering of synchrotron radiation

Time-resolved nuclear resonant scattering of synchrotron radiation is applied to determine the spin structure of magnetic nanostructures on surfaces. From the temporal beat pattern the magnitude and the direction of magnetic hyperfine fields in the sample can be determined. We describe an algorithm to extract the magnetic structure function from a series of such measurements at different sample orientations. This reconstruction technique is applied to study the remanent spin structure of relaxed Fe islands on the surface of a W(110) single crystal. Unexpectedly, we find two orthogonal magnetic sublattices oriented along the in-plane [001] and $\left[11¯0\right]$ directions in a proportion of 4:1. This spin structure appears to be independent of capping layers that consist of Ag or C. A completely different spin structure is found for a different shape distribution of the islands. These results are discussed in terms of magnetic anisotropies that are present in this system. Moreover, the results demonstrate that the outstanding brilliance of present-day synchrotron-radiation sources allows one to determine the magnetic spin structure of magnetic clusters and nanoparticles on surfaces with sensitivities reaching into the monolayer regime.