The role of Fe-doping on structural and magnetic properties of Fe nanoclusters in thick Yb films

• Fe-nanoclusters embedded in Yb films have been prepared by vapor co-deposition.
• For the highest Fe concentration a very weakly interacting clusters was found.
• Clusters stay superparamagnetic down to 3 K for low Fe concentrations.
• The average ratio of orbital to spin magnetic moment of Fe atoms decreases with increasing Fe-content.

Structural and magnetic properties of co-deposited (x   at.% Fe)Yb (0.3≤x≤5.00.3≤x≤5.0) films have systematically been investigated by X-ray absorption spectroscopy, 57Fe Mössbauer spectroscopy, magnetization measurements, and Ferromagnetic Resonance (FMR) experiments. Mössbauer and magnetization data indicate formation of two types of Fe clusters that are supposed to be at grain boundaries in fcc- and hcp-like Yb structures. Clusters stay superparamagnetic down to 3 K for low Fe concentrations x. For the highest studied Fe concentration x=5.0 we find blocking behavior typical for only very weakly interacting cluster magnetic moments with blocking temperature of ca. 7 K. EXAFS can only resolve one type of Fe–Fe and one of Fe–Yb nearest neighbor coordination, both with a lack of long-range structural order. While the coordination number of Fe increases and that of Yb decreases with increasing Fe concentration (as expected for a growing size of Fe clusters), the nearest neighbor distances remain practically unchanged for different Fe content. Estimated cluster sizes are on the order of nm. FMR experiments suggest that the average ratio of orbital to spin magnetic moment of Fe in (x at.% Fe)Yb films decreases with increasing x thus indicating the decreasing contribution from the fraction of Fe atoms on the cluster surfaces.