Kondo Response of a Single Antiferromagnetic Chromium Trimer

The triangular Cr trimer $\left({\mathrm{Cr}}_3\right)$ is a fundamental component in a number of frustrated, antiferromagnetic systems. We have used atomic manipulation and scanning tunneling spectroscopy to probe the local behavior of this basic magnetic substructure by fabricating and analyzing individual Cr trimers at the surface of gold. We find that Cr trimers can be reversibly switched between two distinct electronic states. This phenomenon can be explained as the Kondo response of a spin-switching, magnetically frustrated nanocluster. Such behavior is consistent with noncollinear magnetic states predicted for Cr trimers whose structures differ by the position of a single atom.