Signs of Budding Magnetism in Atom-By-Atom Designed Spin Structures

The regime between ~5 and ~100 coupled spins marks the transition region between quantum and classical magnetism. Harboring the mysterious beginnings of many bulk magnetic phenomena, this regime is frustratingly difficult to access, both experimentally and computationally. In our research we use STM atom manipulation combined with local electron tunneling spectroscopy as a way to chart this promising region. By arranging Fe atoms on a Cu₂N surface we can both detect and control magnetic anisotropy as well as spin coupling between neighboring atoms. In chains comprising as few as five atoms, we start to see signs of magnetic reversal at timescales in the order of seconds. Numerical calculations reveal that delocalized spin wave states play an important role in the switching dynamics of the chain.