Physics and Astronomy Calendar

Nanoscale magnets are attractive model systems for studying fundamental spin interactions. These structures are also being used to increase data storage capacities and are promising candidates for implementations of novel spin-based computation techniques. The imaging, manipulation, and spectroscopy capabilities of scanning tunneling microscopes (STMs) make them versatile tools for studying nanoscale structures with atomic resolution. Through the use of a spin-polarized tunneling current, the STM can image the spin orientation of two-dimensional layers and small magnetic islands. At the single-atom level, the STM has been used to detect the Kondo interactions between conduction electrons and a single adsorbed impurity spin. In-situ atomic manipulation can further be used to construct magnetic dimers and trimers, which display evidence of coupled-spin behavior

By placing magnetic atoms on a thin insulating layer above a metal substrate, we can isolate atomic spins from the underlying conduction electrons and still perform STM studies. Using the atomically precise manipulation capabilities of the STM, we can now build individual magnetic structures one atom at a time on copper nitride, a well-characterized isolating surface. With STM-based inelastic spectroscopy, we then measure the spin excitation spectra of individual structures in-situ and follow the evolution of the spectra as additional atoms are added. We observe excitations of the coupled atomic spins that can change both the total spin and its orientation. Comparison with a model spin-interaction Hamiltonian yields the collective spin configuration and the strength of the exchange coupling between the atomic spins.