L. Niebergall

Spin-Dependent Quantum Interference Within a Single Magnetic Nanostructure

Wave-Particle Duality The dual-wave nature of particles is nowhere more evident than in a confined space, where standing waves are formed with wavelengths that depend on particle energy. This so-called quantum interference has been observed in nanostructures using surface probes such as scanning tunneling microscopy. Now, Oka et al. (p. 843) use the spin-polarized version of this technique to study spin-dependent quantum interference on a triangular nanoscale cobalt island deposited on a copper surface. They observe the modulation of the magnetization, with the pattern depending on the energy of the interfering electrons. The experimental results are in good agreement with simulations, which indicate that the magnetization at a given energy and position largely depends on which of two electron spin states present dominates. Magnetization modulation is observed on a cobalt nanoisland using spin-polarized scanning tunneling microscopy. Quantum interference is a coherent quantum phenomenon that takes place in confined geometries. Using spin-polarized scanning tunneling microscopy, we found that quantum interference of electrons causes spatial modulation of spin polarization within a single magnetic nanostructure. We observed changes in both the sign and magnitude of the spin polarization on a subnanometer scale. A comparison of our experimental results with ab initio calculations shows that at a given energy, the modulation of the spin polarization can be ascribed to the difference between the spatially modulated local density of states of the majority spin and the nonmodulated minority spin contribution.

Ab initio study of mirages and magnetic interactions in quantum corrals.

The state of the art ab initio calculations of quantum mirages, the spin polarization of surface-state electrons, and the exchange interaction between magnetic adatoms in Cu and Co corrals on Cu(111) are presented. We find that the spin polarization of the surface-state electrons caused by magnetic adatoms can be projected to a remote location and can be strongly enhanced in corrals, compared to an open surface. Our studies give clear evidence that quantum corrals could permit one to tailor the exchange interaction between magnetic adatoms at large separations.

Ab Initio approach for atomic relaxation in supported magnetic clusters

We present a newly developed scheme for atomic relaxations of magnetic supported clusters. Our approach is based on the full potential Korringa–Kohn–Rostoker Greens function method and the second moment tight-binding approximation for many-body potentials. We demonstrate that only a few iterations in ab initio calculations are necessary to find an equilibrium structure for supported clusters. As an example, we present our results for small Co clusters on Cu(001). Changes in the electronic and magnetic states of the clusters due to atomic relaxations are revealed.

Effect of quantum confinement of surface electrons on adatom?adatom interactions

The quantum confinement of surface-state electrons in atomic-scale nanostructures is studied by means of the Korringa?Kohn?Rostoker (KKR) Greens function method. We demonstrate that the surface-state mediated interaction between adatoms can be significantly modified by the quantum confinement of surface electrons. We show that quantum corrals and quantum mirrors constructed on metal surfaces can be used to tailor the exchange interaction between magnetic adatoms at large distances. We discuss the self-organization of adatoms on metal surfaces caused by quantum confinement.

New insights into nanomagnetism: spin-polarized scanning tunneling microscopy and spectroscopy studies

We perform low-temperature spin-polarized scanning tunneling microscopy (SP-STM) and spectroscopy measurements in magnetic fields to gain new insights into nanomagnetism. We use the magnetic field to change and control magnetizations of a sample and a magnetic tip, and measure the magnetic hysteresis loops of individual Co nano-islands on Cu(111). We also exploit the high spatial resolution of SP-STM in magnetic fields to measure maps of the differential conductance within a single Co nano-island. In connection with ab initio calculations, we find that the spin polarization is not homogeneous but spatially modulated within the nano-island. We ascribe the spatial variation of the spin polarization to spin-dependent electron confinement within the Co nano-island.