M. C. Muñoz

Magnetic states at the Oxygen surfaces of ZnO and Co-doped ZnO

First principles calculations of the O surfaces of Co-ZnO show that substitutional Co ions develop large magnetic moments which long-range order depends on their mutual distance. The local spin polarization induced at the O atoms is 3 times larger at the surface than in the bulk, and the surface stability is considerably reinforced by Co. Moreover, a robust ferromagnetic state is predicted at the O (0001) surface even in the absence of magnetic atoms, correlated with the number of p holes in the valence band of the oxide, and with a highly anisotropic distribution of the magnetic charge even in the absence of spin-orbit coupling.

Effect of Spin-Orbit Interaction on a Magnetic Impurity in the Vicinity of a Surface

We propose a new mechanism for surface-induced magnetic anisotropy to explain the thickness dependence of the Kondo resistivity of thin films of dilute magnetic alloys. The surface anisotropy energy, generated by spin-orbit coupling on the magnetic impurity itself, is an oscillating function of the distance d from the surface and decays as 1/d2. Numerical estimates based on simple models suggest that this mechanism, unlike its alternatives, gives rise to an effect of the desired order of magnitude.

Reversible enhancement of the magnetism of ultrathin Co films by H adsorption

By means of ab initio calculations, we have investigated the effect of H adsorption in the structural, electronic and magnetic properties of ultrathin Co films on Ru(0001). Our calculations predict that H occupies hollow sites preserving the two-dimensional 3-fold symmetry. The formation of a complete H overlayer leads to a very stable surface with strong H-Co bonds. H tends to suppress surface features, in particular, the enhancement of the magnetic moments of the bare film. The H-induced effects are mostly confined to the Co atoms bonded to H, independent of the H coverage or of the thickness and the structure of the Co film. However, for partial H coverages a significant increase occurs in the magnetic moment for the surface Co atoms not bonded to H, leading to a net enhancement of surface magnetism.

Friedel-oscillations-induced surface magnetic anisotropy

We present detailed numerical studies of the magnetic anisotropy energy of a magnetic impurity near the surface of metallic hosts (Au and Cu) that we describe in terms of the tight-binding surface Greens-function technique. We study the case when spin-orbit coupling originates from the

Novel 0D Devices: Carbon-Nanotube Quantum Dots

d

Band-filling effects in the magnetic anisotropy of atomic thin layers of Co

band of the host material and we also investigate the case of a strong local spin-orbit coupling on the impurity itself. The splitting of the impuritys spin states is calculated to leading order in the exchange interaction between the impurity and the host atoms using the diagrammatic Greens-function technique. The magnetic anisotropy constant is an oscillating function of the separation

Tubular Fermi Surfaces Of Co/Ni

d

CARBON-NANOTUBE-BASED QUANTUM DOT

from the surface. It asymptotically decays as

Spin splitting induced by spin-orbit interaction in chiral nanotubes.

\ensuremath{\sim}1/{d}^{2}

Coulomb interactions in carbon nanotubes

and its oscillation period is determined by the extremal vectors of the hosts Fermi surface. Our results clearly show that the host-induced magnetic anisotropy energy is by several orders of magnitude smaller than the anisotropy induced by the local mechanism, which provides sufficiently large anisotropy values to explain the size dependence of the Kondo resistance observed experimentally.