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Shrinking spintronic devices to the nanoscale ultimately requires localized control of individual atomic magnetic moments. At these length scales, the exchange interaction plays important roles, such as in the stabilization of spin-quantization axes, the production of spin frustration, and creation of magnetic ordering. Here, we demonstrate the precise control of the exchange bias experienced by a single atom on a surface, covering an energy range of 4 orders of magnitude. The exchange interaction is continuously tunable from milli-eV to micro-eV by adjusting the separation between a spin-1/2 atom on a surface and the magnetic tip of a scanning tunneling microscope. We seamlessly combine inelastic electron tunneling spectroscopy and electron spin resonance to map out the different energy scales. This control of exchange bias over a wide span of energies provides versatile control of spin states, with applications ranging from precise tuning of quantum state properties, to strong exchange bias for local spin doping. In addition, we show that a time-varying exchange interaction generates a localized ac magnetic field that resonantly drives the surface spin. The static and dynamic control of the exchange interaction at the atomic scale provides a new tool to tune the quantum states of coupled-spin systems. Fil: Yang, Kai. Ibm Research; Estados Unidos Fil: Paul, William. Ibm Research; Estados Unidos Fil: Natterer, Fabian D.. Ibm Research; Estados Unidos. Universitat Zurich; Suiza Fil: Lado, Jose Luis. Eidgenössische Technische Hochschule; Suiza Fil: Bae, Yujeong. Ewha Womans University; Corea del Sur. Ibm Research; Estados Unidos Fil: Willke, Philip. Ibm Research; Estados Unidos. Institute for Basic Science; Corea del Sur Fil: Choi, Taeyoung. Institute for Basic Science; Corea del Sur. Ewha Womans University; Corea del Sur Fil: Ferrón, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentina Fil: Fernandez Rossier, Joaquín. Universidad de Alicante; España. International Iberian Nanotechnology Laboratory; Portugal Fil: Heinrich, Andreas. Institute for Basic Science; Corea del Sur. Ewha Womans University; Corea del Sur Fil: Lutz, Christopher. Ibm Research; Estados Unidos

We present a simple method for obtaining reliable angular and energy distributions of electrons ejected from arbitrary condensed biomaterials by proton impact. Relying on a suitable description of the electronic excitation spectrum and a physically motivated relation between the ion and electron scattering angles, it yields cross sections in rather good agreement with experimental data in a broad range of ejection angles and energies, by only using as input the target composition and density. The versatility and simplicity of the method, which can be also extended to other charged particles, make it especially suited for obtaining ionization data for any complex biomaterial present in realistic cellular environments. The authors recognize the financial support from the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (Project No. FIS2010–17225). PdV acknowledges financial support from the European Union’s FP7-People Program (Marie Curie Actions) within the Initial Training Network No. 608163 "ARGENT". Support from the European COST Action MP1002 NanoIBCT is gratefully acknowledged.

We present a semiempirical model for calculating the electron emission from any organic compound after ion impact. With only the input of the density and composition of the target we are able to evaluate its ionization cross sections using plausible approximations. Results for protons impacting in the most representative biological targets (such as water or DNA components) show a very good comparison with experimental data. Because of its simplicity and great predictive effectiveness, the method can be immediately extended to any combination of biological target and charged particle of interest in ion beam cancer therapy. Financial support from the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund within the Project No. FIS2010-17225, and from the Conselleria d’Educació, Cultura i Esport de la Generalitat Valenciana for granting PdV within the VALi+d program. Support from the COST Action MP1002 Nano-IBCT is gratefully acknowledged.

We report electrical conductance measurements of Bi nanocontacts created by repeated tip-surface indentation using a scanning tunneling microscope at temperatures of 4 and 300 K. As a function of the elongation of the nanocontact, we measure robust, tens of nanometers long plateaus of conductance G 0=2e2/h at room temperature. This observation can be accounted for by the mechanical exfoliation of a Bi(111) bilayer, a predicted quantum spin Hall (QSH) insulator, in the retracing process following a tip-surface contact. The formation of the bilayer is further supported by the additional observation of conductance steps below G0 before breakup at both temperatures. Our finding provides the first experimental evidence of the possibility of mechanical exfoliation of Bi bilayers, the existence of the QSH phase in a two-dimensional crystal, and, most importantly, the observation of the QSH phase at room temperature, We thank the Spanish MICINN for financial support through Grants No. FIS2010- 21883, No. FIS2011-23488, and No. CONSOLIDER CSD2007-0010, and Generalitat Valenciana through Grants No. ACCOMP/2012/127 and No. PROMETEO/ 2012/011. D. G.-M. acknowledges the Centro de Computación Científica at UAM for computational support. Cristina Almansa is gratefully acknowledged for her help with the transmission electron microscope

We theoretically show how the spin orientation of a single magnetic adatom can be controlled by spin polarized electrons in a scanning tunneling microscope configuration. The underlying physical mechanism is spin assisted inelastic tunneling. By changing the direction of the applied current, the orientation of the magnetic adatom can be completely reversed on a time scale that ranges from a few nanoseconds to microseconds, depending on bias and temperature. The changes in the adatom magnetization direction are, in turn, reflected in the tunneling conductance., 5 pages, 3 figures

We study the magnetic properties of nanometer-sized graphene structures with triangular and hexagonal shapes terminated by zig-zag edges. We discuss how the shape of the island, the imbalance in the number of atoms belonging to the two graphene sublattices, the existence of zero-energy states, and the total and local magnetic moment are intimately related. We consider electronic interactions both in a mean-field approximation of the one-orbital Hubbard model and with density functional calculations. Both descriptions yield values for the ground state total spin, $S$, consistent with Lieb's theorem for bipartite lattices. Triangles have a finite $S$ for all sizes whereas hexagons have S=0 and develop local moments above a critical size of $\approx 1.5$ nm., Comment: Published version