Correction: Influence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds.

Correction for 'Influence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds' by L. Fernandez et al., Nanoscale, 2020, 12, 22258-22267, DOI: 10.1039/D0NR04964F.

Influence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds.

One-atom-thick rare-earth/noble metal (RE-NM) compounds are attractive materials to investigate two-dimensional magnetism, since they are easy to synthesize into a common RE-NM2 structure with high crystal perfection. Here we perform a comparative study of the GdAu2, HoAu2, and YbAu2 monolayer compounds grown on Au(111). We find the same atomic lattice quality and moiré superlattice periodicity in the three cases, but different electronic properties and magnetism. The YbAu2 monolayer reveals the characteristic electronic signatures of a mixed-valence configuration in the Yb atom. In contrast, GdAu2 and HoAu2 show the trivalent character of the rare-earth and ferromagnetic transitions below 22 K. Yet, the GdAu2 monolayer has an in-plane magnetic easy-axis, versus the out-of-plane one in HoAu2. The electronic bands of the two trivalent compounds are very similar, while the divalent YbAu2 monolayer exhibits different band features. In the latter, a strong 4f-5d hybridization is manifested in neatly resolved avoided crossings near the Fermi level. First principles theory points to a residual presence of empty 4f states, explaining the fluctuating valence of Yb in the YbAu2 monolayer.

Vibron-assisted spin excitation in a magnetically anisotropic molecule.

The electrical control and readout of molecular spin states are key for high-density storage. Expectations are that electrically-driven spin and vibrational excitations in a molecule should give rise to new conductance features in the presence of magnetic anisotropy, offering alternative routes to study and, ultimately, manipulate molecular magnetism. Here, we use inelastic electron tunneling spectroscopy to promote and detect the excited spin states of a prototypical molecule with magnetic anisotropy. We demonstrate the existence of a vibron-assisted spin excitation that can exceed in energy and in amplitude a simple excitation among spin states. This excitation, which can be quenched by structural changes in the magnetic molecule, is explained using first-principles calculations that include dynamical electronic correlations.

Atomic-scale spin sensing with a single molecule at the apex of a scanning tunneling microscope.

Recent advances in scanning probe techniques rely on the chemical functionalization of the probe-tip termination by a single molecule. The success of this approach opens the prospect of introducing spin sensitivity through functionalization by a magnetic molecule. We used a nickelocene-terminated tip (Nc-tip), which offered the possibility of producing spin excitations on the tip apex of a scanning tunneling microscope (STM). When the Nc-tip was 100 picometers away from point contact with a surface-supported object, magnetic effects could be probed through changes in the spin excitation spectrum of nickelocene. We used this detection scheme to simultaneously determine the exchange field and the spin polarization of iron atoms and cobalt films on a copper surface with atomic-scale resolution.

Controlled spin switching in a metallocene molecular junction.

The active control of a molecular spin represents one of the main challenges in molecular spintronics. Up to now spin manipulation has been achieved through the modification of the molecular structure either by chemical doping or by external stimuli. However, the spin of a molecule adsorbed on a surface depends primarily on the interaction between its localized orbitals and the electronic states of the substrate. Here we change the effective spin of a single molecule by modifying the molecule/metal interface in a controlled way using a low-temperature scanning tunneling microscope. A nickelocene molecule reversibly switches from a spin 1 to 1/2 when varying the electrode-electrode distance from tunnel to contact regime. This switching is experimentally evidenced by inelastic and elastic spin-flip mechanisms observed in reproducible conductance measurements and understood using first principle calculations. Our work demonstrates the active control over the spin state of single molecule devices through interface manipulation.

Silvopastoral System Economical and Financial feasibility with Jatropha curcas L. in Manabí, Ecuador / Viabilidad económica y financiera de sistemas silvopastoriles con Jatropha curcas L. en Manabí, Ecuador

ABSTRACT Objective. To assess the economic and financial feasibility of traditional silvopastoral systems for the biofuels production as a contribution to the sustainability of "Piñón for Galapagos" project. Materials and methods. A survey was conducted to 450 small livestock producer in 10 cantons of the Manabí province in order to collect basic agronomic knowledge, management, establishment and costs involved in production of the Piñón ((Jatropha curcas L.)/Savoy (Megathyrsus maximus) silvopastoral systems. For Piñón CP041 production recording plantation in live fence were stablished and for the tradition Piñón, the production of 10 sites were recorded, both systems since 2009. With those data were calculated the following economic indicators: ratio benefit/cost, net present value (NPV), internal rate ratio (IRR) and land expectation value (LEV). Results. The study exhibited a production decrease of Piñón with the passage of time. The CP041 INIAP improved silvopastoral system Piñón showed a B/C 1.07, NPV of USD$ 404.11, LEV US$ 970.23 and IRR of 18%. Followed by silvopastoral system with a local Piñón with a B/C 1.06, NPV of USD$ 363.66, LEV USD$ 873.10 and IRR of 17% and finally silvopastoral system without harvesting Piñón with a B/C 1.05, NPV of USD$ 285.72, LEV USD$ 685.99 and IRR of 15%. Conclusions. The alternative biofuels production was the silvopastoral systems (INIAP CP041)/Savoya in Manabí and is economically feasible. This system does not compete for arable land for food production and would not affect food security.

RESUMEN Objetivo. Evaluar la viabilidad económica y financiera de los sistemas silvopastoriles tradicionales para la producción de Biocombustibles como aporte a la sostenibilidad del proyecto "Piñón para Galápagos". Materiales y Métodos. Se llevaron a cabo encuestas a 450 pequeños productores ganaderos de 10 cantones de la provincia de Manabí con la finalidad de colectar información agronómica, manejo, costos implicados en establecimiento y producción de los sistemas silvopastoriles vigentes de Piñón (Jatropha curcas L.)/Saboya (Megathyrsus maximus). Para recopilar datos de producción del Piñón establecido en cercas vivas de Piñón INIAP CP041 e igualmente se registró la producción de sistemas en 10 sitios, desde el año 2009. Con estos datos se calcularon los siguientes indicadores financieros radio beneficio/costo (B/C), valor actual neto (VAN), tasa interna de retorno (TIR) y valor de expectativa de la tierra (VET). Resultados. El estudio mostró una disminución de la producción del Piñón con el transcurso del tiempo. El sistema silvopastoril mejorado con Piñón INIAP CP041 mostró B/C 1.07, VAN de USD$ 404.11, VET USD$ 970.23 y TIR de 18%. Seguido del sistema silvopastoril con Piñón local con un B/C 1.06, VAN de USD$ 363.66, VET USD$ 873.10 y TIR de 17% y finalmente sistema silvopastoril sin cosecha del Piñón con un B/C 1.05, VAN de USD$ 285.72, VET USD$ 685.99 y TIR de 15%. Conclusiones. La alternativa de producción de biocombustibles con sistemas silvopastoriles Piñón (INIAP CP041)/Saboya en Manabí es el sistema de mayor rentabilidad y no competiría por superficies de cultivo para la producción de alimentos, sin afectar a la seguridad alimentaria.

Kondo Resonance of a Co Atom Exchange Coupled to a Ferromagnetic Tip.

The Kondo effect of a Co atom on Cu(100) was investigated with a low-temperature scanning tunneling microscope using a monoatomically sharp nickel tip. Upon a tip-Co contact, the differential conductance spectra exhibit a spin-split asymmetric Kondo resonance. The computed ab initio value of the exchange coupling is too small to suppress the Kondo effect, but sufficiently large to produce the splitting observed. A quantitative analysis of the line shape using the numerical renormalization group technique indicates that the junction spin polarization is weak.

High Temperature Ferromagnetism in a GdAg2 Monolayer.

Materials that exhibit ferromagnetism, interfacial stability, and tunability are highly desired for the realization of emerging magnetoelectronic phenomena in heterostructures. Here we present the GdAg2 monolayer alloy, which possesses all such qualities. By combining X-ray absorption, Kerr effect, and angle-resolved photoemission with ab initio calculations, we have investigated the ferromagnetic nature of this class of Gd-based alloys. The Curie temperature can increase from 19 K in GdAu2 to a remarkably high 85 K in GdAg2. We find that the exchange coupling between Gd atoms is barely affected by their full coordination with noble metal atoms, and instead, magnetic coupling is effectively mediated by noble metal-Gd hybrid s,p-d bands. The direct comparison between isostructural GdAu2 and GdAg2 monolayers explains how the higher degree of surface confinement and electron occupation of such hybrid s,p-d bands promote the high Curie temperature in the latter. Finally, the chemical composition and structural robustness of the GdAg2 alloy has been demonstrated by interfacing them with organic semiconductors or magnetic nanodots. These results encourage systematic investigations of rare-earth/noble metal surface alloys and interfaces, in order to exploit them in magnetoelectronic applications.

Rare-earth surface alloying: a new phase for GdAu2.

Surface alloying is a powerful way of varying physical and chemical properties of metals, for a number of applications from catalysis to nuclear and green technologies. Surfaces offer many degrees of freedom, giving rise to new phases that do not have a bulk counterpart. However, the atomic characterization of distinct surface compounds is a major task, which demands powerful experimental and theoretical tools. Here we illustrate the process for the case of a GdAu2 surface phase of extraordinary crystallinity. The combined use of surface-sensitive techniques and state-of-the-art ab initio calculations disentangles its atomic and electronic properties. In particular, the stacking of the surface layers allows for gadolinium's natural ferromagnetic state, at variance with the bulk phase, where frustration leads to antiferromagnetic interlayer coupling.