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Synthetic control of the mutual arrangement of the cyclometalated ligands (C^N) in Ir(III) dimers, [Ir(C^N)(2)Cl](2), and cationic bis-cyclometalated Ir(III) complexes, [Ir(C^N)(2)(L^L)](+) (L^L = neutral ligand), is described for the first time. Using 1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole (HdfptrBz) as a cyclometalating ligand, two different Ir(III) dimers, [Ir(dfptrBz)(2)Cl](2), are synthesized depending on the reaction conditions. At 80 °C, the dimer with an unusual mutual cis-C,C and cis-N,N configuration of the C^N ligands is isolated. In contrast, at higher temperature (140 °C), the geometrical isomer with the common cis-C,C and trans-N,N arrangement of the C^N ligand is obtained. In both cases, an asymmetric bridge, formed by a chloro ligand and two adjacent nitrogens of the triazole ring of one of the cyclometalated ligands, is observed. The dimers are cleaved in coordinating solvents to give the solvento complexes [Ir(dfptrBz)(2)Cl(S)] (S = DMSO or acetonitrile), which maintain the C^N arrangement of the parent dimers. Controlling the C^N ligand arrangement in the dimers allows for the preparation of the first example of geometrical isomers of a cationic bis-cyclometalated Ir(III) complex. Thus, N,N-trans-[Ir(dfptrBz)(2)(dmbpy)](+) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), with cis-C,C and trans-N,N arrangement of the C^N ligands, as well as N,N-cis-[Ir(dfptrBz)(2)(dmbpy)](+), with cis-C,C and cis-N,N C^N ligand orientation, are synthesized and characterized. Interestingly, both isomers show significantly different photophysical and electroluminescent properties, depending on the mutual arrangement of the C^N ligands. Furthermore, quantum chemical calculations give insight into the observed photophysical experimental data.

The peculiar features of domain walls observed in ferroelectrics make them promising active elements for next-generation non-volatile memories, logic gates and energy-harvesting devices. Although extensive research activity has been devoted recently to making full use of this technological potential, concrete realizations of working nanodevices exploiting these functional properties are yet to be demonstrated. Here, we fabricate a multiferroic tunnel junction based on ferromagnetic LaSrMnO electrodes separated by an ultrathin ferroelectric BaTiO tunnel barrier, where a head-to-head domain wall is constrained. An electron gas stabilized by oxygen vacancies is confined within the domain wall, displaying discrete quantum-well energy levels. These states assist resonant electron tunnelling processes across the barrier, leading to strong quantum oscillations of the electrical conductance.

The occurence of spin-polarization at ZrO2, Al2O3 and MgO surfaces is proved by means of abinitio calculations within the density functional theory. Large spin moments, as high as 1.56 µB, develop at O-ended polar terminations, transforming the non-magnetic insulator into a half-metal. The magnetic moments mainly reside in the surface oxygen atoms and their origin is related to the existence of 2p holes of well-defined spin polarization at the valence band of the ionic oxide. The direct relation between magnetization and local loss of donor charge makes possible to extend the magnetization mechanism beyond surface properties.PACS numbers: 75.70. Rf, 73.20.At, When dimensions are reduced to the nanoscale, we are faced to a new understanding of the physical properties of matter: bulk insulators and semiconductors exhibit metallic surfaces [1], non-magnetic materials get spin polarization when forming nanoparticles [2], unstable bulk structures exist in ultrathin film form [3,4], etc. At the origin of these phenomena are the reduced dimensionality and the enhanced role of the surfaces or boundaries in the final properties of the system. Together with its inherent fundamental interest, this has important technological consequences, auspicating the birth of new technologies [5,6]. Special attention is devoted to magnetic low dimensional structures, in particular as sources of spin current in the emerging field of spintronics [5].In this letter, we report on the existence of large magnetic moments and half-metallicity at the O-rich surfaces of ceramic oxides, focusing on ZrO 2 , Al 2 O 3 and MgO. These are non-magnetic ionic insulators widely applied in bulk and thick film form, that have also been grown as ultrathin films and nanometric grains [7]. Their electronic structure can be roughly described as a valence band formed by the filled O 2p orbitals and a conduction band formed by the empty metal levels. When a M x O y unit -M being the metal donor and x,y accounting for the particular metal to oxygen ratio-is broken to form the surface, the loss of coordination of the surface O atoms originates 2p holes in the valence band of the oxide. Our results show that this generates high spin moments at the topmost O layer, which induce magnetization at the adjacent planes and, remarkably, alter the electronic structure of the oxide from insulating to half-metallic.Very recently unexpected ferromagnetism has been measured in thin films of undoped non-magnetic oxides, like HfO 2 and ZrO 2 , possibly assigned to the presence of lattice defects concentrated at the film interface. [8,9]. Here we prove the existence of a magnetization mechanism rooted in the loss of donor charge of the O atoms, something that can also occur in films with cation vacancies. This provides an explanation for the origin of the magnetic moments of these so called 'd-zero' ferromagnets. Furthermore, we predict that this kind of magnetism can be extended to a wider class of non-magnetic oxides, like MgO and Al 2 O 3 , where the cation is not necessarily...

We show both theoretical and experimental evidences of the appearance of ferromagnetism in MgO thin films. First-principles calculations allow predicting the possibility of the formation of a local moment in MgO, provided the existence of Mg vacancies which create holes on acceptor levels near the O 2p-dominated valence band. Magnetic measurements evidence of the existence of room-temperature ferromagnetism in MgO thin films. High-resolution transmission electron microscopy demonstrates the existence of cation vacancies in our samples. Finally, by applying the element specificity of the x-ray magnetic circular dichroism technique, we also demonstrate that the magnetic moments of the system arise from the spin polarization of the 2p electrons of oxygen atoms surrounding Mg vacancies.

We study the gas-surface dynamics of O 2 at Ag(111) with the particular objective to unravel whether electronic non-adiabatic effects are contributing to the experimentally established inertness of the surface with respect to oxygen uptake. We employ a first-principles divide and conquer approach based on an extensive density-functional theory mapping of the adiabatic potential energy surface (PES) along the six O 2 molecular degrees of freedom. Neural networks are subsequently used to interpolate these grid data to a continuous representation. The low computational cost with which forces are available from this PES representation allows then for a sufficiently large number of molecular dynamics trajectories to quantitatively determine the very low initial dissociative sticking coefficient at this surface. Already these adiabatic calculations yield dissociation probabilities close to the scattered experimental data. Our analysis shows that this low reactivity is governed by large energy barriers in excess of 1.1 eV very close to the surface. Unfortunately, these 6

We report on the formation of strong chemical bonds at the Ni(100)/cubic-ZrO 2 (100) polar interfaces. Ab initio density functional theory calculations demonstrate that both Zr/Ni and O/Ni junctions are energetically stable, and predict that two different interactions determine the interface adhesion. Our results reveal that O-Ni ionic bonds are formed by Ni electron donation, while the Zr-Ni bonds show a mixed character with ionic and electron hybridization contributions.

A plethora of technological applications justify why titanium dioxide is probably the most studied oxide, and an optimal exploitation of its properties quite frequently requires a controlled modification of the surface. Low-energy ion bombardment is one of the most extended techniques for this purpose and has been recently used in titanium oxides, among other applications, to favour resistive switching mechanisms or to form transparent conductive layers. Surfaces modified in this way are frequently described as reduced and defective, with a high density of oxygen vacancies. Here we show, at variance with this view, that high ion doses on rutile titanium dioxide (110) induce its transformation into a nanometric and single-crystalline titanium monoxide (001) thin film with rocksalt structure. The discovery of this ability may pave the way to new technical applications of ion bombardment not previously reported, which can be used to fabricate heterostructures and interfaces.