No abstract available

No abstract available

[en] We attempt a classification of different colloidal gels based on colloid-colloid interactions. We discriminate primarily between non-equilibrium and equilibrium routes to gelation, the former case being slaved to thermodynamic phase separation while the latter is individuated in the framework of competing interactions and of patchy colloids. Emphasis is put on recent numerical simulations of colloidal gelation and their connection to experiments. Finally, we underline typical signatures of different gel types, to be looked at, in more detail, in experiments. (topical review)

[en] (In_1-xFe_x)₂O_3-v amorphous ferromagnetic semiconductor films were prepared by sputtering under thermal non-equilibrium conditions, and their corresponding Fe-In₂O₃ granular films were obtained by annealing. Unexpectedly, they both showed Mott variable range hopping behavior in the low temperature range, indicating that the interaction between the carriers can be neglected in the hopping process. For a system with a high carrier concentration the negligible interaction between the carriers was due to the electronic screening effect on the long range Coulomb interaction. The magnetoresistance in (In_1-xFe_x)₂O_3-v magnetic semiconductor and Fe-In₂O₃ granular films is also discussed. However, electronic transport through intergrain tunneling was not observed in the annealed Fe-In₂O₃ granular films

[en] We present a detailed muon spin relaxation (μ⁺SR) study of the spin-ice material Dy₂Ti₂O₇. Polycrystalline samples of this material have been studied in the temperature range 0.02 K< T<300 K in applied longitudinal magnetic fields of up to 2.7 T. At high temperature our study confirms previous bulk results showing that dynamics are dominated by spin-phonon-mediated relaxation of the electronic spin system. Below about 60 K the depolarization of the muon ensemble becomes too fast and the signal is almost completely lost. However, the recovery at lower temperature of the resolved asymmetry to roughly 1/3 of the total value allows us to confirm that it is the development of strong quasi-static local fields and not only dynamical effects that causes this depolarization. Finally, we find evidence of remanent spin fluctuations at temperatures as low as 0.02 K, well inside the quenched spin-ice state. We tentatively ascribe these to the hyperfine interaction with the ¹⁶¹Dy and ¹⁶³Dy nuclear spins

[en] We discuss how different properties at surfaces could require for different theoretical treatments within the first-principles density functional theory. Energies and structures are accurately determined by adopting the supercell geometry. Surface states are more conveniently described by the Green function embedding approach, which is able to take into account a truly semi-infinite solid and hence real continuous spectra. In this way a detailed analysis of discrete and resonant states is provided. We mainly describe the embedding method and provide examples to compare the two approaches. We focus next on the structural and electronic properties of alkali adatoms. The adsorption structure of Na/Cu(001) at low coverages is calculated within the supercell geometry motivated by the results of the Cambridge group on surface diffusion by ³He spin echo scattering. The dispersion, energy, effective mass, and width of surface (quantum well and image) states of alkali atoms on Cu(111) are worked out by the embedding approach and compared with experiments. (topical review)

[en] We report a first-principles study about the structural and electronic properties of two hybrid organic-molecule/inorganic-surface interfaces. We consider the adsorption of cysteine amino acids on Au(111) and of styrene molecules on the dimerized Si(100)-(2 x 1) surface, as prototypical systems for the functionalization of both metallic and semiconducting substrates. We focus on the adsorption mechanisms at the submonolayer regime, that we describe in terms of molecule/surface and molecule/molecule interactions. In both cases, our results show a strong electronic mixing and the formation of hybrid bonding states at the interface

[en] An isochronal annealing series was performed in order to investigate the thermal behaviour of as-grown defects in Al-doped 6H-SiC. Five hole traps have been detected, by means of deep level transient spectroscopy (DLTS), above the valence band (E_V) in the 0.2-1.3 eV energy range. One trap, labelled MZ2, anneals out after a 1800 ⁰C heat treatment, while the others display higher thermal stability. The nature of these centres is discussed on the basis of the previous experimental and theoretical data found in the literature. Particular emphasis has been given to a trap labelled MZ3, which we identified as the D-centre, and to the effect that the electric field has on its emission time constant

[en] Half-metallic Heusler alloys are amongst the most promising materials for future magneto-electronic applications. We review some recent results on the electronic properties of these compounds. The origin of the gap in these half-metallic alloys and its connection to the magnetic properties are well understood. Changing the lattice parameter slightly shifts the Fermi level. Spin-orbit coupling induces states within the gap but the alloys keep a very high degree of spin polarization at the Fermi level. Small degrees of doping and disorder as well as defects with low formation energy have little effect on the properties of the gap, while temperature effects can lead to a quick loss of half-metallicity. Finally, we discuss two special issues: the case of quaternary Heusler alloys and the half-metallic ferrimagnets

[en] Several aspects of half-metallic magnetism at finite temperature are discussed. Since NiMnSb is the simplest half-metal and the longest known it will be used as an example. Also it is a half-metal with remarkable little on-site Coulomb repulsion. Consequently it is a half-metal that is not notably corrupted by non-quasiparticle states. There exists an anomaly at 90 K, described before, that will be shown to be unrelated to the position of the Fermi level in the bandgap. Several substitutions are investigated that could shed some light on the origin of the transition. The calculated phonon spectrum is compared with experimental neutron scattering data. Finally, the spin-polarization of interfaces of NiMnSb with the transition metal based non-magnetic semiconductors NiTiSn and CoTiSb is investigated and the electronic structure of an infinite two-dimensional array of NiMnSb quantum dots embedded in NiScSb is reported