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YMnO₃ exhibits a ferroelectric transition at high temperature (≈900 K) and magnetic ordering at T_N≈70 K, where the dielectric constant shows an anomaly indicative of the magneto-dielectric effect. Here we report powder neutron diffraction experiments in this compound that show that the magnetic moment at saturation is reduced by application of hydrostatic pressure. Our results yield further insight about the nature of the spin–lattice interaction in ferroic materials.

A systematic⁵⁷Fe Mössbauer effect study in a varying temperature range between 5.0 and 296.6 K and in an external magnetic field of 9.0 T on a high-quality stable decagonal quasicrystal Al₆₅Co₁₅Cu_19.9Fe_0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, −1.90(10) × 10²¹ V m⁻², 0.97(15) and −3.95(12) × 10²¹ V m⁻², 0.00(17). The average quadrupole splitting decreases with temperature as T^3/2. The vibrations of the Fe atoms are well described by a Debye model, with the Debye temperature of 546(7) K.

Density functional theory (DFT) of electrolytes is applied to the electrical double layer under a wide range of conditions. The ions are charged, hard spheres of different size and valence, and the wall creating the double layer is uncharged, weakly charged, and strongly charged. Under all conditions, the density and electrostatic potential profiles calculated using the recently proposed RFD electrostatic functional (Gillespie et al 2002 J. Phys.: Condens. Matter 14 12129; 2003 Phys. Rev. E 68 031503) compare well to Monte Carlo simulations. When the wall is strongly charged, the RFD functional results agree with the results of a simpler perturbative electrostatic DFT, but the two functionals' results qualitatively disagree when the wall is uncharged or weakly charged. The RFD functional reproduces these phenomena of weakly charged double layers. It also reproduces bulk thermodynamic quantities calculated from pair correlation functions.

A theoretical approach to the crystalline-to-amorphous phase transformation during self-irradiation is proposed. The different stages of the amorphization process (metamictization) are shown to correspond to internally stressed equilibrium states, associated with the minima of a free-energy functional, in which the elastic distortions induced by the creation of amorphous material are compensated by an internal stress-field, deriving from a unique stress-field potential. The transformation dynamics is described in terms of a nucleation and growth mechanism of amorphous regions involving a critical size.

The single-particle spectral-weight function of the ionic Hubbard model (IHM) at half-filling shows an abrupt change of regime at a critical value of the coupling constant (Hubbard U). Specifically, this function jumps at the Fermi points k_F = ± π/2 from a two-peak to a four-peak structure accompanied by a (non-vanishing) minimum of the single-particle charge gap. This jump separates a weak-coupling regime, the band insulating phase, from a strong-coupling regime which evolves gradually into the Mott–Hubbard phase. We take advantage of this critical behaviour to model several quasi-one-dimensional materials in terms of the IHM instead of the simpler one-band Hubbard model. For instance, the two regimes are physically realized in the angle-resolved photoelectron spectra of (TaSe₄)₂I, and the blue-bronze K_0.3MoO₃, respectively.

The effects of Ti, B and O co-segregating on the α-Fe Σ5 [001]/(010) grain boundary are studied by a first-principles method, DMol. We found that (Ti+B) acts as an enhancer, but O can completely offset the beneficial effect of Ti. Based on the segregation energy analysis, it is also found that Ti can effectively prohibit O from segregating to the grain boundary and therefore eliminate the embrittlement of grain boundary induced by O. Thus, Ti is a kind of desirable addition in α-Fe to improve the mechanical properties.

Crystallographic and magnetic properties of Co₂Mn_1−xFe_xSn and Co₂Mn_1−y Cr_ySn Heusler alloys were studied using x-ray diffraction, scanning electron microscopy with energy dispersive x-ray analysis, magnetization measurements and Mössbauer spectroscopy. We found that the intermetallic compounds crystallize into a single phase with the L 2₁-type Heusler structure at the concentration of 0≤x≤0.5 for Co₂Mn_1−xFe_xSn and 0≤y≤0.3 for Co₂Mn_1−yCr_ySn. The spontaneous magnetization increases when Mn is substituted with Fe and decreases when Mn is substituted with Cr. The values of hyperfine field at the Sn nuclear sites in Co₂Mn_1−xFe_xSn and Co₂Mn_1−yCr_ySn also increase or decrease in combination with the size of magnetization. These measurements suggest that the Slater–Pauling behaviour in half-metallic full-Heusler alloys provides a good description of the substitution effect of Mn with Fe or Cr.

We theoretically study the electron transport property for a semiconductor quantum wire irradiated under a longitudinally polarized electromagnetic field within a finite range. We obtain the non-perturbative solutions of the single-electron time-dependent Schrödinger equation both inside and outside the field-irradiated region of the wire according to the Floquet theorem. A general infinite matrix equation which determines the Floquet scattering coefficients is derived straightforwardly through the wavefunction matching scheme at the two interfaces between regions with and without field irradiation. The examples of numerically calculated transmission dependence on the electron incident energy for different field parameters exhibit both Fano and Rabi resonances, and the structure of the transmission is sensitive to the field parameters of amplitude and frequency as well as the irradiation length.

The mobility of charge carriers in a semiconductor nanowire is explored as a function of increasing radius, assuming low temperatures where impurity scattering dominates. The competition between increased cross-section and the concurrent increase in available scattering channels causes strongly non-monotonic dependence of the mobility on the radius. The inter-band scattering causes sharp declines in the mobility at the wire radii at which each new channel becomes available. At intermediate radii with the number of channels unchanged the mobility is seen to maintain an exponential growth even with multiple channels. We also compare the effects of changing the radial scaling of the impurity distribution. We use transverse carrier wavefunctions that are consistent with boundary conditions and demonstrate that the δ-function approximate transverse profile leads to errors in the case of remote impurities.

The effects of spin–phonon interaction on the temperature dependence of the spin-wave and phonon spectrum in ferromagnetic semiconducting thin films are studied using a Green's function formalism beyond the random phase approximation. It is shown that due to the surface modes and the anharmonic spin–phonon interaction the spin-wave damping effects in thin ferromagnetic films are enhanced in comparison to the bulk. The phonon spectrum is discussed, too. Additional phonon damping and phonon frequency shift arise when the spin–phonon interaction is properly included.

A model Hamiltonian representing the Cu spins in La₂CuO₄ in its low-temperature body-centred orthorhombic phase, that includes both spin–orbit-generated Dzyaloshinskii–Moriya interactions and interplanar exchange, is examined within the RPA utilizing a Tyablikov decoupling of various high-order Green's functions. The magnetic susceptibility is evaluated as a function of temperature and the parameters quantifying these interactions, and compared to recently obtained experimental data of Lavrov, Ando, and collaborators. An effective Hamiltonian corresponding to a simple tetragonal structure is shown to reproduce both the magnon spectra and the susceptibility of the more complicated body-centred orthorhombic model.

An ac photopyroelectric calorimeter has been used to measure the thermal diffusivity and specific heat of the perovskite manganites RMnO₃ (R = La, Pr, Nd) close to their magnetic transitions. Taking into account that the inverse of the thermal diffusivity has the same critical behaviour as the specific heat, the critical exponent α of the magnetic transition has been obtained by means of both magnitudes. The results in all cases are consistent with the Heisenberg model (α = −0.11), irrespective of the rare-earth ion.

The (1− x)PbMg_1/3Nb_2/3O₃–xPbTiO₃ ((1− x)PMN –xPT) single crystals with x equal to 0, 0.22, 0.28, 0.32, 0.37, 0.47, 0.69 and 1 were studied by x-ray diffraction and x-ray photoelectron spectroscopy. X-ray diffraction results reveal that with increase of Ti content the crystal symmetry changes from pseudo-cubic, characteristic for PbMg_1/3Nb_2/3O₃ (PMN), to rhombohedral, then to monoclinic at the vicinity of the morphotropic phase boundary (MPB) region and finally to tetragonal, specific for PbTiO₃ (PT). High-resolution core level spectra of the Pb 4f, O 1s, Nb 3d and Ti 2p states show that the bulk of the (1− x)PMN –xPT crystals, except PbTiO₃ where Pb²⁺ and Pb⁴⁺ were detected, is characterized by only one chemical state for each element. However, in the case of the Pb and O spectra, apart from the main lines attributed to the lattice states, the satellite lines related to the surface states were also observed. The evolution of the lattice components of all core level spectra points to regular concentration dependence of the full width at half maximum (FWHM). With the rise of the Ti content the FWHMs increase and reach maxima for the MPB region, then decrease and achieve the smallest values for the pure PT. This characteristic FWHM behaviour points to disorder as an origin of the core level line broadening and it is discussed within the framework of the random field model. The FWHM of the Bragg's reflections show similar concentration behaviour which confirms the existence of the highest structural disorder in (1− x)PMN –xPT system near the MPB.

Rare-earth-doped crystals can be attractive materials for quantum information processing, because of the long coherence times that can be expected, in particular, from non-Kramers ions. In this paper, Ho³⁺-doped yttrium and lutetium vanadate single crystals have been investigated using linear and coherent optical spectroscopy. For Ho³⁺:YVO₄, the crystal-field levels of the ⁵I₈, ⁵F₅, ⁵F₄ and ⁵S₂ multiplets have been determined and compared with crystal-field level calculations. This allowed us to unambiguously assign most of the observed transitions, although some results suggest that the site symmetry of the Ho³⁺ ion could deviate from D_2d. Similar conclusions were reached for Ho³⁺:LuVO₄. Hole burning measurements indicate that the coherence time of the ⁵I₈–⁵F₅ optical transitions is rather short in both compounds (around 40 ns). Assuming that the coherence is limited by spin interactions, this is accounted for by the high nuclear moment of the nearby vanadium ions, since the large crystal-field level splittings of the ⁵I₈ and ⁵F₅ multiplets do not favour a large enhanced nuclear Zeeman effect.

The effect of dilute titanium (Ti⁴⁺)-doping on the magnetic after-effect (MAE) spectra of stoichiometric magnetite single crystals, Fe_3−xTi_xO₄ – with 0.0001≤x≤0.008 – is studied in the temperature range and analysed in terms of our revised relaxation model. The effects of these relatively low doping rates comprise: (i) strong impact on low-temperature (4 K<T< 35 K) incoherent electron (e⁻)-tunnelling and combined intra-ionic thermal excitation; (ii) minor, though highly instructive, modifications of thermally activated electron hopping (50 K< T<125 K), and (iii) low-temperature shifting of the Verwey transition (T_V) relative to the temperature of zero-crossing of the crystal anisotropy (T_K1). Due to the high oxygen stoichiometry of the crystals (absence of B-site vacancies), no further MAEs appear in the high-temperature range (T>T_V).

The recently accentuated discussion concerning the appropriate timescale of electron transport – deduced from modern x-ray resonant scattering to be about , over the whole temperature range (T≷T_V), in contrast to up to thousands of seconds as determined from high-precision MAE experiments, in the low-temperature phase (T<T_V) – gives us the chance to sharpen our arguments in favour of a clarification of the electronic conductivity mechanisms in magnetite.