Thermal properties and crystallization of iron phosphate glasses containing up to 25 wt% additions of Si-, Al-, Na- and U-oxides

The thermal properties (expansion, T_g and T_SOFT.) of glasses, having 56-66% P₂O₅, 14.8-34.2% Fe₂O₃ and 2-25 wt% additions of SiO₂, Al₂O₃, Na₂O and UO₂, were comparatively estimated from dilatometric measurements in similar conditions. The T_g reversibility was clearly verified by varying the heating rates between 1 and 5 °C min⁻¹. From linear equations fits of the various glass properties as functions of the six components it is suggested the iron, sodium and uranium oxides decrease the thermal expansion (for 50 < T ? 300 °C), T_g and T_SOFT. From DTA/XRD analysis of three glasses it was confirmed the crystallization tendency decreased with increasing the UO₂ level in the glasses. Leaching test data for two compositions containing Na₂O suggest addition of UO₂ increases the chemical durability of the related glass. The roles of UO₂, Na₂O and Fe-oxide species as structural components of the glass network are discussed.     

Nonlinear magnetic response in ruthenocuprates

We have performed an investigation of the nonlinear magnetic response in ruthenocuprates. A negative, diverging-like peak at the main magnetic transition T_N in RuSr₂ RECu₂O₈ (RE = Gd, Y) indicates a possible canted antiferromagnetic order. Another well defined feature above T_N points to a blocking of superparamagnetic particles through the T^-3 dependence of the third harmonic at higher temperatures. Below T_N a nondiverging peak appears, which is strongly affected by the addition of 10% of Cu ions in the RuO₂ planes. In RuSr₂ RE _2-xCe_xCu₂O₁₀ the main magnetic transition T_M is accompanied by two characteristic temperatures in the third harmonic of the ac susceptibility, in agreement with recent studies from μSR and M?ssbauer spectroscopy. We find that the spin-spin correlation temperature is the same in both families of ruthenocuprates.     

Pressure behaviour and thermal expansion of NiMnSb from first principles calculations

A computational study of the pressure and thermal behaviour of NiMnSb within the framework of density functional theory and the Debye-Grüneisen model is reported. The theoretical values of equilibrium lattice parameter, bulk modulus, its pressure derivative, Debye temperature, Grüneisen constant and coefficient of thermal expansion are estimated from electronic structure calculated by the full-potential nonorthogonal local-orbital minimum basis method (FPLO). The bulk modulus and its pressure derivative have been computed using the Murnaghan form of the equation of states. The volume-temperature dependence was obtained by minimisation of the free energy as a sum of the total energy of the rigid lattice and the free energy of the vibration lattice. The thermal expansion coefficient for the studied NiMnSb, obtained within the Debye theory including anharmonicity, is in good agreement with experimental results.     

Leptonic Origin of TeV Gamma-Ray Emission from Crab Nebula

We study the nonthermal emission of the Crab nebula in the bands from radio to TeV γ-ray on a simplified timedependent injection model. In this model, relativistic electrons in the Crab nebula consists of two components and their injected spectrum is a broken power law with different indices and a break energy. The relativistic electrons emit nonthermal photons through synchrotron and inverse Compton scattering off soft photon fields inside the nebula. The resulting spectrum calculated with the model is well consistent with the observed data ranging from radio to very high energy γ-rays for the Crab nebula, where the emission from radio to medium γ-rays is from electron＇s synchrotron emission, whereas the emission above ～ 100 MeV primarily comes from the inverse Compton scattering of the relativistic electrons on synchrotron photons.     

Explicit solutions to phenomenological models of magnetization reversal of thin ferromagnetic films in the presence of a sawtooth magnetic field

Explicit solutions are derived for several phenomenological models of magnetization reversal in thin ferromagnetic films driven by a sawtooth magnetic field. For a domain wall velocity that is linear in the magnetic field, it is found that the dynamic coercive field follows a square-root power-law in the slope of the magnetic field, shifted by the depinning field. For a more general domain wall velocity different power-law exponents are found, yet the overall form for the scaling of the area of the hysteresis loop remains a power-law shifted by the depinning field. This shifted power-law could be interpreted to be a crossover between adiabatic and dynamic regimes.