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Multiferroic composites with the composition (1 − x) BaTi0.8Sn0.2O3–(x) La0.5Ca0.5MnO3 (x = 0, 0.3, 0.5, 0.7, 0.9 and 1) were prepared by sol–gel techniques. Rietveld refinements of the composites with 0–3 and 3–0 type connectivities exhibit the formation of pure phases and confirm the fraction of the composite samples. It was found that the composites grain size decreases slightly with increasing the La0.5Ca0.5MnO3 content. Magnetic measurements of the composite ceramics exhibit a gradual increase in saturation and remanent magnetization with increasing La0.5Ca0.5MnO3 content. Dielectric data demonstrate that the composite materials show high values of the dielectric constant in comparison with the parent compound BaTi0.8Sn0.2O3 (BTSO). In addition, an attempt is made to measure the magnetoelectric coupling coefficient and to explain the negative permittivity and losses occurring in these materials at a certain frequency and temperature conditions. [ABSTRACT FROM AUTHOR]

Perovskite manganite La0.5Ca0.5−x□xMnO3 (LCMO) nanomaterials were elaborated using the sucrose modified auto combustion method. Rietveld refinements of the X-ray diffraction patterns of the crystalline structure confirm a single-phase orthorhombic state with Pbnm space group (No. 62). The Ca-vacancies were voluntarily created in the LCMO structure in order to study their influence on the magnetic behaviour in the system. The magnetic susceptibility was found to be highly enhanced in the sample with Ca-vacancies. Paramagnetic-to-ferromagnetic phase transition was evidenced in both samples around 254 K. This transition is, characterized by a drastic jump of the susceptibility in the sample with Ca-vacancies. The maximum of entropy change, observed for both compounds at magnetic field of 6 T was 2.30 J kg−1 K−1 and 2.70 J kg−1 K−1 for the parent compound and the lacunar one respectively. The magnetocaloric adiabatic temperature change value calculated by indirect method was 5.6 K and 5.2 K for the non-lacunar and Ca-vacancy compound, respectively. The Ca-lacunar La0.5Ca0.5−x□xMnO3 (x = 0.05) reported in this work demonstrated overall enhancement of the magnetocaloric effect over the LCMO. The technique used to elaborate LCMO materials was beneficial to enhance the magnetocaloric effect and magnetic behaviour. Therefore, we conclude that this less costly environmentally friendly system can be considered as more advantageous candidate for magnetic refrigeration applications then the commonly Gd-based compounds. [ABSTRACT FROM AUTHOR]

By using the effective field theory (EFT), the mixed spin-1/2 and spin-3/2 Ising ferrimagnetic model adapted to a double perovskite structure has been studied. The EFT calculations have been carried out from Ising Hamiltonian by taking into account first and second nearest-neighbors interactions and the crystal and external magnetic fields. Both first- and second-order phase transitions have been found in phase diagrams of interest. Depending on crystal-field values, the thermodynamic behavior of total magnetization indicated the compensation phenomenon existence. The hysteresis behaviors are studied by investigating the reduced magnetic field dependence of total magnetization and a series of hysteresis loops are shown for different reduced temperatures around the critical one. [ABSTRACT FROM AUTHOR]

The multi-component Ising-like network model on x-y rectangular lattice was developed to describe the ferroelectric phase transition in Tetragonal Tungsten Bronze (TTB) compounds. Using Monte Carlo simulation with Metropolis algorithm we reproduced the phase diagram of this model as a function of the temperature and exchange interaction and demonstrated it coherence with experimental data. [ABSTRACT FROM AUTHOR]

The influence of a non-perfect surface on the critical properties of magnetic spin-1/2 Ising film on a cubic lattice structure is studied using Monte Carlo simulations based on Metropolis algorithm. The surface magnetization and the surface effective exponent have been studied for several concentration p. Far from the critical temperature, the surface effective exponent βeffs decreases with increasing the concentration p. [ABSTRACT FROM AUTHOR]

Using Monte Carlo simulation with the Metropolis algorithm, we have studied the critical behaviour of magnetic spin 1/2 Ising film on a cubic lattice structure. We drive the effective exponent of the each layer βeff(z,t) and of the film βefff (t) as a function of reduced temperature t. A particular attention is paid for the evaluation of the variation of the critical exponents with the film thickness. [ABSTRACT FROM AUTHOR]

Glass-ceramics in the system xBaTiO3-(1-x)NaPO3 (0 ≤ x ≤ 14, x in mol%) have been prepared and characterized. The structural organization of the glass-ceramics has been studied using XRD diffraction and infra-red (FTIR), 31P Magic angle spinning (MAS-NMR) and dielectric spectroscopies. Results suggest two distinct regions comprising the glass structure, one with low-BaTiO3 content and the other with higher content of the ferroelectric compound BaTiO3. The depolymerisation effects and the structure changes, promoted by BaTiO3 addition, are evidenced by means of the IR and NMR results. Dielectric permittivity shows that the ferroelectric-paraelectric transition temperature of each glass-ceramic appears at the same temperature for a pure BaTiO3 ceramic. [ABSTRACT FROM AUTHOR]

Samples of zelliges, from the Dar-El Beïda Palace built in Meknes (Morocco) in the 18th century, were studied by optical absorption and Raman spectroscopies. The results obtained by the two techniques were in agreement and show that the glazes of the zelliges are lead oxide-rich in composition. Other phases were also detected, mainly the SnO2 cassiterite opacifier for the white glaze, and heamatite (α-Fe2O3) in association with magnetite Fe3O4 and manganese oxide (MnO2) for the brown glaze. For the blue and green glazes, the elements responsible for the coloring are cobalt (Co2+) and copper (Cu2+), respectively. [ABSTRACT FROM AUTHOR]

Glasses belonging to the series yA2O-(1-y)[0.25(WO3)2-0.75P2O5] ( y=0.10-0.60) are elaborated. DTA experiments reveal that the glass-network of the glasses are broken with increasing of modifier content. EPR spectra show the presence of two signals due to W5+ and Mo5+, as impuritie. The intensity of these EPR centres decreases when the concentration of A2O increases. The variation of Tg upon the modifier content is ascribed to structural changes occurring in the matrix of these glasses. [ABSTRACT FROM AUTHOR]

Using Monte Carlo simulations, we studied phase diagrams and magnetic properties of a ferromagnetic/antiferromagnetic Ising nanoparticles assembly with the spin-1/2 core and spin-3/2 shell. The system consists of nanocubes with equivalent exchange couplings of core and shell. However, the exchange couplings between the adjacent spins of the core and shell and between the nanocubes are assumed to vary. Thus, the effects of the exchange couplings and the system size on the phase diagrams are analyzing. Interesting behaviors are found when investigating the critical behavior of the system, the magnetizations, the magnetic susceptibility and the hysteresis loops. The increase of the core/shell size involves that of the temperature one. In addition, the increase in positive exchange interactions between the spins of the core and shell, on the one hand, and between the nanocubes, on the other hand, also increase the critical temperature, which favors the stable phase (3/2, 1/2). • Monte Carlo Simulation is used to study the magnetic properties of an assembly of cubic Core-Shell nanoparticles. • Phases diagrams of critical temperature with the exchange interactions and anisotropy parameter have been studied. • The increase of positive J2/J1 and J4/J1 increase the critical temperature, favoring the stable phase (3/2, 1/2). • Core and Shell sizes, anisotropy and interactions parameters effects on Magnetic hysteresis cycles are given. • Dependent coercivity with sizes and parameters of interactions are found. [ABSTRACT FROM AUTHOR]

Abstract: The present study concerns the system 0.5[xNa2O–(1− x)Li2O]–0.5[0.4(MoO3)2–0.6P2O5], with x varying between 0 and 1. The elaborated glass samples have been characterised using powder X-ray diffraction (XRD), differential thermal analysis (DTA) and impedance spectroscopy. The total alkali oxide content is chosen in order to ensure that the electrical conductivity of the glasses under study is entirely ionic. It was evidenced that the conductivity minimum corresponds to the maximum of the activation energy. The glass transition temperature seems to present a minimum for the ratio Na/(Na+Li)=0.5. On the other hand, the density appears very linearly versus Na/(Na+Li). The mixed alkali effect (MAE) is resulting here in a conductivity minimum observed for the composition corresponding to Na/(Na+Li)=0.5, (x =0.5). It could be attributed to the fact that the two types of alkali ions are randomly mixed and have distinct conduction pathways. This implies that Li ions tend to block the pathways for the Na ions and vice versa. [Copyright &y& Elsevier]