Multiferroic

The mode assignment of the cubic phase of anhydrous Na2MoO4 was carried out on the basis of lattice dynamic calculation using the classical rigid-ion model. Temperature-dependent studies indicate that this crystal remains in the cubic structure in the 15–773 K range and undergoes a phase transition at around 783 K. The behavior of the Raman modes indicates that this transition is strongly first-order in nature and the phase above 773 K may have an orthorhombic symmetry. This transition is connected with tilting and/or rotations of the MoO4 tetrahedra, which lead to a disorder at the MoO4 sites. Our results give also evidence that the MoO bond lengths decrease in the high-temperature phase. Copyright © 2008 John Wiley & Sons, Ltd.

Electrical and magnetic properties of ferroelectric polymer (polyvinyledene fluoride) and ferromagnetic metal [nanocrystalline nickel ( nc -Ni)] composites have been investigated as a function of volume fractions of nc -Ni ( f Ni ). A significant enhancement in saturation magnetization of 24 emu/g, measure of permeability (μ') of 1.11 and dielectric constant of 2050 at 100 Hz has been observed at the electrical percolation threshold ( f c ) of the composite. The critical exponents ( x and y ) obtained are within the universal regime. The decrease of magnetization of the composite with decrease in f Ni is attributed to the dilution effect and magnetic dipolar exchange interaction. The constancy of coercive field ( H c ) has been explained on the basis of Stoner-Wohlfarth model. The value of μ' increases linearly with increase of f Ni as the magnetic flux concentrates over individual n c -Ni clusters/particles even beyond f c . On the other hand, the value of μ' decreases ...

Multiferroic BiFeO3 films have been deposited on a number of substrates by RF magnetron sputtering. Two routes were adopted in order to obtain the films of high phase purity and accurate stoichiometry. The first was to sputter films at room temperature and then the ...

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Polycrystalline lead-free (1-x)BaFe12O19–x(K0.5Na0.5)NbO3 magnetoelectric ceramic composites (x = 10, 20 and 30 wt%) were fabricated for the first time, comparing various synthesis techniques, namely solid state reaction, sol-gel, co-precipitation and citrate combustion methods for the synthesis of the ferrite phase. As well as the four synthesis routes, comparisons were made between uniaxial pressing and cold isostatic pressing of the samples prior to sintering at 1200 °C/2 h. Formation of separate magnetic hexaferrite BaFe12O19 (BaM) and ferroelectric (K0.5Na0.5)NbO3 (KNN) phases in the composites was confirmed using x-ray diffraction. The microstructural features revealed distribution of BaM and KNN grains in all the composite systems. Piezoresponse (PFM) and magnetic force (MFM) modes of scanning probe microscopy (SPM) were utilised to assess responses from piezoelectric and magnetic grains. Localised piezoelectric hysteresis loops were measured on KNN grains in composites made by all four methods. Typical hard magnetic hysteresis loops for BaM were observed exhibiting high coercivity values (up to 281 kA m−1 or 3530 Oe), and those composites made using solid state reaction and citrate combustion methods, which contained no impurity phases, had close to maximum magnetisation values (equivalent to ~70 A m2 kg−1 for the BaM phase). SEM, MFM and magnetisation measurements all suggested that the grain size of the BaM in the composites made using solid state reaction, co-precipitation and citrate combustion methods was around 1 µm, and consisting of single magnetic domains. As a result, it is likely that these samples will exhibit a high degree of magnetoelectric coupling.

"Investigation on structural, vibrational, dielectric and ferroelectric properties of Bi1xPrxFeO3 (x ¼ 0.0, 0.15, 0.25) ceramic samples has been carried out. Room temperature Rietveld-refined X-ray diffraction pattern shows the crystal structure of Bi1xPrxFeO3 is rhombohedral for x ¼ 0 and triclinic for x ¼ 0.15, 0.25. The changes in Raman normal modes with increasing doping concentration infer the structural
transformation is due to Pr substitution at A-site in BiFeO3. Raman spectra also reveal suppression of ferroelectric behavior due to Pr doping. The dielectric parameters, namely, dielectric permittivity (ε0) and loss tangent (tan (d)) were evaluated as a function of frequency at room temperature. The ferroelectric polarization reduces in Pr doped bulk BFO samples due to structural change."