This study evaluates the structural, microstructural, electric and magnetic properties of nickel ferrite samples prepared through the solid state reaction. It was observed that an increase in the sintering temperature produces a higher cation concentration in the A site when compared to the B site. The assessment of magnetic properties showed that an increase in grain size leads to a decrease in the coercive fields verging on superparamagnetic values, while the saturation magnetization increases up to 46.5 Am 2 .kg -1 for samples sintered at 1200 °C. The dc electric resistivity behavior of samples was attributed to the increase in the cross-sectional area of grains as well as the different oxidation states and distribution of cations amongst the lattice sites of the spinel structure.

In this paper structural, electric, magnetic, and M€ ossbauer spectroscopy studies were conducted in (x)BiFeO 3-(1-x)BaTiO 3 , 0.9 ! x ! 0.3, solid solutions. X-ray diffraction and Rietveld refinement studies indicated the formation of single-phased materials crystallized in a distorted perovskite structure with the coexistence of rhombohedral and monoclinic symmetries. Room temperature ferroelectric hysteresis loops showed that the electric polarization increases with the increase of the BaTiO 3 content due to the singular structural evolution of the studied solid solutions. All samples presented weak ferromagnetic ordering, which indicates that the BaTiO 3 substitution in the BiFeO 3 matrix released the latent magnetization. M€ ossbauer studies revealed a magnetic spectral signature corresponding to ordered Fe 3þ ions, and a decrease of the magnetic hyperfine magnetic fields with the increase of the BaTiO 3 content. The composition 0.3BiFeO 3-0.7BaTiO 3 presented a spectral signature corresponding to a paramagnetic behavior, which strongly suggests that the observed magnetization in this sample is due to the Ti 3þ ions. V

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In this paper, the relationship between ferroic states and the physicochemical mechanism which governs the (Bi/Pb/La)–O bonds in polycrystalline La doped (0.6)BiFeO3–(0.4)PbTiO3 compounds were investigated. An abrupt change in the symmetries of perovskite-structured samples, from tetragonal (P4mm) to rhombohedral (R3c), occurs with the increase of the La concentration, highlighting the diminishment of the hybridization of the (Bi/Pb)–O bonds when La is added into the solid solution, and the emergence of a characteristic morphotropic phase boundary tuned by doping. A maximum remnant polarization (10 μC/cm2) was observed for low La concentrations (where R3c and P4mm phases coexist), while the maximum remnant magnetization (∼75 × 10−3 emu/g) was observed for highly La concentrated samples. These results show that ferroelectric and weak-ferromagnetic orders are strongly correlated to the structural arrangement, which in turn are directly related to the chemical A–O and B–O bonds (long-range and short-range forces) and with the chemical characteristics of the elements that fulfills the A site of the perovskite structure.

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