Ni-Zn ferrites, with the general formula Ni 1-x Zn x Fe 2 O 4 (x = 0.0, 0.3, 0.5, 0.7, 1.0), CoFe 2 O 4 , BaTiO 3 and PbZr 0.52 Ti 0.48 O 3 powders were synthesized by auto-combustion method. The composites were prepared by mixing the appropriate amounts of individual phases, pressing and conventional sintering. X-ray analysis, for individual phase and composites, indicated the formation of crystallized structure of NiZnFe 2 O 4 , BaTiO 3 and PbZr 0.52 Ti 0.48 O 3 without the presence of secondary phases or any impurities. SEM analyses indicated a formation of uniform grain distribution for ferromagnetic and ferroelectric phases and formation of two types of grains, polygonal and rounded, respectively. Magneto-dielectric effect was exhibited in all samples because of the applied stress occurring due to the piezomagnetic effect and the magnetic field induced the variation of the dielectric constant. For all samples the dielectric constant was higher in applied magnetic field. At the low frequency, the dispersion of dielectric losses appeared, while at the higher frequency the value of tan δ become constant (Maxwell-Wagner relaxation). Investigation of J-E relation between leakage and electric field revealed that both nickel zinc ferrite and composites have three different regions of conduction: region with ohmic conduction mechanism, region with the trap-controlled space charge limited current mechanism and region with space charge limited current mechanism.
Multiferroic composites containing ferroelectric Ba(Ti0.80Zr0.20)O3 (BT80Zr20) phase and magnetic Ni0.7Zn0.3Fe2O4 (NZF), CoFe2O4 (CF) or Ni0.7Cu0.01Sm0.05Zn0.29Fe1.95O4 (NCuSmZF) phase were investigated in this study. Three composites, BT80Zr20-NZF, BT80Zr20-CF and BT80Zr20-NCuSmZF were prepared by mixing chemically synthesized powders in the planetary mill, uniaxial pressing and sintering at 1300?C. X-ray diffraction data for the single phase and composites ceramics indicated the formation of crystallized structure of both ferrites and barium zirconium titanate, without the presence of undesirable phases. Microstructure analysis has shown the formation of two types of nanosized grains, polygonal ferromagnetic andd rounded ferroelectric grains. Non-saturated hysteresis loops were evident in all composite samples possibly due to the presence of very high conductive ferrite phases. The BT80Zr20-CF has shown the lowest conductivity values in comparison with other two compounds and therefore the highest potential for ferroelectric application. The impedance investigations confirmed the presence of different relaxation processes that originate from the grain and grain boundary contributions. Investigation of J-E relation between leakage and electric field for the BT80Zr20 and composites revealed the presence of four possible mechanisms of conduction in these materials.
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