Magneto-dielectric properties of ferrites and ferrite/ferroelectric multiferroic composites

Ni-Zn ferrites, with the general formula Ni1-xZnxFe2O4 (x = 0.0, 0.3, 0.5, 0.7, 1.0), CoFe2O4, BaTiO3 and PbZr0.52Ti0.48O3 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 NiZnFe2O4, BaTiO3 and PbZr0.52Ti0.48O3 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. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 45021]