Multiferroeics are a special group of solid-state materials in which at least two ferroic orders, such as magnetic-ferroelectric coexist. Magnetoelectric materials are an intresting and 1 crystallize in the trigonal P-3c1 space group and for x=2 the crystal structure was found to be orthorhombic with space group Pbcn. Rietveld analysis on ND data revealed an in-plane weakly non-collinear AFM con?guration for x=0 and 1. In agreement with ND results, magnetization and speci?c heat studies show that x=1 undergoes an antiferromagnetic phase transition around 31 K. On the other hand, for x=2, two possible ferrimagnetic structures with magnetic moments lying in the ab plane were derived from ND data. DFT calculations distinguished the most likely magnetic con?guration for this sample. The compound shows a hard-type ferrimagnetic behavior below the transition of Tc=47 K. Our result showed that for x=1, substitution of Ni weakens the magnetoelectric coupling in Co 4 Nb 2 O 9. For x=2, substitution of Ni changes both crystal and magnetic structure of this compound and no magnetoelectric coupling is observed. In second part of this research, magnetoelectric effect in composite samples consisting of 0.97[Bi 0.67 Ba 0.33 Fe 0.67 Ti 0.33 O 3 ]- 0.03[Bi(Zn 0.5 Ti 0.5 )O 3 ] as the ferroelectric phase and CoFe 2 O 4 as the magnetic phase were studied. The results showed that the pure ferroelectric phase shows a non-dispersive and sharp phase transition, while the composites exhibit relaxor behavior. The ME voltage coefficient was studied as a complex quantity and discussed within the framework of dynamic magnetostriction. The highest value of the voltage coefficient was obtained for the sample containing 30% CoFe 2 O 4 , which was comparable to the values reported for lead-based composites. The results showed that the composite with nickel ferrite produces larger ME voltage than cobalt frrite confirming that magnetostriction has a crucial role on the ME properties of the multiferroic composites.
