الفهرس 
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Abstract
Pure BaTiO and CoFe
O phases are prepared by sol-gel and
autocombustion methods respectively. Two groups of double phase magnetoelectric composites with the molecular formula xCoFe :(1x)BaTiO and yBaTiO :(1-y)CoFe O (x and y are molecular weight ratios) are prepared by two step chemical method . The XRD patterns measured of all samples proves that both BaTiO
and CoFe O phases with tetragonal perovskite and spinel cubic structures
respectively are present. The analysis of XRD Patterns show that, all prepared
samples have crystallite size in the nano scale, and the lattice parameters ,
crystallite size and strain change depending on the composition ratio. Also
HRTEM micrographs for some selected samples show that the composites
have particles with sizes in the nanoscale.
Magnetic hysteresis loops measured for all composite samples with CoFe content show that, the samples have normal ferromagnetic behavior up to 500
K. Saturation and residual magnetization depends linearly on CoFe content.
The relation between coercivity and particle size as well as field cooling zero
field cooling (FC-ZFC) curves prove the existence of magnetic nanoparticles
with single magnetic domain. The dielectric permittivity (e’) and dielectric loss (e’’) spectra measured for
all samples depend on the composition ratio. When a magnetic field with
different strength is applied during measurements , (e’ ) and (e’’)spectra are
suppressed, the effect is represented by magnetocapacitance (MC). MC is found
to be frequency and field dependent. After removing the external field, (e’ ) and
(e’’)spectra have values lower that in the absence of field, this is attributed to
irreversible direct reaction between magnetic field and electric dipoles.