15662

1593 دكتري

دكتري

ماده چگال تجربي

اصفهان : دانشگاه صنعتي اصفهان

1398

نوزده، 132ص.: مصور، جدول، نمودار

حسين احمدوند

پرويز كاملي

حميده شاكري پور، مرتضي مظفري، علي رستم نژاد

1399/05/07

كتابنامه

فيزيك

فيزيك

1399/05/11

2624365

AbstractMultiferroeics are a special group of solid state materials in which at least two ferroic orders suchas magnetic ferroelectric coexist Magnetoelectric materials are an intresting class of multiferroeicsin which magnetic and ferroelectric orders are observed simultaneously In these materials electricpolarization magnetization can be controlled by an applied magnetic electric field There aremany potential applications for these materials such as writing information in magnetic memoriesby an electric field without the need for current magnetoelectric sensors medical imaging automobiles microphones printers etc In the first part of this dissertation in order to study themagnetoelectric effect in single phase materials structural dielectric magnetic andmagnetoelectric properties of Co4 xNixNb2O9 were investigated using neutron diffraction ND experiments magnetization heat capacity DFT calculations and dielectric constant Highresolution ND pattern showed that the compounds with x 0 and 1 crystallize in the trigonal P 3c1space 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 forx 0 and 1 In agreement with ND results magnetization and speci c heat studies show that x 1undergoes an antiferromagnetic phase transition around 31 K On the other hand for x 2 twopossible ferrimagnetic structures with magnetic moments lying in the ab plane were derived fromND 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 Ourresult showed that for x 1 substitution of Ni weakens the magnetoelectric coupling in Co4Nb2O9 For x 2 substitution of Ni changes both crystal and magnetic structure of this compound and nomagnetoelectric coupling is observed In second part of this research magnetoelectric effect incomposite samples consisting of 0 97 Bi0 67Ba0 33Fe0 67Ti0 33O3 0 03 Bi Zn0 5Ti0 5 O3 as theferroelectric phase and CoFe2O4 as the magnetic phase were studied The results showed that thepure ferroelectric phase shows a non dispersive and sharp phase transition while the compositesexhibit relaxor behavior The ME voltage coefficient was studied as a complex quantity anddiscussed within the framework of dynamic magnetostriction The highest value of the voltagecoefficient was obtained for the sample containing 30 CoFe2O4 which wascomparable to the values reported for lead based composites The results showed that thecomposite with nickel ferrite produces larger ME voltage than cobalt frrite confirming thatmagnetostriction has a crucial role on the ME properties of the multiferroic composites Keywords Multiferroeic Magnetoelectric Neutron diffraction Heat capacity Electric hysteresisloop Dielectric constant Magnetoelectric voltage coefficient Composites 133

حسين احمدوند

پرويز كاملي

حميده شاكري پور، مرتضي مظفري، علي رستم نژاد